[Experimental study on the pathogenesis of mitral annular calcification: calcium deposits in mitral complex lesions induced by vagal stimulation in rabbits]

Cervical vagal stimulation in rabbits frequently causes peculiar mitral complex lesions which are detected by deposition of colloidal carbon. The present study examined the effects of vagal stimulation on the calcium (Ca) contents in the mitral complex lesions. Anesthetized rabbits were forced into the supine position with electrocardiographic monitoring. The animals were divided into those with vagal stimulation (n = 37), and those without manipulation as controls (n = 25). Colloidal carbon (1 ml) was intravenously injected into the animals on the next day. All animals were sacrificed after 1 week. After perfusion of the heart by heparinized saline, Ca content per g myocardium in the mitral annulus, papillary muscle, free wall or apex in the left ventricle was measured by the atomic absorption method. Immediately after vagal stimulation, bigeminy due to premature ventricular contractions was observed in 76%, and systolic murmur was heard in 30%. Mitral complex lesions detected by carbon deposits were found in 73% of the rabbits with vagal stimulation. Ca content in the mitral annulus or papillary muscle was significantly greater than that in the free wall or apex (p < 0.001). Ca content in the mitral annulus was significantly greater in the rabbits with vagal stimulation than in the control group (p < 0.001). In the former group, Ca content in the mitral annulus in animals with mitral complex lesions was significantly greater than that in those without mitral complex lesions (p < 0.01). These results suggest that these mitral complex lesions might provide an experimental model of mitral annular calcification, and that the autonomic nervous system and arrhythmia might be involved in the mechanism of this calcification.