Are Pressure-Volume Relations at End-Systole a Reflection of Left Ventricular Myocardial Contractility?

Abstract

The pressure-volume relation at end-systole is reportedly altered by changes in contractility. To explore the potential of this ratio in man 185 subjects including 23 normals (Group I) were studied. In 35 patients of Group II (16 with mitral stenosis, 7 with atrial septal defect, and 12 with cor pulmonale) ESP/ESV like an index of contractility measuring force-velocity-length rela tionship (Cy Ix) was insignificantly different from Group I (ESP/ESV and Cy Ix in I = 1.73 ± .31 mmHg/sec, 1.46 ± .09 cm/sec/cm vs 1.44 ± .10, 1.31 ± .05 in II respectively.) With significantly reduced Cy Ix (1.03 ± .04, P<0.00001) ESP/ ESV was likewise reduced (1.16 ± .07, P<0.007) in 108 patients with compen sated LV disease (34 with alcoholic cardiomyopathy, 16 coronary artery dis ease, 30 aortic valve disease, 8 hypertension and 16 with other heart muscle disease.) Like the Cy Ix (0.70 ± .05, P<0.001) ESP/ESV was even lower (0.84 ± .13, P<0.05) in 14 patients with decompensated LV (Group IV). It was insensitive to changes in pressure (angiotensin and volume (dextran). However unlike the Cy Ix it did not vary with acute changes in inotropy (exercise and pacing). The correlations between ESP/ESV and ejection fraction and contractility index in the entire series though weak, were significant (r = .50 and .20 respectively, each P<0.006). Exclusion of patients with aortic valve disease and hypertension in the analysis tended to improve the relationship between the contractility and end-systolic pressure-volume parameters. In the latter two subgroups neither the ESV nor the ESP/ESV ratio related to the contractil ity index, both parameters however did correlate significantly with the ejection fraction. These results indicate that end-systolic pressure-volume relations provide useful measures of LV performance in man, though not expressing the contractility either in all patients or under all situations.