Hypertrophic cardiomyopathy in pigs: quantitative pathologic features in 55 cases.

naturally occurring hypertrophic cardiomyopathy (HCM) was diagnosed in 55 purebred pigs 6 to 12 months of age. Ten (18%) of the pigs died suddenly during auction or shipment or were found dead by their keepers. The other 45 pigs failed to meet the criteria for brediing stock. Forty-six purebred and 64 hybrid pigs were studied for control. Heart weights were significantly heavier (p < 0.001) in the pigs with HCM (473.5 ± 31.8 g; heart weight [HW]/body weight [BW] ratio 4.6 ± 0.7) than in the purebred (334.4 ± 29.7 g; HW/BW 3.4 ± 0.3) and hybrid (344.3 ± 28.9 g; HW/BW 3.4 ± 0.1) pigs without HCM. The ventricular septum (VS) in the 55 pigs with HCM was significantly thicker (26.0 ± 3.1 mm; p < 0.001) than in the purebred (19.6 ± 2.6 mm) and hybrid (14.1 ± 0.5 mm) pigs without HCM. The left ventricular free wall (LV) was significantly thicker (p < 0.001) in the pigs with HCM (20.0 ± 2.7 mm) than in the purebred (18.1 ± 2.1 mm) and hybrid (15.6 ± 0.3 mm) pigs without HCM. Asymmetric septal hypertrophy was evident because the ratio of VS to LV was significantly greater (p < 0.001) in the pigs with HCM (1.3 ± 0.2) than in the purebred (1.0 ± 0.2) and hybrid (0.9 ± 0.01) pigs without HCM. The anterior portion of the VS appeared to bulge into and impinge upon the left ventricular outflow tract, in which a fibrotic endocardial plaque was often seen. Histologic features included marked muscle cell disorganization in the VS, LV, right ventricular free wall. Abnormal intramural coronary arteries and myocardial fibrosis were seen in most pigs with HCM. Silver impregnation stains showed that there were marked increases in perimysial coils, pericellular weaves, and cell-to-cell struts. Matrix disorientation was evident in the hearts with HCM. Quantitation revealed that the collagen protein in the hearts with HCM (23.8 ± 2.8 μg/mg protein) was significantly higher (p < 0.001) than in the hearts of purebred (15.7 ± 1.8 μg/mg protein) and hybrid (13.9 ± 4.2 μg/m pprotein) pigs without HCM. Total muscle protein in the hearts of the purebred pigs with (51.6 ± 3.3 mg) and without (51.9 ± 3.0 mg) HCM was not different; however, in hearts with HCM (51.6 ± 3.3 mg) it was significantly higher (p < 0.001) than in those of hybrid pigs (47.6 ± 4.4 mg) without HCM. There was 47% to 52% more stainable collagen in the heart with HCM (44.7 ± 5.2 μg collagen/mg protein) than in the purebred (30.3 ± 4.0 μg collagen/mg protein) and hybrid (28.3 ± 8.1 μg collagen/mg protein) hearts without HCM. Gross and histologic features and connective tissue abnormalities in the pigs with HCM were strikingly similar to those in humans, cats, and dogs with HCM. Thus we conclude that spontaneous porcine HCM presents a new and important model for the cardiovascular investigator.