Hypoplastic Left Heart Syndrome Across the Lifespan: Clinical Considerations for Care of the Fetus, Child, and Adult

Hypoplastic left heart syndrome (HLHS) is the most common anatomic lesion in children born with single ventricle physiology and is characterized by the presence of a dominant right ventricle and a hypoplastic left ventricle along with small left-sided heart structures. Diagnostic subgroups of HLHS reflect the extent of inflow and outflow obstruction at the aortic and mitral valves, specifically stenosis or atresia. If left unpalliated, HLHS is a uniformly fatal lesion in infancy. Following introduction of the Norwood operation, early survival has steadily improved over the past four decades, mirroring advances in operative and peri-operative management as well as reflecting refinements in patient surveillance and interstage clinical care. Notably, survival following staged palliation has increased from 0% to a 5-year survival of 60-65% for children in some centres. Despite the prevalence of HLHS in childhood with relatively favourable surgical outcomes in contemporary series, this cohort is only now reaching early adult life and longer-term outcomes have yet to be elucidated. In this article we focus on contemporary clinical management strategies for patients with HLHS across the lifespan, from fetal to adult life. Nomenclature and diagnostic considerations are discussed and current literature pertaining to putative genetic etiologies is reviewed. The spectrum of fetal and pediatric interventional strategies, both percutaneous and surgical, are described. Clinical, patient-reported and neurodevelopmental outcomes of HLHS are delineated. Finally, note is made of current areas of clinical uncertainty and suggested directions for future research are highlighted.

Pathologic Characteristics of 119 Archived Specimens Showing the Phenotypic Features of Hypoplastic Left Heart Syndrome

To assess the phenotypic variations found among hearts diagnosed at autopsy with hypoplastic left heart syndrome, with attention to implications related to this syndrome as an acquired disease of fetal life, rather than being the consequence of abnormal embryogenesis. We assessed 119 specimens, from 2 archives, diagnosed initially as representing hypoplastic left heart syndrome. Among the 119 specimens, the majority of which had been entered into the archives prior to the availability of surgical treatment for the syndrome, 36 (30%) had the combination of mitral and aortic atresia, 26 (22%) had mitral and aortic stenosis, and 57 (48%) had mitral stenosis combined with aortic atresia. Of the hearts with combined atresia, 92% (33 specimens) had slit-like left ventricles, compared to 12% (3 specimens) of hearts with stenosis of both aortic and mitral valves, and 2 hearts (4%) with mitral stenosis and aortic atresia (P < 0.001). Hypoplasia of the left atrial appendage was present in half (18 specimens, 51%) of those with combined atresia, as opposed to just 18% (10 specimens) of mitral stenosis combined with aortic atresia (P = 0.001). Small left ventricles with valves deemed proportional in size were found in 11 (42%) of those with combined mitral and aortic stenosis. Fibroelastosis was significantly more common in the hearts with mitral stenosis compared to those with mitral atresia (76% vs 11%, P < 0.001). The ascending aorta was significantly smaller in the hearts with aortic atresia. The variability in the morphologic findings support the notion that the lesions seen represent acquired disease occurring subsequent to closure of the embryonic interventricular communication, rather than representing abnormal embryogenesis.

Coronary Arterial Abnormalities in Hypoplastic Left Heart Syndrome: Pathologic Characteristics of Archived Specimens

Palliation of patients with hypoplastic left heart syndrome remains challenging. Although coronary ischemia can be catastrophic, the prevalence and pathologies of anomalies of the coronary arteries remains unknown. We reviewed 119 specimens with the features of hypoplastic left heart syndrome, focusing our attention on the aortic root and the coronary arteries. We found 36 (30%) specimens with the combination of mitral and aortic atresia, 26 (22%) with mitral and aortic stenosis, and 57 (48%) with mitral stenosis combined with aortic atresia. In 29 specimens (24%), the coronary arteries were not located in the center of any sinuses, while in 24 specimens (21%) at least 1 coronary artery was located very proximal to a raphe or commissure, with potential for obstruction. The specimens with combined stenosis were more likely to have eccentric positions of the coronary arteries (11 specimens, 42%), compared to the 3 specimens with combined atresia (9%, P = 0.009). The specimens with combined stenosis were also more likely to have positioning at risk for obstruction (9 specimens, 35%), compared to those with combined atresia (3 specimens, 9%, P = 0.05). Coronary arterial fistulous communications were found in 11 specimens (9%), significantly more frequently in specimens with mitral stenosis and aortic atresia (9 specimens, 16%, P = 0.041). The origins of the coronary arteries in patients with hypoplastic left heart syndrome place them at potential risk for ischemia, with fistulous communications being a particular risk in those with mitral stenosis combined with aortic atresia.

Right ventricular failure in congenital heart disease

PURPOSE OF REVIEW

We aim to review select literature pertaining to congenital heart disease (CHD)-induced right ventricular (RV) function and failure.

RECENT FINDINGS

We review recent findings pertaining to children and adults with repaired tetralogy of Fallot (rTOF), systemic RV and hypoplastic left heart syndrome (HLHS). We emphasize pathophysiological mechanisms contributing to RV dysfunction in these conditions, the risk factors for adverse outcomes and the continuing challenges in treating these patients. We discuss how recent pathology findings, as well as developments in imaging and computer modeling have broadened our understanding of the pathophysiology of these conditions. We further review developments in the molecular and cellular basis of RV failure; and in particular, the RV molecular response to stress in repaired tetralogy of Fallot (rTOF). We highlight some of the genetic complexities in HLHS and how these may influence the long-term outcomes in these patients.

SUMMARY

Recent literature has led to new understandings in the pathology, pathophysiology, risk factors for adverse outcomes, molecular and genetic basis for RV dysfunction and failure in CHD. Although these findings provide new therapeutic targets, the treatment of RV failure at this time remains limited.