Hypoplastic Left Heart Syndrome: Uni-ventricular or Bi-ventricular Repair

By Viviane G. Nasr, MD; Annette Schure, MD; James A. DiNardo, MD
Department of Anesthesiology, Perioperative and Pain Medicine
Boston Children's Hospital
Harvard Medical School

Hypoplastic left heart syndrome (HLHS) occurs in approximately 1 in 10,000 live births and is one of the more common complex congenital heart defects. Forty years ago, comfort care was often the only option offered to parents, but over the last decades, a staged surgical approach to repair/palliation of this lesion, the single ventricle pathway (SVP), has been developed.1 It usually involves a first stage repair within a few days after birth, either in form of a classical Norwood procedure with a modified Blalock-Taussig shunt or the alternative right ventricle (RV) to pulmonary artery (PA) Sano shunt.2 Another option is a combined interventional/surgical “hybrid” procedure with stenting of the ductus arteriosus and bilateral banding of the pulmonary arteries.3 Following Stage 1 repair, HLHS patients proceed to Stage 2- the Bidirectional Glenn at age 3-8 months. For the Glenn, pulmonary blood flow is derived from creation of an end-to-side anastomosis of the SVC to the right pulmonary artery. This procedure substantially reduces the volume load on the single ventricle and allows ventricular remodeling to occur prior to completion of the single ventricle palliation with the Fontan procedure at 2-5 years of age.

In the first years after the introduction of the SVP, less than 30% of patients survived. As perioperative management including anesthetic, surgical and postoperative care improved, the survival rates increased and many patients will now reach adolescence and adulthood. Studies have shown that the survival rate after Stage 1 increased from 68% in 2002 to more than 80% in 2009. The 1-year survival after Stage 2 is over 95% and the short-term survival after Fontan is over 95%.4

However, long-term outcomes remain poor with 5-year and 10-year survival rates of 50-70% and significant morbidity. These patients are at a higher risk of arrhythmias (7-50%) including supraventricular tachycardia (50%), ventricular tachycardia (3%) and sudden cardiac death, decreased exercise tolerance and heart failure that worsen with age. Other long-term complications include impaired systolic and diastolic function, progressive hypoxemia, elevated pulmonary vascular resistance (PVR), thromboembolism, cerebrovascular accidents, hepatic dysfunction, protein-losing enteropathy (3.7-24%), and plastic bronchitis. Adults with single ventricle palliation often experience substantial restrictions in their daily activities of life and require rigorous lifelong follow-up including regular visits to the cardiologist, frequent diagnostic imaging [(echocardiography, magnetic resonance imaging (MRI)], anticoagulation therapy, and treatment for arrhythmias. Recognition of these poor long-term results of SVP and the limited treatment options for the “failing Fontan” physiology has lead to the aggressive pursuit of different surgical strategies such as the biventricular repair.

It is now well recognized that there is a wide spectrum of hypoplasia of left heart structures inherent in the diagnosis of HLHS. Patients with mild LV hypoplasia and aortic stenosis are good candidates for a biventricular repair while patients with severe left ventricular (LV) hypoplasia with aortic and mitral atresia continue to be managed with SVP. However, a subset of HLHS patients is described as having a “borderline” LV, i.e. a sufficient LV volume and adequate mitral and aortic valve function to be considered candidates for a staged approach to a biventricular repair.5,6

The “borderline” left heart
There is no strict definition of a “borderline” left heart. This designation is made based on data regarding LV, mitral valve (MV), and aortic valve (AV) size and function and the extent of endocardial fibroelastosis (EFE) delineated by MRI, echocardiogram and cardiac catheterization. MRI is the preferred imaging modality to quantify EFE and LV volumes in patients with borderline left heart structures. The anatomic features defining “borderline” left heart include: aortic and mitral valve stenosis, coarctation, small LV cavity volume globular or elongated and apex forming, ventricular restriction caused by the presence of EFE, and Z scores between -5 and -0.5.

The left heart rehabilitation
Left heart rehabilitation consists of a variety of interventions to relieve inflow and/or outflow tract obstructions, either by catheter-based balloon dilation of the aortic valve or surgical repair of coarctation of the aorta and EFE resection. These interventions are based on the concept that the myocardium in infants and children can potentially grow. In fact, the growth potential of the LV has been demonstrated in patients with borderline left heart structures who undergo primary biventricular repair by balloon dilation of the aortic valve in the catheterization laboratory and surgical repair of aortic coarctation, aortic stenosis, and mitral stenosis if necessary.7 In both the Boston and Toronto series, balloon dilation of critical aortic stenosis in neonates with associated LV hypoplasia was associated with near normalization of LV dimensions in this group of patients.7,8

Staged LV recruitment
A “staged LV recruitment” strategy is applied for patients at high risk of failure with primary biventricular repair. Persistent left atrial hypertension, pulmonary edema, and pulmonary hypertension may occur despite relief of anatomic obstructions in patients with EFE and impaired systolic and diastolic myocardial function.

Candidates for the staged LV recruitment are patients with left ventricular Z scores between -5 and -0.5 and usually include those with unbalanced AV canal defects, variants of HLHS and Shone’s complex.

This strategy is designed to improve blood flow and loading conditions for the LV in an effort to stimulate flow- and load-mediated growth. The circulation is initially supported via the SVP with a stage 1 procedure followed by superior cavopulmonary anastomosis, while the left heart is rehabilitated.

Surgical techniques for rehabilitation of the left ventricle include: 1- endocardial fibroelastosis resection which implies removal of the non-compliant, restrictive, membrane-like lining of the LV by sharp dissection, 2 - mitral valvuloplasty, 3 - redistribution of the AV valve in an unbalanced canal, 4 - aortic valvuloplasty, 5 - atrial septal defect restriction and occasionally, 6- creation of an additional source of pulmonary blood flow (aortopulmonary shunt or RV-PA conduit) in order to further augment LV preload. Emani et al retrospectively analyzed 34 patients with hypoplastic left heart and borderline LV who underwent a staged biventricular repair using the LV recruitment strategy, comparing them to 34 HLHS patients palliated via the SVP. Left heart dimension z-scores increased significantly over time after the LV recruitment strategy whereas they declined after traditional SVP.9

Biventricular conversion
The term “biventricular conversion” is used for patients who initially underwent SVP palliations and are later “surgically converted” to a biventricular circulation with the goal of avoiding the previously described long-term complications associated with SVP. Typical candidates are SVP patients with historically poor outcomes due to tricuspid regurgitation, RV dysfunction, genetic syndromes, noncardiac comorbidities, and elevated pulmonary vascular resistance. The biventricular conversion procedure following staged SVP and staged LV recruitment includes: 1) takedown of the aortopulmonary anastomosis, 2) re-establishment of separate left and right ventricles, and 3) establishment of separate outflow tracts from the left and right ventricle by fixing the native outflow or conduit placement.10

Postoperative care
Depending on the timing and extent of the surgical procedure the postoperative care can be quite complex. In addition to the need for multiple vasoactive medications, 75% of these patients have open chests and delayed sternal closure, 10% require extracorporeal membrane oxygenation (ECMO), and 15% require cardiopulmonary resuscitation. Their ICU stay is often extended, involving frequent diagnostic imaging studies, interventional catheterizations or even re-operations.

Patients undergoing SVP, primary or staged biventricular repair, and biventricular conversion require careful postoperative monitoring and medical management. Future studies comparing the long-term outcomes of the different strategies for biventricular repair and the traditional SVP are necessary.

EXPERT COMMENTARY

References:

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