BLUNTED CORONARY RESERVE IN MYOTONIC-DYSTROPHY - AN EARLY AND GENE-RELATED PHENOMENON

Background In myotonic dystrophy (DM), striated muscle is involved in relation to the size of the DNA mutation. Smooth muscle may be similar ly impaired at the level of the urinary and digestive apparatus and po ssibly at the level of small vessels, since microangiopathy has been d escribed in the iris and digital capillaries. Our purpose was to study the function of the myocardial microvasculature in relation to the si ze of the mutation in DM patients without clinical cardiac involvement and with normal left ventricular dimensions and function and normal l arge coronary arteries. Methods and Results In 6 control subjects and 10 DM patients, we investigated the coronary blood flow reserve using positron emission tomography with O-15-labeled water. Global and regio nal flow reserves were obtained from myocardial regions of interest ma nually drawn on a static FDG image encompassing, respectively, the who le left ventricle and the anterior, septal, and lateral walls. The DNA mutation size was determined on circulating lymphocytes in each DM pa tient. Compared with control subjects, DM patients had decreased globa l (2.39+/-0.39 versus 4.00+/-0.67, P=.00003) and regional (anterior, 2 .39+/-0.64 versus 3.87+/-0.92, P=.002; septal, 2.60+/-0.48 versus 4.00 +/-0.70, P=.0003; lateral, 2.26+/-0.58 versus 4.16+/-1.11, P=.0005) co ronary reserves. In DM patients, the coronary reserve correlated stron gly and inversely with the DNA mutation size (r=-.77, P=.009). Conclus ions The study demonstrated that global and regional coronary reserves are impaired, in relation to the DNA mutation size, in symptom-free D IM patients with normal ventricular dimensions and function and normal large coronary vessels. We suggest that a gene-related blunted corona ry reserve resulting from an impairment of vascular smooth muscle is a n early component of DM cardiomyopathy.