Response to Letters Regarding Article, “Heart Rate Predicts Outcomes in an Implantable Cardioverter-Defibrillator Population”
On the basis of our findings,1 Drs Fazio and Carlomagno and Dr Lin and colleagues considered that a J-shaped relationship may exist between heart rate and outcomes. Like the U-shaped relationship we saw with an increasing percentage of right ventricular pacing and outcomes,2 we suspected that a J- or U-shaped relationship may exist between heart rate and outcomes. However, we could not discern with certainty that the slowest heart rates were associated with worse outcomes even though a trend in that direction appeared.
Dr Lin and colleagues also suspected that a J-shaped relationship may be present in those with mild heart failure in lieu of a linear heart rate/outcome relationship that may occur in those with advanced heart failure. Dividing data into these small subgroups did not provide definitive answers. We agree, as Dr Lin and colleagues cautioned, that there is need to interpret the data carefully. Nevertheless, this issue remains worthy of further study because some,3 but not all,4,5 data regarding heart rate support a J-shaped relationship, albeit in different populations and for different outcomes.
Dr Lin and colleagues wondered if slow heart rates are related to increasing amounts of right ventricular pacing. Heart rate was a predictor of outcomes independently of right ventricular pacing. Although right ventricular pacing predicted outcomes, heart rate was the stronger predictor.
The pacemaker programming we used would not necessarily promote high amounts of right ventricular pacing at slow rates. Indeed, some right ventricular pacing in the Inhibition of Unnecessary Right Ventricular Pacing With Atrioventricular Search Hysteresis in Implantable Cardioverter Defibrillators (INTRINSIC RV) study was associated with favorable outcomes.2 Despite this, the relationship between right ventricular pacing and outcomes in the context of slow heart rates requires further study.
We agree with Drs Fazio and Carlomagno that important relationships between lifestyle, physical activity, and heart rate may exist and that they can be difficult to discern in assessments of heart rate over prolonged periods. Nevertheless, mean heart rate effectively predicted outcomes. Transtelephonic implantable cardioverter-defibrillator monitoring may better define relationships between level of exercise and its correlation with heart rate during exercise and at rest. Although our study did not permit investigation of resting heart rate and its change under exercise, understanding the relationships between heart rate and specific daily activities or lifestyles and even circadian variations could provide new insight into how heart rate is associated with outcomes.
Dr Day has received honoraria from Boston Scientific and St Jude Medical. Dr Bunch has received honoraria from Boston Scientific Cardiac Rhythm Management. Dr Stolen has ownership interest in and is an employee of Boston Scientific Cardiac Rhythm Management. Dr Brown is an employee of The Integra Group, a consultant company for Boston Scientific Cardiac Rhythm Management. Dr Olshansky has received honoraria from and/or been a consultant to Boston Scientific, Medtronic, St Jude, and BioControl. The other authors report no conflicts.
Ahmadi-Kashani M, Kessler DJ, Day J, Bunch TJ, Stolen KQ, Brown S, Sbaity S, 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.
Kolloch R, Legler UF, Champion A, Cooper-Dehoff RM, Handberg E, Zhou Q, Pepine CJ. Impact of resting heart rate on outcomes in hypertensive patients with coronary artery disease: findings from the International Verapamil-Sr/Trandolapril Study (INVEST). Eur Heart J. 2008; 29: 1327–1334.
Palatini P, Thijs L, Staessen JA, Fagard RH, Bulpitt CJ, Clement DL, de Leeuw PW, Jaaskivi M, Leonetti G, Nachev C, O'Brien ET, Parati G, Rodicio JL, Roman E, Sarti C, Tuomilehto J. Predictive value of clinic and ambulatory heart rate for mortality in elderly subjects with systolic hypertension. Arch Intern Med. 2002; 162: 2313–2321.