differential effects of the angiotensin-converting enzyme inhibitor lisinopril versus the beta-adrenergic receptor blocker atenolol on hemodynamics and left ventricular contractile function in experimental mitral regurgitation

Objectives The goal of this study was to determine the therapeutic efficacy of angiotensin-converting enzyme (ACE) inhibitors and beta-adrenergic receptor blockers in experimental chronic mitral regurgitation (MR), gaining knowledge using methods difficult to apply in humans. Background Both ACE inhibitors and beta-blockers are cornerstones in the treatment of human congestive heart failure. However, the roles of these treatments for chronic MR is unclear. Methods Mitral regurgitation was created in 11 closed-chest dogs. Three months after the creation, the ACE inhibitor lisinopril 20 mg was given orally daily. After three months of lisinopril therapy, the beta-blocker atenolol was added to lisinopril for another three months. Atenolol was begun at a dose of 12.5 mg daily and increased gradually to 100 mg daily. Hemodynamics and left ventricular (LV) function were assessed throughout the study. Results Regurgitant fraction was consistently >50% over the course of this study. Pulmonary capillary wedge pressure and LV end-diastolic pressure were significantly increased after three months of MR and decreased during both lisinopril and the combined therapy in which it was not different from baseline. Left ventricular contractility measured by the end-systolic stiffness constant was depressed from 3.66 ± 0.20 to 2.65 ± 0.12 (p < 0.05) at three months of MR and rose insignificantly after lisinopril treatment (2.99 ± 0.17). When atenolol was added, it rose significantly and returned to normal (3.50 ± 0.22, p < 0.05). Conclusions Although lisinopril significantly reduced preload, its effect on LV contractility was insignificant in experimental MR. Conversely, atenolol, when added to lisinopril, achieved maximum hemodynamic benefit and also restored LV contractility.