PACING-INDUCED DILATED CARDIOMYOPATHY INCREASES LEFT-TO-RIGHT VENTRICULAR SYSTOLIC INTERACTION

Background. The right ventricle (RV) receives part of its systolic pumping force from the left ventricle through systolic ventricular interaction. The purpose of this study was to determine the effects of dilated cardiomyopathy on left ventricular to right ventricular (LV-to-RV) systolic interaction. Methods and Results. Studies were performed in six normal pigs and in six pigs in which dilated cardiomyopathy resulting in congestive heart failure (CHF) was produced with rapid ventricular pacing at 230 beats per minute for 1 week. In all pigs, we rapidly withdrew blood from the LV apex into a prosthetic ventricle in a single beat, which reduced LV systolic pressure without changing RV or LV end-diastolic pressure, and the resultant instantaneous changes in RV systolic pressure and pulmonary artery flow were determined. The LV-to-RV mean systolic interaction gain was calculated as the change from a normal beat to the instantaneous unloaded bent in mean RV systolic pressure divided by the change in mean LV systolic pressure. Mean systolic pressure gain was approximately 2 1/2 times greater (P<.05) in the CHF animals (0.103+/-0.018 mm Hg/mm Hg) than in the normal pigs (0.040+/-0.011 mm Hg/mm Hg). Conclusions. These data demonstrate that left-to-right ventricular systolic interaction is significantly greater in dilated cardiomyopathy compared with the normal heart, indicating that the contribution of the left ventricle to RV systolic pressure generation has increased. This is consistent with decreased elastance of the interventricular septum resulting in increased coupling between the ventricles.