Coronary microcirculation remodeling in patients with idiopathic dilated cardiomyopathy.

BACKGROUND In patients with idiopathic dilated cardiomyopathy (IDCM), the myocardial blood flow is markedly depressed. The presence of alterations in the number and length of the coronary microcirculation has not been explored. METHODS In explanted hearts of 6 patients with IDCM and in 6 normal control hearts, the arteriolar length density and capillary numerical density were determined in sections stained with orcein (vessels 50-200 μm in diameter), for smooth muscle actin (vessels 6-50 μm in diameter) and CD34 (capillaries). RESULTS No difference with normal hearts was observed in capillary numerical density and in length density of vessels above 50 μm in diameter. In IDCM, more than 50% of arterioles below 50 μm in diameter displayed an incomplete smooth muscle wall, and length density, especially for arterioles between 6 and 20 μm in diameter, was significantly lower (42.84 ± 8.51 mm/mm(3)) than in controls (75.34 ± 3.05 mm/mm(3), p = 0.001). CONCLUSIONS In IDCM, arterioles below 50 μm in diameter display an incomplete smooth muscle wall and a significant decrease in length density. These observations provide an anatomical basis for a decreased coronary flow reserve in IDCM.