Risks of graded exercise testing

Abstract

In this issue of the Journal, Irving and Bruce 1 report their observations on postexertional ventricular fibrillation. During the course of 10,700 maximal treadmill exercise tests carried out in 15 different laboratories as a part of the Seattle Heart Watch Study, 2 five cases of ventricular fibrillation were observed for an overall incidence rate of 0.05 percent. It appears from their data that all episodes of ventricular fibrillation occurred in patients with coronary artery disease manifested clinically by a prior myocardial infarction or angina pectoris. In addition, every patient who experienced ventricular fibrillation also demonstrated exercise hypotension as defined by the authors. 1 Thus, in the subgroup of 228 patients who manifested both of these abnormalities (coronary artery disease and exercise hypotension) the incidence rate of exercise-induced ventricular fibrillation was 2.2 percent, a rather significant rate that justifies careful analysis. During the past 9 years we have been studying the frequency and types of ventricular arrhythmias recorded during and after treadmill exercise testing in normal subjects and patients with coronary heart disease. 3-6 We have also been investigating the blood pressure responses of these patients to determine the clinical significance of decreases in systolic blood pressure observed during progressive treadmill exercise testing in patients with coronary heart disease. During this period more than 12,000 maximal or near-maximal treadmill exercise tests have been conducted in some 6,000 subjects in the Exercise Laboratories at the Indiana University Medical Center. We have yet to encounter a cardiac arrhythmia during or after exercise that required electrical cardioversion. Let us examine some possible reasons for the differences in experience in the two studies.