REGIONAL HETEROGENEITY OF FUNCTION IN HYPERTROPHIC CARDIOMYOPATHY

Background In patients with hypertrophic cardiomyopathy (HCM), left ventricular ejection performance may be normal while segmental myocardial function is distinctly abnormal. The advent of magnetic resonance tissue tagging has allowed the noninvasive evaluation of intramyocardial segmental shortening in vivo in a topographic and temporal manner. Methods and Results Ten patients with HCM documented by echocardiography and 10 healthy volunteers were studied with magnetic resonance tissue tagging by spatial modulation of magnetization. Percent circumferential myocardial shortening (%S) was compared at endocardium, midwall, and epicardial levels at four regions around the left ventricular short axis and from four short axis slices from apex to base at four or five time intervals during systole. In 8 patients and 8 control subjects, longitudinal shortening was evaluated within the septum and the lateral free wall at three levels from apex to base. Circumferential %S was less in HCM patients than in control subjects in the septal (13+/-5% versus 24+/-6%, P=.0002), inferior (13+/-5% versus 21+/-4%, P=.001), and anterior (17+/-5% versus 21+/-3%, P<.03) regions but not in the lateral region. Circumferential end-systolic %S was reduced in patients with HCM compared with control subjects at all levels from apex to base. The normal transmural gradient in circumferential end-systolic shortening was preserved with greatest %S at the endocardium. Most of the total cumulative circumferential shortening occurred earlier in systole in patients compared with control subjects, especially within the septum. Longitudinal end-systolic %S was depressed throughout the septum in patients compared with control subjects, most markedly at the base, but was normal in the lateral free wall. Conclusions Circumferential myocardial segment shortening is depressed in HCM in the septum, inferior, and anterior regions and at all levels from apex to base, and much of the total cumulative shortening occurs early in systole. Longitudinal shortening is reduced in the basal septum in HCM. The heterogeneity of regional function in these patients may reflect the regional variation in the myocardial disarray and fibrosis that is characteristic of this disorder.