Sinoatrial node arteriosclerosis in two young dogs

Two 11-month-old 7-kg unrelated female Beagles had clinical signs referable to the cardiovascular system. Histologic studies in both dogs revealed strikingly similar findings of sclerosis of the arteries of the sinoatrial node. Histologic changes included intimal thickening and fibrosis, with marked luminal narrowing; medial hypertrophy, fibrosis, and smooth muscle cell proliferation; and elastic fiber disruption and reduplication. Possible differential diagnoses for this condition included systemic necrotizing vasculitis (canine pain syndrome), coronary polyarteritis, and atherosclerosis.