Strickberger et al. August 1994 American Heart Journal 11. 12. 13. 14. 15. Haissaguerre M, Gaita F, Fischer B, Commenges D, Montser- rat P, d’Ivernois C, Lemetayer P, Warin JF. Elimination of atrioventricular node reentrant tachycardia using discrete slow potentials to guide application of radiofrequency energy. Circulation 1992;85:2162-75. Wu D, Yeh SJ, Wang CC, Wen MS, Chang HJ, Lin FC. Na- ture of dual atrioventricular node pathways and the tachycar- dia circuit as defined by radiofrequency ablation technique. J Am Co11 Cardiol 1992;20%84-95. Wu D, Yeh SJ, Wang CC, Wen MS, Lin FC. A simple technique for selective radiofrequency ablation of the slow pathway in atrioventricular node reentrant tachycardia. J Am Co11 Cardiol 1993;21:1612-21. Kay GN, Chong F, Epstein AE, Dailey SM, Plumb VJ. Radiofrequency ablation for treatment of primary atria1 tachycardia. J Am Co11 Cardiol 1993;21:901-9. Tracy CM, Swartz JF, Fletcher RD, Hoops HG, Solomon AJ, Karasik PE, Mukherjee D. Radiofrequency catheter ablation of ectopic atria1 tachycardia using paced activation sequence mapping. J Am Co11 Cardiol 1993;21:910-7. 16. 17. 18. 19. 20. Wen MS, Yeh SJ, Wang CC, Lin FC, Wu D. Radiofrequency ablation therapy in three patients with paroxysmal atria1 tachy- cardia. PACE 1993;16:2146-56. Chen SA, Chiang CE, Yang CJ, Cheng CC, Wu TJ, Wang SP, Chiang BN, Chang MS. Radiofrequency catheter ablation of sustained intra-atria1 reentrant tachycardia in adult patients: identification of electrophysiological characteristics and en- docardial mapping techniques. Circulation 1993;88:578-87. Klein LS, Shih HT, Hackett FK, Zipes DP, Miles WM. Radiofrequency catheter ablation of ventricular tachycardia in patients without structural heart disease. Circulation 1992;85:1666-74. Calkins H, Kalbfleisch SJ, El-Atassi R, Langberg JJ, Morady F. Relation between efficacy of radiofrequency catheter abla- tion and site of origin of idiopathic ventricular tachycardia. Am J Cardiol 1993;71:827-33.‘ Mitrani RD, Klein LS, Hackett K, Zipes DP, Miles WM. Ra- diofrequency ablation for atrioventricular node reentrant tachycardia: comparison between fast (anterior) and slow (posterior) pathway ablation. J Am Co11 Cardiol 1993;21:432- 41. Relation between impedance and endocardial contact during radiofrequency catheter ablation Lesion size during radiofrequency catheter ablation in patients with paroxysmal supraventricular tachycardia (PSVT) is thought to be related to multiple factors, including contact pressure at the catheter-endocardial interface. Therefore a predictor of contact pressure at a potential target site for ablation might be useful. In this study 25 patients underwent duplicate 2 W applications of radiofrequency energy with the catheter in poor and firm contact with the right ventricular endocardium after successful ablation treatment for PSVT. The mean age of the patients was 44 + 15 years. Fifteen patients underwent slow pathway ablation for atrioventricular nodal reentrant tachycardia, and 10 patients underwent ablation for an accessory pathway. The mean impedance for low-energy applications in firm contact (139 k 24 ohms) was 22% f 13% greater (p 0.0001) than in poor contact with the right ventricle (113 k 16 ohms). The maximum impedance was 27% greater when the catheter was in firm (147 + 26 ohms) rather than poor contact (116 k 16 ohms), with the endocardium (p 0.0001). These results suggest that higher impedance measurements may be obtained with low-energy applications of 2 W when the ablation catheter is in firm contact with the endocardium. (AM HEART J 1994;126:226-9.) S. Adam Strickberger, MD, Vicken R. Vorperian, MD, K. Ching Man, DO, Brian D. Williamson, MD, Steven J. Kalbfleisch, MD, Carol Hasse, RN, MSN, Fred Morady, MD, and Jonathan J. Langberg, MD Ann Arbor, Mich. From the Division of Cardiology, Department of Internal Medicine, Catheter ablation of accessory pathways using ra- University of Michigan Medical Center. diofrequency energy is the therapy of choice for par- Received for publication Oct. 15, 1993; accepted Dec. 1, 1993. oxysmal supraventricular tachycardia (PSVT).lm4 Reprint requests: S. Adam Strickberger, MD, University of Michigan Med- ical Center, 1500 East Medical Center Dr. Ann Arbor, MI 48109-0022. Copyright @ 1994 by Mosby-Year Book, Inc. 0002.8703/94/$3.00 + 0 4/l/56692 The efficacy rates are high, but multiple applications are required and the procedure can be protracted. Experiments in animals have demonstrated a direct 226