CLINICAL SIGNIFICANCE OF NORMAL CARDIAC SILHOUETTE IN DILATED CARDIOMYOPATHY : Evaluation Based Upon Echocardiography and Magnetic Resonance Imaging

Abstract

It is generally believed that patients with dilated cardiomyopathy have a large cardiac silhouette on chest roentgenography. Contrary to this general belief, we have recently examined several patients with a dilated left ventricle (LV) on echocardiography but in whom the cardiothoracic ratio (CTR) was within normal limits. To investigate this apparent discrepancy, we evaluated the relation-ship between LV dimensions, measured on M-mode echocardiography, and CTR in 49 patients with dilated cardiomyopathy. Among these patients, 11 (22%) had a CTR less than 50% and 38 (78%) had a CTR greater than 50%. The spacial orientation (cardiac rotation) of the LV within the thorax was evaluated by magnetic resonance imaging (MRI) in 5 patients with a CTR less than 50% and in 7 patients with a CTR greater than 50%, in comparison with 7 normal controls. In each of these patients, cardiac rotation was assessed from both a transverse and a frontal MRI section. In both groups, LV end-diastolic dimension was greater than 5 cm. Transverse cardiac rotation was 32±8 degrees in patients with a CTR less than 50%. This was significantly lower than in the 7 normal controls (43±7 degrees) (p<0.05). In patients with a CTR greater than 50%, however, transverse cardiac rotation (55±5 degrees) was significantly greater than in normal controls (p<0.01). No differences in frontal cardiac rotation was observed between the 2 groups. These data indicate that a normal cardiac silhouette in patients with dilated cardiomyopathy can be explained on the basis of a counterclockwise transverse rotation of the heart with-in the thorax, and it cannot always rule out the dilatation of the LV.