Indication of the radiofrequency induced lesion size by pre-ablation measurements

During radiofrequency ablation of arrhythmias tissue heating and hence lesion size depend on electrode–tissue contact and cooling of the electrode tip caused by cavitary blood flow. These factors are unique and unknown for each catheter placement in the beating heart. A tool for assessing these factors prior to ablation may indicate the lesion size which will be obtained for any given catheter position.

Radiofrequency ablation was performed in vitro on strips of left ventricular porcine myocardium during two different levels of convective cooling (0 or 0.1 m/s), two different contact pressures (10 or 30 g) and parallel or perpendicular electrode–tissue orientation using 7F 4 mm tip catheters. Prior to ablation the impedance rise (ΔIMP) caused by the obtained contact and the temperature rise with a 0.6 W 5 s test pulse (ΔT) were measured. Subsequently, during unchanged conditions, radiofrequency ablation was performed as either temperature-controlled, power-controlled or irrigated tip ablation and lesion size was determined.

ΔIMP increased significantly (P < 0.05) by improved contact, whereas it was not affected by convective cooling. ΔT was significantly increased by increasing contact pressure (P < 0.05) and significantly decreased by increased cooling (P < 0.001). ΔT was not systematically affected by electrode orientation. The product of ΔT and ΔIMP showed a significant correlation between the obtained lesion size and power output for temperature-controlled and between lesion size and tip temperature for power-controlled ablation (P < 0.001).

Pre-ablation measurement of ΔIMP and ΔT can indicate the lesion size resulting after ablation in temperature-controlled, power-controlled and irrigated ablation in vitro, since ΔT reflects cavitary cooling and to a smaller extent electrode–tissue contact, and ΔIMP reflects only electrode–tissue contact.