Cardiac Rest and Reserve Function in Patients With Fontan Circulation

Cardiac Rest and Reserve Function in Patients With Fontan Circulation Hideaki Senzaki, Satoshi Masutani, Hirotaka Ishido, Mio Taketazu, Toshiki Kobayashi, Nozomu Sasaki, Haruhiko Asano, Toshiyuki Katogi, Shunei Kyo, Yuji Yokote We systematically tested cardiac rest and reserve function in patients with Fontan physiology, to check for inherent limitations that could account for adverse outcome after Fontan surgery. Fontan circulation was associated with: 1) abnormal ventricular-vascular interaction; and 2) limited ventricular reserve function in response to increased heart rate and beta-adrenergic stimulation. Because normal ventricular-vascular interaction and normal ventricular reserve function are needed to maintain cardiac output and exercise capacity, improvement of prognosis after Fontan surgery requires the development of new medical interventions that can overcome these limitations inherent in Fontan physiology. In the present study, we systematically tested cardiac rest and reserve function in patients with Fontan physiology to check for inherent limitations of this circulation. Details of the mechanisms of cardiac performance that could account for adverse outcome after Fontan surgery are not well understood. The subjects were 17 Fontan patients with good functional status (Fontan group) and 20 patients with normal two-ventricle circulation (control group). We examined baseline ventricular contractility, diastolic function, and loading factors, and examined changes in those parameters in response to increased heart rate (HR) due to atrial pacing and in response to beta-adrenergic stimulation, using ventricular pressure-area relationships during preload reduction. At baseline, the Fontan patients exhibited minimal abnormality of cardiac properties, but the significant increase in afterload resulted in decreased cardiac index. In addition, Fontan circulation was associated with limited inotropic response and worsening of diastolic filling with increased HR, leading to decreased systolic pressure and elevation of central venous pressure at higher HRs (p < 0.05 vs. control). Furthermore, beta-adrenergic reserve was markedly decreased in the Fontan group, compared with controls, owing to limited preload reserve rather than limited contractile reserve. Because normal ventricular-vascular interaction and augmentation of cardiac performance during increased HR and adrenergic stimulation are important for maintaining cardiac output and exercise capacity, t