Anatomic Assessment of Variations in Myocardial Approaches to the Atrioventricular Node

INTRODUCTION: The tissues in the posteroinferior atrioventricular (AV) junction around the AV node are important in procedures for ablating and manipulation of catheters in and around the coronary sinus (CS). However, information with regard to the histological arrangement of perinodal myocardium relative to the CS is lacking. METHODS AND RESULTS: We examined 21 postmortem human hearts without any abnormalities (9 women; mean age 68.8 ± 14.3 years). After making measurements, the posteroinferior AV junction was removed and processed for histology. Sections were cut parallel to the septum. We assessed the myocardial arrangements from the atrial septum and the CS toward the AV nodal tissue, including the transitional cell zone, and measured the dimensions between the compact AV node and the CS, and the circumference of the CS. We observed 3 patterns of myocardial approaches to the AV node: extension of myocardium from the atrial septum (Group A; n = 6); extension of CS musculature (Group B; n = 6); and both septal and CS musculature (Group C; n = 9). The distance between the AV node and the CS in Group A was significantly longer than in the other groups (mean 11.5 ± 3.1 mm, 1.7 ± 0.6 mm, 3.8 ± 1.5 mm, respectively; P < 0.0001), and the circumference of the CS in Group B was longer than in Group A (mean 31.1 ± 7.9 mm*, 44.4 ± 8.4 mm*, 33.7 ± 6.9 mm, respectively; P < 0.05). CONCLUSION: The myocardial approaches including the transitional cell zone toward the AV node are variable in normal hearts. The location and size of the CS can affect the myocardial arrangements and the area of transitional cells around the AV node.