Fascicular
Blocks: Not Interpretable Electrocardiogram David H. Spodick,
I
ntroduction of the concept of hemiblock of the left bundle branch system’ (less erroneously termed “fascicular block”) was a pioneering effort that enabled electrocardiographers to think clinically in terms of the pathophysiology of conduction system lesions. Few would dispute that blocks can exist in particular parts of the conduction system, with or without accompanying myocardial lesions. However, it is questionable that one can securely deduce from the ordinary electrocardiogram the presence of such specific forms of interrupted conduction and highly questionable that their anatomic locations can be predicted. Much evidence now exists that the left bundle system only rarely approaches being biiascicular2~3 (negating any idea of hemiblock, which implies a bifascicular system); although an effective septal ramus can be demonstrated,4 even a trifascicular system remains too simplistic when d§ions of the left bundle system consistently show broader and narrower portions connected by loops and bridges, almost always among an assortment of fan-like smaller fascicles.2-5 These complex arrangements are further confounded by great intersubject variability.2,4 Moreover, tine dissection limited to the left bundle conducting system in patients whose electrocardiograms show either left- or right-axis deviation - necessary to even consider a fascicular block from the electrocardiogram - disclose a plethora of lesions, most quite proximal to the proposed anterior and posterior major fasci~les.**~ Furthermore, many patients with appropriate axis deviations have additional or isolated lesions of the myocardium both adjacent to and remote from the bundle system.4Jj Long ago, for example, Grant6 showed that a myocardial lesion in an appropriate location could slow intramyocardiil conduction so that the terminal portion of the QRS would be generated in such slowed areas, skewing the net QRS vector toward them. Thus, an. anterolateral infarct, for example, would tend to generate a left-axis deviation on this basis with or without involvement of the conducting system. Reeent eAeneer Phase analysis using a variety of approaches-is has found wide clinical and investigative application, primarily as a method for evaluating ventricular regional wall motion abnormalities in the diagnosis of ischemic heart disease. New evidence bearing on putative fascicular block has appeared using phase image characterization of ventricular contraction in patients with a range of left-axis deviation and left-axis deviation combined with right bundle branch block.” From the Cardiology Division, St. Vincent Hospital; and the Department of Medicine, University of Massachusetts Medical School, Worcester, Massachusetts. Manuscript received March 2,1992; revised manuscript received and accepted June 1,1992. Address for reprints: David H. Spcdick, MD, Cardiology Division, St. Vincent Hospital, Worcester, Massachusetts 01604.
from the
MD, DSC
The investigators used an electrocardiographic-gated blood pool scan using first-harmonic Fourier analysis of the images to determine whether left anterior “hemiblock” was present in patients with left-axis deviation and no contraction abnormalities. They reasoned that phase changes in particular regions would follow their electric activation sequence, and if this was abnormal then myocardial responses would follow the same sequence. In 20 cases of left-axis deviation, including 5 with values of Z-60’, they found no difference in the phase image compared with that in normal control subjects. They conceded that the phase image does not netessarily track the electrical conduction system itself, but definitely expresses the process of regional ventricular contraction accompanying electric conduction. Whereas a possibility of theoretical fascicular block cannot be excluded on the basis of the phase image alone, the results indicate that such isolated disorders of some left anterior “fascicle” without myocardial lesions may well exist, but must be comparatively rare.’ l The authors found no conclusive reason why, in 5 patients with right bundle branch block and left-axis deviation, phase image results more compatible with an anterior fascicular block were noted, however, they offered the hypothesis that left-axis deviation complicated by right bundle branch block is primarily caused by abnormalities exclusively in the conduction system, whereas isolated left-axis deviation could be due to myocardial factors. Meticulous anatomopathologic studies of the left bundle system support this conclusion.2~3J2 Evldmtlary synopsis (Tabk I): The report by Ono et al” is only the most recent in a large amount of evidence that makes it impossible to conclude from an ordinary electrocardiogram that some kind of fascicular block is