Pediatr Cardiol (2014) 35:1321–1326 DOI 10.1007/s00246-014-1019-y

REVIEW ARTICLE

Timing of Aortic Valve Intervention in Pediatric Chronic Aortic Insufficiency Justin T. Tretter • Alan Langsner

Received: 30 May 2014 / Accepted: 22 August 2014 / Published online: 2 September 2014 Ó Springer Science+Business Media New York 2014

Abstract The timing of aortic valve intervention (AVI) in pediatric patients with chronic aortic insufficiency (AI) is largely based on adult experience, which is fraught with uncertainty and controversy. Current adult guidelines in the absence of symptoms use left ventricular (LV) systolic function and LV dimensions to guide AVI timing, with few studies translating these recommendations to pediatric patients. This article reviews the current guidelines for AVI timing in chronic AI along with the emerging data for pediatric patients. Keywords Aortic insufficiency
Aortic regurgitation
Aortic valve replacement
Aortic valve repair
Aortic valve intervention
Left ventricular dysfunction
Surgical timing

Introduction Chronic aortic insufficiency (AI) is characterized by a prolonged, stable clinical course with risk of irreversible myocardial injury if intervention is excessively delayed [8, 27]. The natural history of AI has been well described. Initially, there is left ventricular (LV) dilation with proportional compensatory hypertrophy. This phase may last for a prolonged period of time, until the hypertrophy fails to keep up with the progressive increase in ventricular volume, resulting in elevated afterload and end-systolic LV wall stress, clinically detected by a decrease in systolic function. As this continues, ventricular dysfunction is further J. T. Tretter (&)
A. Langsner Division of Pediatric Cardiology, New York University School of Medicine, New York, NY, USA e-mail: [email protected]

worsened by reduced intrinsic myocardial contractility. If severe volume overload is allowed to continue, eventually a stage of irreversible myocardial injury is reached [15, 43]. Timing for aortic valve intervention (AVI) for chronic AI has been a subject of uncertainty and controversy in both adult and pediatric patients [2]. This contrasts to the relatively specific guidelines for management in mitral regurgitation, mitral stenosis, and aortic stenosis for which there is extensive clinical experience and substantial natural history data available to guide management decisions [26, 29, 40, 41]. The cardiologist must determine when the AI is severe enough to warrant AVI, but has not progressed to the point of irreversible ventricular dysfunction. This can be difficult, since many patients with chronic AI may remain asymptomatic with normal LV systolic function for many years despite significant LV volume load, and by the time they are symptomatic, many have already developed irreversible myocardial dysfunction. Multiple studies have assessed risk factors associated with poor clinical outcomes following AVI in adult patients to determine ideal surgical timing, with limited information available in pediatrics [35, 37].

Etiology AI is a common entity in pediatric patients with both preand post-operative congenital heart disease. Common etiologies for chronic AI include previous intervention for congenital aortic valve stenosis, AI related to a bicommissural or unicommissural valve without prior intervention and aortic valve leaflet prolapse associated with a ventricular septal defect. Less common etiologies include isolated congenital AI, infective endocarditis, rheumatic heart disease, arterial switch operation, Marfan syndrome,

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and Takayasu arteritis [10, 35]. One study showed that 32 % of unoperated bicuspid aortic valve patients eventually developed more-than-trivial AI [12]. Another study showed that 20 % of postoperative patients with tetralogy of Fallot developed significant AI [38]. A standard approach to assessing and determining the ideal timing for AVI in pediatric AI would be beneficial.

