Low-energy bipolar radiofrequency ablation using an inserted needle with a local temperature sensor: comparison of series and parallel electrical circuit connections

Background

Ventricular arrhythmias (VA) originating deep within the thick myocardium are difficult to treat using conventional catheter ablation.

Purpose

An experimental study (approved by our institution) was performed to clarify whether low-energy bipolar (BIP) radiofrequency (RF) ablation using an intramural 18-gauge plastic needle(equipped with a small electrode tip and temperature sensor)－connected either in series or in parallel－could create an intramural lesion with a minimal risk of steam pop.

Methods

BIP ablation with series connection (A: 5W, 60-seconds, n=13) was performed between an irrigation catheter placed on the endocardial surface and a plastic needle inserted in mid-myocardium, in the segments of coronary perfusing porcine hearts. In BIP ablation with parallel connection, two ablation catheters were placed on opposite endocardial and epicardial surfaces of each myocardium. A plastic needle was inserted in the myocardium. The cable ends of both the epicardial ablation catheter and the plastic needle were connected together, and these were plugged into the cutaneous electrode connector, whereas cable-end of the endocardial catheter was plugged into the catheter connector of the generator. BIP ablation (B: 10W, 60-seconds, n=13, C: 10W, 90-seconds, n=13) was delivered simultaneously between the two ablation catheters and between the plastic needle and the endocardial ablation catheter.

Results

Ablation: BIP ablation was successfully completed in all in B and C, and steam-pop occurred in 5/13 in A. Initial impedance, total impedance decline (TID) and %TID were greater in A rather than B and C.

Temperature: Maximum temperatures at the endocardial ablation catheter were not different among the three procedures, but the temperature monitoring through a needle sensor were higher in A as compared to in B and C.

Lesions: BIP ablation created an isolated spherical myocardial lesion, surrounding the inserted electrode tip. Vertical and horizontal diameters of the lesions in the transmural myocardial section were larger in A followed by C and B. There were no visual RF lesions at the ablation catheter contacting surface myocardium.

Discussions

During ablation, current concentration around the small intramyocardial needle electrode increased local temperature and created an isolated myocardial lesion. Low-energy BIP ablation with a parallel connection was performed safely, and created reasonably large lesions as the application time became longer. However, BIP ablation with series connection had a narrow safety margin. Steam-pop may be preventable under monitoring via a local temperature sensor.

Conclusions

Low energy BIP ablation using a parallel connected inserted needle with a local temperature sensor, may contribute to the improvement of VA ablation, although further studies and technological adjustments are required before clinical use.Figure