present. Fascicular blocks or some equivalent in a very complex system may really exist, but interpretation is confounded by (1) marked anatomic differences in the proximal organization of the left conduction system, (2) any resultant concentration in 2 and 23 virtual TABLE I Fascicular Blocks: Factors Limiting or Rendering Improbable Their Diagnosis from the Electrocardiogram Basic anatomic complexity and marked intersubject variability of the left bundle system Most anatomically demonstrable lesions far from sites of electrocardiogram-indicated fascicular interruption Phase imaging showing ventricular contraction sequence to be unpredictable from sites of electrocardiogram-suggested fascicular blocks Low probability of lesions strictly confined to the conduction system. Corollary: contribution to net QRS vector (hence axis) of associated or additional myocardial lesions extrinsic to the bundle system Confounding factor: inherent inaccuracy of the Einthoven equilateral triangle, making axis determination intrinsically imprecise
EDITORIALS
809
(or ultimate) fascicular end-organs,and (3) the common presenceof a variety of myocardial abnormalitie,~.~,~*~J l-l3 Thii is further confoundedby the massive inaccuracy of the Einthoven triangle, an equilateral (hence unnatural) assumptionthat applies with precision only rarely, if ever.12(In nature, anything equilateral, smooth, perfectly round or linear must exist only by accident.) We use thii triangle becauseit simplifies constructionof a frontal plane axis.Even if the Einthoven triangle could apply to every individual axis confmed to the frontal plane of a 3-dimensionalstructure, axis change must nearly always occur in spacerather than only in 1 plane,making the traditional “QRS axis” (shorthand for frontal plane axis) inherently imprecise. Thus, constructingexact axis ranges (e.g., 5-45O) to define an impossible,or at best clinically improbable, diagnosislike fascicular block will introduce other imprecisions. Ceneh&n: The electrocardiographershould report exactly what he sees:a frontal plane axis basedon the Einthoven triangle. The consumer of this information will understand that one of the possibilitiesof marked axis deviation from normal is a fascicular block, actual or virtual (i.e., an equivalent at the anterosuperior or posterior extreme of the complex left conducting system), but it is misleadingto use thoseterms in electrocardiographic interpretation when an electrocardiographic axis cannot provide precise and certainly not conclusiveevidence.Qn the other hand, to use the kind of physiologicthinking introduced by Rosenbaumet al1 is an important adjunct to electrocardiography and
should not be neglected.Meanwhile, it is to be hoped that the electrophysiologists will further developclinical electrophysiologyof the bundle branches to bring us nearer to an acceptableresolution of this problem.
REFERENCES 1. Rosenbaum MB, Eliiri MV, Jzzari 0. L.os Hemibloqus. Buenos Airex Ed Paidos, 1968. 2. Rosai L. Hi&pathology of conducting system in left anterior hemiblock. Br h%wr J 1976;38:1304-1311. 3. Uhley HN. Some controversy regarding the peripheral distribution of the conduction system. Am J Cardiol 1972;30:919-920. 4. Nakaya Y, Hiiga T. Reaaaeasment of the subdivision block of the left bundle branch. Jpn Circ J 1981;45:503-516. 1. Massing GK, James TN. Anatomical confiition of the Hi Bundle and Bundle branches in the human heart. Circularion 1976;53:609-621. S. Grant RP. Left axis deviation: an electmcardiographic-patholo@c correlation study. Circulation 1956;14:233-249. 7. Verba JW, Bomatein I. Alaamki NP, Taylor A, Bhargava V, Shabetai R, L-eWiiter M. Gnset and progxaaion of meohanical systole derived from gatad radionuclide tecbniqucs and diiplayed id tine format. J Nucl Med 1979;20: 625-626. 8. B&nick E, Dunn R, Fraia M, O’Connell W, Shosa D, He&ens R, Scheinman M. The phase images its relationship to patterns of contraction and conduction. Circulation 1982;65:5Sl-560. 9. Frais MA, Botvinick EH, Shosa DW, O’Connell WJ, Scheinman MM, Hattuer RS, Morady F. Phase image characterization of ventricular contraction in left and right bundle branch block. Am J Cardiol 1982;50:95-105. 10. Kuecherer HF. Abbott JA, Botvinick EH, Schebunan ED, O’ConueU JW, Scheimnan MM, Foster E, Schiller NB. Twodimenaional eehoranliographic phase analysis: its potential for noninvaaive localization of aaxasory pathways in patients with Wolff-Parkinson-White syndrome. Circulation 1992;85:130-142. 11. Ono A, Mizuno H, Tahara Y, Ishikawa K. Phase image characterization of ventricular contraction in left anterior hemibkxk. Jpn Circ J 1991;55:473-480. 12. Spodick DH. Left-axis deviation and left anterior faacicular block. Am J Cardiol 1988;61:869-870. 13. Demoulii C, Kulberhu HE. Histopathological examination of concept of left hemiblock. Br Heart J 1972;34:807-814.
