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THE PHYSICIAN AND SPORTSMEDICINE - VOL 26 - NO. 2 - FEBRUARY 98


Heart rate response in smokers often poor

A quarter to a third of smokers have a blunted heart-rate response to exercise, and this characteristic is associated with an increased risk of death and cardiac events, according to researchers who studied 3,000 men and women in the reknowned Framingham Offspring Study (1).

The participants, all in their early to mid-40s, underwent exercise stress testing. Among smokers, 25% of men and 32% of women failed to reach 85% of their predicted maximum heart rate, compared with 15% of nonsmoking men and 18% of nonsmoking women. The more cigarettes smoked daily, the worse was the heart rate response to exercise.

Eight years later, the all-cause death rate for male smokers with blunted heart-rate response to exercise was 10% and the rate of coronary events was 17%. For male smokers who had a normal heart-rate response to exercise, the death rate was 4% and the rate of coronary disease was 8%. The death and coronary disease rates for nonsmokers who had a blunted heart rate response to exercise were 3% and 6%. For nonsmokers with a normal cardiac response, the rates were 2% and 4%, respectively. Too few coronary events occurred in the mostly premenopausal women for comparison. Exercise-related deaths and cardiac events were not reported in the study.

The study redefines the role of exercise testing as a marker for cardiac disease risk in smokers, according to Michael S. Lauer, MD, a cardiologist who headed the study and codirects the coronary care unit at the Cleveland Clinic in Ohio. Smokers often undergo exercise stress tests because they are more likely to have heart disease. If they fail to reach their target heart rate, the results are classified as inconclusive. Such labeling greatly understates the risk, says Lauer. Smokers who have a blunted cardiac response to exercise are at high risk for having a major coronary event or even dying and should be considered for further cardiac investigation and referral to a cardiologist, he says.

The study has significant implications for physicians who treat active people who smoke, says Andrew Pipe, MD, a family physician and director of the smoking cessation clinic at the University of Ottawa Heart Institute. "It's very important that we counsel all patients about smoking cessation," says Pipe, who is an editorial board member of The Physician and Sportsmedicine. He says, "The challenge is to ensure that we are also of specific assistance to patients in that respect."

The reason smoking blunts cardiac response to exercise is unclear, according to the researchers, though smoking has been associated with coronary vasoconstriction, abnormal coronary endothelial function, increased ischemic burden, increased peripheral vascular resistance, and subclinical pulmonary disease. Pipe says the study seems to support the long-held theory that nicotine mimics epinephrine. Nicotine is thought to dull the heart's response to exercise by bombarding receptors in the heart, altering receptor availability.

Exercise Issues

When making exercise recommendations for patients who smoke, physicians should look at more than just the exercise test results, Lauer says. The safety of exercise for each patient will depend on the physician's analysis of electrocardiography changes, blood pressure response, and chest and leg pains. "You can't make a blanket recommendation for everyone," he says. However, he adds, patients should know that the cardiovascular harm of smoking greatly outweighs the cardiovascular benefits of exercise.

The study results should not prevent physicians from recommending moderate exercise to all patients, including those who smoke, says Pipe. Adopting an exercise routine, he says, complements other healthy lifestyle modifications, including smoking cessation.

Smoking cessation counseling for smokers who have a blunted cardiac response to exercise should be aggressive, Lauer says. Prescription treatments for nicotine addiction include nicotine gums and patches. More information on how to counsel smokers and prescribe treatments can be found in the Agency for Health Care Policy and Research's clinical practice guideline on smoking cessation (available on the Web at https://www.ahcpr.gov/clinic/smokepcc.htm).

Another form of smoking cessation treatment has been available since May 1997: a slow-release version of bupropion hydrochloride, an antidepressant. A double-blind, placebo-controlled study (2) of 615 men and women demonstrated that sustained-release bupropion was effective for smoking cessation and produced less weight gain than placebo.

Bupropion is contraindicated in patients who have a history of or risk for seizures. Insurance coverage for bupropion varies in the United States and Canada. According to the drug's manufacturer, Glaxo Wellcome, Inc, based in Research Triangle Park, North Carolina, a 7-week course of treatment typically costs about $125.

References

  1. Lauer MS, Pashkow FJ, Larson MG, et al: Association of cigarette smoking with chronotropic incompetence and prognosis in the Framingham Heart Study. Circulation 1997;96(3):897-903
  2. Hurt RD, Sachs DPL, Glover ED, et al: A comparision of sustained-release bupropion and placebo for smoking cessation. N Engl J Med 1997;227(17):1195-1202

Carol Potera
Great Falls, Montana


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