Slowing Sinus Tachycardia in Heart Transplant Recipients: Is It Time?

In the article published in Revista Española de Cardiologı́a, Barge-Caballero et al report on the results of a single-center retrospective observational study to explore the prognostic significance of the mean resting heart rate (HR) at 1 year after heart transplantation and its temporal trend. The authors concluded that elevated resting HR after heart transplantation is a poor prognostic marker, being associated with increased mortality. This topic is of keen interest to the field of heart transplantation particularly as it questions whether HR slowing medications may be of value for patients with sinus tachycardia. The ‘‘resting HR’’ in the intact heart is predominately determined by vagal influence and hence it is slower than the intrinsic HR. The ‘‘intrinsic HR’’ refers to the HR following complete pharmacologic blockade of the cardiac autonomic system; it has been shown to be related to age, physical fitness and probably to the overall state of health of the myocardium. Over the past few decades, several epidemiological studies have shown an association between elevated resting HR in the intact heart and all-cause and cardiovascular mortality in the general population, as well as in groups with various cardiovascular diseases. Also, inference from clinical trials has suggested that the mortality benefit from beta-blocker use in patients with acute myocardial infarction or heart failure is at least in part related to the drug-mediated reduction in the resting HR. More recently, novel pharmacologic intervention with the drug ivabradine has targeted elevated resting HR as a modifiable cardiovascular risk factor with promising results. In heart transplantation, transection of the autonomic fibers during transplant surgery has 2 major outcomes: delayed and blunted HR response to exercise due to sympathetic denervation, and elevated resting HR due to vagal denervation. The ‘‘normal’’ range of resting HR in heart transplant recipients is not clearly defined but generally a value between 90 and 110 beats per minute (bpm) is considered acceptable. The relevant unanswered questions in heart transplantation include: a) is the elevated resting HR an