Conduction System in the Swine Heart: Essential Landmarks for Gross Dissection

Background: The components of the cardiac conduction system (CCS) were discovered almost two centuries and presented in the diagrammatic forms. This should be due to the difficulty in distinguishing the CCS from the surrounding cardiac tissues and the lack of information concerning the precise landmarks for gross dissection. Furthermore the CCS in pig, the animal regarded as a suitable model for the assessment of catheter based intervention, has not been reported. The aims of the present study were to demonstrate the gross anatomic architecture of CCS in the swine heart, and to provide the valuable landmarks for the gross anatomic dissection of the CCS. Materials, Methods & Results: Twenty hearts of adult Large White pigs (Sus Scrofa domesticus) were used. Fifteen hearts were elucidated by gross anatomic dissection. The tissue blocks of the sinoatrial node (SAN) and atrioventricular conduction tissue of the five hearts were prepared for histological investigation by staining with Masson's trichrome. It was found histologically that the cardiac conduction tissues were clearly distinguishable from the surrounding cardiac myocardium and connective tissue. Moreover, the histological information also navigated the location and anatomical architecture of the CCS which provided essential guideline for gross dissection. The SAN was somewhat spindle in shape which embedded in epicardial connective tissue of the terminal sulcus. In some cases, it was quite difficult to identify the SAN, so the sinoatrial node artery was used as a clue. The AVN was an elliptical shaped which situated in subendocardial tissue at apex of the triangle of Koch on the atrial surface of the central fibrous body. The distal extremity of the AVN extended into the central fibrous body to form the penetrating bundle of His. At the boundary between the membranous and muscular parts of the interventricular septum, the AV bundle of His divided into the right (RBB) and left bundle branches (LBB). The RBB coursed downward in the muscular part of the interventricular septum around the base of the anterior papillary muscle and then traveled along the septomarginal trabecula. The LBB passed through the lower rim of the membranous septum and appeared on the endocardial surface of the left ventricle at the commissure between the right coronary and non-coronary leaflets of the aortic valve. However, intramural branches of the Purkinje network could not be identified. Discussion: The present study reveals that the anatomic architecture and location of the CCS in the pig heart could be demonstrated by gross anatomic dissection, and the essential landmarks for gross investigation were suggested. The crucial landmarks for the identification of the SAN, the AV conduction tissue and the LBB are the superior cavoatrial junction, the attachment of the septal leaflet adjoining the membranous septum, and the junction between the right coronary and noncoronary leaflets of the aortic valve, respectively. These landmarks are useful not only for gross anatomic dissection of the CCS in the pig heart but also provide the fundamental information for cardiac arrhythmia and sudden death experimentation in this animal. Therefore these findings should be valuable for anatomists, cardiovascular researchers and veterinary clinicians as well as veterinary and medical students.