Clinical Anatomy 00:00–00 (2014)

ORIGINAL COMMUNICATION

The Clinical Anatomy of the Right Ventricle HORIA MURESIAN* Cardiovascular Surgery Department, The University Hospital of Bucharest, 169, Splaiul Independentei, Bucharest, Romania

Because the systemic and pulmonary circulations are arranged in series, the right and left ventricles of the human heart have similar stroke volumes (with only minute beat-to-beat changes). Besides propelling the same volume of blood through the corresponding circulations, the two ventricles also share common structures such as the pericardium, the interventricular septum and the coronary arteries and veins—all of which complete the dynamic and integrated picture of the human heart. However, there are marked differences between the left and right ventricles as each is adapted to separate and dissimilar vascular beds, including particular reactivity to stress, hormones, and drugs. Of the two, the right ventricle (RV) has so far been either more difficult to approach from the diagnostic point of view or even overlooked, while the left ventricle (LV) has been considered the main pump, and diagnostic and therapeutic measures have been considered to apply equally to the LV and RV. This review article presents an update, portraying the RV from the clinical anatomical point of view, and endeavors to underscore the main particulars of the RV with clinical and surgical applications. Clin. Anat. 00:000–000, 2014. VC 2014 Wiley Periodicals, Inc.

Key words: right ventricle; tricuspid valve; pulmonary valve; ventricular septum; coronary circulation; myocardial infarction; heart failure; congenital heart disease; cardiac surgery

INTRODUCTION There is a growing body of evidence supporting the view that the right ventricle (RV) behaves differently from its left counterpart under both normal circumstances and in disease. Right ventricular dysfunction is directly related to survival (Di Salvo et al., 1995) and predicts adverse outcomes in patients with left ventricular (LV) failure or coronary artery disease (with or without RV or atrial involvement) (Polak et al., 1983; De Groote et al., 1998). The response of the RV to disease is different from that of the LV. Diagnostic approaches and emerging therapeutic measures are not identical or automatically and equally applicable to the RV and LV (Walker and Buttrick, 2013). The differences between the RV and LV can be traced at various levels: embryological, gross anatomical, mechanical, microscopical and biochemical (Dell’Italia, 1991; Kondo et al., 2006). A thorough clinical anatomical re-evaluation and reanalysis of all the elements characterizing the RV is of utmost importance for understanding this compo-

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nent of the heart and its function under various physiological circumstances as well as in disease, and for considering the most suitable diagnostic and therapeutic measures.

GENERAL DISPOSITION The right heart chambers are located anterior to their left counterparts; the RV is most anterior; Abbreviations used: ARVC, Arrhythmogenic right ventricular cardiomyopathy; LV, left ventricle; RV, right ventricle; TDI, tissue Doppler imaging; TOF, tetralogy of Fallot. *Correspondence to: Horia Muresian, Cardiovascular Surgery Department, The University Hospital of Bucharest, 169 Splaiul Independentei, Bucharest 050098, Romania. E-mail: [email protected] Received 17 September 2014; Accepted 12 October 2014 Published online in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/ca.22484

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opposite, the left atrium is most posterior and median. The RV forms nearly the entire sterno-costal surface of the heart and the inferior border of the cardiac silhouette, sharing only a limited portion of the diaphragmatic aspect of the heart with the LV and consequently hiding most of the remainder of the cardiac chambers from view. The proximate retrosternal location of the RV renders its echographic approach more difficult and makes it more prone to injury during median sternotomy especially when dilated or in redo operations. Also, the most apparent of the great vessels is the proximal pulmonary trunk together with its infundibulum when the heart is accessed from anterior (Fig. 1). Owing to the reciprocal spiraling of the aorta and the pulmonary trunk, the ascending aorta becomes noticeable immediately above the level of the pulmonary valve. The pulmonary valve is superior to all the other heart valves and shares no fibrous continuity with any of them (Muresian, 2006). The spiraling (“cross-over”) relationship between the aorta and pulmonary trunk represents the continuation of a similar disposition of the left and right ventricular outflow tracts. Closer inspection of the interventricular septum also demonstrates the non-planar disposition of the latter in its distal, outflow segment (Fig. 2). The presence of parallel outflow tracts heralds important congenital cardiac conditions such as complete transposition, this disposition being particularly sought during fetal cardiac ultrasound examination. Because the disposition of the heart “in situ” is oblique, the apex of the RV is located inferior to the left although the apex of the LV is remotest in longitudinal coordinates (Figs. 3 and 4). Under most circumstances the apex of the RV is not readily visible; however, when it is conspicuous, the apex of the heart appears bifid. The sterno-costal surface of the RV is usually covered with epicardial fat but there is less fat on the diaphragmatic and subinfundibular portions. The superficial myocardial fibers and the branches of the right coronary artery are disposed horizontally (transversely). The right atrial appendage partially covers the incipient part of the right coronary sulcus, the origin of artery itself being buried under conspicuous epicardial fat. It is also from this area that the artery of the sinus node usually takes off (Fig. 4). In contrast to the LV, the tricuspid and the pulmonary valves are broadly separated, the RV skirting between these two structures. As surface markings, the right coronary sulcus and the pulmonary ventriculo-arterial junction can be used to delimit the RV approximately. Hence, the RV appears pyramidal in shape and seems to wind around the LV. This disposition is evident from the inside, after the cavity of the RV is opened (Fig. 5)

THE MORPHOLOGY OF THE RIGHT VENTRICLE The muscular walls of the RV span between the right (tricuspid) atrioventricular junction and the pulmonary ventriculo-arterial junction, both bordered by

Fig. 1. Parasagittal section through the heart, illustrating the reciprocal relationships between the right and left chambers. The RV is most anterior and the right ventricular outflow winds around the aortic root. Note the non-planar disposition of the septum. Figure 1a demonstrates a human heart specimen. Figure 1b depicts an MRI image in a similar section. Ao 5 aortic root. CS 5 coronary sinus. LAA 5 left atrial appendage. LCA 5 left coronary artery (bifurcation of the main trunk). PT 5 pulmonary trunk. RCA 5 right coronary artery. RVOT 5right ventricular outflow tract. A, S and P 5 tricuspid valve leaflets: Anterior, septal, and posterior, respectively. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

the corresponding valves. The interior of the RV appears heavily trabeculated, except immediately underneath the septal leaflet of the tricuspid valve and, respectively, underneath the pulmonary valve. All trabeculae appear coarser than those in the LV (Kosinski et al., 2012) (Fig. 5). The RV can be divided into either two or three components. From the two-compartment perspective, the RV consists of the sinus (the pumping chamber) and the infundibulum, a disposition well illustrated by double-chambered RVs (with mid-cavitary obstruction) (Choi and Parl, 2010; Loukas et al., 2013;

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transposition of the great arteries with the posterior aorta (the infundibulum is attached to the LV and supports the pulmonary trunk). The sinus portion can be further subdivided into an AV canal portion (or inlet, underneath the septal leaflet of the tricuspid valve) and a trabeculated portion extending to the apex of the RV (however, the distinction is less evident at the posterior/diaphragmatic level as the posteriordiaphragmatic papillary muscle group merges into the apical trabeculae). The infundibulum can be also subdivided into a trabeculated proximal portion and a distal portion comprising the septal and parietal bands and the conal septum (Geva, 1997). From the three-compartment point of view the RV consists of inlet, apical trabecular and outlet. This tripartite concept appears more correct from the embryological point of view and more useful, as one or more of the three components may be lacking in malformed hearts (Goor and Lilehei, 1975). The bases of the papillary muscles of the tricuspid valve, and especially at the diaphragmatic level, merge into the trabecular apical section; consequently it is difficult to distinguish sharply between the two compartments in this area of the RV. The difference is better appreciated underneath the septal leaflet of the tricuspid valve. The three leaflets of the tricuspid valve are located (with the heart in anatomically correct position) septally/medially (the septal leaflet), anterosuperiorly

