Disparity between ejection and end-systolic indexes of left ventricular contractility in mitral regurgitation

To examine left ventricular function in mitral regurgitation (MR), we compared the ejection phase indexes of left ventricular contractility with maximal systolic elastance (Emax) in an experimental preparation of MR. In eight anesthetized open-chest dogs, pressure-volume loops were derived during afterload manipulation with methoxamine and nitroprusside from simultaneous left ventricular pressure and dimensional (sonomicrometry techniques) data before and after creation of MR. From these data maximal systolic elastance (Emax), the end-systolic pressure-volume relationship (ESPVR), and the end-systolic stress-volume relationship (ESSVR) were determined by linear regression analysis. After creation of MR, end-diastolic volume increased significantly (40 ± 13 to 53 ± 18 ml, p < .001); likewise end-systolic volume increased (28 ± 11 to 33 ± 15 ml, p < .05). Ejection fraction increased after MR (35 ± 6% to 44 ± 8%, p < .005), as did the mean velocity of fiber shortening (0.62 ± 0.20 to 1.02 ± 0.39 sec^-1, p < .02). In contrast, Emax declined significantly (4.63 ± 2.5 to 3.54 ± 1.94 mm Hg/ml, p < .05); ESPVR and ESSVR showed similar directional changes. An inverse relationship was found between systolic elastance and end-diastolic volume in both control and MR states. When Emax, ESPVR, and ESSVR were normalized to end-diastolic volume, they were unchanged after MR. These results suggest that either there was a decline in left ventricular contractile state after MR, or that contractility was unchanged (if elastance is normalized for the increase in heart size). In this preparation of MR the observed increase in shortening was not due to increased contractility, but occurred as a consequence of increased preload with no significant change in afterload.