Use of a Conductance Catheter to Detect Increased Left Ventricular Inotropic State by End-systolic Pressure-volume Analysis

The slope of the left ventricular end-systolic pressure-volume relationship is thought to be a load-independent index of contractile state. However, clinical application requires a practical technique to simultaneously measure pressure and volume in man. We used a left ventricular conductance catheter to derive the left ventricular end-systolic pressure-volume relationship over a range of arterial pressures during nitroprusside infusion and washout in 14 patients, and to characterize the effect of dobutamine, a positive inotropic drug. End-systole was defined as the maximum pressure-to-volume ratio. Dobutamine (5 micrograms/kg/min) increased the slope of the end-systolic pressure-volume relationship in 11 of 14 patients, the mean slope increasing by 43% from 1.4 +/- 0.1 to 2.1 +/- 0.2 mm Hg/% end-diastolic volume (p less than 0.01). In 12 of 14 patients there was a leftward and upward shift of the end-systolic pressure-volume relationship with dobutamine. T quantitate this shift, we derived left ventricular pressure at control end-systolic volume before and after dobutamine. Dobutamine increased the mean end-systolic pressure at control end-systolic volume in 12 of 14 patients, the average increased by 37% from 134 +/- 10 to 189 +/- 23 mm Hg (p less than 0.01). We conclude that the conductance catheter can be used in man to detect a drug-induced change in left ventricular contractile state. This technique may be useful in the evaluation of drugs with positive inotropic actions, and in assessing the response of individual patients to positive inotropic agents.