From the Guidelines
The mitral valve and atrioventricular (AV) node are anatomically related through their proximity in the heart, with the AV node positioned near the coronary sinus in the triangle of Koch, and the mitral valve located between the left atrium and left ventricle, with studies suggesting that damage to the atrioventricular nodal artery during mitral valve surgery may lead to atrioventricular block in up to 23.5% of patients 1.
Anatomical Relationships
The mitral valve consists of anterior and posterior leaflets that prevent backflow of blood during ventricular contraction, while the AV node is positioned in the interatrial septum near the coronary sinus, in the triangle of Koch. Key points about their relationship include:
- The AV node receives electrical impulses from the sinoatrial node and delays them before transmission to the ventricles, coordinating proper timing between atrial and ventricular contractions, including mitral valve closure.
- The mitral valve and AV node are functionally related through the cardiac conduction system.
- During mitral valve surgeries, care must be taken to avoid damage to the conduction system, as damage to the atrioventricular nodal artery may play a role in the development of atrioventricular block after mitral valve surgery, with the need for a pacemaker ranging from 1% to 9% 1.
Clinical Significance
Understanding the relationship between the mitral valve and AV node is essential for:
- Interpreting ECG changes in mitral valve disease
- Planning interventional procedures, such as mitral valve repair or replacement, where the risk of damaging the AV node or atrioventricular nodal artery must be considered, as suggested by a pathologic study examining 55 hearts from patients who had not undergone surgery, which found that 23% had an atrioventricular nodal artery that ran close to the mitral valve 1.
From the Research
Anatomical Relations of the Mitral Valve and the Atrioventricular (AV) Node
The mitral valve and the atrioventricular (AV) node have specific anatomical relations that are crucial for understanding the potential complications of heart valve surgeries. The key findings are:
- The AV node artery runs in close proximity to the annulus of the mitral valve in 23% of cases, as discovered in dry-dissected human hearts 2, 3.
- The left AV node artery is closely related to the mitral valve attachment, especially at the area of the left proximal part of the posterior leaflet 3.
- The upper pole of the compact AV node is located at the level of the mitral valve leaflet in 50% of cases, while the lower pole is located vertically above the tricuspid septal leaflet in 100% of cases 4.
- The right and left posterior extensions of the AV node span from the mitral valve leaflet to 2.9±1.3 mm above the tricuspid septal leaflet 4.
- A rectangular area (2.5 mm × 12 mm) in the Koch's triangle is devoid of AV nodal tissue and could be labeled as a safe area with no risk of conduction defects during valve surgeries 4.
Clinical Implications
The anatomical relations between the mitral valve and the AV node have significant clinical implications, including:
- The risk of intraoperative damage to the left AV node artery during manipulation of the mitral valve annulus fibrosus 3.
- The potential for postoperative atrioventricular block (AVB) after mitral valve implantation and ring annuloplasty, with an incidence ranging from 20% to 37% 3.
- The importance of understanding the dynamic anatomy of the mitral valve complex, as revealed by non-invasive imaging techniques, for a correct interpretation of the wide spectrum of patho-morphological mitral valve diseases 5.
- The need to minimize iatrogenic complications by knowledge of the precise three-dimensional relationships between the structures, such as the distance between the mitral annulus and the left circumflex artery 6.