Tissue-Specific Variability in Human Epicardial Impedance

Methods: Patients undergoing elective surgery for coronary artery or valve disease were enrolled. A reference patch was placed on the patients' back between the scapulae and connected to a standard RF generator (Stockert, GmBH, Germany). Impedance was measured by passing a 1 mu A, 50 kHz current from the catheter tip to the patch. After sternotomy but before initiation of cardiopulmonary bypass, an ablation catheter (Celsius, Biosense Webster, Diamond Bar, CA, USA) was placed onto the epicardial surface in ventricular regions visually identified as fat or myocardium. At each site, impedance was recorded from the generator. Results: A total of 37 (7 patients) points were sampled. Impedance was significantly higher in regions of fat versus normal muscle (697 vs. 301 ; P = 0.01). Moreover, normal sites from the LV had higher impedance than from the RV (381 vs. 271 ; P = 0.01). Conclusions: Human epicardial fat has higher tissue impedance than normal muscle. Using epicardial impedance and voltage mapping in conjunction may improve differentiation of arrhythmia substrate from epicardial fat and improve the efficacy of epicardial ablation. (J Cardiovasc Electrophysiol, Vol. 22, pp. 436-439).