Intramural radiofrequency ablation: effects of electrode temperature and length

The aim of this study was to evaluate intramural temperature-controlled radiofrequency ablation by determining the intramural temperature profile during ablation and by correlating lesion geometry with intramural electrode size and temperature. Intramural ablation might be useful to create deeper lesions for ventricular tachycardia secondary to underlying heart disease. Intramural radiofrequency ablation was performed in 17 greyhounds at thoracotomy, from an epicardial approach, using a 21-gauge needle electrode. Sixty-eight lesions were created in 11 dogs at electrode temperatures of 70 degrees C, 80 degrees C, 90 degrees C, and 100 degrees C for 60 seconds. Intramural thermocouples at 1-, 2-, 3-, 4-, and 5-mm distances were used to identify simultaneous intramural temperature profile. An epicardial approach was used to ensure accurate positioning of the ablating and temperature monitoring needles within the myocardium with fixed interneedle distances. Ninety-nine radiofrequency ablations were performed in six greyhounds using three different intramural electrode lengths (1 mm, 2.5 mm, and 5.5 mm). Lesions were created at 70 degrees C, 80 degrees C, and 90 degrees C for 60 seconds. All lesions were measured after staining with Gomori Trichrome. Lesion dimensions increased in a highly predictable manner with increasing electrode temperature or length. There was no popping or charring, even with target electrode temperature of 100 degrees C. There was significant correlation between intramural temperature 4 mm from the ablating electrode and lesion width (P < 0.001, R2= 0.45) and depth (P = 0.02, R2= 0.08). Feedback control of electrode temperature enables reliable intramural radiofrequency ablation without impedance rise even with target electrode temperature of 100 degrees C. Increasing the length of the intramural ablating electrode to > or = 5.5 mm and increasing temperatures to 90 degrees C-100 degrees C creates the largest lesions.