Exercise induced defects during thallium scintigraphy that normalize at rest occur commonly in patients with hypertrophic cardiomyopathy. However, it is not known whether or not these defects are indicative of myocardial ischemia. To assess the pathophysiologic relevance of reversible thallium defects, 50 patients with hypertrophic cardiomyopathy underwent exercise thallium scintigraphy and measurement of myocardial metabolism and hemodynamics during pacing stress. Thirty-seven patients (74%) had thallium abnormalities that normalized after 3 hours of rest. Of these 37 patients, 27 (73%) had metabolic evidence of myocardial ischemia during rapid atrial pacing. Four of 13 patients (31%) with normal thallium scans also had evidence of pacing-induced myocardial ischemia, a significantly lower prevalence (p<0.01). Seven of 10 asymptomatic patients had reversible thallium defects, with 4 of these having evidence of myocardial ischemia during pacing stress. Thus, exercise thallium scintigraphy identifies hypertrophic cardiomyopathy patients with evidence of inducible myocardia ischemia.
