Flattening of oxygen pulse during exercise may detect extensive myocardial ischemia

Flattening of oxygen pulse curve during incremental cardiopulmonary exercise testing has been proposed for the improvement of diagnostic accuracy of exercise-induced myocardial ischemia. In this study, we compare the oxygen pulse response to incremental treadmill exercise in patients with and without ischemia as detected by myocardial perfusion scintigraphy.

Eighty-seven patients referred to exercise myocardial perfusion scintigraphy were also evaluated with incremental treadmill cardiopulmonary exercise testing. One investigator prospectively identified patients who presented transient exercise-induced perfusion defects on 99mTc sestamibi myocardial scintigraphies. Another investigator evaluated the response of oxygen pulse to incremental exercise testing without knowledge of electrocardiographic response or scintigraphic findings.

Exercise myocardial perfusion scintigraphy detected transient perfusion defects in 36% of the patients. Compared with patients with normal perfusion studies, patients with exercise-induced ischemia presented similar peak double product, peak oxygen uptake, and anaerobic threshold. Oxygen pulse at 25% of peak (ischemia: 9.7 +/- 2 mL per beat; no ischemia: 9.3 +/- 2 mL per beat), 50% of peak (11.2 +/- 3 vs 10.8 +/- 3 mL per beat), 75% of peak (12.5 +/- 3 vs 11.9 +/- 3 mL per beat), and at peak exercise (13 +/- 4 vs 13 +/- 4 mL per beat) were not different in exercise-induced ischemia and normal groups, respectively. However, patients who presented extensive transient perfusion defects during exercise had a lower peak oxygen pulse (12.8 +/- 3.8 vs 16.4 +/- 4.6 mL per beat; P < 0.05).

The analysis of the oxygen pulse response to incremental exercise test does not identify mild myocardial ischemia. Flattening of oxygen pulse response during incremental exercise might be present only with extensive myocardial ischemia.