Evaluation Symptoms attributed to significant AI should be elicited, as the presence of such symptoms in severe AI is an indication for surgical intervention. The most common symptoms are those of heart failure; dyspnea on exertion, orthopnea, and paroxysmal nocturnal dyspnea. Patients may also complain of chest pain and palpitations. ECG may show increased LV forces possibly with strain pattern, left atrial enlargement, and sinus tachycardia may be evident in the presence of heart failure. Chest X-ray may show cardiomegaly, and potentially a dilated ascending aorta in certain etiologies. On clinical examination in a patient with significant AI, an early diastolic decrescendo murmur may be present along the left upper sternal border. This may be accompanied by an Austin Flint murmur, a low-pitched mid-diastolic rumble heard best at the apex related to impedance to proper opening of the anterior leaflet of the mitral valve from the aortic regurgitant jet during diastole. An S3 heart sound may be heard in the presence of significant LV volume overload. Numerous peripheral findings from increased pulse pressures may also be noted, including a rapid upstroke and collapse of the carotid artery pulse and pulsation of the capillary bed in the nails. Other symptoms of congestive heart failure may be present, such as tachycardia and tachypnea. Evaluation of AI is based on a comprehensive echocardiographic study, which includes 2-dimensional imaging, color flow mapping, and pulsed and continuous wave Doppler imaging. There is no standard reference used for the evaluation of AI, with commonly used assessments being both qualitative and semi-quantitative. Jet width ratio, vena contracta width, pressure half-time, jet density, diastolic flow reversal in the descending aorta, and the proximal isovelocity service area method are commonly used methods to assess the degree of AI [22]. Cardiac magnetic resonance imaging (CMR) is highly accurate and reproducible for quantitative evaluation of AI [11]; however, echocardiography is more commonly used due to its widespread availability and low cost. Severity of AI is determined by echocardiographic assessment. Findings suggestive of mild AI include the following: jet width \25 % of the LV outflow tract

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Pediatr Cardiol (2014) 35:1321–1326 Table 1 Echocardiographic assessment of aortic insufficiency (AI) severity Mild AI

Moderate AI

Severe AI

Jet width

\25 % LVOT

25–64 % LVOT

[65 % LVOT

Vena contracta

\0.3 cm

0.3–0.6 cm

[0.6 cm

Regurgitant volume

\30 mL/ beat

30–59 mL/ beat

[60 mL/beat

Regurgitant fraction

\30 %

30–49 %

[50 %

Effective regurgitant \0.1 cm2 orifice Pressure half-time

[500 ms

Descending aorta Doppler

Normal

0.1–0.29 cm2 [0.3 cm2 \200 ms

200–500 ms

Holodiastolic reversal

Table 2 Adult indications for aortic valve intervention in chronic aortic insufficiency (AI) [29] Indication

Class of Recommendation

Symptomatic patients with severe chronic AI Asymptomatic patients with severe chronic AI and LV systolic dysfunction (LVEF \ 50 %)

I I

Patients with severe chronic AI undergoing cardiac surgery for other indications

I

Asymptomatic patients with severe chronic AI and normal LV systolic function (LVEF C 50 %) but with severe LV dilation (LVESD [ 50 mm)

IIa

Patients with moderate chronic AI undergoing other cardiac surgery

IIa

Asymptomatic patients with severe chronic AI and normal LV systolic function (LVEF C 50 %) but with progressive severe LV dilation (LVEDD [ 65 mm) if surgical risk is low

IIb

(LVOT), vena contracta \0.3 cm, regurgitant volume (RV) \30 mL/beat, regurgitant fraction (RF) \30 %, effective regurgitant orifice (ERO) \0.1 cm2, and pressure half-time (PHT) [500 ms (ms). Moderate AI findings include jet width 25–64 % of the LVOT, vena contracta 0.3–0.6 cm, RV 30–59 mL/beat, RF 30–49 %, ERO 0.1–0.29 cm2, and PHT 200–500 ms. Severe AI findings include jet width C65 % of LVOT, vena contracta [0.6 cm, RV [ 60 mL/beat, RF [ 50 %, ERO [ 0.3 cm2, PHT \ 200 ms, evidence of LV dilation and holodiastolic flow reversal in the proximal abdominal aorta (Table 1) [29, 44]. LV ejection fraction (EF) is commonly used to assess systolic function in the evaluation of chronic AI. However, it should be noted that in the setting of chronic AI, LVEF is augmented by increased preload, limiting its ability to

