Attenuation of the Threshold for Myocardial Ischemia in Ramp vs Standard Bruce Protocol in Patients with Positive Exercise Stress Test and Angiographically Demonstrated Coronary Artery Narrowing?

Background: Gradual instead of abrupt increases in workload favour a more physiological response in terms of hemodynamic and gas exchange parameters. Therefore, we sought to determine whether myocardial ischemia is attenuated with a ramp compared to a standard Bruce exercise protocol in patients with coronary artery disease (CAD). Methods: We compared ischemic parameters on the Bruce protocol with an individualized ergocycle ramp protocol in 18 men with documented CAD (≥ 70% stenosis) and a reproducible ischemic ECG exercise test. These 2 symptom-limited tests were performed in random order 2 weeks apart. Oxygen consumption (VO2), ischemic threshold [systolic blood pressure x heart rate (RPP) at 1 mm ST-segment depression], and maximum ST-segment depression corresponding to the highest RPP common to the 2 tests (AdjSTmax) were determined. Results: While all subjects showed ischemia on the treadmill, 6/18 did not on the ergocycle. However, ischemic threshold was higher on the ramp than the Bruce protocol (23 420 ± 5 732 vs 20 018 ± 3 542 bpm•min-1•mmHg; P=0.007). Peak RPP was higher during the ramp than with the Bruce protocol (28 492 ± 6 450 vs 25 519 ± 6 067 bpm•min-1•mmHg, respectively; P=0.02), despite similar peak VO2 (25.59 ± 5.05 vs 26.39 ± 4.65 mlO2•kg-1•min-1, respectively; P=0.6). AdjSTmax was less on the ramp than the Bruce protocol (-1.2 ± 0.9 vs -1.9 ± 0.7 mm; P=0.003). Conclusion: Exercise-induced myocardial ischemia is markedly attenuated on the more gradually increasing workload of the individualized ramp ergocycle compared with the standard Bruce treadmill protocol. This effect is unexplained by energy expenditure (VO2) or myocardial work (RPP) and is consistent with a “warm-up” ischemic mechanism. The more gradually increasing workload of the ramp ergocycle protocol may have favoured a “warm-up” ischemic effect despite achieving higher RPP than the Bruce protocol treadmill suggesting it may be physiologically preferable for exercise prescription in patients with CAD