Fig. 2. The general disposition of the interventricular septum. (a) a heart specimen with only the left chambers preserved. Note the non-planar disposition of the septum, bulging toward the RV in the inlet and trabecular portions and more convex toward the LV in the outlet part. The fossa ovalis was preserved, together with the opening of the coronary sinus, in order to reveal the triangle of Koch and the area of the right fibrous trigone. AIVA 5 anterior interventricular artery (clinically called the left anterior descending LAD). CS 5 coronary sinus. FO 5 fossa ovalis. LA 5 left atrium. LAA 5 left atrial appendage. LCA 5 left coronary artery. RFT 5right fibrous trigone. NF and R 5 the non-facing (non-coronary) and the right sinuses of the aorta. Arrowhead indicates the tendon of Todaro. Asterisk 5 membranous septum. (b) The RV was separated from the LV. The septum appears convex toward the RV except in the outflow part of the RV. Ao 5 aorta. AIVA 5 anterior interventricular artery. PT 5 pulmonary trunk. RCA 5 right coronary artery. RVOT 5right ventricular outflow tract. Arrowheads indicate the convexity of the septum toward the LV, in the outflow part. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

Kokotsakis et al., 2014), congenitally-corrected malposition of the great arteries (the infundibulum is attached to the LV and supports the aorta), and

Fig. 3. The right ventricular portion of the septum, where the inlet, trabecular, and outflow portions are evident. The septal leaflet of the tricuspid was left “in situ.” The tricuspid and the pulmonary valves are separated from each other by muscular tissue constituting the septomarginal trabecula. The anterior interventricular artery was excised in order to demonstrate the anterior interventricular sulcus. The apex of the RV is located lower than that of the LV (arrowheads). Note the thin-walled RV (small arrows). Ao 5 aorta. IVS 5 anterior interventricular sulcus. LV 5 left ventricle. PT 5 pulmonary trunk. RCA 5 right coronary artery origin from the aorta. S 5 septal leaflet of the tricuspid valve. TSM 5 septomarginal trabecula. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

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Fig. 5. The general shape of the RV. The RV was separated from the remaining cardiac structures. Note the roughly triangular pyramidal shape of the RV and the angle between the inlet and outlet parts of the RV. The inlet and outlet also appear smoother than the trabecular portion. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

Fig. 4. Right lateral view of the heart and of the right portion of the coronary sulcus. The right atrial appendage and conspicuous epicardial fat cover the right coronary artery and the sinus node artery. (a) Demonstrates an undissected specimen. (b) Depicts a dissected specimen while “c” is a close-up of the latter. Ao 5 aorta. AIVA 5 anterior interventricular artery. IVC 5 inferior vena cava. LV 5 left ventricle. PT 5 pulmonary trunk. RAA 5 right atrial appendage. RMB 5 right marginal branch (from the RCA). SVC 5 superior vena cava. SNA 5 sinus node artery. Arrowheads indicate the apices of the RV and of the LV. Asterisks indicate the infundibular branches (from the RCA). [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

(the anterior leaflet) and diaphragmatic/inferiorly (the posterior leaflet). Each valve leaflet is sustained by tendinous cords originating from two adjacent papillary muscles (Fig. 6). The septal leaflet is sustained by cords from the posterior and medial (septal) papillary muscles (the latter usually represented by multiple cords originating directly from the septum), the anterior leaflet by cords from the anterior and from the papillary muscle of the conus (also called the muscle of Lancisi, representing a distinct portion of the septal papillary group) (Restivo et al., 1989), and the posterior leaflet by cords from the septal and posterior papillary muscles. The anterior papillary muscle supports the anterosuperior leaflet, but often in its middle part rather than at the site of apposition with the inferior leaflet. The anterosuperior leaflet is the most extensive of the three. This leaflet contributes most to the competency of the valve, and its reconstruction is mandatory in conditions such as Ebstein’s disease. The anterosuperior and inferior/diaphragmatic leaflets of the tricuspid valve are together analogous to the mural (“posterior”) leaflet of the mitral valve, although the tricuspid valvar leaflets do not close along a single zone of apposition. The leaflet tissue is redundant, accounting for the functional reserve of the tricuspid valve. The apical trabecular part of the ventricle has particularly coarse trabeculations, this being the most constant feature of the RV in malformed hearts. A prominent trabeculation is seen reinforcing the septal surface, forming a prominent Y configuration at the ventricular base where it clasps the supraventricular crest. This is the septomarginal trabeculation or septal band (Fig. 7). The medial papillary muscle arises from the posterior-caudal limb of the branch point, the anterior papillary muscle taking origin from the body of the trabeculation towards the ventricular apex. A

Right Ventricle Clinical Anatomy

Fig. 6. Advanced and deeper dissection of the RV, illustrating the tricuspid subvalvar apparatus. Part of the interventricular septum is retained. The right coronary artery was deliberately preserved and left in place in order to demonstrate the anatomical relationship with the tricuspid circumference (“annulus”). The papillary muscles of the tricuspid valve are readily apparent. The posterior papillary group (P) consists of two heads. The moderator band (MB) skirts between the septum and the anterior papillary muscle of the tricuspid valve. Note also how each of the valvar leaflets is sustained by two adjacent papillary muscles. The papillary muscle of conus (Lancisi) appears as a distinct head from the septum to sustain part of the anterior leaflet. Ao 5 aorta. AIVA 5 anterior interventricular artery. MB 5 moderator band. RCA 5 right coronary artery. A, P, and M 5 anterior, posterior, and medial papillary muscles of the tricuspid valve. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

further series of trabeculations extends from the anterior surface of the septomarginal trabeculation, running into the free RV wall. One of these septoparietal trabeculations is particularly prominent, joining the anterior papillary muscle and then continuing to the lateral RV wall (Anderson et al., 2014a). This is the moderator band; sometimes it is absent or replaced by two or more similar structures (Fig. 8). The supraventricular crest is often considered to represent a septal structure. In reality, it is no more than the inner curve of the free wall of the RV and is better described as the ventriculo-infundibular fold. A small part of the musculature located deep to the Y of the septomarginal trabeculation can be removed to provide access to the left ventricle (LV), so it represents the true muscular outlet septum. However, this septal component cannot be distinguished from the remainder of the muscular ventricular septum without dissection. Indeed, incisions made outside this restricted area communicate with the outside of the heart. A thorough localization of the outlet septum is mandatory in aortic root replacement/enlargement procedures such as the Ross-Konno operation (Erez et al., 2002). The ventriculo-arterial junction represents the true, anatomical boundary between the RV and the pulmo-

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nary trunk. In contrast to the aortic root, the pulmonary valve leaflets take off from the free-standing musculature of the infundibulum (Fig. 9). All landmarks described in the aortic root are less evident in the pulmonary trunk and valve, including the supravalvar crest (the sinutubular junction). The pulmonary root differs in microscopic structure from the aortic root, predisposing to the dilation of the neo-aortic root after the Ross operation (Muresian, 2001; Lansac et al., 2002). The smoother part of the RV outlet supports the three semilunar valve leaflets of the pulmonary valve. Toward the pulmonary valve, the trabeculae are longitudinally oriented. As with the aortic valve, the numerical nomenclature of the sinuses and leaflets has more practical value in congenitally malformed hearts, especially because the terminology in the Nomina Anatomica does not reflect the actual disposition in the adult (Table 1). In the adult human heart, the sinuses and leaflets of the pulmonary valve are posterior, right anterior and left anterior. The pulmonary root and sinuses appear more prominent than the aortic. A mismatch between the diameters of the aortic and pulmonary roots constitutes a contraindication for performing the Ross procedure (David et al., 1996).

