Ivabradine: Heart Rate and Left Ventricular Function

Ivabradine specifically inhibits the I(f) current in the sinoatrial node to lower heart rate, without affecting other aspects of cardiac function. We aimed to test whether lowering the heart rate with ivabradine reduces cardiovascular death and morbidity in patients with coronary artery disease and left-ventricular systolic dysfunction. Between December, 2004, and December, 2006, we screened 12 473 patients at 781 centres in 33 countries. We enrolled 10 917 eligible patients who had coronary artery disease and a left-ventricular ejection fraction of less than 40% in a randomised, double-blind, placebo-controlled, parallel-group trial. 5479 patients received 5 mg ivabradine, with the intention of increasing to the target dose of 7.5 mg twice a day, and 5438 received matched placebo in addition to appropriate cardiovascular medication. The primary endpoint was a composite of cardiovascular death, admission to hospital for acute myocardial infarction, and admission to hospital for new onset or worsening heart failure. We analysed patients by intention to treat. The study is registered with ClinicalTrials.gov, number NCT00143507. Mean heart rate at baseline was 71.6 (SD 9.9) beats per minute (bpm). Median follow-up was 19 months (IQR 16-24). Ivabradine reduced heart rate by 6 bpm (SE 0.2) at 12 months, corrected for placebo. Most (87%) patients were receiving beta blockers in addition to study drugs, and no safety concerns were identified. Ivabradine did not affect the primary composite endpoint (hazard ratio 1.00, 95% CI 0.91-1.1, p=0.94). 1233 (22.5%) patients in the ivabradine group had serious adverse events, compared with 1239 (22.8%) controls (p=0.70). In a prespecified subgroup of patients with heart rate of 70 bpm or greater, ivabradine treatment did not affect the primary composite outcome (hazard ratio 0.91, 95% CI 0.81-1.04, p=0.17), cardiovascular death, or admission to hospital for new-onset or worsening heart failure. However, it did reduce secondary endpoints: admission to hospital for fatal and non-fatal myocardial infarction (0.64, 95% CI 0.49-0.84, p=0.001) and coronary revascularisation (0.70, 95% CI 0.52-0.93, p=0.016). Reduction in heart rate with ivabradine does not improve cardiac outcomes in all patients with stable coronary artery disease and left-ventricular systolic dysfunction, but could be used to reduce the incidence of coronary artery disease outcomes in a subgroup of patients who have heart rates of 70 bpm or greater.

In congestive heart failure (idiopathic dilated cardiomyopathy), exercise is accompanied by a smaller-than-normal decrease in end-diastolic left ventricular volume, depressed peak rates of left ventricular pressure rise and fall, and depressed heart-rate-dependent potentiation of contractility (bowditch treppe). We studied contractile function of isolated left ventricular myocardium from New York Heart Association class IV-failing and nonfailing hearts at physiological temperature and heart rates in order to identify and quantitate abnormalities in myocardial function that underlie abnormal ventricular function. The isometric tension-generating ability of isolated left ventricular strips from nonfailing and failing human hearts was investigated at 37 degrees C and contraction frequencies ranging from 12 to 240 per minute (min-1). Strips were dissected using a new method of protection against cutting injury with 2,3-butanedione monoxime (BDM) as a cardioplegic agent. In nonfailing myocardium the twitch tension-frequency relation is bell-shaped developing 25 +/- 2 mN/mm2 at a contraction frequency of 72 min-1 and peaking at 44 +/- 3.7 mN/mm2 at a contraction frequency of 174 +/- 4 min-1. In failing myocardium the peak of the curve occurs at lower frequencies between 6 and 120 min-1 averaging 81 +/- 22 min-1, and it develops 48% (p less than 0.001) and 80% (p less than 0.001) less tension than in nonfailing myocardium at 72 and 174 min-1, respectively. Between 60 and 150 min-1 tension increases by 107% in nonfailing myocardium, but it does not change significantly in failing myocardium. Peak rates of rise and fall of isometric twitch tension vary in parallel with twitch tension as stimulation frequency rises in nonfailing myocardium but not in failing myocardium. The quantitative agreement between these results from isolated myocardium and those from catheterization laboratory measurements on intact humans suggest that alterations of myocardial origin, independent of systemic factors, may contribute to the above mentioned abnormalities in left ventricular function seen in dilated cardiomyopathy.

Aims The SHIFT echocardiographic substudy evaluated the effects of ivabradine on left ventricular (LV) remodelling in heart failure (HF). Methods and results Eligible patients had chronic HF and systolic dysfunction [LV ejection fraction (LVEF) ≤35%], were in sinus rhythm, and had resting heart rate ≥70 bpm. Patients were randomly allocated to ivabradine or placebo, superimposed on background therapy for HF. Complete echocardiographic data at baseline and 8 months were available for 411 patients (ivabradine 208, placebo 203). Treatment with ivabradine reduced LVESVI (primary substudy endpoint) vs. placebo [−7.0 ± 16.3 vs. −0.9 ± 17.1 mL/m2; difference (SE), −5.8 (1.6), 95% CI −8.8 to −2.7, P< 0.001]. The reduction in LVESVI was independent of beta-blocker use, HF aetiology, and baseline LVEF. Ivabradine also improved LV end-diastolic volume index (−7.9 ± 18.9 vs. −1.8 ± 19.0 mL/m2, P= 0.002) and LVEF (+2.4 ± 7.7 vs. −0.1 ± 8.0%, P< 0.001). The incidence of the SHIFT primary composite outcome (cardiovascular mortality or hospitalization for worsening HF) was higher in patients with LVESVI above the median (59 mL/m2) at baseline (HR 1.62, 95% CI 1.03–2.56, P= 0.04). Patients with the largest relative reductions in LVESVI had the lowest event rates. Conclusion Ivabradine reverses cardiac remodelling in patients with HF and LV systolic dysfunction.