Correspondence 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 ad-vanced 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. Never-theless, 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 Unneces