Analysis of transient arrhythmias and conduction disturbances occurring during submaximal treadmill exercise testing

Abstract

To determine the incidence, types, and clinical correlates of transient arrhythmias and conduction disturbances that occur with submaximal exercise, the electrocardiogram was recorded continuously during the course of treadmill testing of 713 adults. These subjects had varying degrees of fitness, and 398 of them had known heart disease. Arrhythmias (three or more consecutive beats) occurred in 39 people, an incidence of 5.5 per cent. They occurred most frequently in people with known heart disease who were older than 50 years of age, and were associated with abnormal resting electrocardiograms. Premature beats were seen in the same exercise test in 82.9 per cent of those with arrhythmias. Simultaneous palpitations were not noted by any subject, although one man did report a transient sensation of light-headedness. The induced tachyarrhythmias were brief and all terminated spontaneously. Nine subjects had arrhythmias at low levels of exertion and were able to comfortably tolerate higher levels without subsequent arrhythmia appearance. The transient tachycardias that were seen in four healthy people did not exceed 5 beats in duration. Conduction disturbances were less frequent, occurring in eight subjects, seven of whom had heart disease. Transient changes in intraventricular conduction appeared during walking, and one case with brief prolongation of A-V conduction was seen in the postexercise period. Repeat tests, after several weeks, were performed with 30 of those who had arrhythmias or conduction disturbances in their first tests. Seven, or 23.3 per cent, developed the same change at least once during a repeat test. Conduction disturbances were more often reproducible than were the arrhythmias. There is a wide divergence of current opinion regarding the clinical significance of rhythm or conduction changes with exercise. We do not conclude that a diagnosis of heart disease or a “positive” test should be assumed if the only change is a brief transient arrhythmia or conduction disturbance. Of those with known heart disease who developed an arrhythmia, only seven (20.6 per cent) had exercise-induced ischemic ST changes. Because these arrhythmias do not usually cause symptoms, the use of constant recording or monitoring is suggested for their detection. Serial exercise tests, limited to the comfortable tolerance of each subject, offer a simple means for studying the behavior and natural history of intermittent arrhythmias and conduction disturbances.