Abstract 11757: Low Venous Capacitance and High Venous Return Resistance in the Fontan Circulation: Potential for New Therapies
Background: Preservation of preload reserve is extremely important in patients with Fontan circulation in whom the pulmonary ventricle is lacking. We hypothesized that venous capacitance (Cv) is reduced in the Fontan circulation, accounting for the limited preload reserve in this physiology.
Methods: The study subjects were 79 patients with congenital heart defects (15 Fontan, 64 non-Fontan). During cardiac catheterization, the inferior vena cava (IVC) was temporally occluded just above the hepatic-IVC junction, while changes in diameter and pressure of IVC distal to the occluded site were monitored simultaneously. Cv was then calculated as the diameter change divided by the pressure change. Total blood volume (TBV) was also measured by the dye dilution technique (DDG-3300, Nihon Koden) to estimate mean circulatory filling pressure (Pmcf) and venous return resistance (Rv).
Results: There was no significant difference in body size, age and IVC diameter normalized to body size before occlusion between the Fontan and non-Fontan groups. The Cv was significantly lower in the Fontan group than the non-Fontan group (0.33±0.21 vs 0.95±0.51 mmHg/mm*m2, p<0.0001). TBV was similar in the two groups (66±6 vs. 64±17 ml/kg, p=0.53), and thus the estimated Pmcf and Rv were about 3 times higher in the Fontan group than the non-Fontan group. The Cv correlated inversely with tissue fibrogenesis marker (amino-terminal procollagen type III), plasma renin activity and serum aldosterone level (p=0.005, 0.014 and 0.0006, respectively), but not with any hemodynamic parameter, including central venous pressure (CVP).
Conclusions: Fontan circulation has unique venous return characteristics, including low Cv, high Rv and elevated Pmcf. Structural (fibrosis) and/or functional (constriction) changes in the venous system induced by activation of the renin-angiotensin-aldosterone system may in part be responsible for the low Cv. These results imply the amplified increase in CVP when mobilizing preload volume and thereby increasing cardiac output (limited preload reserve) in the Fontan circulation. Thus, therapies designed to increase venous capacitance may potentially improve Fontan physiology.
- © 2011 by American Heart Association, Inc.