The conduction system in sudden death in Alaskan sled dogs during the Iditarod race and/or during training

Using serial section examination, we studied the conduction system in five Alaskan sled dogs that died suddenly; four during the Iditarod race and one during training. We compared our findings with the conduction system of three sled dogs of similar age that died of natural causes unrelated to the cardiovascular system. The conduction system of sudden death dogs revealed marked fibrosis of the sinoatrial (SA) node and/or its approaches and narrowing of the SA nodal artery in 3 dogs, fibrosis and marked fatty infiltration in and around the AV node in all 5, total isolation and/or tenuous connection of the AV node with its approaches in 4, fat and fibrosis in the AV bundle and bundle branches to a varying degree in all, and focal fibrotic scars in the left ventricle with fat and/or some disarray in 3. The control group revealed mild fibro-fatty changes in the conduction system without fibrotic scar areas in the heart. These findings are similar to the pathological findings in and around the conduction system in cases of sudden death in humans, especially trained athletes. These changes may form an anatomical substrate for an arrhythmic event in susceptible dogs during an altered physiological state.