Evaluation of subthreshold stimulation the predicting the site of successful radiofrequency ablation in supra-ventmcular tachycardia

ABSTRACT

This study is aimed to determine the incidence of terminating the supra-ventricular tachycardia [SVT, [AVNRT and AVRT]] by Subthreshold stimulation [STS] and to evaluate the ultrarapid STS in predicting the site of successful radiofrequency ablation in these arrhythmias. Thirty patients were selected during routine EPS; for this study; fifteen have had AVNRT and fifteen have had AVRT, [patients with other arrhythnhias were excluded]. All patients were well prepared for EPS and subjected to the following Pacing protocol in all cases pacing of the RV was followed to avoid early atrial stimulation that would potentially throw the patients into AF 1- Ventricular stimulation protocol to initiate orthodromic tachycardia and localization the site; and to detect the site of earliest retrograde atrial activation. 2- Atrial stimulation protocol to initiate antidromic wide QRS tachycardia and discover presence or absence of AH jump suggesting dual AVNodal pathway. Subthreshold stimulation [STS] method. Once patient developed AVNRT or AVRT we put ablation catheter near to expect site of ablation either slow pathway in case of AVNRT or accessory pathway in case of AVRT. We started pacing from ablation catheter aiming to terminate the re-entry circuit by STS and not to capture the whole myocardium. STS by threshold ranging between 2-5 mA and cycle length [CL] shorter than that of tachycardia by 50 msec., then decreasing CL every step by 50 msec., until reach CL 200 msec., for aduration of 3-5 sec. continuous pacing each step. If AVNRT or AVRT was terminated in certain site we started ablation in this site and if AVNRT lead to slow Junctional rhythm or AVRT terminated tachycardia with or without VA dissociation this would be considered. a positive result. If AVNRT or AVRT was not terminated in certain site we started ablation in this site and if slow functional rhythm in AVNRT or termination of AVRT with or without AV dissociation in AVRT this would be considered negative result. If AVNRT or AVRT did not terminated by STS as well as by ablation we tried STS and ablation in another site and so on. We achieved [53%] positive results in cases of AVRT and negative results in [47%] of cases; while in AVRT the positive results was [66%] of cases and the negative results was [34%] of cases. STS-guided mapping is a novel tool for the detection of target sites of slow pathway [SP] and accessory pathway [AP] ablation in patients with reproducible inducible and sustained AVNRT and AVRT. This technique helps to reduce the number of RFC pulses required for SF and AP ablation without an increase of fluoroscopy time or procedure duration