Computer analysis of exercise-induced changes in QRS duration in patients with angina pectoris and in normal subjects Exercise-induced changes in ORS duration were assessed in 25 normal subjects and in 17 patients with stable ischemic heart disease. None had bundle branch block or were taking medications, and all patients had angina pectoris induced during the test. QRS duration and ST60 amplitude were measured by computer during rest while standing, at a heart rate of 100 to 110 bpm during exercise, at peak heart rate for the angina patients (mean of 127 bpm), and at the corresponding matched heart rate and peak heart rate for the normals (mean of 174 bpm). As heart rate increased, the patients showed significant ST60 depression. In normal subjects, the QRS duration tended to increase initially but at the matched heart rate level and at peak heart rate it decreased significantly compared to rest (p < 0.01). The ORS duration in the angina patients increased significantly at the heart rate level of 100 to 110 bpm (p < 0.05). Of the eight patients who reached a peak heart rate above 127 bpm, six (75%) during that period further increased QRS duration compared to three (12%) of the 25 normal subjects (p < 0.001). We conclude that a consistent increase in DRS duration during exercise, although subtle, may be a marker of ischemia and consequently a potential diagnostic tool. (AM HEART J 11 l:gO3, 1986.) Staffan Ahnve, M.D., Ph.D., Michael Sullivan, M.A., Jonathan Myers, M.A., and Victor Froelicher, M.D. San Diego, Calif. The effect of acute exercise on QRS duration in healthy subjects has produced conflicting results. Both a decrease1e3 and no change4*5 in QRS duration have been reported with the use of computer tech- niques. The effect of ischemia induced by exercise testing on the QRS duration has not been previously published. The purpose of this study was to investi- gate the exercise-induced changes in QRS duration, both in normal subjects and in patients with stable ischemic heart disease who have angina pectoris induced during exercise testing. METHODS Angina patients. Seventeen men with documented cor- onary artery disease and stable angina pectoris were included in the study. Eleven patients had a history of a Q wave myocardial infarction and three had a history of a From the Cardiology Division, School of Medicine, University of Califor- nia, San Diego. Supported by Specialized Center of Research on Ischemic Heart Disease (SCOR) National Institutes of Health Research Grant No. HL 17682 awarded by the National Heart, Lung, and Blood Institute, and by International Research Fellowship (Dr. Ahnve) No. 1 F05 TW03308-01, Fogarty International Center. Received for publication March 25, 1985; revision received Sept. 6, 1985; accepted Oct. 15. 1985. Reprint requests: Victor F. Froelicher, M.D., Cardiology Section (lllc), VA Medical Center, 5901 E. 7th St., Long Beach, CA 90822. non-Q wave myocardial infarction documented by a thor- ough review of their clinical histories and hospital records. The other three had well-documented angina pectoris, and in addition coronary artery disease was verified by angiography. No patient was post coronary artery bypass operation. No patients had bundle branch block and they were at least 4 months post myocardial infarction or a major change in angina1 symptoms. Patients discontinued use of beta-adrenergic blocking agents for 3 days, digoxin for 2 weeks, and nitrates for at least 12 hours prior to exercise testing. No other drugs were taken. All 17 patients had to fulfill the additional criterion of not having angina pectoris induced until a moderate increase in heart rate was achieved, as we wanted to compare these patients’ ECG responses to those of the normal subjects at selected heart rate levels. The patients all had exercise- induced ST segment depression and were limited by moderately severe angina-i.e., three on a point scale (zero to four), a level at which they would normally stop exercising and take a sublingual nitroglycerin tablet. Normal subjects. Twenty-five normal male volunteers at low risk for cardiovascular disease were included in the study. They were screened during the same time period for beginning an exercise program. They all fulfilled the following criteria: serum cholesterol < 240 mg/dl; resting blood pressure < 140/90 mm Hg and no history of hyper- tension; normal resting ECG; no smoking history; and no family history of cerebrovascular or cardiovascular disease before 60 years of age. All the normal subjects had both a 903