40 巻 (1978) 2 号 p. 131-140
Histopathololgical observations were performed on the heart and cardiac nervous system of 5 horses affected with wandering pacemaker. The histopathological lesions common to all the animals were as follows: (1) Focal fibrosis in the atrial myocardium just beneath the subendocardium and/or in the endo- and subendocardium, and existence of atrial Purkinje-like fibers within the fibrotic lesions, (2) Microvascular altetation, characterized by edematous-loosening and/or fibrous swelling of the walls of the small and minute arteries, in both the atria, (3) Edema in the intracadiac nerves of both the atria, (4) Multifocal loss of nerve fibers in the extracardiac nerves of both the sympathetic and vagal systems, and (5) Medial degeneration in the pulmonary artery and aorta. The atrial focal lesions of myocardial and endo- and subendocardial fibrosis should be regarded as a result of local circulatory insufficiency (ischemia) due to the microvascular alteration. The Purkinje-like fibers witihin the atrial fibrotic lesions might have been given temporary automaticity and, at the same time, might have been under a condition of cardiac nervous fluctuation due to the organic disturbances in both the sympathetic and vagal systems.