Low High-Density Lipoprotein Cholesterol What to Do Abbut It”
and
William B. Kannel, MD
a
lood lipids are fundamental in atherogenesis.Control of lipids is acknowledgedas essentialin preention of coronary diseaseby :he federal guide lines that focus on total cholesteroland its low-density lipoprotein (LDL) cholesterolcomponent.’ Despite the demonstratedstrong relation of low high-density lipoprotein (HDL) cholesterol to the occurrence of core nary artery disease(CAD) and the biologic plausibility From the Department of Medicine, Section of Preventive Medicine and Epidemiology, Evans Memorial Re8carch Foundation, Boston University School of Medicine, Boston, Massachusetts. This study was supported by the Charles A. Dana Fouitdation, New York, New York, Mod, Sharpe & Dobme, R&way, New Jersey, and Grants NOl-HV92922 and NOl-I-IV-52971 from the National Institutes of Health, Jktbcsda, Maryland. Manuscript received March 9.1992; revised manuscriptrcccivedandaaxptedMay 11,1992. Address for reprints: Wii B. Kannel, MD, Boston University/ Framin&am Heart Study, 5 Thurber Street, Fmmingham, Massachu-
setts 01701. *Presented at the National Heart. Lung, and Blood Institute Conference on Chol&erol and High Blood Pressure, Washington, D.C.,
April 1991. 810
THE AMERICAN
JOURNAL
OF CARDIOLOGY
VOLUME
70
of the relation, the Federal guidelineshave beencircumspectconcerning HDL cholesterol.The understanding of the HDL metabolismwas consideredby the expert panel to be too primitive and laboratory measuremer:.: of HDL cholesterol too inaccurate on which to base clinical decisions1Also, there has not yet beena clinical trial conductedto test whether raisii HDL alone reducesrisk of CAD independentof lowering LDL cholesterol. The recently revised guidelines recommend HDL cholesterol determination on all personshaving cholesterolmeasured,but they fail to take into consideration the benefitsof a high HDL cholesterolresultingin an acceptabletotal/HDL cholesterolratio despitean elevatedtotal cholesterolor LDL cholesterol.Recommendations concerning triglycerides also fail to take ade quately into accountthe heterogeneityof this entity, its importancein choosinglipid-lowering agentsand its importance as an indicator of the metabolic problem. Epidemiologic data consistentlydemonstrate that there is a protective HDL cholesterol component involved in removal of cholesterolfrom the tissueswhich
SEPTEMBER
15, 1992
Blocks: Not Interpretable Electrocardiogram David H. Spodick,
I
ntroduction of the concept of hemiblock of the left bundle branch system’ (less erroneously termed “fascicular block”) was a pioneering effort that enabled electrocardiographers to think clinically in terms of the pathophysiology of conduction system lesions. Few would dispute that blocks can exist in particular parts of the conduction system, with or without accompanying myocardial lesions. However, it is questionable that one can securely deduce from the ordinary electrocardiogram the presence of such specific forms of interrupted conduction and highly questionable that their anatomic locations can be predicted. Much evidence now exists that the left bundle system only rarely approaches being biiascicular2~3 (negating any idea of hemiblock, which implies a bifascicular system); although an effective septal ramus can be demonstrated,4 even a trifascicular system remains too simplistic when d§ions of the left bundle system consistently show broader and narrower portions connected by loops and bridges, almost always among an assortment of fan-like smaller fascicles.2-5 These complex arrangements are further confounded by great intersubject variability.2,4 Moreover, tine dissection limited to the left bundle conducting system in patients whose electrocardiograms show either left- or right-axis deviation - necessary to even consider a fascicular block from the electrocardiogram - disclose a plethora of lesions, most quite proximal to the proposed anterior and posterior major fasci~les.**~ Furthermore, many patients with appropriate axis deviations have additional or isolated lesions of the myocardium both adjacent to and remote from the bundle system.4Jj Long ago, for example, Grant6 showed that a myocardial lesion in an appropriate location could slow intramyocardiil conduction so that the terminal portion of the QRS would be generated in such slowed areas, skewing the net QRS vector toward them. Thus, an. anterolateral infarct, for example, would tend to generate a left-axis deviation on this basis with or without involvement of the conducting system. Reeent eAeneer Phase analysis using a variety of approaches-is has found wide clinical and investigative application, primarily as a method for evaluating ventricular regional wall motion abnormalities in the diagnosis of ischemic heart disease. New evidence bearing on putative fascicular block has appeared using phase image characterization of ventricular contraction in patients with a range of left-axis deviation and left-axis deviation combined with right bundle branch block.” From the Cardiology Division, St. Vincent Hospital; and the Department of Medicine, University of Massachusetts Medical School, Worcester, Massachusetts. Manuscript received March 2,1992; revised manuscript received and accepted June 1,1992. Address for reprints: David H. Spcdick, MD, Cardiology Division, St. Vincent Hospital, Worcester, Massachusetts 01604.
