Introduction:

Recently significant offsets between selected and delivered power were discovered in different RF generator models (EP Shuttle, Ampere, SmartAblate), depending on electrical impedance (EP radiofrequency generators - How accurate is their power delivery profile? DGK 2017). The aim of this ex vivo study was to assess the influence and relation of RF generator model, RF power and contact force on resulting ablation lesion sizes. Therefore ablation lesions created with a new dynamic generator (SmartAblate) were compared to lesions created with a conventional standard generator (EP Shuttle/”Stockert”).

Methods:

An experimental ex vivo model was designed to create ablation lesions with adjustable electrical impedance, contact force and power. It consisted of a saline-filled container including a thermostat, a circulating pump, an indifferent electrode, and a porcine heart (Fig. 1). The RF generators and a ThermoCool ST SF ablation catheter were used to create ablation lesions in the porcine cardiac tissue. The ablation catheters were stabilized in a steerable sheath that was mounted on a tripod. The electrical impedance of the experimental setup was adjusted by the ratio of saline and water; the temperature was held at 37° C. Contact force between the ablation electrode and cardiac tissue was monitored using the incorporated contact force sensor of the ThermoCool ST SF catheter.

 Fig. 1: Schematic ex vivo model including a RF generator, a compatible ablation catheter, a thermostat, a circulating pump, an indifferent electrode, a porcine heart, and connecting cables.

Overall n=120 ablation lesions were created with systematically varied impedance, power and contact force settings (100-200Ω, 20-30 Watt, 20-30 sec, 5-30g) using the EP Shuttle and SmartAblate generator. A digital precision caliper was used to measure the geometry of each ablation lesion (surface diameter, maximum depth, maximum diameter, depth at maximum diameter) and the ablation lesion volume was calculated.

Results:

The resulting ablation lesion volumes of different ablation settings are shown in Fig. 1. The lesion volumes when using the SmartAblate and EP Shuttle generator were significantly different (p<0.01), varied impedance values significantly influenced the ablation lesion volume when using the EP Shuttle generator (p<0.01).

Fig. 2: Resulting ablation lesions volumes of different ablation protocols.

Conclusion: