From the Guidelines
The Bundle of His in a transitional atrioventricular (AV) canal is located anteriorly and inferiorly to the aortic valve, with its exact position being crucial for cardiac surgeons and interventional cardiologists to avoid iatrogenic injury to the conduction system. Specifically, the Bundle of His emerges from the AV node in the right atrium, penetrates through the central fibrous body, and then courses along the lower border of the membranous septum before dividing into the left and right bundle branches 1. This anatomical relationship is important because the Bundle of His passes through the region where the AV canal transitions into the ventricular septum. In relation to the aortic valve, the Bundle of His typically runs about 5-10 mm below the non-coronary cusp of the aortic valve. The proximity of the Bundle of His to the aortic valve explains why procedures involving the aortic valve or interventions for ventricular septal defects carry a risk of conduction disturbances, as highlighted in the 2018 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay 1.
Key points to consider include:
- The Bundle of His serves as the only electrical connection between the atria and ventricles, making its preservation critical during cardiac surgeries to prevent complete heart block.
- Understanding this anatomical relationship is essential for cardiac surgeons and interventional cardiologists to avoid iatrogenic injury to the conduction system.
- The location of the Bundle of His is particularly relevant in the context of aortic valve surgery, where the risk of conduction disturbances is higher due to the proximity of the Bundle of His to the aortic valve 1.
- Patients with congenitally corrected TGA (CCTGA) or AV septal defect (AVSD), particularly those with Down syndrome, may be more susceptible to surgical or catheter-induced AV block and should be monitored periodically for AV conduction abnormalities 1.
In the context of a transitional atrioventricular (AV) canal, the Bundle of His is displaced posteriorly, which is an important consideration for surgical repair and interventions in this population 1. However, the most recent and highest quality study, the 2018 ACC/AHA/HRS guideline, provides the most relevant information for clinical practice, emphasizing the importance of preserving the Bundle of His during cardiac surgeries to prevent conduction disturbances 1.
From the Research
Location of the Bundle of His
The Bundle of His is located near the aortic valve in a transitional atrioventricular (AV) canal. Key points to consider:
- The Bundle of His is situated just below the aortic valve, in proximity to the membranous septum, between the noncoronary cusp and right coronary cusp 2
- The His bundle traverses the right interventricular septal crest, and the left bundle branch (LBB) origin is a narrow stem crossing from right to left through the inferior margin of the membranous septum 3
- The membranous portion of the interventricular septum (MPIS) is in close relationship with the aortic valve, with its upper part usually in direct continuity with the attachments of both right and posterior aortic cusps 4
- The ideal location for pacing leads in physiological pacing is still being debated, but the anterior part of the atrio-ventricular (AV) septum at the junction between the membranous and muscular septum appears to be a good target for successfully pacing the His bundle 5
Relationship with the Aortic Valve
The relationship between the Bundle of His and the aortic valve is complex, with key points including:
- The superior border of the MPIS is in close relationship with the aortic valve, with its upper part usually in direct continuity with the attachments of both right and posterior aortic cusps 4
- The distance between the MPIS superior border and the attachment of the right aortic cusp is not greater than 5.89 mm, and the distance between the superior border of the MPIS and the attachment of the posterior aortic cusp is not greater than 5.63 mm 4
- The His bundle is located near the left ventricular outflow tract, which is close to the aortic root and aortic valve 6