Radiofrequency catheter ablation is now the preferred treatment for patients with symptomatic Wolff-Parkinson-White (WPW) syndrome or recurrent symptomatic orthodromic reciprocating tachycardia . Successful ablation depends on the accurate localization of the accessory pathway (AP). Posteroseptal (inferior paraseptal) APs represent the second most common atrioventricular (AV) connection site after left free wall AP and often pose a diagnostic challenge. This is due to complex anatomy at the crux of the four cardiac chambers, where a small area may encompass APs that may be approached from the right or left endocardium, or require an epicardial ablation inside the coronary sinus (CS).
APs located in the posteroseptal area can take a variety of courses. Four different course types may be distinguished.
1. Endocardially between the inferior paraseptal right atrium and the right ventricle. This area includes the inferior part of the Koch's triangle and the area surrounding the CS ostium.
2. Endocardially between the inferior paraseptal left atrium and the left ventricle.
3. Coursing between the inferior paraseptal right atrium and the left ventricle in the pyramidal space, given that the right atrium lies directly on the posterior superior process of the left ventricle. This anatomical conformation results from the fact that the interatrial septum lies leftward to the interventricular septum and the tricuspid annulus is displaced 5-10 mm apically with respect to the mitral annulus. The right atrial endocardial aspect overlying the posterior superior process of the left ventricle lies between the most posterior aspect of the right fibrous trigone and the CS ostium, medial to the tricuspid valve. Because of its close proximity, ablation of these APs may be possible from the proximal CS.
4. Epicardially, connecting the musculature overlying the CS to the ventricle. These connections are related to sleeve-like extensions of the CS musculature that cover the proximal portion of the middle cardiac vein or posterior coronary veins. Most of these APs are ablated with a coronary venous These APs are referred to as 'epicardial CS' APs.
The procedural risks of inferior paraseptal AP ablation differ depending on whether a left-sided approach or a CS ablation is required .
Anteroseptal Aps are rare but associated with lower success rates and higher incidence of atrioventricular(AV) block. Anteroseptal AP can be ablated from right side , however Some including true para-Hisian APs can be safely and effectively ablated from the aortic cusps. Compared with the ablation at the right anteroseptal area, RF delivered at the aortic cusps has a higher immediate success, lower complication rate, and good long-term outcome. The aortic cusps should always be considered as the initial target for ablation of para-Hisian Aps . Data regarding the electro- cardiographic and electrophysiological characteristics as well as the safety and efficacy of catheter ablation of anteroseptal APs through the aortic cusps are limited Considering these differences, an accurate anticipation of location of septal AP is critical to inform the discussion and consent process with the patient and to guide the mapping strategy.
