Ischemia in the ambulatory setting—The total ischemic burden: Relation to exercise testing and investigative and therapeutic implications

Abstract

To establish the relation between treadmill exercise testing and ambulatory ST segment monitoring in the detection of ischemia in patients with coronary artery disease, and to assess whether standard medical therapy affects any such relation, 277 patients with stable angina and angiographically documented coronary artery disease were studied with treadmill exercise testing and 48 h ambulatory ST segment monitoring. One hundred forty-six patients (52%) were studied while receiving no routine antianginal therapy, and 131 (48%) while receiving standard medical therapy.In 187 patients (67%) the exercise test was positive for ischemia. During 11,964 h of ambulatory monitoring, 881 episodes of ischemia (645 [73%] silent) were recorded, of which 809 (92%) occurred in patients with a positive exercise test. The mean heart rate at the onset of ischemic episodes during ambulatory monitoring was significantly less than that at the onset of 1 mm ST segment depression during exercise testing (94.5 versus 105.9 beats/min, p < 0.0001). However, the frequency of ambulatory ischemic episodes was strongly related to a positive exercise test (p < 0.0001), and this relation was similar for both silent and painful ischemia (p < 0.0001 for both) and in patients who were and were not receiving therapy (p < 0.0001 for both). The total duration of ischemia was similarly related to a positive exercise test (p < 0.0001). Only one patient with a negative exercise test had frequent (>5/day) episodes of ischemia on ambulatory monitoring and had documented coronary artery spasm.Thus, exercise testing identifies the majority of patients likely to have significant ischemia during their daily activities. The strong relation between ischemia in the formal exercise and ambulatory settings suggests that the underlying pathophysiologic mechanisms are similar, even though the heart rate at the onset of ischemia in the two settings is different. There is little indication to perform ambulatory ST segment monitoring in patients with a negative exercise test unless the history suggests coronary artery spasm.