Bradycardia and the Role of β-Blockade in the Amelioration of Left Ventricular Dysfunction

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Abstract
Background—It is clear that β-blockers are effective for treatment of congestive heart failure, but their mechanism of action remains controversial. Hypothesized mechanisms include normalization of β-receptor function and myocardial protection from the effects of catecholamines, possibly by the institution of bradycardia. We hypothesized that β-blockade–induced bradycardia was an important mechanism by which these agents were effective for correction of LV dysfunction. Methods and Results—In 2 groups of dogs with mitral regurgitation and LV dysfunction, β-blockers were instituted. In 1 group that received β-blockers and pacing (group β+P), a pacemaker prevented the natural bradycardia that β-blockers cause. In both groups, substantial LV dysfunction developed. Before β-blockade, the end-systolic stiffness constant decreased from 3.5±0.1 to 2.7±0.2 (P<0.01) at 3 months in group β+P. A similar reduction occurred in the group that eventually received only β-blockers (group βB). In group βB, end-systolic stif...