Troponin and Exercise Testing
October 1, 2002 2 minutes read
Abstract & Commentary
Synopsis: Serum troponin I levels do not increase due to stress test induced ischemia.
Source: Choragudi NL, et al. Heart Disease. 2002;4: 216-219.
Troponin i is a very sensitive and specific marker for myocardial damage and can be elevated in patients with clinical presentations previously categorized as ischemic episodes without infarction. The hypothesis tested in this study was that exercise-induced myocardial ischemia will not raise serum troponin I levels. The study population was 134 patients admitted for chest pain in whom an acute coronary syndrome necessitating early intervention was excluded and stress testing was being performed. Troponin I (Abbott) was measured before and 4-48 hours later; 93% measured 12-18 hours post stress. Stress testing was exercise in 43%, dipyridamole in 43%, and dobutamine in 14%. A positive test was defined as a sestamibi identified stress perfusion defect not present at rest. Positive perfusion studies for ischemia were noted in 29 of the 134 patients. Only one patient exhibited a rise in troponin I after exercise. This patient had a dobutamine stress test, which was negative for ischemia, despite having had a recent myocardial infarction (2 weeks ago). Choragudi and colleagues concluded that serum troponin I levels do not increase due to stress test induced ischemia.
Comment by Michael H. Crawford, MD
As new diagnostic tests arrive, we are confronted with the possibilities for false-positive and false-negative studies. Since troponin has now been deemed the pivotal diagnostic modality for acute MI, the issue of whether ischemia can release it is important. By contrast to experience with acute coronary syndrome patients, stress test induced ischemia does not seem to release troponin. However, there are several weaknesses of this study. The population was small and only 29 patients had ischemia on perfusion study. Almost half the patients had dipyridamole stress which is known to only produce frank ischemia, in addition to a perfusion defect, in about one third of patients with known coronary artery disease. In addition, the sampling times for troponin were not standardized and varied widely. Thus, this is not the ideal study, but based upon the findings it would be prudent to consider troponin rises within 2 days of stress testing as MI events and not ignore them as the false-positive results of inducing brief transient ischemia.
Dr. Crawford is Professor of Medicine, Mayo Medical School; Consultant in Cardiovascular Diseases, and Director of Research, Mayo Clinic, Scottsdale, AZ.
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