Impedance monitoring during catheter ablation of atrial fibrillation.
Academic Article
Overview
abstract
BACKGROUND: Delivery of radiofrequency energy in proximity of a pulmonary vein can cause vein stenosis. A sudden decrease in impedance as the catheter is moved from the vein into the left atrium (LA) has been used to define the pulmonary vein-LA transition during ablation procedures. OBJECTIVES: The purpose of this study was to define the variables affecting impedance measurement. METHODS: In vitro analysis of impedance was performed in a saline bath using sheaths and a plastic stereolithographic model of the LA. Impedance was continuously monitored during a calibrated pullback from the pulmonary vein into the LA in 37 veins of 10 patients referred for catheter ablation. Location of the catheter was confirmed by the following imaging modalities: intracardiac echocardiography, contrast venography, electroanatomic mapping, and computed tomography/magnetic resonance imaging (offline) in all patients. RESULTS: Larger cross-sectional areas containing the catheter correlated with lower impedance in an exponential manner both with respect to sheath size (R(2) = 0.99) and in the stereolithographic model (R(2) = 0.91). In vivo, the impedance in the pulmonary veins decreased in an exponential manner as the catheter was pulled back into the LA. However, impedance at the vein orifice was not significantly higher than the LA. A defined cutoff value for defining the pulmonary vein-LA transition could not be identified. CONCLUSION: The primary determinant of impedance is the cross-sectional area of the space containing the catheter. Impedance monitoring alone does not guarantee a catheter tip position outside the pulmonary vein. Intraprocedural imaging confirmation should be considered to avoid radiofrequency application within pulmonary veins.
