Heart rate during exercise: mechanisms, behavior, and therapeutic and prognostic implications in heart failure patients with reduced ejection fraction.

Exercise intolerance is a typical manifestation of patients affected by heart failure with reduced ejection fraction (HFrEF); however, the relationship among functional capacity, mortality, and exercise-induced heart rate response during exercise remains unclear in either sinus rhythm or atrial fibrillation subjects. Heart rate increase during incremental load exercise has a typical pattern in normal subjects, whereas it is commonly compromised in HFrEF patients, mainly due to the imbalance of the autonomic nervous system. In the present review, we aim to describe the behavior of heart rate during exercise in normal subjects and in HFrEF patients in sinus rhythm and atrial fibrillation, understanding and explaining the mechanism leading to a different exercise performance and functional limitation. Moreover, the role of chronotropic incompetence and the need of standardizing the cutoff criteria are also discussed in order to clarify the clinical importance, the prognostic relevance, and the potential therapeutic implications of this condition. Looking into the relative contribution and interaction of heart rate response during exercise might represent an important issue to guide individualized therapeutic interventions and prognostic assessment in HFrEF patients.