Fig. 7. Interior aspect of the RV after opening its anterior wall. The pulmonary valve is wide open revealing the underlying structures: the supraventricular crest and the septomarginal trabecula (TSM) with its superior and inferior limbs, the latter giving origin to the papillary muscle of conus (Lancisi). The moderator band continues the trabecula septomarginalis to the base of the anterior papillary muscle. The anterosuperior leaflet of the tricuspid valve is the largest. Communication between the RV inlet and outlet takes place underneath the anterosuperior leaflet and between the anterior and medial papillary muscles and the moderator band. Note also that the pulmonary valve leaflets take off directly from the infundibular musculature. A 5 anterior papillary muscle of the tricuspid valve. AIVA 5 anterior interventricular artery. MB 5 moderator band. TSM 5 septomarginal trabecula. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

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Muresian cardiomyopathy/dyplasia (ARVC/D) preferentially affects the right ventricular epicardium between the conus and apex, a region called “the triangle of dysplasia”. The RV wall bears higher strains for longer periods of time, has elevated changes in strain over short periods of time, and near the apex is subject to heterogeneity in strain distribution over a small volume (Hariharan et al., 2012). The marked disarray at the RV apex signifies abrupt changes in myocyte

Fig. 8. A close-up of the interior of the RV. The anterior papillary muscle of the tricuspid valve originates directly from the septum with no distinct moderator band. Smaller, shorter and more slender trabeculations replace a well-formed moderator band (arrowhead). A 5 anterior papillary muscle of the tricuspid valve. Ao 5 aortic root (open). M 5 medial papillary muscle group of the tricuspid valve. PT 5 pulmonary trunk (open). RCA 5 right coronary artery. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

The valvar leaflets have no annulus in the sense of a fibrous ring. The crown-shaped insertion of the pulmonary leaflets crosses the anatomical ventriculoarterial junction, and as in the case of the aortic root the interleaflet triangles are incorporated within the RV outflow tract. However, the so-called annulus identified at the entrance to the pulmonary root is no more than a virtual ring that can be constructed by joining together the most proximal attachments of the leaflets. The supraventricular crest is interposed between the tricuspid and the pulmonary valves. The myocytes together with the connective tissue elements are spatially disposed, revealing to the naked eye the visible “grain” or myofibers. In the 2– 5 mm thick RV there is a predominant superficial circumferential disposition and a deeper longitudinal orientation, reflected in the two main types of contraction characterizing the RV: longitudinal shortening and circumferential narrowing (the bellows action of the RV). A hypertrophied RV as in the tetralogy of Fallot (TOF) reflects a change in architecture resembling the “sandwich” pattern of the normal LV with circular myofibers between two predominantly longitudinal layers (Sanchez-Quintana et al., 1996). The fiber orientation is not homogenous in the same layer and also differs in various parts of the heart. However, direct observation of subepicardial fiber contractility as during heart surgery is misleading, as the deeper layers cannot be thoroughly assessed except by transesophageal echography. Nevertheless, the structural attributes and the mechanical strains of the RV are region-dependent and can either cause, facilitate or perpetuate various types of dysrhythmias. Arrhythmogenic right ventricular

Fig. 9. The pulmonary valve leaflets take off directly from the infundibular musculature. (a) Anterior portion of a heart specimen, viewed from its posterior (endoventricular) aspect. On the right side: the RV; on the left: a small portion of the LV is visible, together with the anterolateral papillary muscle of the mitral valve. Note the more longitudinal disposition of the trabeculae in the outflow of the RV. AL 5 anterolateral papillary muscle of the mitral valve. LAA 5 left atrial appendage. L and R 5 left and right aortic sinuses. (b) Illustrates the same entirely muscular origin of the pulmonary valve leaflets after harvesting the pulmonary autograft during the Ross procedure (aortic valve replacement with pulmonary autograft). Ao 5 aortic root, prepared for autograft implantation, after the valve and sinuses are removed. LCA 5 left coronary button (to be reimplanted after autograft insertion). [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

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TABLE 1. Systematic Classification of the Sinuses of the Arterial Roots (adapted from Muresian, 2009b) Systematic classification of the sinuses of the arterial roots Numerical nomenclature (Leyden) Aortic root Pulmonary root

1 2 Non-facing 1 2 non-facing

Nomina anatomica Right Left Posterior/non-coronary Left Right Anterior

Actual disposition in the adult heart Anterior Left posterior Right posterior Posterior Right anterior Left anterior

Note: as in the case of the aortic root, the sinuses are numbered as from the point of view of an observer located in the non-facing (non-adjacent) sinus. The right-handed sinus is sinus #1, while the left-handed sinus is sinus #2.

orientation and loss of end-to-end coupling. However, the conduction abnormalities are not necessarily the result of preformed alterations in cardiac tissue, as cardiac structures can appear unaltered during the early stages of conditions such as ARVC/D. Of course, a particular region of interest among the components of the RV is the interventricular portion of the membranous septum, normally covered by the septal leaflet of the tricuspid valve. The bifurcating fascicle of His passes just underneath this portion of the membranous septum.

DEVELOPMENTAL HIGHLIGHTS Not all the myocardium of the growing heart tube will form heart chamber: the initially-formed heart tube will give rise only to the LV and the muscular ventricular septum, the remainder of the myocardium being recruited from the surrounding mesoderm (Cai et al., 2003). The potentially cardiogenic component of the mesoderm is larger than generally thought (Moorman et al., 2007). There are no primitive cavities in the linear heart tube that correspond to the definitive cardiac chambers. The definitive chambers do not differentiate as circumferential segments along the length of the primitive heart tube but rather as modules, perpendicular to the axis of the looping heart tube; this mechanism is called “the ballooning model” (Moorman et al., 2003; Van den Berg and Moorman, 2009). The RV, outflow tract and atria are formed by cardiomyocytes added to the heart at the arterial pole from the pharyngeal mesoderm (Cai et al., 2003). The ventricular septum is formed by the caudal fusion of the left and right heart-forming regions. Once the heart tube has looped, the developing heart chambers can be recognized as separate entities, with the appearance of the atrial appendages and of the apical components of the RV and LV. The persistence of the initial linear tube in the inner curvature permits the pathways to be remodeled for flow, the atria becoming connected with their corresponding ventricles and the latter with the appropriate arterial trunks (such re-arrangement is necessary because the atrioventricular canal is initially supported by the LV while the outlet is supported by the RV). A third population of cardiomyocytes is subsequently added, forming the dorsal wall of the left atrium and contributing to the formation of the primary atrial septum (Soufan et al., 2004). Prior to the expansion of the

