2019 Volume 72 Issue 3 Pages 162-166
A histological examination of the atrioventricular (AV) conduction system was performed in a 12-year-old mixed-breed dog with complete AV block. The dog had undergone surgical resection of the fifth digit of the right forelimb for nail bed melanoma 11 months before its death. At necropsy, longitudinal and cross sections of the heart demonstrated extensive infiltration of dark brown or almost black neoplastic tissue into the myocardium. Histopathology of the affected myocardium provided a diagnosis of cardiac metastasis of malignant melanoma. Histological findings in the AV conduction system included severe infiltration of malignant melanoma cells into the AV nodal region, resulting in total disappearance of the AV node. In addition, severe neoplastic cell infiltration had entrapped the penetrating portion of the AV bundle, causing complete loss of conduction fibers. These neoplastic lesions on the AV conduction system were thought to have preceded the blockage of the AV conduction of cardiac impulses.
