Abstract 1875: Chronic Monotherapy with Atenolol Is Inferior to Metoprolol Succinate in Improving Left Ventricular Ejection Fraction and Preventing Ventricular Remodeling in Dogs with Heart Failure
Background: Atenolol (ATE), a beta-1 selective adrenoceptor blocker, is frequently used for the treatment of patients with chronic heart failure (HF) despite the absence of clinical trial evidence-based efficacy data. In this study, we compared the effects of long-term monotherapy with ATE to that of sustained release metoprolol succinate (MET), also a beta-1 selective adrenoceptor blocker, on LV ejection fraction (EF) and end-systolic volume (ESV), indicators of long-term mortality and morbidity, and on LV structural remodeling in dogs with coronary microembolization-induced HF (EF 30%– 40%).
Methods: Nineteen HF dogs were randomized to 3 months oral therapy with ATE (50 mg once daily, n=6), MET (100 mg, once daily, n=6) or no therapy at all (Controls, n=7). LV EF and ESV were measured at randomization, before initiating therapy (PRE), and after 3 months of therapy (POST). Volume fraction of interstitial fibrosis (VFIF) and cardiomyocyte cross-sectional area (MCSA), measures of myocardial structural remodeling, were assessed at POST therapy using standard histomorphometric methods. To examine “treatment effect”, the change (Δ) in EF and ESV between PRE and POST therapy was calculated and compared among the 3 study groups.
Results: Data are shown in the table⇓. In controls, EF decreased and ESV increased. ATE did not increase EF and did not decrease ESV. In contrast, MET significantly increased EF and decreased ESV. Treatment effect comparisons showed significantly greater improvements in EF and ESV with MET compared to ATE (EF: 6 ± 1% vs 2 ± 1%, p<0.05 and ESV: −4 ± 1 ml vs −1 ± 1 ml, p<0.05). VFIF and MCSA decreased with both ATE and MET compared to controls. The decrease in both, however, was significantly greater with MET compared to ATE.
Conclusions: In dogs with HF, long-term therapy with ATE does not elicit the same LV hemodynamic and remodeling benefits as those derived from MET. These results do not support the use of ATE as a replacement for MET to treat chronic HF.