atrioventricular canal the RV possesses only apical and outlet components, as found in malformed hearts with double-inlet LV and tricuspid atresia (Anderson et al., 2011). Following the expansion and rightward movement of the atrioventricular canal, the valvar orifice becomes continuous with the developing RV. Further remodeling leads to the transfer of half the outflow tract to the developing LV. The proximal parts of the outflow cushions, packed with cells of neural crest origin, produce the infundibulum and separate it from the aortic vestibule. The aortic root is transferred to the LV by remodeling of the leftward side of the primary interventricular foramen. The different building blocks of the heart and their definitive dispositions are mirrored in the ECG pattern with fast-conducting components interposed between persisting slow-conducting segments belonging to the primary myocardium. These latter parts are incorporated in the atrial vestibules—the atrioventricular ring tissue (Yanni et al., 2009)—and persist as the atrioventricular node. Additional parts are found in the aortic root: the dead-end tract (Kurosawa and Becker, 1985; Wessels et al., 1992). This disposition also explains the morphology of the atrioventricular node and bundle of His in cases with straddling tricuspid valves (Milo et al., 1979), double-inlet LV (Anderson et al., 1974a) and congenitally-corrected transposition (Anderson et al., 1974b). The extensive trabecular component of the RV wall is subsequently remodeled. The trabecular meshwork compacts to form the papillary muscles and gives rise to the subendocardial ventricular conduction pathways. It is likely that the growth of the compact layer normally outstrips that of the trabecular component. The abnormally continued growth of the latter accounts for the appearance of ventricular noncompaction (Freedom et al., 2005). RV stroke volume exceeds LV stroke volume by about one-third throughout gestation (Kenny et al., 1986). However, during fetal development of the circulation, the distribution of the cardiac output differs because of preload and afterload: the RV ejects into a low resistance/high compliance circuit of vessels, while the LV ejects into a high resistance/poor compliance circuit consisting of the coronary arteries, the upper body and the fetal head (Cuneo, 2014). Consequently, although it is dominant, the RV functions from very early stages as a volume pump. This is also reflected in the differences in weight between the LV and RV: the LV plus septum weighs about one-quarter

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Fig. 10. Serial sections through the heart by following a plane perpendicular to the long axis of the LV (as in the classical short-axis view). However, owing to the particular form and spatial disposition of the RV (which is not cylindrical/conical), and to the fact that the same plane of section does not cut the RV perpendicular to its long axis, the RV appears polymorphous—either crescent-shaped, spade-shaped, tubular, or so forth—depending on the cutting level. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

more than the RV at birth. RV function still predominates during the first 2–3 months of life, but the work of the RV decreases slowly and progressively relative to the LV. The LV becomes twice as thick as the RV by the second year and thrice by puberty (Anderson et al., 2014b). The combined and individual ventricular weights increase steadily with age and at similar rates. Throughout fetal life the LV plus septum is larger than the RV but the RV forms a greater proportion of the total ventricular mass than it does in the child or the adult (Hislop and Reid, 1972). Altogether, the fetal myocardium is different from the adult myocardium, with fewer and more immature contractile units, poorly-developed T-tubules and sarcoplasmic reticulum, fewer beta-adrenergic receptors and reduced sympathetic innervation (Lebowitz et al., 1972; Birk et al., 1992). The primary mechanism for increasing cardiac output resides in an increment of heart rate (rather than stroke volume) in the fetal heart. The RV has a much reduced ability to tolerate increased diastolic filling pressures (Thornburg and Morton, 1986; Reller et al., 1987) and this is aggravated by the reduced compliance of the chest wall, pericardium and fetal lungs (Grant et al., 1992).

COMPARISON BETWEEN THE RIGHT AND LEFT VENTRICLES The two ventricles appear totally different in shape and this is reflected in the contraction parameters of each. The LV can be described as almost cylindrical with a conical apex. The anterior leaflet of the mitral

valve alternatively separates the inflow from the outflow compartments of the LV. The base of the cylindrical-conical LV is equally shared by the aortic and mitral valves and part of the mitral valve also takes part in the makeup and function of the aortic root (Muresian, 2009a). The RV is described as “triangular,” “pyramidal,” “crescent-shaped,” “spadeshaped” etc. because of its particular form and the various modes of visualizing it. For example, shortaxis sections (such as the parasternal) cut perpendicularly through the long axis of the LV and the RV appear crescent-shaped or as an “appendix” of the LV. In this case, the plane of section passes obliquely through the RV (Fig. 10). In the apical four-chamber plane (parallel with the diaphragmatic surface of the heart), the LV and RV seem to have the same shape though the RV is smaller (Fig. 11). In this view, it seems tempting to use the same methods to measure the contraction parameters of the LV and RV. In the parasternal long-axis view, the RV appears spadeshaped; actually, this view reveals the RV inflow and its communication with the right atrium (Fig. 12). In the basal short-axis view the RV appears tubular and winding around the centrally-located aortic root. This is actually the outflow portion of the RV (Figs. 1 and 13). Diagnostic interrogation of the RV is evidently more complex than that of the LV: in each of the main views some portions of the RV can be better appreciated, others less well or not at all.

Fig. 11. Section through the heart as in a fourchamber plane, parallel to the inferior/diaphragmatic aspect of the heart. Valve leaflets and papillary muscles are apparent in both LV and RV. The lower insertion of the tricuspid valve divides the membranous portion of the septum into atrioventricular and interventricular parts. A, S 5 anterior and septal leaflets of the tricuspid valve. AML 5 anterior (aortic) leaflet of the mitral valve. AL and PM 5 anterolateral and posteromedial papillary muscles of the mitral valve. L and NC 5 left and non-facing sinuses of the aorta. Ao 5 aortic root, LAA 5 left atrial appendage. RCA 5 right coronary artery. [Color figure can be viewed in the online issue, which is available at wileyonline library.com.]

Right Ventricle Clinical Anatomy

Fig. 12. Section of the heart resembling the parasternal long-axis view. The RV appears spade-shaped. The communication with the right atrium is evident in this particular view as the RV inlet is easily distinguishable. Note also that the RV inlet merges into the trabecular portion and that it is difficult to distinguish clearly between the two compartments at the posterior level. Ao 5 aorta. L 5 origin of left coronary artery. P 5 posterior (inferior/ diaphragmatic) wall of the RV. PT 5 pulmonary trunk. RA 5 right atrium. S 5 septal leaflet of the tricuspid valve. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

Strictly anatomically speaking, the RV is a particular heart chamber possessing a main core consisting of the inflow and outflow compartments, continuous with each other between the septal and anterior papillary muscles, and underneath the anterior leaflet of the tricuspid valve (Figs. 6 and 7). This main core has extensions in the basal and apical directions communicating with the trabecular compartment. This can be illustrated under certain conditions such as Ebstein’s disease, in which the dysplastic leaflets of the tricuspid valve are concomitantly displaced toward the RV inlet–outlet junction. The trabecular compartment can become conspicuous, at times forming a prominent shelf at the inlet-trabecular junction (Fig. 14). The main core of the RV winds around the LV and septum such that the inlet, trabecular and outlet portions of the septum can be described only as viewed from the RV side and not from the LV aspect (Fig. 15). Indeed, the RV inflow corresponds to the LV outflow tract on the other side of the septum. The RV appears as a tube impressed by the bulging septum and having extensions toward the trabecular compartment. However, no conspicuous compression of the RV due to septal bulging with consequent RV failure (the socalled Bernheim syndrome) was demonstrated (Chung et al., 2013). Rather, the reverse condition of leftward bulging of the septum in RV dilatation can lead to LV failure. The wall is about three times as thick in the LV (2– 5 mm for the RV and 7–11 mm for the LV) and the LV weighs about three times more than the RV (26 6 5 g/ m2 for the RV versus 87 6 12 g/m2 for the LV), while

