The annular fat stripe as a fluoroscopic guide to anatomic sites during diagnostic and interventional...

Few radiographic landmarks are visible during electrophysiology procedures to aid in catheter positioning other than the catheters themselves. In the 35 degrees -45 degrees RAO projection, a linear radio-opacity corresponding to the rings of fat surrounding both annuli can be easily identified. This "fat stripe" can serve as a useful landmark for several important anatomic sites. Intracardiac catheters positioned left of (posterior) the fat stripe lie within an atrial cavity while those positioned to the right (anterior) lie within a ventricular cavity. The superior third of the stripe corresponds to the region of the right and left atrial appendages while the inferior end identifies the site of the coronary sinus os. The middle third serves as a reference for the fast AV nodal pathway and compact AV node. The region corresponding to the slow AV nodal pathway superimposes on the lower third of the fat stripe. Electrophysiological recordings from catheters positioned along the fat stripe always exhibit both an atrial and ventricular component consistent with an annular recording, whether the catheter is septal or free wall in its location. Coronary sinus os engagement and catheterization can be simplified by using the fat stripe as an anatomic guide. In addition to facilitating catheter positioning for evaluating normal AV conduction, the fat stripe can serve as an excellent guide for targeting the majority of structures intended for ablation because of their annular location. These include the compact AV node, the slow AV nodal pathway, the subeustachian isthmus and any accessory pathway. Good ablation catheter tip contact with annular structures is confirmed by observing its movement in unison with the fat stripe.