Application Study Of Termination Site Of Reentrant SVT By USTS During Mapping The Sites Of RFCA

Objectives: The present study sought to investigate the clinical application value of termination site of atrioventricular node reentrant tachycardia(AVNRT) and of atrioventricular reentrant tachycardia(AVRT) with a left lateral accessory pathway by ultrarapid subthreshold train stimulation(USTS) during mapping the target sites of radiofrequency catheter ablation(RFCA).Background: Previous studies have demonstrated the capability of an subthreshold electrical stimulus to give rise to an unpropagated alterations of electrotonic potentials in local myocardial tissue. Both inhibition and summation of subthreshold electrical impulses were observed, being mediated by electrotonic activity from local stimulated tissue. High-frequency, long-time subthreshold train stimulation more easily resulted in cardiac inhibition, and reentrant tachycadia was terminated by subthreshold stimulation(STS) through special mechanisms. Longer distance of subthreshold electrical impulses, lesser effect on membrane potential, that is very strong spatial limitation of inhibition by STS. Utilizing cardiac electrophysiologic properties of STS, STS might become a new idea and method for mapping and localize definitely target sites of radiofrequency catheter ablation(RFCA) for clinical reentranttachycadia.Methods: patients with AVNRT and patients with AVRT were prospectively included in the study, sustained tachycardia was reproducibly inducible, and much more clear diagnoses based on conventional methods of electrophysiologic examination in all patients in the course of procedure, patients with spontaneous termination of the tachycardia were excluded before the mapping. Mapping the target sites of ablation in patients with AVNRT: Ablation electrode tip was introduced and placed within middle-posterseptal region between lower rim of coronary sinus ostium and His bundle through a punctured femoral vein, and pacing threshold of located site was measured through SEC-2102 model programmed electrical stimulator. When locally endocardiac electrograms recorded at the posteroseptal to midseptal region were accepted as target sites for USTS if the characteristics were present: smaller atrial electrogram amplitude(A) and biger ventricular electrogram amplitude (V), fractionated and longer duration atrial electrogram, atrial electrogram amplitude less of ventricular electrogram amplitude(A/V rate<1.0). Subsequently, sustained AVNRT was induced by electrical stimulation at initially induced site, sustained AVNRT was terminated by USTS delivered through Ablation electrode. After atrial or ventricular capture or dislocation of the electrode catheter was excluded at local electrogram recordings, the termination sites were accepted as target sites for RFCA, positive predictive value(sensibitity) was observed. If sustained AVNRT was not terminated by USTS, endocardiac electrograms determined whether the mapping sites were eligible for ablation or not, if the sites were accepted as target sites for ablation, negative predictive value(specificity) was observed. Mapping the target sites of ablation in patients with AVRT: Ablation electrode tip was introduced and placed within the region around mitral valve though a punctured femoral artery,and pacing threshold of located site was measured. After mapping early ventricular activity(EVA) or early atrial activity(EAA), sustained AVRT was induced electrical stimulation at initially induced site, sustained AVRT was terminated by USTS delivered through Ablation electrode. The protocol performed of AVRT was similar to that of AVNRT. Parameters of USTS: pluse width, 0.5-1.0ms; frequency, 600-1000ppm; stimulation maintained time, 10 seconds; intensity, 20-80% threshold current. At the same time, observing and recording occurrent arrhythmia.Results: Mapping of slow pathway guided by USTS in 6 patients with AVNRT of slow-fast type. Sustained AVNRT was terminated by USTS in 3 among 6 patients, 3 termination sites were performed ablation, which were successful ablation sites, the sensitivity of AVNRT terminat...