Background: In patients with ischemic heart disease (IHD), the current guidelines on exercise prescription recommend that exercise training intensity be 10 beats/min below the heart rate at which there is >1 mm ST-segment depression (ischemic threshold). However, it is not well established that exercise training above the ischemic threshold is harmful.
Methods: Twenty-two patients with angiographically documented IHD (>70% stenosis) were randomized to exercise training either at a target intensity that induced myocardial ischemia (ischemic group) or that adhered to current guidelines (control group). Training was progressively increased to 60 min under continuous ECG monitoring. Cardiac troponin T (cTnT) was measured at regular intervals. Ambulatory ECG monitoring was performed before and after 6 wkof training and left ventricular function was evaluated by echocardiography in the ischemic group after at least 6 wk of training.
Results: The ischemic training sessions were very well tolerated. The ischemic group had myocardial ischemia during the first 20, 40, and 60 min exercise sessions for 12.3 ± 6.8 min, 29.0 ± 12.9 min and 49.8 ± 2.2 min, respectively, with ST-segment depression ranging from 1.0 to 2.1 mm. The estimated myocardial work (as expressed by RPP) during the training session was also higher in the ischemic than in the control group for the first 20 min (17 354 ± 6 528 vs 13 355 ± 2 936 beats/min • mmHg, respectively; P=0.08), 40 min (16 329 ± 5 407 vs 12 452 ± 2 330 beats/min • mmHg, respectively; P=0.04), and 60 min training sessions (18 750 ± 5 698 vs 13 352 ± 2 947 beats/min • mmHg, respectively; P=0.02) No patient in either group demonstrated significant arrhythmias nor increased cTnT. The measured cTnT stayed below the detectable values of the essay (>0.01μg/l) for all patients at all times. Left ventricular function remained unchanged in the ischemic group.
Conclusion: In patients with IHD, prolonged and repeated ischemic training sessions up to 60 min can be well tolerated without evidence of myocardial injury, significant arrhythmias or left ventricular dysfunction. Thus exercising at or above the ischemic threshold does not appear deleterious under this kind of supervision
