Atrioventricular nodal reentrant tachycardia (AVNRT) is one of the more common arrhythmias ablated in the U.S. There is an estimated 2-6% major and minor complication rate during electrophysiology (EP) studies with ablation. [1-3] The average age of AVNRT patients in a prior analysis of my cases  was 53+/-21 years. These patients are often young with no major comorbidities and the risk of damaging the compact AV node and causing complete heart block is low but always present.
Radial intracardiac echo (UltraICE™, Boston Scientific, Natick, MA, USA) can be used to anatomically guide slow pathway modification and ensure stable endocardial-catheter contact. The example below is a patient with AVNRT (and persistent left superior vena cava) that could not be ablated via the traditional fluoroscopy and electrogram (EGM) guided technique despite “good” EGM’s and multiple lesions. The ICE video shown below depicts the initial catheter position encountered when ICE catheter first placed in right atrium using steerable sheath (St. Jude Medical, Agilis). You can see the ablation catheter adjacent to the ICE catheter and overlying the tricuspid valve though not in contact with the anatomic location of the slow AV nodal pathway.
We then positioned the ablation catheter at the anatomic location of the the slow AV nodal pathway; near the anterior aspect of the coronary sinus (CS) os at the septal insertion of the tricuspid valve leaflet. You can see the ablation catheter positioned right on this area and single RFA resulted in long run of junctional beats and successful ablation.
I use adjunctive ICE-guidance for most AVNRT ablations; though it adds some time and complexity, I feel it maximizes patient safety and successful outcomes. There is a great summary article by Fisher et al  and I have shown one of their figures below to better show the anatomy of the AV node and coronary sinus.
1 Chen S-A, Chiang C-E, Tai C-T, et al. ‘‘Complications of diagnostic electrophysiologic studies and radiofrequency catheter ablation in patients with tachyarrhythmias: An eight-year survey of 3,966 consecutive procedures in a tertiary referral center’’. Am J Cardiol 1996; 77:41–46. 12.
2 ZadoES,CallansDJ,GottliebCD,etal.Efficacyandsafetyof catheter ablation in octogenarians. JACC 2000; 35:458–462. 13.
3 O’Hara GE, Philippon F, Champagne J, et al. Catheter ablation for cardiac arrhythmias: A 14-year experience with 5330 consecutive patients at the Quebec Heart Institute, Laval Hospital. Can J Cardiol 2007; 23(Suppl B):67B–70B.
4 Williams JL, Valencia V, Lugg D, Gray R, Hollis D, Toth JW, Benson R, DeFrancesco-Loukas MA, Stevenson R, Teiken PJ, “High Frequency Jet Ventilation During Ablation of Supraventricular and Ventricular Arrhythmias: Efficacy, Patient Tolerance and Safety,” The Journal of Innovations in Cardiac Rhythm Management, 2 (2011), 1–7.
5 Fisher WG, Pelini MA, Bacon ME, “Adjunctive Intracardiac Echocardiography to Guide Slow Pathway Ablation in Human Atrioventricular Nodal Reentrant Tachycardia,” Circulation, V. 96 (1997), pp. 3021-3029.