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the RV end-diastolic volume is slightly greater (75 6 13 mL/m2 in the RV versus 65 6 12 mL/m2 in the LV); the RV has a slightly lower ejection fraction (Walker and Buttrick, 2013). The RV has a work per beat ratio about a quarter of that of the LV, where the ratio between the pulmonary and systemic vascular resistances is 1/10 (Voelkel et al., 2006). The stroke volume is basically the same, although there can also be beat-per-beat differences depending on pulmonary vasculature capacitance, phase of the respiratory cycle, standing or sitting patient, degree of pulmonary or peripheral vasodilation etc. Besides the possible genetic divergence between the ventricles (Drake et al., 2011), such differences should be considered in the general context of the two distinct circulatory systems: pulmonary and systemic, volume-driven and pressure-driven respectively. As stated earlier, the RV always functions as a volume pump, including during the fetal period, and this explains its particular sensitivity to pressure overload and the late failure or limits of the systemic RV (as in malformed hearts or after surgical correction). In the RV the meridional (longitudinal) shortening dominates while in the LV the circumferential shortening is predominant, the latter being more marked at the subendocardial level and resulting in thickening of the LV wall and a concomitant and corresponding shrinking of the cavity (Naito et al., 1995). In the normal heart, RV pressure does not rise immediately although the RV is stimulated before the LV because the LV free wall and septum are still lax. RV ejection requires the development of tension in the septum, exerting a counterforce to the circumferential contraction of the

Fig. 13. Parasagittal section at the level of the heart base. The “highest” portions of the RV are visible: the pulmonary valve and trunk and part of the tricuspid valve. The lower portion of the atrial septum is also visible. Ao 5 aorta. LA 5 left atrium. PT 5 pulmonary trunk. RA 5 right atrium. RFT 5right fibrous trigone. LCA and LFT 5 left coronary artery and left fibrous trigone. R, L, and NL 5 aortic sinuses and valve leaflets: right, left and non-facing. Asterisks 5 orifices of the pulmonary veins. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

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Muresian contraction of the transverse fibers (the bellows action); and (3) traction on the free wall of the RV by the contracting LV and septum (Rushmer and Crystal, 1951; Rushmer and Thal, 1951). However, the phases of isovolumic contraction and relaxation are difficult to define in the RV. The normal RV pressure-volume loop appears triangular, differing significantly from the square or rectangle of the normal LV loop (Redington et al., 1988). There is another important difference regarding diastolic filling: the RV lacks the active diastolic suction that characterizes the LV (Buckberg, 2005; Yotti et al., 2005) and the contribution of the right atrium to RV diastolic filling is important. Right atrial infarction can complicate the dynamics of the right-sided heart chambers. Most atrial infarctions are right sided with two main types described: type 1—ventral, isolated and involving the right atrial appendage and adjacent areas; type 2 – dorsal, extensive, including posterior/ inferior biventricular infarctions. Right atrial infarctions also complicate the clinical picture by dysrhythmias, pulmonary embolism or, rarely, rupture. Various grades of right atrial infarction can be described, also depending on coronary typology and dominance (Table 2). It is important to consider the role of the pericardium (Smiseth et al., 1985). The pericardium can produce a constrictive and consequently deleterious

Fig. 14. Ebstein’s disease. (a) Anterior half of the RV and (b) posterior half of the RV—both viewed from the interior of the RV cavity. Note the dysplastic and attached leaflets of the tricuspid valve with no free margin, with short and disorganized tendinous cords and no definite papillary muscles. A prominent shelf is apparent at the inlet-trabecular junction (arrowhead). The posterior leaflet is displaced toward the apex of the RV, leaving a large atrialized part of the RV (backlit in Fig. 14b). The level of the normal insertion of the posterior leaflet is indicated by arrowheads in figure 14b. A, S, P 5 anterior, septal and posterior leaflets of the tricuspid valve. AL and PM 5 anterolateral and posteromedial papillary muscles of the mitral valve. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

RV. The RV will eventually empty after the LV even though the basal part develops contraction first. There is ventricular interdependence, as the septal wall is shared by both compartments. The pulmonary valve does not open only after the contraction of the RV transverse fibers, contraction of the septum being mandatory. The mechanisms of blood ejection from the RV can be summarized as follows: (1) meridional (longitudinal shortening): the tricuspid valve annulus moves in the apical direction (currently determined by measuring TAPSE, i.e., tricuspid annular plane systolic excursion); (2) compression of the RV chamber by

Fig. 15. The component parts of the two ventricles do not correspond with each other at the level of the septum. The LV inflow is separated by the LV outflow by the shifting anterior (aortic) leaflet of the mitral valve. Consequently, the LV aspect of the septum corresponds only to the trabeculated and outflow portions, while all three parts are distinguishable on the RV side. Left panel: the LV aspect of the septum after the mitral valve and all the subvalvar apparatus are removed. Right panel: the RV side of the septum. AIVA 5 anterior interventricular artery. AL 5 base of the anterolateral papillary muscle of the mitral valve. L 5 left coronary sinus of the aorta with LCA 5 left coronary artery. OM 5 obtuse marginal branch. RCA 5 right coronary artery. L and NF 5 left and nonfacing sinuses of the aorta. I, O, and T 5 inlet, outlet, and trabecular portions of the RV. [Color figure can be viewed in the online issue, which is available at wileyonline library.com.]

Right Ventricle Clinical Anatomy TABLE 2. Right Ventricular Infarction Grade 1 2 3 4

Necrosis 50% of RV diaphragmatic/posterior wall RV diaphragmatic/posterior wall and 50% of RV anterior wall

effect, especially in acute states, when the RV is prone to dilatation because of volume overload (augmented RV preload as in tricuspid or pulmonary valve insufficiency, atrial septal defect, anomalous pulmonary venous return), impaired contractility (as in RV ischemia/infarction, amyloid, sarcoid infiltration of the RV etc.), or pressure overload (afterload augmentation as in LV failure, pulmonary embolism, pulmonary hypertension, pulmonary valvar or infundibular stenosis). On the other hand, in chronic states, a new equilibrium is created between the intracavitary RV pressure, the external pressure produced by pericardial constriction and the intrinsic contractile properties of the RV. In such cases, pericardial drainage or pericardectomy can disturb this equilibrium, precipitating rightsided heart failure (Loukas et al., 2012).

