Postexercise VO2 “Hump” phenomenon as an indicator for inducible myocardial ischemia in patients with acute anterior myocardial infarction

Objectives At exercise testing with respiratory gas analysis in patients with inducible myocardial ischemia, we have occasionally observed abnormal transient oxygen uptake (VO2) components with a characteristic “Hump”-shaped morphology early after exercise, which may serve as an index for inducible ischemia. We examined this hypothesis in patients with anterior q-wave myocardial infarction in whom the accuracy to identify ischemia by exercise ECG is limited. Design From patients with acute anterior q-wave infarction but without clinically overt heart failure who underwent pre-discharge exercise testing, we examined patients with (Group-I, n = 30) and without (Group-N, n = 29) inducible ischemia. To identify “Hump”, postexercise VO2 (up to 4 min) standardized for peak VO2 was exponentially fitted with use of peak VO2 and VO2 of 90–240 s, yielding “expected VO2”. “D-curve” was obtained by subtracting “expected VO2” from measured VO2. Results Although exercise-induced ST depressions more frequently appeared in Group-I (27%) than in Group-N (3%, p < 0.05), the prevalence was low. D-curve peaked later (p < 0.01) and its value was greater (p < 0.05) in Group-I than in Group-N. When “Hump” was defined to be present if D-curve peaked ≥ 40 s and its peak value ≥ 15%, it was far more frequently found in Group-I (n = 17 / 30) than in Group-N (n = 1 / 29, p < 0.01). Thus, “Hump” could diagnose inducible ischemia with a sensitivity of 57% and a specificity of 97%. Conclusions Although not highly sensitive, postexercise VO2 “Hump” with its peak occurring around 60 s after exercise is a specific marker for inducible ischemia. The identification may be useful, particularly in patients with limited accuracy of exercise ECG such as those with q-wave anterior infarction.