Introduction: Radiofrequency catheter ablation of the tricuspid valve-inferior vena cava (TV-IVC) isthmus for treatment of atrial flutter (AFL), may in some cases require a large number of energy applications and a long procedure and fluoroscopy time.
Aims of study: Therefore, we studied the safety and efficacy of a 4 cm long microwave antenna mounted on a steerable 9Fr catheter for linear ablation of the TV-IVC isthmus.
Methods: In 6 anesthetized dogs, multi-electrode catheters were positioned in the coronary sinus (decapolar), at the His bundle (quadripolar) and around the TV annulus (decapolar) for pacing and recording atrial activation sequences before and after ablation. The microwave antenna was then positioned across the TV-IVC isthmus from the TV annulus (identified by equal A and V potentials) to the inferior vena cava with slight traction on the catheter to ensure adequate endocardial contact. Microwave energy was then applied at a fixed power for 120 seconds during each ablation attempt. Ablation was repeated until bi-directional isthmus block was demonstrated during pacing from the coronary sinus ostium and low lateral right atrium, respectively.
Results: Linear microwave ablation of the TV-IVC isthmus was completed in all ten dogs using a total of 2.6 +/- 1.17 energy applications per dog. Power was applied in a range of 45-50 watts. There were no acute procedural complications. Bi-directional TV-IVC isthmus block was achieved in all ten dogs, as demonstrated by a strictly descending activation wavefront in the ipsilateral atrial wall, during pacing from the CSO and LLRA respectively. In addition, after ablation conduction time to the LLRA during pacing from the CSO increased from 52 +/- 16.62 before to 87 +/- 12.74 msec (p <.05), and to the CSO during pacing from the LLRA from 51 +/- 12.43 before to 79.50 +/- 9.85 msec (p <.05). Gross and histological examination of the TV-IVC isthmus after ablation revealed continuous transmural lesions, ranging from 3-5 mm in width, spanning the entire TV-IVC isthmus in all ten dogs.
Conclusions: (1) Microwave ablation of the TV-IVC isthmus was safe and effective in this study. (2) Ablation of the entire width and thickness of the TV-IVC isthmus can be rapidly achieved using a long microwave antenna in a fixed trans-isthmus position.