The LETR‐Principle: A Novel Method to Assess Electrode‐Tissue Contact in Radiofrequency Ablation

Minimal Power RF Application. Introduction: Stable electrode‐tissue contact is crucial for successful radiofrequency ablation of cardiac tachyarrhythmias. In this in vitro study, a custom‐made radiofrequency generator was used to evaluate the correlation between tip temperature response to a minimal radiofrequency power delivery (Low Energy Temperature Response: LETR‐Principle) and electrode‐tissue contact as well as lesion size. Methods and Results : A battery‐powered radiofrequency generator (LETR‐Box, 500 kHz, 0.1 to 0.3 W) could measure the temperature increase at the tip electrode with 0.01°C accuracy. The device was tested in vitro using isolated porcine ventricular tissue. For various electrode‐tissue settings (i.e., 0 to 0.89 N contact force), the temperature increase (δT) due to 0.1‐W power delivery for 10 seconds was recorded. Subsequently, for the same electrode‐tissue contact, a temperature‐controlled radiofrequency ablation was performed (70°C target temperature. 50‐W maximum output, 30 sec). Thereafter, the lesion size was measured histologically. To prove the safety of the applied LETR‐Principle, the tissue was inspected microscopically after continuous radiofrequency power delivery of 0.3 W for 1 hour with high contact pressure (1.33 N). The delivery of 0.1‐W radiofrequency power resulted in an average δT of 0.18° plusmn; 0.13°C. During temperature‐controlled radiofrequency ablation, the tip temperature was 59° 8.5°C, resulting in a lesion depth of 4.8 ± 0.6 mm. The correlation coefficient between δT and contact force was 0.97 and 0.81. respectively, for lesion depth. No lesion was microscopically visible after power delivery of 0.3 W for 1 hour with 1.33 N contact pressure. Conclusion : The LETR‐Principle safely indicates electrode‐tissue contact and lesion depth under in vitro conditions and can be useful for catheter positioning during radiofrequency ablation procedures.