Defining end systole for end-systolic pressure-volume ratio.

The end-systolic pressure-volume (ESPV) ratio (Emax) has recently been accepted as a valid cardiac contractility index. However, in vivo, it is difficult to define end systole (ES) precisely. This study was designed to analyze the effects of eight different ES definitions on Emax. Nine chronically instrumented dogs were studied prior to and during the sequential infusions of phenylephrine (0.2 mg/min), epinephrine (2.0 micrograms/min), and dobutamine (10 micrograms/kg/min). Left ventricular (LV) dimensions and pressure were measured with sonomicrometers and micromanometer. ES was defined at peak LV pressure (PLVP), end-ejection, dp/dt min, 10, 20, 30 msec before dp/dt min, minimum volume before dp/dt min, and left-upper-corner of pressure volume loop (LUC). Although ESPV relationship from each definition was linear (mean r 0.89 +/- 0.3, range 0.76 to 0.99) and sensitive to inotropic changes, the Emax's were not all the same. The r was highest with LUC (mean 0.94 +/- .02, range 0.90 to 0.99) and lowest with PLVP (mean 0.85 +/- 0.03, range 0.76 to 0.92). Emax from PLVP was least sensitive to epinephrine and dobutamine infusions. Thus, in order to compare different values of Emax, the definition of ES must be precise and consistent. Although all the above eight definitions of ES appeared to produce reasonable ESPV relationship, PLVP appeared to be the worst while LUC appeared to be the best ES definition for determining Emax.