Heart rate as a prognostic marker and therapeutic target in acute and chronic heart failure

Since increased heart rate (HR) is associated with higher mortality in several cardiac disorders, HR is considered not only a physiological indicator but also a prognostic and biological marker. In heart failure (HF), it represents a therapeutic target in chronic phase. The use or up-titration of beta-blockers, a milestone in HF with reduced left ventricular ejection fraction (LVEF) treatment, is at times limited by patients' hemodynamic profile or intolerance. Ivabradine, a HR-lowering drug inhibiting the f-current in pacemaker cells, has been shown to improve outcome in patients with chronic HF, in sinus rhythm with increased HR beyond beta-blocker therapy. The rationale for this review is to update the role of HR as a prognostic biomarker and a potential therapeutic target in other scenarios than chronic HF; namely, in patients with coexisting atrial fibrillation (AF), in HF with preserved LVEF (HFpEF), in acute HF, and in patients discharged after an episode of acute HF. Preliminary studies and case reports that evaluated the use of ivabradine in the setting of acute HF will be summarized. Recent results of HR reduction in the setting of HFpEF with ivabradine will be presented. Finally, data from large registries and trials that evaluated the prognostic impact of HR in patients with acute HF and sinus rhythm or AF will be reviewed, showing that only patients in sinus rhythm may benefit from HR reduction.