The early response of the systemic ventricle during transition to the Fontan circulation—an acute hypertrophic cardiomyopathy?

Summary Using combined epicardial echocardiography and high-fidelity intraventricular pressure recordings, the acute effects of transition to a Fontan circulation were studied in 10 patients. Measurements were made before and after cardiopulmonary bypass. The Fontan operation had no significant effect on load-dependent indices, or on a load independent index (Vmax) of ventricular systolic function. Large changes were observed in ventricular geometry. Maximum and minimum cavity dimensions were reduced, while maximum and minimum thicknesses of the posterior wall were increased.While simultaneous Doppler/intraventricular pressure measurements suggested that the compliance of the ventricle was unchanged, the pattern of atrioventricular flow changed from predominantly early diastolic (E wave) to predominantly atrial systolic (A wave) as a result of surgery in four patients. The time constant of ventricular relaxation was prolonged in all patients and five developed Doppler echocardiographic evidence of incoordinate relaxation of the ventricle, with intraventricular flow occurring during isovolumic relaxation. Thus, the Fontan operation causes acute hypertrophy of the systemic ventricle due to a sudden reduction in ventricular preload in the presence of a maintained shortening fraction. While global ventricular diastolic compliance may be unchanged by the operative procedure, filling of the ventricle during early diastole is altered as a result of incoordinate relaxation and a prolonged time constant of ventricular relaxation.