DURHAM, N.C. -- Patients with a history of coronary artery disease who test positive on experimental mental stress tests are almost three times more likely to suffer a serious cardiac event than those who don´t, according to a new study by Duke University Medical Center researchers. The researchers concluded that treadmill tests, the method most commonly used by cardiologists to determine the risk of future heart attacks, missed many heart patients who were at the greatest risk. In this group of patients, treadmill tests were not a strong predictor of future cardiac events. The findings are published in the June 5 issue of the Journal of the American Medical Association.
Of 126 heart patients followed for up to five years, Duke researchers found that more than 27 percent of those who responded adversely to mental stress testing experienced a significant cardiac event, compared to only 12 percent of those who did not. The cardiac events included death, heart attack and unstable or progressive angina, or chest pain requiring surgery or coronary angioplasty. "Our data suggest that there is a large subgroup of at-risk heart patients who are not being identified by standard treadmill testing," said psychologist James Blumenthal, lead investigator of the study. ³If the results are confirmed by larger studies, it would suggest that physicians should reconsider the way we evaluate patients with heart disease. "Another implication of our study suggests that stress management techniques might be an effective strategy in potentially reducing the risk of future cardiac events in this group of patients." The study was supported by grants from the National Institutes of the Health.
Using radiologic and electrophysiologic tests on all study participants, the Duke researchers measured a condition known as myocardial ischemia, which occurs when heart muscle does not receive enough oxygen-rich blood. The lack of blood flow, when prolonged, may ultimately cause damage or death to the heart muscle starved of oxygen. While ischemia caused by exercise is often felt as chest pain by heart patients, ischemia caused by mental stress is almost always "silent," Blumenthal said. "During exercise, such as the treadmill test, ischemia is largely due to the fact that the body cannot keep up with the increased demand of the heart for more blood and oxygen.² "However, with mental stress, reduced supply of blood may be more critical," said Dr. Wei Jiang, one of the study's cardiologists. "For reasons that are not entirely clear, the blood vessels supplying the heart constrict during mental stress. This type of ischemia normally occurs at low heart rates and goes largely unnoticed by patients.² While the exact cause of this constriction is not known for certain, Jiang said that stress hormones may be to blame.
Because mental stress-induced ischemia goes unfelt by patients, Blumenthal said it is especially important to be able to predict which patients are at greatest risk. The mental stresses used in the study were induced in the laboratory through a battery of five prototype tests, each lasting about three minutes. Patients were asked to:
- Give a speech on a current events topic to a group of observers.
- Read a short passage from a magazine.
- Participate in a standardized interview to assess "Type A" personality.
- Trace the outline of a star from its reflection on a mirror.
- Perform a series of complex serial additions.
In the last two tests, patients were continually encouraged to perform at an increasingly faster rate without making mistakes. Data published last year in the journal Circulation by the Duke researchers showed a strong correlation exists between the mental stress induced in a research laboratory and the stresses of everyday life. Currently, the Duke team is evaluating the effectiveness of different behavioral strategies on those patients involved in the current study who demonstrated mental stress-induced ischemia to determine if there is any beneficial effect on future cardiac events. Also participating in the study were the following Duke researchers: psychologists Michael Babyak and David Krantz, Dr. Robert Waugh, Dr. R. Edward Coleman, Dr. Michael Hanson, Dr. David Frid, Steve McNulty, Dr. James Morris and Dr. Christopher Connor.