Nocturnal patterns of heart rate and the risk of mortality after acute myocardial infarction

Background The purposes of this study were to identify nocturnal patterns of heart rate (HR) in depressed and nondepressed patients after an acute myocardial infarction (MI) and to determine which patterns, if any, are associated with all-cause mortality or recurrent infarction. Methods Functional data analysis and model-based clustering methods were used to identify nocturnal HR patterns in 245 depressed and 247 nondepressed patients with a recent MI. All-cause mortality and recurrent infarctions were ascertained over a median follow-up of 24 months. Results Three HR activity patterns were identified. In the first, HR gradually declined during the nighttime and increased the next morning. The second pattern was similar, but with a higher overall HR during the recording interval. The third showed almost no decrease in HR at night (ie, "nondipping"). All-cause mortality was higher among patients with pattern 3 than pattern 1 (P =.007), and the combined end point of recurrent MI or all-cause mortality was higher in pattern 3 than pattern 2 (P =.05). Patterns 2 and 3 were more common in the depressed than in the nondepressed patients. Conclusions The nondipping nocturnal HR independently predicts all-cause mortality and recurrent MI. Future studies should examine the underlying causes of nondipping nocturnal HR and its association with depression and investigate the effects of treatment on survival.