A simple method for performing routine histopathological examination of the cardiac conduction tissue in the dog.

In standard toxicity studies, the cardiac conduction tissue is not systematically sampled and examined for histopathological changes. Most methods described use serial sectioning perpendicular to the long axis of the sinoauricular node (SAN) and atrioventricular node (AVN). Dozens of slides are needed to allow examination of a significant portion of the SAN and AVN. A simple method was developed to be used in routine histopathologic examination of the dog heart. With a plane parallel to the external wall and the upper edge of the right auricle, the SAN and its arterial supply were easily sectioned and examined. The frontal plane parallel to the interventricular crest was the most appropriate plane for observing a large portion of the AVN and the bundle of His. Based on these results, the heart of 240 dogs from toxicology studies were successfully sampled and processed utilizing this technique. An average of 5 slides per node was needed to perform a satisfactory examination of each of the SANs and AVNs.