MYOCARDIAL METABOLIC, HEMODYNAMIC, AND ELECTROCARDIOGRAPHIC SIGNIFICANCE OF REVERSIBLE TL-201 ABNORMALITIES IN HYPERTROPHIC CARDIOMYOPATHY

Background. Exercise-induced abnormalities during thallium-201 scintigraphy that normalize at rest frequently occur in patients with hypertrophic cardiomyopathy. However, it is not known whether these abnormalities are indicative of myocardial ischemia. Methods and Results. Fifty patients with hypertrophic cardiomyopathy underwent exercise Tl-201 scintigraphy and, during the same week, measurement of myocardial lactate metabolism and hemodynamics during pacing stress. Thirty-seven patients (74%) had one or more Tl-201 abnormalities that completely normalized after 3 hours of rest; 26 had regional myocardial Tl-201 defects, and 26 had apparent left ventricular cavity dilatation with exercise, with 15 having coexistence of these abnormal findings. Of the 37 patients with reversible Tl-201 abnormalities, 27 (73%) had metabolic evidence of myocardial ischemia during rapid atrial pacing (myocardial lactate extraction of 0 mmol/l or less) compared with four of 13 patients (31%) with normal Tl-201 scans (p < 0.01). Eleven patients had apparent cavity dilatation as their only Tl-201 abnormality; their mean postpacing left ventricular end-diastolic pressure was significantly higher than that of the 13 patients with normal Tl-201 studies (33 +/- 5 versus 21 +/- 10 mm Hg, p < 0.001). There was no correlation between the angiographic presence of systolic septal or epicardial coronary arterial compression and the presence or distribution of Tl-201 abnormalities. Patients with ischemic ST segment responses to exercise had an 80% prevalence rate of reversible Tl-201 abnormalities and a 70% prevalence rate of pacing-induced ischemia. However, 69% of patients with nonischemic ST segment responses had reversible Tl-201 abnormalities, and 55% had pacing-induced ischemia. Conclusions. Reversible Tl-201 abnormalities during exercise stress are markers of myocardial ischemia in hypertrophic cardiomyopathy and most likely identify relatively underperfused myocardium. In contrast, ST segment changes with exercise and systolic compression of coronary arteries on angiography are unreliable markers of inducible myocardial ischemia in hypertrophic cardiomyopathy. Apparent cavity dilatation during Tl-201 scintigraphy may indicate ischemia-related changes in left ventricular filling, with elevation in diastolic pressures and endocardial compression.