Ben-Dov IZ et al. (2007) Blunted heart rate dip during sleep and all-cause mortality. Arch Intern Med 167: 2116–2121

While evidence exists regarding the negative effects of high blood pressure on mortality, the correlation between heart rate and mortality has not been heavily investigated. Ben-Dov et al. report that lack of a reduction in heart rate from awake to nocturnal levels is independently associated with increased mortality.

The investigators analyzed information from a service database for the period 1991–2005. Heart rate data from 24 h ambulatory blood pressure monitoring were available for a total of 3,957 patients.

In Cox proportional hazard analysis adjusted for age, sex, BMI, treated diabetes, and treated hypertension, the magnitude of the dip between awake and sleeping heart rates was a strong predictor of mortality, independent of systolic blood pressure dip (P <0.001 trend for deciles of heart rate dip) and had greater predictive power than awake and sleeping heart rates. Female sex, a high BMI, older age and being treated for hypertension or diabetes were all factors associated with reduced (<10%) heart rate dip.

In addition, when blood pressure dipping was taken into account together with the heart rate dip, it was shown that patients who lacked a 10% or more reduction in both blood pressure and heart rate had the highest mortality (P = 0.002).

The authors conclude that ambulatory heart rate adds prognostic information beyond other currently used ambulatory blood pressure measurements, and that an elevated sleeping heart rate—resulting in a smaller dip from the awake heart rate—may be of particular value in predicting mortality.