705-1 Radio Frequency Lesion Depth vs. Width Maturation: Two Contrasting Parameters

Catheter to tissue contact, RF power level, and RF application time are factors that define the rate of lesion growth and final lesion size. In this investigation of the determinants of lesion width (W) and depth (D), we attempted to define optimal requirements to maximize lesion depth. In 5 dogs LV free wall epicardial lesions were generated with 10, 20, 30, 40, and 50 watts of RF power applied with a temperature-monitoring 4mm tip ablation electrode. The lesions were created with the catheter tip electrode contacting the tissue at various levels. The catheter tip was pressed 3mm (+3) and 1mm (+ 1) into the epicardium or placed lightly over the epicardium (0). The RF application time was varied from 10–120 sec. The heart and electrode were immersed in circulating blood at a constant temperature of 37°C. The width of the lesion matured within 10–20 seconds for the largest lesions [W = 9.3 ± 1.3mm at 50 watts and +3 contact,*W = 8 ± 0.7mm with +1 contact, and *#W = 6.3 ± 1mm with 0 contact (*p < 0.05 vs. +3 contact; #p < 0.05 vs. + 1 contact)]. The overall maximum lesion depth (9.2 ± 1.2mm) was measured with +3 contact and 20 watts of power applied for 100 sec. With +1 contact, the greatest lesion depth (8.7 ± 2mm) was the result of 40 sec of 30 watt RF power. At 0 contact, the maximum depth (8 ± 0.7mm) was obtained with 30 watts applied for 100 seconds. At 40 and 50 watts, 70% of the lesions were terminated by rapid impedance rise 10–30 sec after the intiation of RF application. At all contact and power levels, lesion depth was significantly smaller if the power application was terminated before 40 sec (D = 6.1 ± 1.3mm, p < 0,05 vs. 60 sec or greater).Conclusions(1) lesion width matured within the first 20 sec of power application for all power and contact levels. (2) Over 1.5 minutes of power application is required for deeper RF lesions to mature. (3) The use of power levels of 40 or 50 watts often results in an impedance rise before depth maturation. (4) Since contact level is not known prior to power application, the power level should be limited to 20–30 watts or less and applied for 1.5 minutes