Effect of the pericardium on systolic ventricular interdependence in the dog

Systolic ventricular interdependence, whereby changes in left ventricular (LV) ejection alter right ventricular (RV) ejection, has been described. It is unclear, however, whether this interaction is influenced by pericardial volume constraint or by myocardial mechanical coupling. We hypothesized that if mechanical coupling were the primary factor determining systolic ventricular interdependence then it should be unaltered by the presence or absence of an intact pericardium, but affected by changes in LV end-systolic volume. We tested this hypothesis by observing the changes in RV stroke volume (SVrv) and peak systolic pressure (PSPrv) during a single LV isovolumic contraction under conditions of normal or increased (1.3 x normal) RV end-diastolic volume with and without an intact pericardium. In 10 anesthetized, open-chested dogs SVrv was derived from the integrated pulmonary arterial flow probe signal and RV ejection fraction (EFrv) was derived from the thermodilution plateau method and a rapidly responsive thermistor in the pulmonary artery. Right ventricular end-diastolic volume was considered to be the ratio of SVrv to EFrv. Left ventricular isovolumic contraction increased SVrv and PSPrv during all conditions (P < .01). However, PSPrv increased more when the pericardium was intact (P < .05). These data suggest that LV ejection can enhance SVrv and that this interaction is not appreciably altered by volume loading or the presence of an intact pericardium. Pericardial interactions may alter PSPrv but do not affect SVrv.