Target heart rate in heart failure with reduced ejection fraction and atrial fibrillation: Goldilocks zone.

The rates of atrial fibrillation (AF) and heart failure with reduced ejection fraction (HFrEF) continue to grow with many patients suffering from their combined impact on quality of life and prognosis. A lower heart rate (HR) in HFrEF is associated with reduced morbidity and mortality due to beta-blocker and ivabradine therapy. Postulated mechanisms include reduced neurohumoral activation, increased diastolic filling time and myocardial energy conservation. In contrast, the landmark randomised controlled non-inferiority RACE II trial demonstrated that a lenient rate control strategy (target HR <110 beats per minute [bpm]) was more attainable and safer than a strict rate control strategy (resting HR <80 bpm) in permanent AF. Physiologically, a higher HR is needed to compensate for the lost 'atrial kick' that contributes to the cardiac output by coordinated atrial contractions in normal sinus rhythm. This leaves the not insignificant number of patients with HFrEF and AF in a conundrum over optimal HR control. Retrospective analyses of AF and HR control in landmark HFrEF trials (e.g. CHARM, PARADIGM and ATMOSPHERE) point towards better outcomes with a less stringent target HR. However, this association disappears after adjustment for known prognostic markers in HFrEF, including left ventricular ejection fraction, New York Heart Association class and NT-proBNP levels. There is a clear need for dedicated randomised controlled trials, investigating rate control strategies in this increasingly large subgroup of patients. Regardless of rate control strategy, effective anti-coagulation and guideline-directed medical therapy must not be forgotten in the treatment of patients with HFrEF and AF.