Clinical studies of regional myocardial thallium-201 washout rate in hypertrophic cardiomyopathy

A trial was undertaken to elucidate the cause of disproportional hypertrophy (DPH) in hypertrophic cardiomyopathy (HCM). Twenty-eight HCM patients in whom coronary arteriography was normal and 10 normal volunteers underwent thallium-201 myocardial imaging during exercise. Based on ventriculographic findings, the sites of DPH were classified as interventricular septum (IVS), IVS-apical anterior wall, apical anterior wall, and whole wall. Washout rate (WR) and early uptake rate (UT) were obtained by analyzing circumferential profiles from Tl-201 images. The mean UT was significantly low from the apex to the bottom of the anterior ventricular septum, and significantly high in the basal portion of the anterior ventricular septum, as compared with the control group. The mean WR was significantly decreased in all the segments in any type of HCM group. Decreased WR was also observed in the site showing increased UT. Seventeen patients (61 %) showed abnormally decreased UT and/or WR for 25 segments. Twenty-one (84 %) segments had a decrease in WR only, 16 of which had been specifically thickened. In 20 patients with normal UT, WR was significantly decreased in the thinnest postero-lateral wall. The results indicate that HCM is characterized by decreased WR in the DPH sites. It is supposed that damaged coronary microcirculation may be a contributing factor to the decrease in WR and UT, and disturbed metabolism in myocardial cells may be involved in the sole decrease of WR as well. Both disturbances are considered closely related to the cause of DPH. (Namekawa, K.)