from the
MD, DSC
The investigators used an electrocardiographic-gated blood pool scan using first-harmonic Fourier analysis of the images to determine whether left anterior “hemiblock” was present in patients with left-axis deviation and no contraction abnormalities. They reasoned that phase changes in particular regions would follow their electric activation sequence, and if this was abnormal then myocardial responses would follow the same sequence. In 20 cases of left-axis deviation, including 5 with values of Z-60’, they found no difference in the phase image compared with that in normal control subjects. They conceded that the phase image does not netessarily track the electrical conduction system itself, but definitely expresses the process of regional ventricular contraction accompanying electric conduction. Whereas a possibility of theoretical fascicular block cannot be excluded on the basis of the phase image alone, the results indicate that such isolated disorders of some left anterior “fascicle” without myocardial lesions may well exist, but must be comparatively rare.’ l The authors found no conclusive reason why, in 5 patients with right bundle branch block and left-axis deviation, phase image results more compatible with an anterior fascicular block were noted, however, they offered the hypothesis that left-axis deviation complicated by right bundle branch block is primarily caused by abnormalities exclusively in the conduction system, whereas isolated left-axis deviation could be due to myocardial factors. Meticulous anatomopathologic studies of the left bundle system support this conclusion.2~3J2 Evldmtlary synopsis (Tabk I): The report by Ono et al” is only the most recent in a large amount of evidence that makes it impossible to conclude from an ordinary electrocardiogram that some kind of fascicular block is present. Fascicular blocks or some equivalent in a very complex system may really exist, but interpretation is confounded by (1) marked anatomic differences in the proximal organization of the left conduction system, (2) any resultant concentration in 2 and 23 virtual TABLE I Fascicular Blocks: Factors Limiting or Rendering Improbable Their Diagnosis from the Electrocardiogram Basic anatomic complexity and marked intersubject variability of the left bundle system Most anatomically demonstrable lesions far from sites of electrocardiogram-indicated fascicular interruption Phase imaging showing ventricular contraction sequence to be unpredictable from sites of electrocardiogram-suggested fascicular blocks Low probability of lesions strictly confined to the conduction system. Corollary: contribution to net QRS vector (hence axis) of associated or additional myocardial lesions extrinsic to the bundle system Confounding factor: inherent inaccuracy of the Einthoven equilateral triangle, making axis determination intrinsically imprecise
EDITORIALS
809
(or ultimate) fascicular end-organs,and (3) the common presenceof a variety of myocardial abnormalitie,~.~,~*~J l-l3 Thii is further confoundedby the massive inaccuracy of the Einthoven triangle, an equilateral (hence unnatural) assumptionthat applies with precision only rarely, if ever.12(In nature, anything equilateral, smooth, perfectly round or linear must exist only by accident.) We use thii triangle becauseit simplifies constructionof a frontal plane axis.Even if the Einthoven triangle could apply to every individual axis confmed to the frontal plane of a 3-dimensionalstructure, axis change must nearly always occur in spacerather than only in 1 plane,making the traditional “QRS axis” (shorthand for frontal plane axis) inherently imprecise. Thus, constructingexact axis ranges (e.g., 5-45O) to define an impossible,or at best clinically improbable, diagnosislike fascicular block will introduce other imprecisions. Ceneh&n: The electrocardiographershould report exactly what he sees:a frontal plane axis basedon the Einthoven triangle. The consumer of this information will understand that one of the possibilitiesof marked axis deviation from normal is a fascicular block, actual or virtual (i.e., an equivalent at the anterosuperior or posterior extreme of the complex left conducting system), but it is misleadingto use thoseterms in electrocardiographic interpretation when an electrocardiographic axis cannot provide precise and certainly not conclusiveevidence.Qn the other hand, to use the kind of physiologicthinking introduced by Rosenbaumet al1 is an important adjunct to electrocardiography and
should not be neglected.Meanwhile, it is to be hoped that the electrophysiologists will further developclinical electrophysiologyof the bundle branches to bring us nearer to an acceptableresolution of this problem.