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proximal septal artery (or arteries). Such branches are distributed to the muscular portion of the aortic root (anastomosing with the atrioventricular node artery, usually a branch of the right coronary artery), to the medial papillary muscle group of the tricuspid valve, and to the moderator band and base of the anterior papillary muscle of the tricuspid valve (where it eventually anastomoses with anterior branches from the right coronary artery) (Muresian, 2006). However, experimental studies must take the RV–LV interdependence into account (Muller-Strahl et al., 2002). While the septum is generally included in the LV, the method for delineating the body of the RV relative to the trabeculation and papillary muscles in ventricular volume analysis might matter more, especially when these structures are hypertrophied as occurs in congenital heart disease, either operated or not. When the trabeculations and papillary muscles are included in the RV volume the volumes are higher and ejection fractions lower. On the other hand, excluding these structures from the RV results in less inter-observer variability and shorter acquisition times (Winter et al., 2008). Some important clinical and diagnostic parameters must be taken into account. The RV is usually described by referring to qualitative features, e.g., in echography: “large,” “apex-forming.” The right atrial size represents an important marker for various types of cardiopulmonary disease (Raymond et al., 2002). The measurement of right atrial pressure and the

THE DEFINITION OF THE RV Differentiation of the RV from the LV would have both clinical and experimental value (Deng et al., 2012). Echographic and MRI interrogations of the RV have now become routine, precise delimitation and measurement of the structural and functional parameters of the RV being mandatory for the diagnosis and timing of therapy for an ischemic RV and for other non-ischemic disease states such as congenital heart disease (Geva, 2006; Knauth et al., 2008), pulmonary hypertension, and RV cardiomyopathy. Most studies include the septum as part of the LV (Hislop and Reid, 1972) as this component of the heart appears directly continuous with the remainder of the LV. Despite this anatomical congruence, the “epicardial” fiber shortening of the septum (i.e., the part of the septum facing the RV) exceeds that on the endocardial side, a situation contrary to that in the remainder of the LV wall. Moreover, closer anatomical interrogation reveals the impossibility of dividing the septum into distinct right and left parts. The septum develops and grows mostly by apposition of the adjacent ballooning RV and LV and a separate apex can be outlined for each ventricle; however, the septum itself appears as a condensed structure. The larger septal arteries divide into right and left branches, each vascularizing the corresponding side of the septum. Selective embolization or alcoholization or leftward-facing branches can induce limited areas of necrosis beneficial for treating hypertrophic cardiomyopathy. However, there is no demonstrable sidedness within the septum and no preferential arteries for one side or the other (Figs. 2, 6, and 16). As an example: the right side of the septum is traveled by branches originating in the main

Fig. 16. Vascularization of the RV—anterior view. Compare with Fig. 7. The entire anterior RV wall was removed together with most of the RV side of the interventricular septum. Most of the arterial branches vascularizing the RV are visible. The anterior interventricular artery (AIVA) gives off a diagonal branch (D) and seven anterior septal branches (1–7). The right coronary artery (RCA) gives off the right marginal branch (RMB) and a branch for the anterior RV wall, the latter anastomosing at the base of the anterior papillary muscle (A) with branches from the first and second septal arteries (establishing an intercoronary anastomosis). M 5 medial papillary muscle of the tricuspid valve. PT 5 pulmonary trunk. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

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TABLE 3. Vascularization of the Right Ventricle Vascularizaton of the right ventricle Region Infundibulum

RV anterior wall and acute margin RV inferior/ diaphragmatic wall Posterior septum

Medial papillary muscle group of the tricuspid valve Posterior/diaphragmatic papillary muscle group of the tricuspid valve Anterior papillary muscle of the tricuspid valve Atrioventricular node and surrounding area

Artery Right anterior infundibular branch

Origin RCA or conus artery right aortic sinus

Right posterior infundibular branch

RCA or conus artery (rarely, directly from the right aortic sinus) LCA or left aortic sinus

Left posterior infundibular branch Left anterior infundibular branch “Right diagonal branches” Anterior RV branches Right marginal branch Posterior RV branches

Posterior septal arteries

Anterior septal branches (usually first, second) Same as RV inferior/ diaphragmatic wall (see above) Anterior RV branches AV node artery

Notes The most constant of the infundibular branches May anastomoze with the first septal artery Inconstant branch

AIVA AIVA RCA, conus artery, third coronary artery RCA accessory (double) RCA Inferior interventricular artery Inferior interventricular artery AIVA recurrent tract

Rare, inconstant

A branch of the RCA or Cx Branch of the RCA or Cx May ascend up to the crux cordis

AIVA

RCA right marginal branch One branch from RCA One branch from Cx Two branches from RCA One branch from each coronary

Single artery or doubled

AIVA 5 anterior interventricular artery (clinically called LAD: left anterior descending). Cx 5 circumflex branch of the left coronary artery. LCA 5 left coronary artery. RCA 5 right coronary artery. Adapted from Muresian, 2009b.

diameter and dynamics of the inferior vena cava will offer important additional data. Functional tricuspid regurgitation (absence of tricuspid valve pathology) is prevalent in patients with right heart disease. Besides the RV area and volume, the ultrasound interrogation must also estimate the dimensions of the RV outflow tract (Rudski et al., 2010), RV wall thickness (Schnittger et al., 1983), longitudinal shortening (TAPSE), tricuspid annular velocity, functional area change (Anavekar et al., 2007), the myocardial performance index (Tei et al., 1996), the determination of RV strain by tissue Doppler imaging (TDI), and not least, the measurement of pulmonary artery pressure.

VASCULARIZATION OF THE RIGHT VENTRICLE AND RIGHT VENTRICULAR ISCHEMIA/INFARCTION Both coronary arteries contribute branches to the vascularization of the RV (Table 3). Adjacent regions of the RV and LV are often vascularized by branches

with a common origin (Fig. 16). While the infundibulum and anterior RV wall receive a more constant arterial supply (Table 3), the vascularization of the inferior/diaphragmatic wall and posterior septum depends on coronary typology and on the relative dominance (Figs. 17 and 18). Arterial branches from the left coronary system supply the free wall of the RV adjacent to the anterior part of the septum, the apical area of the RV, the moderator band and sometimes the posterior septum and the medial and posterior papillary muscle group of the tricuspid valve. However, the right coronary artery is almost always the main arterial supply towards the base of the RV. In most cases, the RV and right atrium share a common arterial supply from the right coronary artery; consequently, occlusion of the proximal right coronary artery can lead to RV and right atrial infarction (see also below). In particular, the sinus node, the atrioventricular node, and the His fascicle and its main branches can also become involved as a consequence of ischemia (Figs. 17–21). At microscopic level, the vascular patterns of the RV and LV are similar, both having branching and

Right Ventricle Clinical Anatomy

Fig. 17. Vascularization of the RV—posterior view. The specimen illustrates a case of right coronary artery dominance (RCA), as this artery gives off the inferior interventricular artery together with inferior left ventricular branches, almost reaching the obtuse margin of the heart. Two arteries for the atrioventricular node are visible (arrowheads), both originating in the RCA. The circumflex branch (Cx) is short, ending with an obtuse marginal branch (OM), and the anterior interventricular artery has no recurrent tract. LA 5 left atrium. LV 5 left ventricle. NF 5 non-facing (non-coronary) sinus of the aorta. RA 5 right atrium, (of which large portions were removed in order to demonstrate the underlying NF aortic sinus). RV—right ventricle. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary. com.]

straight types of arteries (Baroldi and Scomazzoni, 1967; Farrer-Brown, 1968). The thinness of the RV in comparison to the LV accounts for its alleged relative paucity of vascularization. On the other hand, the RV possesses numerous Thebesian vessels that could offer alternative pathways in chronic stenotic coronary disease. It is also of interest that there is a continuity of myocardial sinusoids between the RV and LV (Vineberg and Lwin, 1972). The RV appears relatively resistant to ischemia. The systolic/diastolic coronary blood flow ratio is higher in the RV; it has a reduced oxygen demand, and it has an increased capacity to extract oxygen under conditions of hemodynamic stress. The possible role of the Thebesian vessels and an extensive collateral circulation must be also considered (Cross, 1962; Saito et al., 1989; Setaro and Cabin, 1992). Nevertheless, such differences could also be related to differences in ventricular wall stress and intraventricular pressure dynamics (Kusachi et al., 1982). Increased myocardial impingement on right coronary artery flow during systole, which can occur in RV hypertension, could be an important factor leading to RV failure (Brooks et al., 1971). Ischemic RV dysfunction can range from mild states to cardiogenic shock. The return to normal function generally takes place over weeks or months, being a classical example of

