An increase in resting heart rate over five years in middle-aged men predicts a significantly increased risk for death over the next 20 years compared with an unchanged or decreased resting rate, according to a presentation at the annual meeting of the American Heart Association.

Indeed, the French researchers found that a long-term rise in resting heart rate increased the risk of death by almost 50 percent, whereas a long-term decrease in resting heart rate reduced the risk by almost 20 percent.

Other studies have shown that a high resting heart rate is associated with a higher risk of death, but the study by the French team is the first to investigate the significance of changes in rate over years.

Researchers examined the health histories of 4,320 native Frenchmen ages 42 to 53 years. The men were recruited between 1967 and 1972 and had yearly examinations during the next five years in the same standardized conditions. The participants underwent electrocardiograms and physical examinations, provided blood samples for laboratory tests, and answered questionnaires administered by trained interviewers. Resting heart rate was determined by measuring the radial pulse during a one-minute recording, after a five-minute rest lying down.

During the follow-up of more than 20 years, 1,018 men died from various causes, including cardiovascular disease. The researchers examined the individual heart rate trends over five years, and categorized the men into groups based on the degree of change in resting heart rate and baseline heart rate.

After adjusting for other risk factors such as age, physical activity, tobacco consumption, body mass index, systolic blood pressure, blood glucose level, and total cholesterol, the researchers found that the men whose resting heart rate increased by more than 7 beats per minute had an increase in mortality of 47 percent, while men whose resting heart rate decreased by more than 7 beats per minute had a decrease in mortality of 18 percent.

The researchers concluded that resting heart rate and its changes may be independent risk factors of mortality in the general population. The study’s lead author, Xavier P. Jouven, MD, PhD, of Hopital Europeen Georges Pompidou INSERM, Paris, said the findings raise several questions:

“We don’t know why resting heart rate goes down or up over time,” Jouven said. “It might be related to lifestyle changes, such as less activity. We also cannot say for sure whether the increase in resting heart rate is only a marker for some other disease process or whether it is directly associated with mortality.”

Jouven also noted that when the original study was designed in 1965, it was thought that men were mainly at risk for heart disease, so the study included only middle-aged men. A separate study should be done on middle-aged women, he said.

Although there is no international standard, the optimal method for measuring resting heart rate in a doctor’s office or clinic, Jouven said, is for the patient to rest lying down for about five minutes before rate is measured for a full minute.