Impedance monitoring during catheter ablation of atrial fibrillation Marmar Vaseghi, MD, David A. Cesario, MD, PhD, Miguel Valderrabano, MD, Noel G. Boyle, MD, PhD, Osman Ratib, MD, PhD, J. Paul Finn, MD, PhD, Isaac Wiener, MD, Kalyanam Shivkumar, MD, PhD From UCLA Cardiac Arrhythmia Center, Division of Cardiology, Department of Medicine, David Geffen School of Medicine at UCLA, Los Angeles, California. 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 echocardi- ography, contrast venography, electroanatomic mapping, and computed tomography/magnetic reso- nance 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 contain- ing 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. KEYWORDS Impedance; Pulmonary vein stenosis; Catheter ablation (Heart Rhythm 2005;2:914 –920) © 2005 Heart Rhythm Society. All rights reserved. Introduction Pulmonary vein (PV) stenosis is a well-known complication of catheter ablation of atrial fibrillation that occurs regard- less of the type of ablation (targeted focal “sites,” circum- ferential or segmental isolation at the venoatrial junction, or electrical isolation of PVs). 1–12 Furthermore, with the dra- matically increasing rise in atrial fibrillation ablations per- formed worldwide, the incidence of this complication likely will increase. 2 The rate of asymptomatic PV stenosis fol- lowing catheter ablation procedures has been reported to be as high as 16% to 24%. 13,14 The rate of symptomatic ste- nosis, usually caused by the involvement of more than one PV with 70% stenosis, has been reported in 1% to 10% of patients. 1–7,13–16 The site of stenosis typically is within 1 cm of the pulmonary ostia, although it can range between 0.4 and 3.5 cm. 1,14 Moreover, ablation in and around the PVs induces changes in morphology and mechanical function that extend beyond the ablation zone, and inadvertent ra- Dr. Shivkumar is supported by the Doris Duke Charitable Foundation, New York, and the American Heart Association. Dr. Vaseghi is supported by the American Heart Association. Dr. Cesario is supported by a Pfizer Fellowship Grant. Presented at the 2003 Annual Scientific Sessions of the American Heart Association. Address reprint requests and correspondence: Dr. Kalyanam Shivkumar, UCLA Cardiac Arrhythmia Center, Division of Cardiology, Department of Medicine, 47-123 CHS, David Geffen School of Medi- cine at UCLA, 10833 Le Conte Avenue, Los Angeles, California 90095-1679. E-mail address: kshivkumar@mednet.ucla.edu. (Received April 13, 2005; accepted June 11, 2005.) 1547-5271/$ -see front matter © 2005 Heart Rhythm Society. All rights reserved. doi:10.1016/j.hrthm.2005.06.007