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myocardial stunning rather than irreversible necrosis. The free wall of the RV bulges, becoming almost aneurysmal (rather than thickened and akinetic), and with ischemia both systolic and diastolic dysfunctions are evident. Marked dilatation of the RV can impede diastolic filling of the LV. The clinical condition can be aggravated by septal infarction, LV infarction/dysfunction, atrial infarction, volume depletion, or administration of diuretics or nitrates. When higher pressures develop in the right atrium a probe-patent foramen ovale can open, leading to a right-to-left shunt and persistent, refractory hypoxia. RV and septal protection during cardiac surgery and proper revascularizaton is mandatory. Observations of proper contractility in the superficial fibers of the RV (infudibulum and anterior RV wall) is misleading; while the patient is being weaned from a cardiopulmonary bypass, transesophageal ultrasound interrogation provides the most relevant and clinically useful details. Extensive incisions involving the RV anterior wall and infundibulum can compromise the contractility of the RV. Incisions through the septum, as in the Konno and Ross-Konno procedures, will interfere with one or more septal arteries and it is difficult to establish a long-term prognosis, especially for pediatric patients. The vascularization of the RV can also reflect numerous variations in coronary artery origin, tract and distribution. Some can interfere with surgical

Fig. 18. Vascularization of the RV—posterior view. The specimen illustrates a case of left coronary artery dominance. The right coronary artery (RCA) gives off a short and slender inferior interventricular artery, while the anterior interventricular artery (AIVA) follows a long recurrent tract. The circumflex branch (Cx) gives off a large obtuse marginal branch (OM), winds around the mitral annulus and ends with the atrioventricular node artery (visible as it goes deep to the fossa ovalis (FO). The sinus node artery (arrowhead) also originates from the Cx. AIVA rec. 5 recurrent tract of the anterior interventricular artery. Ao 5 aorta. IVC 5 inferior vena cava. LV 5 left ventricle. RA 5 right atrium. RV 5 right ventricle. SVC 5 superior vena cava. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary. com.]

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Muresian 2011), abnormal origin of the coronary arteries from the pulmonary trunk (Ochos-Ramirez et al., 2005), origin of the anterior interventricular artery from the pulmonary trunk (Prost et al. 1976), origin of the left main coronary artery from the right aortic sinus and preinfundibular course, origin of the anterior (or accessory) interventricular artery from the right coronary artery or the right aortic sinus (Canga et al., 2010), single coronary artery with origin in the left aortic sinus, and a preinfundibular course of the right coronary artery. The numerous coronary arterial variations in congenitally malformed hearts are not discussed in this article. Few of the RV veins drain into the coronary system; most are non-coronary sinus tributaries draining directly into the right atrium. The anterior veins of the RV unite to various extents with the infundibular veins or right marginal vein and may form the so-called small cardiac vein, eventually opening either separately into the RA or joining the coronary sinus. This anatomical disposition can render the RV more vulnerable to ischemic injury during cardiac surgery as retrograde cardioplegic solution delivery might not reach all areas of the RV.

Fig. 19. Vascularization of the pulmonary infundibulum, right lateral aspect (Fig. 19a) and anterior aspect (Fig. 19b). The pulmonary trunk (PT) is retracted anteriorly. The arterial branches vascularizing the infundibulum are visible (arrowheads). The right coronary artery (RCA) and the conus artery (conus) give off right anterior and right posterior branches. The anterior interventricular artery (AIVA) gives off a left posterior infundibular branch. Note also the sinus node artery (SNA) originating from the RCA. Ao 5 aorta. LCA 5 left coronary artery (main trunk). RMB 5 right marginal branch. The posterior (right and left) infundibular pedicles are clearly visible (arrowheads) in the anterior view (Fig. 19b). The anatomical relationship between the first septal branch (S1) and the infundibular pedicles is of surgical relevance, as the S1 must be preserved while the pulmonary autograft is harvested during the Ross procedure. The aorta and pulmonary trunk were artificially separated at the level of the distal (outlet) septum. Further dissection would inevitably lead into the cavity of the RV (which is thinner). For this reason, the surgeon must “err” toward the LV when harvesting the pulmonary autograft. [Color figure can be viewed in the online issue, which is available at wiley onlinelibrary.com.]

reconstruction, especially major arterial branches crossing the infundibulum: an aberrant right coronary artery from the pulmonary trunk (Winner et al.,

Fig. 20. Vascularization of the RV and atria. Superior, basal aspect of the heart specimen. The valve leaflets and sinuses of the centrally-located aortic root are visible: R 5 right, L 5 left, and NF 5 non-facing (non-coronary) as well as the origin of the right (RCA) and left coronary artery, the latter dividing into the anterior interventricular artery (AIVA) and circumflex branch (Cx). The infundibular and anterior right ventricular branches from the RCA are visible. Two posterior infundibular branches are also apparent, one originating directly from the right aortic sinus and the other directly from the proximal AIVA (arrowheads). Note also the origin and position of the first septal branch (S1). The RCA and the Cx give off atrial branches that anastomose in a retroaortic position and two branches for the sinus node arise from them (SNA). LAA 5 left atrial appendage. PT 5 pulmonary trunk. RAA 5 right atrial appendage. SVC 5 superior vena cava. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

Right Ventricle Clinical Anatomy

Fig. 21. Vascularization of the ventricles. Posterior basal view. Advanced dissection both main coronary trunks are visible from their aortic origin to their termination. The right coronary (RCA) dominance is evident, the RCA terminating by giving off posterior left ventricular branches (PLV) and two atrioventricular branches (arrowheads) after winding around the tricuspid valve “annulus.” The similar disposition of the circumflex branch (Cx) is also apparent, encircling the mitral valve annulus. The three leaflets of the tricuspid valve, A 5 anterior, P 5 posterior, and S 5 septal, appear as in closed position. Note the cleft between the anterior and septal leaflets, corresponding to the membranous septum. The mitral valve leaflets: aml 5 anterolateral and pml 5 posteromedial appear as in the open position. The aortic sinuses (R5 right, L 5 left, and NF 5 non-facing) were excised in order to demonstrate the aortic valve leaflets and the origin of the coronary arteries. RMB 5 right marginal branch. conus 5 conus artery. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

THE RV IN MALFORMED HEARTS AND IN VARIOUS DISEASE STATES The response of the RV to a pathological load is complex and reflects the nature, severity, and chronicity of the insult. The timing of the insult is equally important and its effects differ depending on whether it appears during fetal, neo-natal, pediatric or adult life (Walker and Buttrick, 2013). The RV is more tolerant of volume overload than pressure overload and more tolerant of pulmonary valvar stenosis than the equivalent degree of RV hypertension produced by pulmonary vascular disease. In the hypertrophied RV, and especially when there is pressure overload, there is a shift from mitochondrially mediated oxidative metabolism to glycolysis. Nonetheless, in chronic pressure overload, a hyperplastic response has also been demonstrated (Leeuwenburgh et al., 2008). Therapies that are obviously beneficial in LV failure, such as beta-blockade and angiotensin converting enzyme inhibition, have not demonstrated clinically significant benefits in RV failure. In some models of pure RV failure the use of beta-blockers has proved