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detect developing myocardial dysfunction. Therefore, other modes of assessing myocardial function noninvasively and predicting postoperative LV systolic dysfunction are necessary [25]. Established Adult Surgical Indications Indications for surgery in adults with chronic severe AI have been established (Table 2), and include the following: those with symptoms (class I indication), those undergoing cardiac surgery for other indications (class I indication) or moderate AI who are undergoing other cardiac surgery (class IIa), and those whom are asymptomatic with LV dysfunction. This can be defined as those with LV ejection fraction \50 % (class I indication), those with LV endsystolic diameter (ESD) [50 mm (class IIa indication), or LV end-diastolic diameter (EDD) [65–70 mm (class IIb indication) [29, 40]. The following sections discuss additional findings that may guide management decisions in pediatric chronic AI supported by the limited available literature. Indexed Values Indexed values of indexed LVESD C 25 mm/m2 and indexed LVEDD C 35 mm/m2 have been established as comparable to the absolute values mentioned previously. Indexed values are particularly significant in patients with BSA B 25th percentile values, with a review showing that these patients were referred for more severe symptoms and with lower LVESD than patients with BSA [ 25th percentile when using non-indexed values. Indexed values are also better at identifying patients with depressed LVEF at 1-year follow-up from AVI [6, 34]. A study by Selamet Tierney et al. assessed echocardiographic predictors of LV dysfunction after AVI in children. They determined that LVEF z-score \-1 was the most sensitive (89 %) but least specific (58 %), whereas LVESD z-score C5 was the most specific (95 %) but least sensitive (60 %) outcome identifier, with the combination of preoperative shortening fraction z-score \-1 or LVESD z-score C5 having the best combined sensitivity and specificity in identifying postoperative LV dysfunction [35]. Buddhe et al. assessed similar parameters in children with isolated AI requiring AVI. They found that preoperative LVEDD z-score [4 predicted persistent LV dilation (z-score [2) at early postoperative and 1-year follow-up, whereas only preoperative decreased LV function, defined as shortening fraction \28 %, was a significant predictor of persistent LV dysfunction at early follow-up and predicted requirement for repeat interventions [7].

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Strain and Strain Rate LV strain and strain rate hold promise for use in assessing LV systolic function in the setting of chronic AI. Although strain and strain rate are load dependent, studies of myocardial function in adults have shown that tissue Doppler echocardiography-derived strain and strain rate can detect early subclinical abnormalities in adults with AI as well as assist in determining prognosis of postsurgical LV function [30, 31]. A preoperative LV global longitudinal strain value of B-15.3 and global longitudinal strain rate of -0.79/s or less have been shown to be predictors of postoperative ventricular dysfunction in pediatric AI, which may help determine the optimal timing of surgery [25]. Di Salvo et al.[9] showed that a risk factor for progressive AI in asymptomatic pediatric patients was significantly reduced longitudinal strain values \-19.5. However, Leonardi et al. showed that LV strain measures were normal in patients with AI, independent of abnormalities in cardiac geometry. They believed that these findings were consistent with the known adaptive response of the LV to chronic volume overload, with eccentric hypertrophy and normalization of afterload, with maintenance of a normal LVEF [23]. Further studies are necessary to fully define the utility of strain and strain rate assessment in chronic AI, and establish vendor-specific values. Stress Echocardiography Stress echocardiography has the potential advantage of providing information in a physiologic setting more closely mimicking the typically active state of children. It has been shown in adults to enable a more accurate definition of the optimal timing of intervention in patients with valvular regurgitation. There are two types of stress echocardiography: treadmill and cycle ergometer, with the latter having the advantage of the ability to perform echocardiography during all stages of exercise [19]. The potential utility of stress echocardiography is in detecting subclinical or occult pathology by assessing the contractile reserve or magnitude of augmentation in cardiac performance during exercise. The normal contractile response to exercise stress has been established in young adults [20]. Exercise echocardiography has been shown to unmask latent LV dysfunction in AI, focusing on LVEF during exercise. Bonow et al. [3, 4] showed that LVEF response to stress was related to the degree of LV dilation at rest, with reduction of exercise LVEF in the majority of patients with an LVESD [ 50 mm. Failure to reduce LVESD or increase LVEF at exercise was specific for predicting LV dysfunction at follow-up with earlier need for surgery and higher event rates [5, 24]. Wahi et al. [42] showed that the absence of contractile reserve, defined by a decrease in LVEF by 5 % during exercise,

