Letter by Fazio and Carlomagno Regarding Article, “Heart Rate Predicts Outcomes in an Implantable Cardioverter-Defibrillator Population”
To the Editor:
We read with great interest the recent report by Ahmadi-Kashani and colleagues1 highlighting the prognostic significance of mean intrinsic heart rate (HR) in a heterogeneous population of heart failure outpatients. HR is an extensively studied marker in various cardiovascular conditions, at rest, during and after exercise, during sleep, and throughout the day, as HR variability. In some clinical settings, a high-normal resting HR bears a well-recognized prognostic significance, reflecting the imbalance between parasympathetic and sympathetic tone, a hallmark of cardiovascular disease.2 On the contrary, a physiological increase in HR during maximal effort predicts a better prognosis, even in the general population.3
A higher-than-median mean whole-day HR is a very raw finding that one can explain in several ways, depending on the clinical setting, severity of heart failure, patient’s lifestyle, and pharmacological therapy. For example, a patient with a mean HR of 80 bpm could be an 80-year-old sedentary man with scarce β-blockade, high resting HR, and very low HR variability or a well-compensated, physically active middle-aged woman with New York Heart Association class II symptoms and good chronotropic response to exercise. Given our actual knowledge, a mean HR of 80 bpm would carry a different prognostic meaning in these 2 people with chronic heart failure. This observation is also reinforced by the J-shaped pattern of the histograms, with patients with very low intrinsic ventricular rates (and most likely very low HR variability) experiencing increased event rates and mortality.
We believe that data about the variability of HR patterns, especially addressing day-to-night variations, and information regarding the degree of daily physical activities in the examined patients would add important pathophysiological meaning and clinical applicability to these interesting findings. This would be particularly true for patients with good functional status, in many of whom mildly increased mean HR can be supposed to reflect satisfactory β-blockade at rest and preserved chronotropism during daily physical activities. In addition, we wonder whether simple resting HR, as assessed during implantable cardioverter-defibrillator reprogramming, was included in the predictive model because it appears at the moment to be the single most valuable candidate parameter to be followed in such patients.4
Ahmadi-Kashani M, Kessler DJ, Day J, Bunch TJ, Stolen KQ, Brown S, Sbaity A, Olshansky B, on behalf of the INTRINSIC RV Study Investigators. Heart rate predicts outcomes in an implantable cardioverter-defibrillator population. Circulation. 2009; 120: 2040–2045.
Frenneaux MP. Autonomic changes in patients with heart failure and in post-myocardial infarction patients. Heart. 2004; 90: 1248–1255.