Therapy and Prevention - Left Ventricular Function

The response of the maximum value of the left ventricular pressure-volume ratio to preload augmentation by blood or plasma expanders was studied in 1 1 patients during the first 24 hr after coronary artery bypass graft surgery. Increasing the mean left atrial pressure from 10 to 15 and 20 mm Hg resulted in no change in the maximum pressure-volume ratio in the group as a whole. In certain individual patients, however, the maximum pressure-volume ratio changed with volume infusion, and these changes were accompanied by simultaneous changes in afterload. The observed changes in pressure-volume ratio were in the same direction as the changes in afterload (systolic pressure), suggesting a dependence of maximum pressure-volume ratio on afterload. These results show that the maximum pressure-volume ratio is independent of preload in the first 24 hr after coronary artery bypass graft surgery with the pericardium open; thus the maximum pressure-volume ratio is a useful index of postoperative left ventricular function when afterload is unchanged. However, because this ratio (a single-point assessment of the pressure-volume relationship) may not be a good estimate of Emax, we recommend a more complete determination of the locus of the "upper left corners" of the pressurevolume loops for measurement of Emax to provide a more accurate indicator of the myocardial contractile state. Circulation 71, No. 5, 945-950, 1985. THE POINTS on pressure-volume diagrams of the left ventricle where the ratio of instantaneous ventricular transmural pressure to instantaneous ventricular volume is at a maximum (i.e., the upper left corners of the loops, which occur at a time near end-systole) lie on a straight line that is independent of loading conditions over a wide range. 1.2 The slope of this line, which has been called Emax,3 changes with inotropic interventions and has been shown to be a useful index of left ventricular contractility. Various assessments of Emax, based on measurement of pressure-volume, pressure-dimension, stress-dimension, and similar relationships, can be very useful indexes of ventricular performance. 41 The ratio of end-systolic pressure to end-systolic From the Research Institute of the Palo Alto Medical Foundation and Department of Cardiovascular Surgery and Division of Cardiology, Stanford University School of Medicine, Palo Alto, CA. Supported in part by NIH grant HL 29589. Address for correspondence: George T. Daughters, M.S., Senior Investigator, Palo Alto Medical Foundation, 860 Bryant St., Palo Alto, CA 94301. Received Aug. 31, 1984; revision accepted Jan. 24, 1985. Vol. 71, No. 5, May 1985 volume, a popular estimate of Emax, is reduced in patients with chronic volume overload,'2 and end-systolic volume (even when uncorrected for its pressure dependence) is a useful prognostic indicator in such patients.'3 A single measurement of the end-systolic stress-volume ratio can be a useful predictor of operative risk in patients with chronic mitral regurgitation.'4 It is compelling to think that a simple ratio, calculated from single measurements of left ventricular pressure and volume near end-systole, might reflect the myocardial contractile state accurately enough to be clinically meaningful. 1517 Moreover, such an approach would markedly reduce the technical complexity and number of interventional procedures required for assessment of the contractile state. We therefore tested the hypothesis that the maximum left ventricular systolic pressure-volume ratio [(P/V)max] is independent of preload in intact man, using a technique that allowed repeated measurement of left ventricular pressure-volume relationships as frequently as desired in the first 24 hr after cardiac surgery. 945 by gest on Jauary 5, 2018 http://ciajournals.org/ D ow nladed from