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seemed to identify the presence of latent LV dysfunction earlier than conventional resting echocardiography parameters. Conversely, Goldman et al. [14] found no correlation between EF response to exercise and the resting LV dimensions in patients with AI. Stress echocardiography has not been well studied in pediatrics, but has potential to yield important functional information that could improve the ability to predict which patients should be referred for earlier surgical intervention. A major limitation is the lack of natural history data validating using information from this modality as outcome variables [19], as well as the limited utility in younger children who are unable to fully participate. Exercise Testing Many patients with chronic AI tolerate the volume overload well and do not manifest symptoms. Exercise stress testing is useful in objectively assessing for symptoms and functional capacity during exercise in patients with AI [29]. Rhodes et al. assessed the utility of exercise testing in pediatric patients with chronic AI and found that although the majority of patients with moderate to severe AI compensated well to their valvular disease, a subset of patients with AI had diminished exercise capacity with an inability to augment forward stroke volume during exercise. The baseline echocardiogram of these patients did not differ significantly from those with normal exercise capacity. They concluded that exercise testing may be useful in identifying pediatric patients with AI who need further evaluation and possible surgical intervention, and should be a component of the standard evaluation of these patients [32]. Cardiac MRI CMR has emerged as a reference standard for quantification of ventricular volumes [16, 36]. Although there is good correlation between echocardiographic and CMR assessment of LV mass, volume and EF measurements, assessment of AI grade with echocardiography has been shown to be inconsistent and somewhat subjective, especially when assessing more severe AI [21]. CMR should be considered in patients with moderate or severe AI and suboptimal echocardiographic images for assessment of LV systolic function, systolic and diastolic volumes, and measurement of AI severity, as well as in patients in whom there is discordance between clinical assessment and severity of AI by echocardiography [29].

Medical Management AI is a volume overloading condition leading to LV dilation and eccentric hypertrophy with deleterious LV

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remodeling, which theoretically could benefit from diuretic therapy and afterload reduction. In adults, treatment of hypertension is recommended in patient with chronic AI, preferably with dihydropyridine calcium channel blockers, angiotensin-converting enzyme (ACE) inhibitors, or angiotensin receptor blockers (ARBs) or for patients with chronic AI in whom surgical intervention is indicated but not performed due to comorbidities [29]. In children, the benefits of medical management have not consistently been shown to delay progression of deleterious LV changes in significant AI. A controlled study by Mori et al. [28] of 24 patients with chronic overload from either mitral regurgitation or AI showed that long-term treatment with ACE inhibitors in these children was effective in reducing both LV volume overload and LV hypertrophy, potentially postponing surgical intervention. However, a retrospective study by Gisler et al. [13] assessing ACE inhibitors in 18 pediatric patients with mid-to-severe AI did not show any significant improvement of LV dilation, LV posterior wall thickness, shortening fraction, or grade of AI, and concluded that ACE inhibitors may not alter LV overload in this population. Similar to adult studies, a clear benefit of medical therapy in delaying the need for surgical intervention has not clearly been demonstrated.

Surgical Interventions The majority of patients who require aortic valve surgery for chronic AI will require aortic valve replacement [29]. There is growing experience in aortic valve repair in properly selected pediatric patients with chronic AI in whom their aortic valve is not thickened, deformed, or calcified. The advantages of aortic valve repair include growth potential, avoidance of anticoagulation, and preservation of future valve replacement options. The major concern is the lack of durability and the high likelihood of some degree of residual hemodynamic lesions. This remains a promising management option in experienced centers, but further refinement of patient selection criteria is needed [17, 39]. Aortic valve replacement in children poses unique challenges that have made it difficult to identify the ideal prosthesis. Although center dependent, recent studies have shown the Ross procedure to have good durability with the advantage of growth potential and lack of need for anticoagulation, making this an attractive option for young children as well as physically active adolescents and young adults in whom anticoagulation may be unappealing. Concerns persist for making a one-valve disease into a two-valve disease. Homograft and bioprosthetic valves achieve superior hemodynamic results initially, but at the cost of accelerated degeneration and lack of growth potential. Mechanical valves have the advantage

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of improved durability, but disadvantage of lifelong need for anticoagulation and lack of growth potential, making them unattractive for the use in young children and physically active adolescents and young adults [1, 18, 33]. The best strategy for surgical intervention in pediatric AI is currently controversial, but with longer follow-up of previously operated patients and improved surgical experience, the optimal approach may be better defined.

Conclusion Current practice in evaluation of chronic AI in pediatric patients is largely guided by adult literature. More sensitive indicators of LV systolic dysfunction will improve identification of asymptomatic pediatric patients with chronic AI who are at risk of developing irreversible LV systolic dysfunction and should undergo AVI. Future investigations should continue to assess risk factors in pediatric patients with chronic AI that predict postoperative LV function following AVI to determine the optimal timing for repair.

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