Ambulatory heart rate as a predictor of cardiovascular events

This study investigated the connection between ambulatory heart rate and the incidence of cardiovascular events in patients with hypertension. 

Patients with hypertension (abnormally high blood pressure) are at high risk of developing acute cardiovascular events such as heart attack and stroke. Several studies have shown an association between resting heart rate and cardiovascular mortality in hypertensive patients.  Ambulatory heart rate monitoring is a noninvasive method of obtaining heart rate readings over 24 hours, while the patient is in their own environment undergoing their usual activities. In contrast to measurements preformed in a clinic or other medical facility, this represents a true reflection of patient heart rate as it excludes any emotional stress which might influence the results. 

The purpose of this study was to evaluate whether ambulatory heart rate measurements can predict the incidence of cardiovascular events.

The study included 7600 patients with hypertension. For each patient, ambulatory heart rate and blood pressure were measured.

During an average follow-up of five years, 639 cardiovascular events were reported. This included 250 strokes (37 fatal) and 145 heart attacks (18 fatal). The average ambulatory night-time heart rate was 65.5 beats/min, while the average day-time heart rate was 77.4 beats/min.

Among the ambulatory heart rates, the risk of cardiovascular events was higher for night time heart rate than day time heart rate. Night time heart rate consistently predicted cardiac events. This study also demonstrated that for every 10-beats/min increase in night-time heart rate, the risk of cardiovascular events increased by 13%.

Conversely, in the 996 patients treated with beta blockers (drugs used to reduce heart rate and relieve the load on the heart in patients with heart diseases) there was no relationship between night-time heart rate and cardiovascular outcomes.  

It was found that systolic blood pressure (the pressure in the arteries when the heart contracts), measured either in a clinical setting or in an ambulatory manner, was a strong predictor of cardiovascular events. 

In summary, night-time heart rate measurement was a better predictor of cardiovascular events than day-time heart rate. However, this relationship was modified by drugs that affect heart rate such as beta blockers.

In some patients, the high heart rate at night time may have been caused by an underlying disease not diagnosed at the beginning of the study.