Role of Heart Rate Reduction in the Prevention of Experimental Heart Failure

To investigate whether heart rate reduction via I(f)-channel blockade and β-receptor blockade prevents left ventricular (LV) dysfunction, we studied ivabradine and metoprolol in angiotensin II-induced heart failure. Cardiac dysfunction in C57BL/6J mice was induced by implantation of osmotic pumps for continuous subcutaneous dosing of angiotensin II (1.8 mg/kg per day SC) over a period of 3 weeks. Ivabradine (10 mg/kg per day) and metoprolol (90 mg/kg per day), which resulted in similar heart rate reduction, or placebo treatments were simultaneously started with infusion of angiotensin II. After 3 weeks, LV function was estimated by conductance catheter technique, cardiac remodeling assessed by estimation of cardiac hypertrophy, fibrosis, and inflammatory stress response by immunohistochemistry or PCR, respectively. Compared with controls, angiotensin II infusion resulted in hypertension in impaired systolic (LV contractility, stroke volume, end systolic elastance, afterload, index of arterial-ventricular coupling, and cardiac output; P<0.05) and diastolic (LV relaxation, LV end diastolic pressure, τ, and stiffness constant β; P<0.05) LV function. This was associated with a significant increase in cardiac hypertrophy and fibrosis. Increased cardiac stress was also indicated by an increase in cardiac inflammation and apoptosis. Both ivabradine and metoprolol led to a similar reduction in heart rate. Metoprolol also reduced systolic blood pressure. Ivabradine led to a significant improvement in systolic and diastolic LV function (P<0.05). This was associated with less cardiac hypertrophy, fibrosis, inflammation, and cardiac apoptosis (P<0.05). Metoprolol treatment did not prevent the reduction in cardiac function and adverse remodeling, despite a reduction of the inflammatory stress response. Behind heart rate reduction, additional beneficial cardiac effects contribute to heart failure prevention with I(f)-channel inhibition.