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| |  Exercise Treadmill Score Effective In Measuring Subsequent Cardiac Risk CHICAGO, IL -- September 14, 1999 -- A treadmill exercise score is an effective method of evaluating a heart patient’s risk of future cardiac death and other cardiac events, according to an article in the September 15 issue of The Journal of the American Medical Association (JAMA). The study was conducted by Jennifer M.F. Kwok, M.B., Ch.B., formerly of the Mayo Clinic and Mayo Foundation, Rochester, Minn., Todd Miller, M.D., from the Mayo Clinic and Mayo Foundation, and colleagues. Dr. Kwok is currently with the Princess Margaret Hospital in Kowloon, Hong Kong. The researchers followed 939 patients who experienced symptoms of chest pain or difficult breathing and who underwent exercise thallium testing at the Mayo Clinic between 1989 and 1991. The study group patients showed non-specific ST-T abnormalities on resting electrocardiogram (ECG) results. Patients in the study group were compared with 1,466 other patients who also experienced symptoms and underwent exercise thallium testing, but who showed normal resting ECG results. The ECG measures electrical activity of the heart, represented by a graph of a series of waves that are known as P, Q, R, S, and T waves. The part of the ECG tracing between the S wave and T wave is called the ST segment. The study authors point out that patients with ST-T abnormalities have a higher prevalence of coronary artery disease (CAD), severe CAD, left ventricular dysfunction, and higher cardiac disease and death rates than those with normal results on resting ECG. In this study, the authors used the Duke treadmill exercise score (developed at Duke University), which summarizes prognostic information in a simple quantitative equation, to classify patients as low, intermediate, or high risk. The researchers looked at rates of overall mortality, cardiac death, non-fatal heart attack, and angioplasty or coronary bypass procedures performed during a seven-year follow-up period. In both the study population and the control population, the researchers found a significant association between the Duke treadmill score and outcome. "Our data demonstrate that the Duke treadmill score is capable of predicting not only cardiac death but also total cardiac events," they assert. When patients with ST-T abnormalities were classified into risk groups according to the Duke treadmill score, there were significant overall differences among the risk groups for all outcome end points. "Seven-year cardiac survival for the low-risk group was 97 percent (annual cardiac mortality rate, 0.4 percent per year); for the intermediate-risk group, 92 percent (annual cardiac mortality rate, 1.1 percent); and for the high-risk group, 76 percent (annual cardiac mortality rate, 3.4 percent)," they write. "Risk stratification for the other end points (combined cardiac death, non-fatal myocardial infarction, and late revascularization, and for overall mortality) was also well demonstrated." The study group as a whole had a 94 percent cardiac survival rate, compared to 98 percent for the control group. "In our study, patients with resting ST-T abnormalities had consistently higher event rates than patients with normal findings on resting ECG," the authors write. "The Duke treadmill score allows risk stratification of both the study and control populations, despite their different overall event rates," they continue. "The results of the present study extend the findings of previous studies and emphasize the importance of considering the resting ECG when using exercise testing for risk stratification." The researchers point out that all the patients they studied were referred for exercise thallium imaging, a radionuclide scanning process which can reveal areas of the heart muscle that have a poor blood supply, or that have been damaged by a heart attack. They caution that the study results need to be confirmed in patient groups referred for standard exercise testing before they can be generalized to the entire population of patients with ST-T abnormalities. The authors write that their study supports national guidelines, which recommend standard exercise treadmill testing with the use of the Duke treadmill score for risk stratification in patients with normal findings on resting ECG or mild ST-T abnormalities. "The results of this study document that the standard exercise treadmill test with use of the Duke treadmill score is an effective initial method for prognostication in these patients," they conclude.
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