To assess regional coronary reserve in hypertrophic cardiomyopathy, regional myocardial blood flow was measured in 23 patients with hypertrophic cardiomyopathy and 12 control subjects by means of nitrogen-13 ammonia and dynamic positron emission tomography. In patients with hypertrophic cardiomyopathy at baseline study, regional myocardial blood flow was 1.14 ± 0.43 ml/min per g in the hypertrophied (20 ± 3 mm) interventricular septum and 0.90 ± 0.35 ml/min per g (p <0.05 versus septal flow) in the nonhypertrophied (10 ± 2 mm) left ventricular free wall. These were not statistically different from the corresponding values in control subjects (1.04 ± 0.25 and 0.91 ± 0.21 ml/min per g, respectively, p = NS). After pharmacologically induced coronary vasodilation (dipyridamole, 0.56 mg/kg intravenously over 4 min), regional myocardial blood flow in patients with hypertrophic cardiomyopathy increased significantly less than in control subjects both in the septum (1.63 ± 0.58 versus 2.99 ± 1.06 ml/min per g, p <0.001) and in the free wall (1.47 ± 0.58 versus 2.44 ± 0.82 ml min per g, p <0.001). In addition, patients with hypertrophic cardiomyopathy who had a history of chest pain had more pronounced impairment of coronary vasodilator reserve than did those without a history of chest pain. After dipyridamole, coronary resistance in the septum decreased by 38% in patients without a history of chest pain, but decreased by only 14% in those with such a history (p <0.05). Coronary resistance in the free wall decreased by 45% in patients without and by 27% in those with a history of chest pain (p = 0.06). These results show that, in patients with hypertrophic cardiomyopathy, coronary vasodilator reserve is abnormal not only in the hypertrophied interventricular septum, but also in the nonhypertrophied free wall of the left ventricle. This finding suggests that the reduction in coronary reserve is not necessarily due to myocardial hypertrophy, but may be a primary defect.
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