The value of an objective exercise test for the assessment of the functional results of aortocoronary bypass was investigated in 19 patients who were studied before and six months after the operation. For positive tests the end point was defined as a net ST segment depression of 0·1 mv 80 ms after the J point of the ECG. For negative tests the end point was 85% of the age-predicted maximal heart rate response. One patient who was not able to attain either of these points after the operation was excluded. In the remaining 18 patients three indices were used in the analysis. First, the heart rate (HR) and the product of heart rate and systolic blood pressure (RPP) were measured at the defined level of ST segment depression during positive exercise tests to yield HR/ST and RPP/ST threshold respectively. Second, the HR and RPP were measured at the end point of the negative tests. Third, the duration of exercise till the end point of the tests was measured. In each patient the duration of the postoperative test was longer than that of the preoperative test. While all the patients had a positive exercise test before the operation, the test was negative in 11 after it. In 10 of these 11 patients the HR and RPP attained at the end point of the postoperative test had increased; the HR and RPP remained unchanged in one patient. Positive tests were still present in seven of the 18 patients. In five of these the HR/ST threshold and RPP/ST threshold were greater after than before operation, and they remained unchanged in two. An improvement in myocardial blood supply after aortocoronary bypass was suggested indirectly by the ability to attain, during exercise, a higher HR and RPP at the end point of the test. The test proved especially valuable in patients who retained a positive exercise test after the operation.
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