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Resting heart rate predicts MI in women

The association between resting heart rate and coronary events is well documented in men.1,2 A large prospective cohort study has now confirmed that this association also applies to women.3

Lowering resting heart rate is an accepted target of anti-ischaemic therapy. It follows that if the resting heart rate is a marker of autonomic tone then a higher heart rate will be the clinical manifestation of higher sympathetic nervous system activity. This in turn could influence blood pressure, glucose metabolism and lipids or indeed could be an independent risk factor for cardiovascular disease.

The Women's Health Initiative (WHI) study included almost 162,000 postmenopausal women who were enrolled at 40 clinical sites into four randomised trials and an observational study between 1993 and 1998. This particular cohort was composed of 129,135 women from both the observational and randomised trials. Those women with a history of previous MI, stroke, or coronary revascularisation and those on rate-limiting medication such as beta-blockers, digoxin, or non-dihydropyridine calcium channel blockers were excluded.

The primary outcome measure was clinical cardiovascular events and these were recorded throughout the study by self-reporting and collection of mortality and hospitalisation data.

After a mean of 7.8 years of follow up there were 2,281 coronary events (MI or coronary deaths) and 1,877 strokes in the cohort. The results were adjusted by means of multivariant analysis for factors, which might have affected heart rate and CV risk such as hypertension, smoking, caffeine, alcohol, diabetes mellitus, physical activity and high cholesterol.

For statistical analysis the cohort was divided into resting heart rate quintiles (<62, 63-66, 67-70, 71-76 and >76 beats/min). The incidence of coronary events was significantly greater in the highest heart rate group (>76 beats/min) compared with the lowest heart rate group (<62 beats/min) with a hazard ratio of 1.26 (95% CI 1.11 to 1.42, P=0.001). This association was independent of ethnicity and was stronger in women aged 50-64 years at baseline than in those aged 65-79 (P=0.009). Interestingly, coronary risk was consistent across the lower quintiles of heart rate with the hazard ratio only significantly increasing in the highest quintile. This could be clinically useful as a threshold for heart rate can be identified above which risk increases and therefore aggressive management of risk factors can be implemented. However, the strength of this association is less than that seen with smoking or diabetes. There was no significant association seen between resting heart rate and the incidence of stroke when corrected for other risk factors.

Therefore this study supports the notion that a higher resting heart rate is independently associated with coronary events in women and particularly so in younger postmenopausal women. However resting heart rate does not appear to be an independent predictor of stroke in this population.

There has been much interest of late in formalised CV risk prediction and discussion of the relative merits of various risk prediction algorithms. There has also been renewed interest in more novel CV risk factors such as CRP and homocysteine with a possible role for such markers in ascribing the degree of CV risk in borderline cases. While no one questions the effectiveness of interventions that stop people smoking and lower BP or cholesterol what is less clear is the value of intervention on novel markers. Resting heart rate is a much more attractive and cost-effective option. It is easy to measure and has a threshold for intervention.

It also responds to both pharmacological and non-pharmacological interventions.

It is refreshing to see that a simple clinical parameter such as resting heart rate could provide a useful adjunct in CV risk assessment.

Author

Dr Peter Savill
BSc MBBS PGDipCard
GPwSI cardiology, Southampton

A threshold for heart rate can be identified above which risk increases and... aggressive management of risk factors can be implemented

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