1EP Bayern, Elektrophysiologie Mallersdorf-Pfaffenberg Mallersdorf-Pfaffenberg, Deutschland; 2EP Bayern, Zentrum für Herzrhythmusstörungen Augsburg Augsburg, Deutschland
Introduction
Radiofrequency (RF) current is the classic ablation technology in the EP lab. By now it is mainly the combination of RF power, duration and contact force that is known to determine RF lesion size. The aim of this ex vivo study was to analyze a by now underestimated factor - the level of electric contact between the RF electrode and cardiac tissue (low vs. full) - on RF lesion formation.
Methods
N=120 RF ablations were performed in an ex vivo model of porcine cardiac preparations. The model was adjusted to provide standardized and comparable conditions (temperature, impedance, convective cooling) during all RF ablations using a thermostat, a heating element and a circulation pump. The Rhythmia mapping system and the Stable Point local impedance measuring ablation catheter were used to create RF lesions at systematically varied levels of RF power (30W, 50W), duration (30sec, 60sec) and contact force (5g, 20g). All settings were applied in a first scenario of low electric contact (Figure A) between the RF electrode and cardiac tissue, in which only the distal part of the electrode was in contact with tissue and in a second scenario of high electric contact (Figure B) in which the whole electrode was embedded in surrounding myocardium. Created lesions were then dissected to measure their depth and diameter using a digital precision caliper for statistical analysis.
Results
Among all evaluated parameters, the level of electric contact (low vs. full) had a significantly higher influence on resulting lesion size when compared to selected power (30W vs. 50W), duration (30sec vs. 60sec) or contact force (5g vs. 20g), p<0.01. Lesions at high electric contact, P=30W, duration=30sec and contact force=5g had significantly larger diameters (9.1±1.1mm) and depths (14.2±1.3mm) when compared to all lesions at low electric contact but a power of 50W (p<0.01). Low and high levels of electric contact and resulting lesion sizes for same parameters of power (30W), duration (30sec) and contact force (5g) are depicted in the Figure. Local impedance drops and local baseline impedance was significantly larger in all high electric contact RF ablation scenarios and showed a high correlation (p<0.01).
Conclusions
Electric current effecting RF lesion formation in cardiac tissue is rather determined by the level of electric contact between the RF electrode and cardiac tissue than by selected RF power alone. Lesions at low power but high electric contact are significantly larger than lesions at high power but low electric contact to the tissue. This finding should be considered in clinical RF application and may be the main reason for insufficient lesion creation but also adverse effects such as steam pops. Local impedance seems to be an important parameter to monitor electric contact.