Prediction of Biventricular Repair by Echocardiography in Borderline Ventricle
Borderline ventricle refers to a spectrum of left or right ventricular underdevelopment, typically associated with severe congenital heart disease (CHD). In patients with borderline ventricle, the decision between biventricular repair and univentricular repair (such as the Fontan-type operation) is complex and critical. Biventricular repair aims to restore normal circulation with two functional ventricles, while univentricular repair is a more conservative approach, often leading to long-term complications such as cardiac insufficiency, arrhythmia, and hepatic dysfunction. The inappropriate pursuit of biventricular repair in borderline candidates can result in adverse clinical outcomes, making accurate preoperative assessment of ventricular development essential. This review focuses on the role of echocardiography in predicting the feasibility of biventricular repair in patients with borderline left ventricle (LV) and right ventricle (RV).
Borderline Left Ventricle
Critical Aortic Stenosis
Critical aortic stenosis (AS) is characterized by severe narrowing of the aortic valve, often requiring a patent ductus arteriosus (PDA) to support systemic circulation. It is frequently associated with LV hypoplasia and dysfunction, compounded by endocardial fibroelastosis (EFE), which further impairs LV function. Several predictive models have been developed to assess the feasibility of biventricular repair in critical AS.
The Rhodes score, introduced in 1991, is a widely recognized predictive equation. It incorporates body surface area (BSA), aortic root dimension indexed to BSA, the ratio of LV long-axis dimension to heart long-axis dimension, and MV area indexed to BSA. A score of less than -0.35 predicts a higher risk of death after biventricular repair. In 2001, the Congenital Heart Surgeons Society (CHSS) proposed a regression equation to predict the 5-year survival benefit of univentricular versus biventricular repair. This model includes factors such as age at entry, z-score of the aortic valve at the sinuses, grade of EFE, ascending aorta diameter, presence of moderate or severe tricuspid regurgitation, and z-score of LV length. EFE, which can be suspected on echocardiography as echo brightness in the LV wall, plays a significant role in determining outcomes. Another scoring system by Colan SD includes BSA, aortic valve annulus z-score, LV long-axis ratio, and the presence of grade 2 or 3 EFE, with a discriminant cutoff of -0.65. Despite these models, no definitive echocardiographic criteria guarantee the success of biventricular repair due to the complexity of the disease.
Aortic Arch Hypoplasia
Aortic arch hypoplasia is often associated with LV hypoplasia but without EFE. The Rhodes score and CHSS regression equation may not be suitable for this condition. Mart and Eckhauser proposed a predictive model for biventricular repair in aortic arch dysplasia, incorporating MV annulus diameter, aortic valve annulus diameter, LV and RV length, and main pulmonary artery diameter. A cutoff value of -16.2 in their cohort predicted biventricular repair with 100% sensitivity and specificity. Another study suggested that a combination of MV to tricuspid valve (TV) ratio of 0.66 or less and an aortic valve annulus z-score of -3 or less could predict biventricular repair failure with 71% sensitivity and 94% specificity. These studies highlight the importance of considering MV and aortic valve annulus diameters and LV size in decision-making for biventricular repair in aortic arch hypoplasia.
Right-Dominant Unbalanced Atrioventricular Septal Defect
In right-dominant unbalanced atrioventricular septal defect (AVSD), the RV is larger, and the LV is hypoplastic, with the common atrioventricular valve located on the right side relative to the interventricular septum. The LV outflow tract is also vulnerable to obstruction. Several echocardiographic indices have been proposed to assess the feasibility of biventricular repair in this condition.
The atrioventricular valve index (AVVI), defined as the ratio of left valve area to right valve area, is a useful indicator. An AVVI of less than 0.67 suggests the need for univentricular repair. The LV inflow index (LVII), which measures the color flow width of the LV inflow relative to the left atrioventricular valve annulus diameter, is another important factor. A greater LVII predicts better survival after biventricular repair in cases of mild or moderate LV hypoplasia. The RV/LV inflow angle, proposed by Cohen et al., is also a predictive index, with a wider angle indicating a higher likelihood of successful biventricular repair. However, even if these criteria are met, biventricular repair may still fail due to left atrioventricular valve stenosis or regurgitation, LV outflow obstruction, or other clinical factors.
