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Night awakening can trigger heart damage.

Night awakening can trigger heart damage

New research shows that people with coronary artery disease who awaken at night -- particularly those who get out of bed -- risk suffering an episode of silent myocardial ischemia, a temporary and often painless reduction in blood flow to the heart muscle. The finding supports the idea that certain activities can damage an already-threatened heart.

Physicians know ischemia and heart attacks occur more often in the morning than at any other time. Scientists suspect this time-related rise in heart trouble relates to certain activities rather than to any innate circadian pattern that makes dawn a risky time. Research reported last week at the American Heart Association's scientific sessions in New Orleans supports the notion that the chance of ischemia in coronary disease patients rises whenever the body makes its transition from sleep to alertness.

Joan Barry, Alan C. Yeung and their colleagues at Harvard Medical School and Brigham and Women's Hospital in Boston studied 117 people with coronary artery disease. For 48 hours straight, patients kept detailed diaries of their activities and wore small devices that record the heart's electrical activity. The scientists found that 30 patients had episodes of nocturnal ischemia. Of these, 21 got out of bed on a total of 36 occasions, usually to go to the bathroom. Two out of three trips in this patient subgroup were marked by a silent ischemic attack, the researchers report.

People who had attacks showed an increase in heart rate that started 30 minutes before they got up, Barry says. That observation fits with the theory that the increased risk at awakening and rising results from the activation of the body's sympathetic nervous system, which boosts heart rate and raises blood pressure by temporarily constricting arteries. For people with arteries already clogged by plaque, the nervous system activation can mean a drastic reduction in oxygenated blood getting through to the heart. Though the ischemic episode can be painless, scientists believe it damages the heart muscle and can increase a person's chance of having a heart attack.

No one is suggesting that people must remain bedbound to avoid a heart attack. "It is not reasonable or appropriate to stop some of the [ischemic] triggers," says Peter H. Stone, a cardiologist at Brigham and Women's Hospital in Boston. People with coronary disease must carry on with their usual activities, and that includes getting out of bed, he says.

The research does suggest, however, that people with coronary artery disease who are prone to ischemic attacks may benefit from more aggressive medical treatment, Barry says. A class of drugs known as beta blockers, which blunt the sympathetic nervous system's activity, may help prevent nighttime ischemic attacks, Yeung says, but he adds that scientists must test that theory before recommending drug treatment for people with nocturnal ischemia.

In a related study, Paul M. Ridker and his colleagues at Harvard Medical School and Brigham and Women's Hospital found that aspirin prevented more heart attacks during the early morning hours than at any other time. In analyzing data from the Physicians' Health Study, in which 22,000 U.S. male physicians took 325 milligrams of aspirin or placebo every other day (SN: 1/30/88, p.68), Ridker's group discovered that aspirin reduced heart attack incidence by 60 percent from 4 a.m. to 10 a.m. and by about 30 percent at other times.

The researchers speculate that aspirin works against heart attacks by blocking the aggregation of platelets. Other studies have shown that these blood components tend to get sticky in the morning and can form blood clots, which in turn can block diseased arteries, leading to a heart attack (SN: 6/27/87, p.409). Ridker says his group now hopes to determine whether participating physicians who worked night shifts suffered more heart attacks soon after rising in the late afternoon.
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Author:Fackelmann, K.A.
Publication:Science News
Date:Nov 25, 1989
Words:643
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