Absence of right ventricular isovolumic relaxation in open-chest anesthetized dogs.

During the left ventricular (LV) pump cycle, peak negative first derivative of pressure vs. time (dP/dt) occurs very close to the end of LV ejection, and there is a well-defined isovolumic relaxation period. Despite similarities between the right ventricular (RV) and LV pump cycles, recent studies indicate uncertainty as to whether peak negative RV dP/dt occurs simultaneously with RV end ejection and whether there is an isovolumic relaxation period during the RV pump cycle. To study these questions, we recorded relative timing of peak negative RV dP/dt, RV end ejection, and right atrial-RV pressure crossover in the open-chest anesthetized dog. The data demonstrate that peak negative RV dP/dt occurs an average of 60 ms before end ejection and that there is no RV isovolumic relaxation period. These findings have implications for the possible use of peak negative RV dP/dt as a marker of RV end ejection and for how time constants of pressure decay obtained during RV relaxation can be interpreted.