The use of exercise electrocardiography provides an estimate of functional capacity after an infarction to prepare patients for cardiac rehabilitation and occupational work evaluation and also provides information regarding adequacy of medical therapy or coronary revascularization therapy and on subsequent cardiac event rates.
Functional capacity and the ability to generate an adequate systolic blood pressure response are major predictors of medium- and long-term mortality after AMI. Patients who are unable to perform an exercise test predischarge because of cardiac causes are high risk subjects with significant increased mortality rates. Inability to complete the exercise protocol because of functional limitations is also associated with a significant increased risk compared to patients able to complete the exercise test (84-86).
In TIMI II, 1-yr mortality was 7.7% in patients unable to perform an exercise test at the time of hospital discharge vs 1.8% in patients who were able to perform the test (84). Similar results were reported by the GISSI-2 investigators (87). Exercise-induced ST-segment depression > 1 mm increased the relative mortality risk in patients assigned to the invasive strategy in TIMI II (84).
Approximately 25% of patients who receive thrombolysis AMI have an abnormal exercise test at the time of hospital discharge (Table 3). The frequency of ischemic responses is increased with symptom-limited as opposed to target heart rate or workload-limited tests (93,94). The positive predictive value of exercise-induced ST-segment depression > 1 mm was 8% in patients who received thrombolysis vs 18% who did not for the end point of recurrent MI or death in a meta-analysis of 54 studies (Fig. 8) (95).
A normal exercise ECG at the time of discharge is associated with a 1-yr mortality rate of <1% with >90% predictive accuracy. Additional noninvasive testing with more expensive modalities in this low-risk patient subset is unlikely to be warranted, since coronary revascularization is unlikely to reduce overall cardiac mortality at 1 yr below 1%. However, no data is available that tests this strategy against 5-yr outcome data. A practical approach to the use of exercise testing in the postinfarct setting adapted from recent ACC/AHA guidelines is illustrated in Fig. 9 (57,96).
Indications for the use of exercise testing after AMI are illustrated in Table 4.
The need to perform exercise electrocardiography in all low risk postinfarct survivors was examined by Bogaty et al. (97). In a study of 121 consecutive patients with acute MI fulfilling low risk criteria, patients were randomized to either: (i) a short hospital stay (80 subjects); or (ii) conventional stay (40 subjects). Short stay patients with no ischemia on ST-segment monitoring were discharged on d 3, returning for an exercise test 1 wk later. During the patient recruitment phase, 41% of all screened patients with AMI would have been medically eligible for the short stay strategy. Twenty-one percent were not discharged early because of ischemia on ST-segment
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