Spontaneously occurring hypertrophic cardiomyopathy in the rat. I. Pathologic features.

The gross anatomic and microscopic appearance of the hearts of young and adult WKY/NCrj rats was examined in comparison with that of normotensive Wistar and SHR/NCrj rats. In a substantial number of the WKY rats, the heart weight and thickness of ventricular septum were much greater than those of the Wistar and SHR rats. The ventricular septum to left ventricular free wall thickness ratio was greater than 1.3 in about one sixth of the WKY rats. In most of the hypertrophied WKY hearts, the transverse area of the left ventricular cavity was smaller in relation to the wall area than in the Wistar and SHR rat hearts, although in a few it was greater. Abnormal fiber arrangement, myocyte hypertrophy, and myocardial fibrosis were far more prominent in the hypertrophied myocardium of the WKY rats compared with the Wistar or SHR rats. Intramural arteries with marked wall thickening existed frequently in the hypertrophied and dilated hearts. Electron microscopic examination revealed marked disarrangement of bundles of myofilaments and widened Z-bands in the hypertrophied myocardium. Blood pressure was not elevated in the rats with cardiac hypertrophy. These findings show that a disease of the myocardium with the pathologic features similar to those of hypertrophic cardiomyopathy in man occurs spontaneously in rats.