Abstract 240: Interruption of Ivabradine Treatment in Middle-Aged Post-MI Rats May Lead to Heart Failure
Background: We have previously demonstrated that heart rate reduction (HRR) with the selective cardiac pacemaker If current inhibitor ivabradine (IVA) improved LV function and coronary perfusion reserve in post-MI middle-aged rats. The beneficial effects of IVA treatment were associated with attenuated collagen accumulation in the surviving LV myocardium and inhibition of the circulatory renin-angiotensin system. However, sustainability of these positive changes after a period of IVA treatment interruption remains to be determined.
Methods: MI was induced in 12-month-old male Sprague-Dawley rats by left coronary artery ligation. Twenty four hours later, the rats with a confirmed large transmural MI were randomly assigned in two experimental groups. In a first group, rats were treated with IVA i.p. via osmotic pumps in a dose of 10.5 mg/kg/d for 4 weeks followed by a 4-week period without treatment (MI+IVA). In a second group, rats received placebo for 4 weeks (MI). Sham-operated rats served as a control. Eight weeks after MI, the various LV parameters were examined.
Results: During 4 weeks of treatment, heart rate in MI+IVA rats was consistently reduced compared to untreated MI rats (mean of HRR was 27%). After IVA withdrawal, heart rate increased to the levels of the placebo group. Eight weeks after MI, the IVA treated group demonstrated smaller LV free wall infarct size (57.5 ± 2.7% vs. 72.5 ± 2.5%, p<0.01) and greater LV weight/body weight ratio (2.54 ± 0.06 vs. 2.26 ± 0.11 mg/g, p<0.05), indicating greater myocardial compensatory hypertrophy. Furthermore, the interstitial collagen content was significantly lower in the remote LV myocardium of MI+IVA rats compared to MI rats (7.5 ± 0.7% vs. 13.3 ± 1.0% in free wall and 7.3 ± 0.8% vs. 11.2 ± 0.9% in septum, p < 0.01). However, compared to non-infarcted controls, rats of both MI groups had markedly lower LV ejection fraction and coronary perfusion reserve.
Conclusions: Our data demonstrate that although beneficial structural changes induced by IVA in post-MI myocardium can be sustainable for a long period of time they cannot prevent deterioration of LV function after withdrawal of treatment. Therefore, we believe that continuous treatment with IVA may be essential for attenuation of heart failure after a large MI.
- © 2012 by American Heart Association, Inc.