Transient disappearance of Q waves of previous myocardial infarction due to exercise-induced ischemia of the contralateral noninfarcted myocardium

The electrocardiogram (ECG) of a 40-year-old woman with an old inferolateral myocardial infarction revealed, in the course of an exercise treadmill/thallium test, gradual disappearance of infarctional Q waves, which reappeared gradually during recovery from exercise. The patient had evidence of exercise-induced myocardial ischemia both by the ECG and by thallium-201 perfusion scintigraphy involving several myocardial regions. The temporal association of transient disappearance of Q waves with the occurrence of reversible ischemia suggested that the latter was instrumental in producing this phenomenon, through a transient failure of the ischemic anterior wall to shift the initial depolarization forces away from the infarcted inferolateral territory. Further evidence for this concept was provided by the case of another patient, a 49-year-old man who also had an old inferolateral myocardial infarction and whose ECG in the course of an exercise treadmill/thallium lest did not reveal any changes in the infarctional Q waves. In this patient, thallium images showed mild, reversible inferolateral myocardial ischemia but a well perfused anterior wall, which provided for early depolarization forces (thus Q waves) directed opposite to the region of infarcted myocardium.