Radial intracardiac echocardiography adds significant anatomic correlation during invasive EP studies. In particular, coronary sinus (CS) anatomy can be evaluated during CS access or ablation of the slow AV nodal pathway during AVNRT ablations. A steerable sheath (Agilis, St. Jude Medical) flushing with saline holds a 9MHz radial ICE catheter (UltraICE, Boston Scientific Corporation) and is positioned along the inferoseptal aspect of the tricuspid annulus.
The left image shows the posterior aspect of the CS os and you can often visualize the right coronary artery (RCA) in this view. One can see a thickened roof of CS (or often a prominent Eustachian ridge). As the steerable sheath holding the ICE probe is advanced toward the right ventricle (RV), the main CS is brought into view as seen in the middle image. As you move more ventricular, the septal insertion of the tricuspid valve leaflet is brought into view. Finally, the right image depicts the radial ICE view when the anterior aspect of the CS os is brought into view as the probe is advanced even closer to the RV. This is where the traditional position of the slow AVN pathway is found – the slow AV node pathway is generally located at the anterior edge of the CS os near the septal insertion of the tricuspid leaflet.
A nice anatomic study from Choure et al (“In Vivo Analysis of the Anatomical Relationship of Coronary Sinus to Mitral Annulus and Left Circumflex Coronary Artery Using Cardiac Multidetector Computed Tomography: Implications for Percutaneous Coronary Sinus Mitral Annuloplasty,” JACC, Vol. 48, No. 10, 2006) shows some detailed CT imaging of the relation between the coronary arteries and coronary sinus. The following image (taken from Choure et al) gives a nice visualization of the CS os and its relation to the RCA. One can see the circumflex crossing the mid-distal CS. They found the circumflex artery crossed the CS at a variable distance from the CS os (ranging 37 to 123 mm).
For more information about the use of radial ICE during EP studies:
Radial Intracardiac Echo Guided Ablation of AVNRT
Radial Intracardiac Echocardiography Guidance in the Electrophysiology Lab
Radial Intracardiac Echo (ICE) Guided Atrial Fibrillation Ablation