Objective In recent years, radiofrequency catheter ablation of right-sided atrioventricular accessory pathway (AP) has improved significantly due to improved ablation catheter, using the long sheath support, application of 3D mapping system and saline-irrigated ablation catheter. However, catheter ablation of the right-sided free wall AP is very difficult in a few cases by using the conventional technique. Some studies reported that the reasons for the difficulty of ablation were the abnormal AP location between the right atrial appendage and right ventricle, or the insertion point of AP away from the tricuspid annulus or the existence of epicardial AP, but the final conclusion has not been reached. The purpose of this study was to investigate the electroanatomical structure, the cardiac electrophysiological characteristics and the ablation strategy of right-sided free wall AP refractory to conventional ablation technique.

Methods Study population consisted of 535 patients (332 males, aged 1 to 82 years) underwent cardiac electrophysiological study and radiofrequency catheter ablation of right-sided AP. All patients had the history of atrioventricular reentrant tachycardia (AVRT). The surface ECG present pre-excitation syndrome in 325 patients, accounting for 60.7% of right-sided APs. 9 patients had structural heart disease. 24 patients had 1–2 times of a failed catheter ablation or recurrence. Ablation of right-sided AP was performed by mapping the earliest pre-excitation ventricular activation site at the tricuspid annulus during sinus rhythm or atrial pacing, or by mapping the earliest atrial activation site during ventricular pacing or AVRT. If repeated ablation attempts failed to eliminate the AP conduction by the above conventional technique, further ablation was performed by mapping and ablating the earliest atrial activation at the tricuspid annulus or its atrial sides until isolation of the AP conduction.

Results Twenty-two patients had refractory right-sided free wall APs, accounting for 4.1% of all right-sided AP patients (22/535 patients), among them 6 cases had a history 1–2 times failed ablation procedures. Of the 22 patients, 3 patients (3.0%, 3/101 patients) had right-sided antero-lateral free wall APs, 19 patients (7.5%, 19/253 patients) had right-sided postero-lateral free wall APs. Nine patients had pre-excitation syndrome, and 13 patients had a concealed AP. Conventional ablation failed to eliminate the AP conduction in all the 22 patients, multiple times of ablation were tried point by point to the sites with earliest atrial activation during AP conduction at the tricuspid annulus or its atrial sides. During ablation, the VA intervals (measured from the onset of QRS wave in surface ECG to the atrial activation of coronary sinus catheter and His bundle catheter) gradually prolonged for 20 to 80 ms in all patients. In the 3 patients with right-sided antero-lateral free wall AP, 1 patient had a successful ablation, 2 patient failed and 1 of them was cured by cardiac surgery. In the 19 patients with right-sided postero-lateral free wall AP, 17 patients had successful ablation, and 2 patients failed. During a period of 1–6 years of follow-up, the 19 patients with successful ablation were free of recurrence.

Conclusions Although conventional ablsation technique could successfully eliminate most of right-sided APs, but a few of right-sided free wall APs (accounting for 4.1% of all the right-sided APs and 6.2% of all the right-sided free wall APs) were refractory or resistant to the conventional ablation technique. By using linear ablation along the tricuspid annulus and its atrial sides to isolate the AP conduction could abolish the APs in most patients with refractory right-sided free wall APs. However, because of a long procedure time, a high-level catheter ablation technique needed, and patient’s safety consideration, the indication of this technique should be strictly used and assessed.