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deleterious, irrespective of the effect on pulmonary vasomotor tonus (Fan et al., 1987; Bolger et al., 2002). The main causes of pressure overload are: LV failure (the most common), pulmonary embolism, pneumonia, pulmonary infiltrative disorders, pulmonary hypertension, and congenital heart disease presenting with pulmonary (valvar, infundibular, or peripheral) stenosis. A particular case involves the systemic RV in congenital heart disease, either operated or not. Precise measurement of RV parameters is mandatory for surgical indication, timing of surgery and follow-up. The principal conditions producing volume overload are tricuspid and pulmonary regurgitation, arteriovenous fistulas, and once again congenital heart disease, for example atrial septal defect and anomalous pulmonary venous return. Impaired RV filling, e.g., in constrictive pericarditis and tricuspid valve stenosis, can also lead to RV failure. The particular intrinsic disorders involving the RV are ischemia, (ARVC/D), infiltrative cardiomyopathy, amyloid, and sarcoidosis. The paradigm offered by congenital heart disease is worth considering. The RV can be the main pumping chamber (Van Praagh et al., 1971; Houyel et al., 1995; Van Praagh et al., 1975; Jaggers et al., 2000) or become the systemic ventricle after repair. The fate and the results depend on associated lesions, shunts, status of the LV and pulmonary vasculature. The distinction between RV hypertrophy as a normal adaptation process versus a risk factor in the post-switch operation period requires precise quantification of structural and functional RV parameters and is better established using cardiac MRI (Grothoff et al., 2012). Ebstein’s disease is characterized by displacement of the leaflets of the tricuspid valve toward the inlettrabecular junction, where there is usually a prominent shelf (Fig. 14). The leaflets are dysplastic and cribiform and their free margins are attached to the shelf. Communication between the RV inflow and outflow tracts is possible only through the commissures or through the leaflets. A large portion of the RV is atrialized. The RV is small and inefficient, the tricuspid valve is insufficient and dysrhythmias are frequent. There are various clinicopathological pictures ranging from mild displacement of the leaflets and a small atrialized RV chamber, to extremely reduced leaflets, marked thinning of the RV wall and a poorly contracting RV. Other arrhythmogenic conditions are Uhl’s anomaly and ARVC/D. Although these are distinct entities they could share a common pathogenesis. The degree of deficiency of the myocardium is maximal in the outlet region and minimal in the inlet region, suggesting a longitudinal rather than a lateral orientation or developmental defect, i.e., selective maldevelopment of the myocardial mantle in the distal (arterial) end of the primitive cardiac tube (Gerlis et al., 1993). In Uhl’s anomaly the myocardial mantle does not develop in the distal part of its primitive precursor. The epicardium and endocardium remain in contact and some myocardium is replaced by adipose tissue. Patchy non-development of muscle and progressive

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Muresian

TABLE 4. UHL’S Anomaly Versus Arrhythmogenic Right Ventricular Cardiomyopathy (Adapted from Romero et al., 2013) Features

Uhl

ARVC/D AD some variants AR Apoptotic dysplasia and fibro-fatty infiltration

Age at presentation Male/Female ratio Clinical presentation

Rarely familial Apoptotic dysplasia and complete absence of myocardium Neonatal, infant 1.27/1 Cyanosis, dyspnea, RV failure

Progression of disease

Not progressive

Inheritance Pathogenesis

degenerative changes in adjacent surviving muscle can allow reassembly from ARVC/D and longer survival. On the other hand, ARVC/D is an uncommon genetic disease principally affecting the RV by adipose or fibrous tissue replacement of the myocardium (Basso and Thiene, 2005; Basso et al., 2008a, 2008b, 2009). It is frequently associated with cutaneous syndromes (Romero et al., 2013). Differentiation from Uhl’s anomaly is itemized in Table 4. In tricuspid atresia the RV lacks its inlet and communicates with the LV through a septal defect. Ventriculo-arterial connections might or might not be concordant. The apex of the LV becomes prominent owing to LV hypertrophy. Very different arrangements are seen depending on the degree of RV underdevelopment and on the ventriculo-arterial connections. Papillary muscles are absent. Alterations in atrial and LV myoarchitecture are related to global cardiac function and the development of dysrhythmias (SanchezQuintana et al., 1999). Non-compacted cardiomyopathy usually involves both ventricles. If the ratio of non-compacted to compacted myocardium exceeds three, and/or three or more segments are involved, the prognosis is poor (Espinola-Zavaleta et al., 2006). The clinical manifestations can range from asymptomatic to congestive heart failure, arrhythmias, and emboli. Involvement of the RV is more difficult to diagnose but should be investigated in cases of LV non-compaction. In TOF (Baillard and Anderson, 2009; Loukas et al., 2014) the combination of a deviated outlet septum and hypertrophied septomarginal trabeculations produces the characteristic RV outflow tract obstruction. The deviation of the muscular outlet septum creates a “malalignment type” of ventricular septal defect and results in aortic override. Across the defect, when the remnant of the interventricular portion of the membranous septum is involved, there is fibrous continuity between the aortic and tricuspid valve leaflets. In a small proportion of patients the anterosuperior margin of the defect is formed by a fibrous continuity between the leaflets of the aortic and pulmonary valves. The obstructive muscular subpulmonary area is due to the narrowing of the RV outflow tract and shows a dynamic pattern exacerbated by volume depletion and catecolamines, leading to sudden and acute episodes of desaturation (hypercyanotic spells). There are numerous other modifications at the level of the RV corresponding to anatomical variants of the

Adolescent 2.28/1 Asymptomatic, palpitations, chest pain, to ventricular arrhythmias and heart failure Progressive; postnatal development

TOF: TOF with pulmonary atresia, TOF with absent pulmonary valve, TOF with double-outlet right ventricle (RV), TOF with atrioventricular septal defect; however, these are not detailed here. Besides the coronary arterial variations, the atrioventricular conduction tissue can be anomalously located in TOF, especially when the orifice of the tricuspid valve is overridden (Millo et al., 1979). As with other congenital cardiac conditions, important questions arise and still need pertinent answers. The issue of surgical indication and timing is paramount, because a balance must be achieved between limiting the burden on the RV on the one hand and minimizing the lifetime number of surgical interventions required for a given patient on the other. The place and timing of percutaneous interventions such as pulmonary valvar plasty, percutaneous replacement of the pulmonary valve, etc. need particular consideration. Indeed, all such issues need to be considered in the general picture of the cardiocirculatory system, not focusing solely on the RV.

FINAL REMARKS The distinct developmental and morpho-functional features of the RV require a thorough diagnostic assessment as there is still no standardized approach. Parallels between the left and RVs are seldom useful in clinical practice. On the one hand, the RV can be bypassed in selected cases with no dramatic short- or mid-term outcomes provided the LV and other cardiocirculatory structures are functioning normally. On the other, long-term results of unrecognized or untreated RV deficiency and progressive functional decline induce a dim prognosis, including irreversible cardiac and multiorgan deterioration. RV dysfunction can manifest insidiously, eventually restricting the therapeutic options. A thorough re-appraisal of the clinical anatomical particulars of the RV is of the utmost importance for the continuous improvement of diagnostic and therapeutic measures in everyday clinical practice.

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