Borderline Right Ventricle
Pulmonary Atresia/Intact Ventricular Septum
Pulmonary atresia with intact ventricular septum (PA/IVS) is characterized by luminal discontinuity between the RV outflow tract (RVOT) and the main pulmonary artery, with significant morphologic heterogeneity ranging from RV hypoplasia to RV dilation. Preoperative imaging is crucial for clinical decision-making in PA/IVS with borderline RV.
Several morphologic indices are used to evaluate RV development, including the z-score of the tricuspid annulus diameter, the ratio of tricuspid to MV diameter, RV inlet length z-score, RV area z-score, RV development index, and RV-TV index. A less objective but practical approach is to classify the RV as tripartite (mild hypoplasia), bipartite (moderate hypoplasia), or unipartite (severe hypoplasia). The presence or absence of RV sinusoids, RV-dependent coronary circulation, and the degree of tricuspid regurgitation are also important considerations.
In PA/IVS with borderline RV, features include a tricuspid annulus z-score between -2.5 and -4.5, usually a bipartite RV, a patent infundibulum, and minor sinusoids. Primary procedures such as radiofrequency valvotomy and PDA stenting are recommended, with balloon atrial septostomy to reduce venous congestion. Some patients achieve RV growth without further interventions, while others may require re-interventions such as bidirectional Glenn shunt, RVOT reconstruction, or TV repair. Conditions favoring biventricular repair include the absence of RV-dependent coronary circulation, a tricuspid annulus z-score greater than -3, and a tricuspid to MV diameter ratio greater than 0.5. A baseline RV area of 6 cm²/m² or greater has 93% sensitivity and 80% specificity for identifying patients who ultimately achieve biventricular circulation, with all patients having an RV area of 8 cm²/m² or greater achieving biventricular circulation.
Left-Dominant Unbalanced Atrioventricular Septal Defect
In left-dominant unbalanced AVSD, the LV is larger, and the RV is hypoplastic, with the common atrioventricular valve located on the left side relative to the interventricular septum. The AVVI is a useful echocardiographic indicator to assess the degree of ventricular hypoplasia. Patients with an AVVI of 0.4 or less (right dominant) or 0.6 or greater (left dominant) are classified as unbalanced. Most patients with balanced AVSD (0.4 < AVVI < 0.6) undergo biventricular repair, while those with an AVVI of less than 0.19 uniformly undergo univentricular repair. For patients with an AVVI between 0.19 and 0.39, decision-making is challenging. Nathan et al. defined mild hypoplasia as LV or RV volumes greater than 30 mL/m², 60% to 80% overriding, an AVVI between 0.19 and 0.39 or 0.61 and 0.80, and apex-forming ventricles. In these cases, primary biventricular repair or initial pulmonary artery banding/shunting with subsequent biventricular conversion is recommended. Moderate hypoplasia, defined as LV or RV volumes between 15 and 30 mL/m², 60% to 80% overriding, an AVVI between 0.19 and 0.39 or 0.61 and 0.80, and near apex-forming ventricles, may require single ventricular palliation and ventricular recruitment with staged biventricular conversion.
Conclusion
Accurate assessment of ventricular development using echocardiography is crucial for surgical decision-making in patients with borderline ventricle. While echocardiography provides valuable insights, it cannot guarantee the success of biventricular repair due to the complexity of the disease and other clinical factors. Predictive models and echocardiographic indices, such as the Rhodes score, CHSS regression equation, AVVI, LVII, and RV/LV inflow angle, offer a relative reference for determining the feasibility of biventricular repair. However, the final decision must consider individual patient characteristics, available surgical options, and institutional experience. Despite uncertainties, advancements in echocardiography and disease understanding continue to improve outcomes for this challenging patient population.
doi.org/10.1097/CM9.0000000000000375
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