Afterload mismatch and preload reserve in chronic aortic regurgitation.

Abstract

The interrelationship of afterload, preload and left ventricular (LV) performance at 2 levels of systolic loading in 20 patients with chronic aortic regurgitation was examined to determine if the concept of afterload mismatch and preload reserve can be applied to this clinical entity. Two groups of patients were identified at different stages in the natural history of volume overload. Patients in group 1 had moderate LV enlargement (LV end-diastolic volume < 150 ml/m2), and patients in group 2 had severe LV enlargement (LV end-diastolic volume > 150 ml/m2). Both groups had sufficient eccentric hypertrophy, measured by LV mass, to keep afterload as measured by mean systolic LV wall stress only slightly above normal; LV mean systolic wall stress was similar in each group. Patients in group 2 had a lower LV ejection fraction and velocity of circumferential fiber shortening than those in group 1 at a similar lower level of afterload. At a similar higher level of afterload, which increased end-diastolic volume from 134 .+-. 4 to 157 .+-. 6 ml/m2 in group 1 and from 191 .+-. 9 to 218 .+-. 13 ml/m2 in group 2 (average increase 18% vs. 14%, NS), patients in group 1 maintained their ejection fraction and forward stroke volume and had a significant increase in total LV stroke volume, whereas patients in group 2 had a decrease in ejection fraction and in forward stroke volume and no significant change in LV stroke volume. The velocity of circumferential fiber shortening decreased in both groups in response to increased afterload. Patients with moderate LV dilatation due to aortic regurgitation and sufficient hypertrophy to normalize afterload apparently have a preload reserve that permits normal LV performance during a basal state as well as during acute increases in afterload. Patients with LV dilatation, despite sufficient hypertrophy to normalize afterload, have afterload mismatch due to a depressed inotropic state, and have exhausted preload reserve such that acute increases in afterload worsen the afterload mismatch and cause further deterioration of LV performance. The velocity of circumferential fiber shortening appears to be a less useful indicator of afterload mismatch than other ejection-phase indexes of contractility. The concept of afterload mismatch and preload reserve describes the natural history of hemodynamic alterations in chronic aortic regurgitation.