Objective

It has not been established whether nocturnal nondipping of heart rate (HR) predicts future cardiovascular disease (CVD). We performed this study to test the hypothesis that nocturnal nondipping of HR predicts the risk of incident CVD independent of nocturnal blood pressure dipping pattern.

Methods

Ambulatory blood pressure monitoring was performed in 457 uncomplicated patients, who were being treated or evaluated for hypertension. They were followed for an average of 72±26 months. Nondipping HR was defined as a night/day HR ratio greater than 0.90. We chose two outcomes for this analysis: CVD events (defined as stroke, myocardial infarction, or sudden cardiac death) and all-cause mortality. Cox regression analyses (stepwise method) were used to estimate hazard ratios and their 95% confidence interval after adjusting for covariates.

Results

In univariate analysis, increased sleep HR and nondipping of HR were associated with increased risk of CVD and all-cause mortality, but awake HR was not. In multivariable analyses, HR nondipping status significantly predicted an increased risk of CVD events (hazard ratio, 2.37; 95% confidence interval, 1.22–4.62; P= 0.01), but not for all-cause mortality. Increased 24-h HR was significantly associated with increased risk of all-cause mortality (hazard ratio, 1.67; 95% confidence interval, 1.11–2.51; P= 0.01).

Conclusion

The risk of future CVD was shown to be 2.4 times higher in those whose HR does not exhibit the typical nocturnal decline. The relationship was independent of nondipping of SBP and was not dependent on diabetes status or blood pressure level.