Wednesday February 4 2009
Heart rate has already been found to predict risk of heart attack in men
According to the Daily Mail today, “the speed of a woman’s heartbeat could predict how likely she is to suffer a heart attack”. The newspaper reports that an eight-year study of 130,000 postmenopausal women found that those with the highest resting pulses (more than 76 beats per minute) were more likely to have heart attacks, and that this risk was independent of how much exercise the women took.
This news story is based on a large study and establishes the link between women’s high resting pulse and the likelihood of heart attack or death due to a coronary (heart related) event. Such a link has been shown before in studies in men, which further strengthens these results. The study also supported the link between coronary events and other known risk factors such as current smoking, diabetes, high blood pressure and increased age.
While overall the link was independent of how much exercise women took, the study did find that people who took regular exercise had lower resting pulse rates, and that people who had diets with a high saturated fat content had a higher resting pulse. To lower your risk of heart disease, the common-sense advice is to eat a healthy diet and take regular exercise.
Where did the story come from?
Drs Judith Hsia and colleagues from George Washington University, the Fred Hutchinson Cancer Research Center, the University of Massachusetts and other academic and medical institutions in the USA carried out this multi-centre study. It was funded by the National Heart, Lung and Blood Institute at the National Institutes of Health. The study was published in the peer-reviewed British Medical Journal.
What kind of scientific study was this?
This prospective cohort study looked at whether resting heart rate could predict coronary events (heart attack, coronary death or stroke) in postmenopausal women. The researchers were particularly interested in whether it predicted heart attacks, death due to coronary events or stroke. Previous studies have established such a link in men, but not yet in women.
As part of the Women’s Health Initiative, 161,808 postmenopausal women had been enrolled across 40 clinical sites to participate in four different randomised controlled trials and an observational study. The current study used data from these women. The researchers excluded women who had suffered a previous heart attack, stroke or vessel disease, as well as women taking certain medications (including beta-blockers), which can affect heart rate. After these exclusions, 129,135 women were available for analysis.
Heart rate was measured at the beginning of the study (baseline pulse) while the woman sat quietly for five minutes. The researchers collected information on factors that can affect the risk of having heart problems. These factors included smoking, caffeine and alcohol consumption, high cholesterol, fat consumption, diabetes and blood pressure, physical activity, use of hormone replacement therapy (HRT) and anxiety/depression.
Every six months the participants reported any emergency hospital visits, overnight hospital stays and heart procedures. Their medical records were also used to find other outcomes of interest, including heart attacks and strokes. The women were followed up for an average of eight years and the researchers compared the outcomes across different categories of resting heart rate (fewer than 63 beats per minute (bpm), 63-66 bpm, 67-70 bpm, 71-76 bpm and more than 76 bpm).
What were the results of the study?
At the end of follow-up there had been a total of 2,281 coronary events (heart attack or death) and 1,877 strokes. In general, women with higher resting pulse rates tended to be older, heavier, took in more saturated fat and had more cardiovascular risk factors (including high blood pressure, diabetes and smoking). Women who exercised more and those who took HRT tended to have lower resting pulse rates.
The researchers found that resting pulse rate was associated with heart attack or coronary death, and this association was still present when they took into account the other factors that can affect heart risk. People in the highest pulse category (more than 76 bpm) were 1.26 times more likely to have one of these events than those in the lowest category. However, there seemed to be no link between baseline pulse and stroke when the other risk factors were accounted for.
Ethnicity and diabetes had no effect on this link, but age did, with a stronger association in women aged 50 to 64 years than in those aged 65 to 79 years.
What interpretations did the researchers draw from these results?
The researchers conclude that resting heart rate is an independent predictor of coronary events and that a higher rate is associated with a greater risk. However, this was only significant when the highest heart rate group was compared with the lowest heart rate group. They also conclude that resting heart rate does not predict stroke.
What does the NHS Knowledge Service make of this study?
The researchers clearly highlight the strengths and limitations of their study, these include the following:
- This is a large cohort study including a diverse group of women and measuring a large number of adverse events. The size of the sample means the study has high power to detect differences between women with different pulse rates.
- The study also collected a lot of information on other factors that can affect heart risk. This is a strength of the study because researchers were able to adjust for the effects of these additional factors on coronary risk.
- One limitation is that the cohort does not include men, or women younger than 50 years.
This result is important as it supports the use of resting heart rate as a predictor of heart problems in women. Previous research has established this in men. The researchers acknowledge that the link is weaker than that with cigarette smoking or diabetes, but is still clinically meaningful.
Whether or how these results will change clinical practice is not clear. Although a high resting pulse rate may indicate the risk of a future coronary event, any such interpretation should always take into account the individual’s circumstances, such as the presence of other coronary risk factors and the many other reasons for a raised pulse, such as current illness or anxiety. Pulse rate can vary due to a number of reasons, and several readings should ideally be taken to confirm the normal resting rate for the person. A useful addition to this study would have been to assess pulse rate during exercise as well as at rest.
Finally, this study found that people who took regular exercise had lower resting pulse rates, and that people who ate diets with a high saturated fat content had a higher resting pulse. Advice to take from this is to eat a healthy diet and take regular exercise to lower your risk of heart disease. This has been well established in previous studies.