Accessory pathway recording and ablation

Beginning in the mid-1970s, surgical ablation of accessory atrioventricular (AV) pathways (APs) was performed at a limited number of centers. The potential to target APs by catheter ablation became apparent in 1982, when Scheinman and coworkers introduced catheter ablation of the AV junction using high-energy direct current (DC) shocks from a defibrillator to produce AV block as palliative therapy for drug-resistant supraventricular tachyarrhythmias. Early attempts at DC shock ablation of APs were associated with some success, 1 Warin J.F. Haissaguerre M. Lemetayer P. et al. Catheter ablation of accessory pathways with a direct approach. Results in 35 patients. Circulation. 1988; 78: 800-815 Crossref PubMed Scopus (103) Google Scholar but the large area of barotrauma limited focused ablation and was associated with risk of cardiac perforation, AV block, and coronary artery injury. Radiofrequency (RF) current, delivered from conventional electrosurgical generators, was explored as a new energy source for ablation. The high-frequency alternating current (500 kHz) prevents nerve and muscle stimulation, and the use of rounded electrodes and lower power than utilized for electrosurgery produces heat for tissue necrosis while limiting coagulation. Initial testing using conventional 6F catheters with 2-mm-tip electrodes required limiting RF power to 4–6 W to prevent an immediate impedance rise due to excessive surface heating and tissue desiccation. The resulting lesions were too small and shallow for significant efficacy. Wittkampf introduced the concept of saline irrigation to cool the tissue interface and prevent impedance rise, allowing a significant increase in RF power and lesion size. Webster, who initially was unable to include both a lumen for saline irrigation and a central pullwire for deflecting the catheter (steerability), created a large tip electrode (7F, 4 mm, without irrigation) in 1988 to allow the surrounding blood flow to cool the electrode. The large tip electrode provided effective RF lesions. 2 Jackman W.M. Wang X. Friday K.J. et al. Catheter ablation of atrioventricular junction using radiofrequency current in 17 patients: comparison of standard and large-tip catheter electrodes. Circulation. 1991; 83: 1562-1576 Crossref PubMed Scopus (169) Google Scholar Five years later he created the irrigated electrode catheter, which provided improved RF power control and allowed higher power delivery. The irrigated electrode produced larger, more effective lesions with reduced thrombus formation and charring. 3 Nakagawa H. Yamanashi W.S. Pitha J.V. et al. Comparison of in vivo tissue temperature profile and lesion geometry for radiofrequency ablation with a saline-irrigated electrode versus temperature control in a canine thigh muscle preparation. Circulation. 1995; 91: 2264-2273 Crossref PubMed Scopus (511) Google Scholar