Radiofrequency Catheter Ablation of AVNRT

Description: https://johnsonfrancis.org/profession...
Discussion on radiofrequency catheter ablation of AVNRT.
Atrioventricular nodal reentrant tachycardia occurs in patients with dual AV nodal physiology. The fast pathway is anteriorly situated along septal portion of tricuspid annulus. Slow pathway is posteriorly situated close to the coronary sinus ostium.
Fast pathway ablation for AVNRT is by the anterior approach and has a 90% success rate. But AV block occurs in about 7%. The recurrence rate for fast pathway ablation is about 9%. Fast pathway ablation is seldom being practised now.
Slow pathway ablation is done by the posterior approach by taking the ablation catheter away from the His bundle catheter towards the region of the coronary sinus catheter. Accelerated junctional rhythm occurring during the delivery of radiofrequency energy is a marker for successful ablation of slow pathway.
The success rate of slow pathway ablation is 95-97%. AV block occurs in less than 0.5-1% cases of slow pathway ablation. The recurrence rate of slow pathway ablation is about 3%.
Posterior approach is preferred due to the higher efficacy, lower recurrence and AV block and higher chance of having of normal PR interval after ablation.
Electrophysiology catheters are shown in left anterior oblique view. The surface ECG electrodes are marked with yellow arrows. The decapolar catheter is situated in the coronary sinus and has been introduced from above using a jugular vein puncture.
The electrodes are numbered from 1 – 10 in a distal to proximal fashion so that the distal pair is 1-2 and the proximal pair is 9-10. The distal electrodes record the potential from the left atrium. One quadripolar catheter is positioned in the region of the bundle of His and another in the right ventricle.
All electrode pairs are connected to a junction box and through it to the EP recorder. Recordings from all electrode pairs are displayed on the EP recorder. Right ventricular catheter is also used for the pacing protocols while inducing tachycardia.
His bundle electrode pairs are named His proximal and His distal. The pattern of activation during sinus rhythm is studied initially to identify the sequence of activation. Changes in the sequence with various pacing protocols are assessed.
The ablation catheter is thicker and tip electrode is bigger with more surface area for the delivery of the radiofrequency energy during radiofrequency catheter ablation.
LAO view is foreshortened while RAO view can pick up supero-inferior catheter tip movements better during slow pathway ablation. Slow pathway ablation is done near the superior lip of the coronary sinus.
EP tracing in sinus rhythm while planning radiofrequency catheter ablation for AVNRT in sinus rhythm. Upper three tracing are surface electrocardiograms – leads I, II and V1 (white).
Next two tracing are from the His bundle catheter – His distal and proximal. The large broad deflections in this tracing is the V (ventricular electrogram) while the triphasic signal prior to it is the His potential (H).
The deflection before that is the atrial electrogram (A). Five pairs of electrodes in coronary sinus are numbered from distal to proximal so that CS 9 – 10 is the proximal pair and CS 1 – 2 is the distal pair, with the other pairs in between. All the tracings from the coronary sinus electrodes are in violet colour.
The earliest atrial activity is in the surface lead V1. The atrial activity in the His electrode comes after that, followed by the proximal coronary sinus electrodes. Distal coronary sinus electrodes pick up the atrial activity later, reflecting later activation of the left atrium.
The distal coronary sinus electrodes also show the ventricular activity, which is more delayed than the ventricular activity picked by the right ventricular electrodes. The mapping electrode (ablation catheter) picks up atrial and ventricular activities and a tiny His potential.
The distal mapping electrode picks up a fractionated atrial electrogram, a tiny His potential and a relatively smaller ventricular electrogram.
This type of electrogram is obtained while mapping the potential site for slow pathway ablation, which is between the His bundle catheter and the coronary sinus catheter, in the posterior approach for AVNRT ablation.
Area of interest for AVNRT ablation: Triangle of Koch bounded by Coronary sinus ostium, septal tricuspid leaflet and Tendon of Todaro; His Bundle is at the apex of the triangle.
Tendon of Todaro runs from the central fibrous body to the Eustachian ridge. Macroscopically, tendon of Todaro is visible only in the fetal and infant heart as a white structure. It involutes later and is visible only microscopically in the adult heart.
If the Koch’s triangle is small as in children, there is a higher risk of complete heart block. In elderly the CS os is higher and the triangle becomes smaller and there is a higher chance of CHB.