REFERENCES 1. Rosenbaum MB, Eliiri MV, Jzzari 0. L.os Hemibloqus. Buenos Airex Ed Paidos, 1968. 2. Rosai L. Hi&pathology of conducting system in left anterior hemiblock. Br h%wr J 1976;38:1304-1311. 3. Uhley HN. Some controversy regarding the peripheral distribution of the conduction system. Am J Cardiol 1972;30:919-920. 4. Nakaya Y, Hiiga T. Reaaaeasment of the subdivision block of the left bundle branch. Jpn Circ J 1981;45:503-516. 1. Massing GK, James TN. Anatomical confiition of the Hi Bundle and Bundle branches in the human heart. Circularion 1976;53:609-621. S. Grant RP. Left axis deviation: an electmcardiographic-patholo@c correlation study. Circulation 1956;14:233-249. 7. Verba JW, Bomatein I. Alaamki NP, Taylor A, Bhargava V, Shabetai R, L-eWiiter M. Gnset and progxaaion of meohanical systole derived from gatad radionuclide tecbniqucs and diiplayed id tine format. J Nucl Med 1979;20: 625-626. 8. B&nick E, Dunn R, Fraia M, O’Connell W, Shosa D, He&ens R, Scheinman M. The phase images its relationship to patterns of contraction and conduction. Circulation 1982;65:5Sl-560. 9. Frais MA, Botvinick EH, Shosa DW, O’Connell WJ, Scheinman MM, Hattuer RS, Morady F. Phase image characterization of ventricular contraction in left and right bundle branch block. Am J Cardiol 1982;50:95-105. 10. Kuecherer HF. Abbott JA, Botvinick EH, Schebunan ED, O’ConueU JW, Scheimnan MM, Foster E, Schiller NB. Twodimenaional eehoranliographic phase analysis: its potential for noninvaaive localization of aaxasory pathways in patients with Wolff-Parkinson-White syndrome. Circulation 1992;85:130-142. 11. Ono A, Mizuno H, Tahara Y, Ishikawa K. Phase image characterization of ventricular contraction in left anterior hemibkxk. Jpn Circ J 1991;55:473-480. 12. Spodick DH. Left-axis deviation and left anterior faacicular block. Am J Cardiol 1988;61:869-870. 13. Demoulii C, Kulberhu HE. Histopathological examination of concept of left hemiblock. Br Heart J 1972;34:807-814.
Low High-Density Lipoprotein Cholesterol What to Do Abbut It”
and
William B. Kannel, MD
a
lood lipids are fundamental in atherogenesis.Control of lipids is acknowledgedas essentialin preention of coronary diseaseby :he federal guide lines that focus on total cholesteroland its low-density lipoprotein (LDL) cholesterolcomponent.’ Despite the demonstratedstrong relation of low high-density lipoprotein (HDL) cholesterol to the occurrence of core nary artery disease(CAD) and the biologic plausibility From the Department of Medicine, Section of Preventive Medicine and Epidemiology, Evans Memorial Re8carch Foundation, Boston University School of Medicine, Boston, Massachusetts. This study was supported by the Charles A. Dana Fouitdation, New York, New York, Mod, Sharpe & Dobme, R&way, New Jersey, and Grants NOl-HV92922 and NOl-I-IV-52971 from the National Institutes of Health, Jktbcsda, Maryland. Manuscript received March 9.1992; revised manuscriptrcccivedandaaxptedMay 11,1992. Address for reprints: Wii B. Kannel, MD, Boston University/ Framin&am Heart Study, 5 Thurber Street, Fmmingham, Massachu-
setts 01701. *Presented at the National Heart. Lung, and Blood Institute Conference on Chol&erol and High Blood Pressure, Washington, D.C.,
April 1991. 810
THE AMERICAN
JOURNAL
OF CARDIOLOGY
VOLUME
70
of the relation, the Federal guidelineshave beencircumspectconcerning HDL cholesterol.The understanding of the HDL metabolismwas consideredby the expert panel to be too primitive and laboratory measuremer:.: of HDL cholesterol too inaccurate on which to base clinical decisions1Also, there has not yet beena clinical trial conductedto test whether raisii HDL alone reducesrisk of CAD independentof lowering LDL cholesterol. The recently revised guidelines recommend HDL cholesterol determination on all personshaving cholesterolmeasured,but they fail to take into consideration the benefitsof a high HDL cholesterolresultingin an acceptabletotal/HDL cholesterolratio despitean elevatedtotal cholesterolor LDL cholesterol.Recommendations concerning triglycerides also fail to take ade quately into accountthe heterogeneityof this entity, its importancein choosinglipid-lowering agentsand its importance as an indicator of the metabolic problem. Epidemiologic data consistentlydemonstrate that there is a protective HDL cholesterol component involved in removal of cholesterolfrom the tissueswhich
SEPTEMBER
15, 1992
