Background: Improvements are known to occur in right ventricular (RV) ejection fraction after the use of a left ventricular assist device (LVAD); less is known, however, about the mechanism of this improvement. The concept of ventricular/arterial coupling was applied to investigate whether systolic pump function or afterload reduction was the major contributing factor leading to the improvement in RV ejection fraction.
Methods and results: Eight consecutive patients who underwent Novacor LVAD implantation as a bridge to transplantation were studied intraoperatively with transesophageal echocardiogram and a catheter-tip manometer to examine the RV end-systolic pressure-area relation (ESPAR) before and after LVAD implantation. Fractional area change (FAC) obtained by echocardiogram was used as an approximation of ejection fraction. End-systolic elastance (Ees), area axis intercept of ESPAR (A0), maximal area (Amax), and pulmonary effective arterial elastance (Ea) were obtained. RV FAC improved from 0.20 +/- 0.09 to 0.29 +/- 0.13 (p < 0.05). There was a decrease in Ea from 12.06 +/- 5.79 to 4.92 +/- 2.51 mm Hg/cm2 (p < 0.01), which indicated a reduction in RV afterload. A0 increased from -0.14 +/- 7.81 to 6.83 +/- 9.42 cm2 (p < 0.05), which implied impaired systolic pump function. There was no difference in Ees and Amax.
Conclusions: The concept of ventricular/arterial coupling predicts that an increase of A0 (reduced RV systolic mechanics) decreases FAC, whereas a reduction in Ea improves FAC. The improvement in RV FAC (improved RV pump performance) may result from the effect of reduced Ea (afterload reduction) overwhelming the effect of increased A0. Afterload reduction is the most likely mechanism by which RV ejection fraction improves after LVAD implantation.