SUMMARY Left ventricular (LV) performance at rest and during multilevel exercise in the supine and upright positions was studied in seven normal subjects with equilibrium radionuclide ventriculography. The mean left ventricular end-diastolic volume (LVEDV) during supine rest was 107 4 10 ml (± SEM) and 85 ± 6 ml (p < 0.02) in the upright position; the mean resting left ventricular end-systolic volumes (LVESV) were not diSferent in the upright and supine positions. The Changes in posture at rest are associated with significant changes in LV filling and stroke volume. A transition from the supine to the upright position produces a decrease in LV end-diastolic pressure1-3 and volume4-6 and in stroke volume.' -4 6-10 The results of previous studies of the alterations in LV enddiastolic volume during exercise in the supine position have varied.5, 6, 11-15 There is general agreement that end-systolic volume is smaller during exercise than at rest;6 11, 12, 14,15 most investigators3' 6, 12, 13 have reported an exercise-induced increase in stroke volume, although others have not.1 4These data are generally consistent with an enhanced contractile state From the Departments of Medicine

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Seventy-six thallium-201 myocardial perfusion studies were performed on twenty-five patients to assess their reproducibility and the effect ofvarying the level of exercise on the results of imaging. Each patient had a thallium-201 study at rest. Fourteen patients had studies on two occasions at maximum exercise, and twelve patients had studies both at light and at maximum exercise. Of 70 segments in the 14 patients assessed on each of two maximum exercise tests, 64 (91%) were reproducible. Only 53% (16/30) of the ischemic defects present at maximum exercise were seen in the light exercise study in the 12 patients assessed at two levels of exercise. Correlation of perfusion defects with arteriographically proven significant coronary stenosis was good for the left anterior descending and right coronary arteries, but not as good for circumflex artery disease. Thallium-201 myocardial imaging at maximum exercise is reproducible within acceptable limits, but careful attention to exercise technique is essential for valid comparative studies.

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SUMMARY To test the hypothesis that patients at risk of future cardiac events can be identified by submaximal exercise testing with radionuclide ventriculography (RVG), 61 patients were studied a mean of 19 ± 1.0 days (± SEM) after acute myocardial infarction (MI). RVGs were used to measure left ventricular ejection fraction (LVEF), wall motion score (WMS), end-diastolic volume (EDV) and end-systolic volume (ESV), and the ratio of systolic blood pressure to ESV (P/V index) at rest and during submaximal exercise. Frank lead ECGs were analyzed for ST-segment change and arrhythmias. These patients were followed for a mean of 9.6 months (60 for 6 months or more and one for 3 months) to determine the incidence of cardiac death, recurrent MI, unstable or medically refractory angina, persistent congestive heart failure (CHF) or limiting angina; these problems were considered to be important cardiac events. At the 6-month follow-up, 37 patients had important complications: four patients died, five had MI, seven had unstable or medically refractory angina, 11 had persistent CHF and 10 had severe limiting angina.The sensitivity and specificity of RVG in predicting the important postinfarct complications listed above were 95% and 96% for failure to increase LVEF by at least 5 units, 95% and 96% for an increase in ESV of more than 5%, 97% and 88% for failure of the P/V Index to increase by more than 35%, and 81% and 88%, respectively, for a decrease in WMS. The sensitivity and specificity of the ECG in predicting important complications were 54% and 58%, respectively.The rest and submaximal exercise RVG variables, the ECG, a history of MI, the location of the infarction, Killip class III, age, sex, and maximal work load performed were analyzed statistically to determine the best predictors of prognosis. The change with exercise in LVEF, ESV and the P/V index were the most significant variables in predicting prognosis during the 6-month follow-up period. When patients with subsequent cardiac events were separated into those with death, recurrent MI and unstable or medically refractory angina as major cardiac events, and patients with persistent CHF and limiting angina as less important ("minor") cardiac events, only the peak submaximal exercise LVEF and history of MI were significant in distinguishing these groups. In patients without important cardiac events during the 3-and 6-month follow-up, 70% and 88%, respectively, had no abnormality in the responses of LVEF, ESV, or P/V index to submaximal exercise. These results suggest that submaximal exercise testing with RVG is a highly sensitive means of classifying patients at the time of hospital discharge after MI according to the likelihood of having cardiac events during the ensuing 6 months. THE PROGNOSIS of patients after myocardial infarction (MI) has been studied extensively. Several clinical criteria and diagnostic procedures have been used to identify patients at risk for subsequent complications;'4 however, the sensitivity and specificity of these tests vary widely.7 ...