EFFECTIVENESS OF PRELOAD RESERVE AS A DETERMINANT OF CLINICAL STATUS IN PATIENTS WITH LEFT-VENTRICULAR SYSTOLIC DYSFUNCTION

The hemodynamic determinants of clinical status in patients with left ventricular (LV) systolic dysfunction have not been established. In the present study, preload reserve - LV distension during exercise - was related to clinical status, and the effect of acute angiotensin-converting enzyme inhibition was examined in 97 patients with ejection fraction less-than-or-equal-to 0.35 enrolled in the trial, Studies of Left Ventricular Dysfunction (SOLVD). Sixty-one asymptomatic patients (group I) were compared with 36 patients with symptomatic heart failure (group II). Radionuclide LV volumes were measured at rest and during maximal cycle exercise. Group II patients had higher resting heart rates, end-diastolic and end-systolic volumes, and lower ejection fractions (all p <0.005). During exercise, only patients in group I had increased stroke volume (from 35 +/- 8 to 39 +/- 11 ml/m2 [mean +/- SD; p <0.0005]) due to an increase in end-diastolic volume (from 119 +/- 29 to 126 +/- 29 ml/m2 [p <0.000.5]), contributing to a greater increase in LV minute output (p <0.0001, group I vs group II). After administration of intravenous enalapril (1.25 mg), LV end-diastolic volume response to exercise was augmented in group II (rest, 140 +/- 42; exercise, 148 +/- 43 ml/m2; p <0.0005) and LV output response increased slightly (p <0.05). Thus, in patients with asymptomatic systolic dysfunction, recruitment of preload during exercise is responsible for maintaining a stroke volume contribution to the cardiac output response. In patients with symptomatic heart failure, preload reserve is absent, and the cardiac output response depends solely on heart rate. Enalapril may augment preload reserve.