Ventricular energetics after the Fontan operation: contractility-afterload mismatch.

OBJECTIVE

Fontan-type operations offer the opportunity to create pulmonary and systemic circulation in series with a single pumping chamber. The effectiveness of such a circulatory pattern determines resting and exercise hemodynamics in these patients. The present study investigated cardiac performance after the Fontan operation by using ventricular-vascular coupling framework analysis.

METHODS

In 12 anesthetized open-chest dogs, Fontan circulation was established by using a cavopulmonary anastomosis. Left ventricular hemodynamic variables were measured by using a combined pressure-volume-conductance catheter. Additionally, aortic flow and pressure were recorded continuously. Ventricular contractility was quantified by using the load-independent slope of the end-systolic pressure-volume relationship. Arterial system properties were quantified by using the end-systolic pressure/stroke volume ratio. The coupling between the left ventricle and arterial system was expressed by using the ratio of end-systolic pressure/stroke volume to slope of the end-systolic pressure-volume relationship. Additionally, external stroke work, total mechanical energy and mechanical efficiency (Mechanical efficiency = Stroke work/Total mechanical energy) were calculated. Impedance spectra were determined by means of Fourier analysis.

RESULTS

During Fontan circulation, the slope of the end-systolic pressure-volume relationship (5.3 +/- 0.6 vs 7.5 +/- 0.6 mm Hg/mL, P <.05) decreased, and the end-systolic pressure-stroke volume relationship (4.2 +/- 0.7 vs 3.3 +/- 0.5 mm Hg/mL, P =.23) increased with parallel increased characteristic impedance. Furthermore, the end-systolic pressure-stroke volume/slope of the end-systolic pressure-volume relationship ratio increased significantly (0.76 +/- 0.04 vs 0.42 +/- 0.03, P <.005). Simultaneously, stroke work (1846 +/- 146 vs 1389 +/- 60 mm Hg/mL, P <.05) and mechanical efficiency (0.82 +/- 0.09 vs 0.56 +/- 0.05, P <.05) were significantly reduced.

CONCLUSIONS

Fontan circulation leads to contractility-afterload mismatch by means of increased impedance caused by additional connection of the pulmonary vascular bed to the systemic vasculature and by means of deterioration of myocardial contractility. The increased ventriculoarterial coupling ratio and reduced mechanical efficiency predict limited cardiac functional reserve after the Fontan operation.