Single-Ventricle Physiology

Abstract

Hypoplastic left heart syndrome (HLHS) is a rare developmental abnormality of the left-sided heart structures that accounts for 3.8 % of congenital cardiac malformations. It comprises a range of defects characterized by a single functional ventricle belonging either to the left or to the right heart complex. A common presentation of the HLHS is a small or nonexistent left ventricle, stenosis of aortic and mitral valve, and hypoplastic ascending aorta. The circulation is achieved by way of the pulmonary artery which supplies the lungs and the systemic circulation via the ductus arteriosus [1] (Fig. 20.1). Unlike in the normal circulation where the two circuits are separated and said to be placed in series, the systemic and pulmonary circuits are arranged in parallel, giving rise to significant mixing of arterial and venous bloods. The increase in pulmonary blood flow tilts the balance between the normal ratio of pulmonary and systemic circulations (Qp:Qs) and results in progressive shunting of the blood away from the systemic circuit. Ductal closure results in a sudden decrease in systemic perfusion, leading to acidosis, oliguria, and shock [1]. As a “duct-dependent” lesion, the condition was universally fatal within days to weeks after closure of the duct and was therefore not amenable to therapeutic intervention until the duct patency could be maintained by administration of PG_E1 in the early 1980s [2]. The empirical approach for palliation of HLHS and associated anomalies with a single-ventricle physiology has evolved gradually over the past 40 years and is based on the pioneering work of Fontan and Baudet in the 1970s who were the first to succeed in anatomical separation of the two circulations [3].