PERSISTENT REGIONAL WALL MOTION ABNORMALITIES FOLLOWING EXERCISE

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Whether stunned myocardium occurs after exercise-induced myocardial ischemia remains controversial. We studied 17 patients with angiographically proven coronary artery disease, all of whom had abnormal left ventricular ejection fraction response from rest (48+/-16%) to exercise (44+/-15%) as assessed by radionuclide angiography. Of the 17 patients, 5 also underwent Rubidium myocardial blood flow study using positron emission tomography (PET). For each patient, 4 sets of radionuclide angiography and Rubidium images were acquired at rest, during maximal supine bicycle exercise, 15 min and 30 min post-exercise. Quantitative regional ejection fraction (REF) was assessed by dividing the left ventricular region of interest into 8 annular sectors. In 15 of 17 patients (88%), regions with abnormal exercise-induced REF had persistent or worsening of REF at 15 min post-exercise and in 11 patients (65%) the abnormal response persisted at 30 min post-exercise. Among the 5 patients with REF and myocardial blood flow studies, 8 regions showed decreased REF during exercise and 15 min post-exercise associated with lower blood flow compared to normal regions. At 30 min post-exercise, myocardial blood flow continued to track REF, with 4 regions demonstrating concordant improvement in REF and blood flow and 4 regions with persistent decrease in REF and blood flow. The finding of decreased myocardial blood flow in regions with decreased REF post-exercise does not conform to the classic definition of stunned myocardium. Although the mechanisms responsible for persistent post-exercise decrease in myocardial blood flow is unknown, any one of the ascribed causes of coronary artery vasoconstriction during exercise i.e sympathetic nervous system activation, endothelial dysfunction or hydrodynamic constriction, may also be operative post-exercise.