Timing and Velocit of Ejection as Major Determinants of End-Systolic Pressure in Isolated Rabbit Hearts

Background Systolic shortening is known to produce mus-cle deactivation. The present study was designed to analyze whether the velocity and the timing of ejection play a role on end-systolic pressure-volume relations (ESPVR). Methods and Results In isolated rabbit hearts, left ventric-ular pressure and volume were recorded and digitized, and left ventricular volume was controlled by a servosystem (4-milli-second cycles) to alter the timing of ejection. A significant deficit in end-systolic pressure was observed when ejection was late in systole with respect to earlier ejection. This was associated with a significantly reduced end-systolic elastance. End-systolic pressure of beats with slow ejection was interme-diate between that of the beats with early ejection and that of beats with late ejection with a significantly increased end-systolic volume compared with beats with early rapid ejection