Histopathology of Monopolar Transcatheter Radiofrequency Ablation at the Mitral Valve Annulus

Abstract

Although monopolar radiofrequency (RF) catheter ablation is being used to interrupt left-sided accessory pathways in patients with tachyarrhythmia, little is known of the histologic effects from this method of treatment. RF ablation at the mitral valve (MV) annulus was performed in ten dogs to examine the histology of the lesion area. A custom 6 French ablation catheter with a 4 mm distal electrode was positioned beneath the MV adjacent to the annulus. Mean preablation atrial to ventricular electrogram ratio (A/V ratio) was 0.26 +/- 0.17. Thirty +/- 1 watts of RF power were applied for 53 +/- 13 seconds between the distal electrode and a large skin electrode. Nine dogs were sacrificed 6 weeks and one dog 2 days following ablation. Annular lesions were seen in eight of the ten dogs. Lesion volume was 136 +/- 41 mm3 and correlated with the A/V ratio (r2 = 0.74, P = 0.006). Lesions consisted of necrosis of the left ventricle with extension into the atrioventricular groove and left atrium. No injury to the coronary sinus or circumflex artery was observed. A small area of injury was noticed on the mitral leaflet in one dog. Monopolar RF ablation creates lesions at the MV annulus without injury to adjacent vascular structures.

Anterograde Slow Pathway Is Not the Same as Retrograde Slow Pathway Conducted in the Reverse Direction in Patients with Uncommon Atrioventricular Nodal Reentrant Tachycardia

“…The A/V ratio is a useful marker for investigating the relative location of the ablation catheter to the AV ring 2 , 4 , 13 . When the catheter is located on the mitral annulus and the A/V ratio is about 1.0, the catheter is suggested to be on the mitral ring 14 . When a bipolar catheter sits on the septal portion of the tricuspid ring, the A/V ratio is less than 0.3 because only thin nonconductive connective tissue separates right atrial from right ventricular tissue 15 .…”

Prospective assessment after pediatric cardiac ablation: Fate of intracardiac structure and function, as assessed by serial echocardiography

“…From the earliest days of RF ablation experiments in animals, the relative lack of direct observable thermal injury to the valve leaflets has been notable. 15,16 The biophysical properties of these tissues that provide relative protection during RF energy delivery are unknown, but one may speculate that leaflet tissue presents a relatively higher impedance to the passage of RF current as compared with the nearby myocardium, and so, resistive heating occurs in the myocardium. Furthermore, there may well be barriers to convective heat transmission from the nearby heated myocardium.…”