Different patterns of the fall of impedance as the result of heating during ostial pulmonary vein ablation: Implications for power titration

Background: A variety of strategies have been proposed to avoid the risks of pulmonary vein ablation for atrial fibrillation. The fall of impedance during radio frequency catheter ablation can be used us a real time measure of tissue heating. The aim of this study was to analyze the impedance fall during ostial pulmonary vein ablution and to evaluate whether adjusting power to the fall of impedance may contribute to a reduction of the risk of complications. Methods: Analysis of biophysical parameters of ablation and determination of ostial diameters during follow-up were performed in 70 patients undergoing impedance-guided segmental ostial pulmonary vein ablation. Repeat radiographic angiography, local electrograms, and baseline impedance were the criteria to define the position of the 4-mm electrode tip at atria] sites or inside the proximal pulmonary veins. Results: Energy application inside the proximal pulmonary veins led to an increased impedance fall inside the first 5-10 mm of the pulmonary veins (1.1 +/- 0.5 Omega/W) as compared to ablation at atria] sites (0.7 +/- 0.3 WTV) (P < 0.01). The analysis of temperature and impedance fall during ostial ablation demonstrated an increased impedance fall with heating at sites inside the proximal pulmonary veins (1.5 +/- 0.6 Omega/degrees C) as compared to atrial sites (1.2 +/- 0.5 Omega/degrees C) (P < 0.001). The regression lines analyzing these correlations indicated that adjusting power to a maximum impedance fall of 20 Omega would limit heating at pulmonary venous sites to lower temperatures (average maximum temperature: 48 Omega than at atrial sites (average maximum temperature: 63 degrees C). The ablution strategy used for segmental ostial ablation in 70 patients, which involved power limitation to a maximum impedance fall of 20 Q, allowed isolation of 89% of targeted pulmonary veins with a low rate of impedance rises (0.3% of applications). No pulmonary vein stenoses > 30% were detected by follow-up computed tomography analysis. Conclusions: An increased impedance fall as the result of heating during ostial ablation was found inside the proximal pulmonary veins as compared to atria] sites. Adjusting power to the fall of impedance during segmental ostial pulmonary vein ablation contributes to the prevention of overheating inside the pulmonary veins and may lower the risk of coagulum formation and pulmonary vein stenosis.