Alternation in the fusion complex during constant pacing of sustained ventricular tachycardia

Morphological variation of nonreentrant idiopathic ventricular tachycardia originating from the right ventricular outflow tract and effect of radiofrequency lesion

RF catheter ablation was performed in 16 patients with nonreentrant idiopathic VT originating from the RVOT. All documented VT was monomorphic, but subtle morphological variation in the VT-QRS complex was observed in 10 (63%) of 16 patients. Through endocardial mapping, VT origin was determined within a narrow site (< 0.5 x 0.5 cm) in 4 of the 10 patients with the morphological variation. In the other 6 of 10 patients, the origin extended to an area of > 0.5 x 0.5 cm. In VT with morphological variation, the local electrogram at the site of VT origin also showed variation in morphology and activation sequence. For VT of narrow origin, RF application to the site eliminated the VT. However, in VT from a wide arrhythmogenic area, RF current had to be delivered to 3-7 distinct sites to cover the possible origin, and specific QRS configuration of VT and/or PVC was ablated at each of the earliest activation site. All but one VT were successfully ablated by RF current. Subtle morphological variation was frequent in this type of VT, and about half were associated with a wide arrhythmogenic area. Precise mapping and analysis of the efficacy of each RF application might be helpful to better understand the relationship between subtle changes of VT-QRS morphology and their origins.

Alternation of QRS morphology and effect of radiofrequency ablation in idiopathic ventricular tachycardia

We performed electrophysiological studies in 13 patients with idiopathic VT and attempted radiofrequency (RF) catheter ablation in 4 of them.

RESULTS

VT was induced by programmed stimulation in all patients and the mean cycle length was 363 +/- 58 msec. In 8 of 13 patients (62%), alternation of either the cycle length and/or morphology of VT was observed. Transient entrainment was achieved in all patients by rapid pacing from the right ventricular outflow tract so reentry was considered the underlying mechanism of VT. The site of earliest activation (EAS) during VT was located at the apicoposterior portion of the left ventricular septum and used as the target site for RF catheter ablation. Spikelike presystolic activity was detected 20-40 msec prior to the large deflection of the local electrogram in four patients. VT was terminated by a few seconds of RF current in all four patients, but subsequently new VTs with a slightly different morphology were induced in three of them and re-mapping showed a shift of the EAS. After additional RF ablation at the new EAS, VT was no longer induced. No complication was noted and VT did not recur during a follow-up period for a mean of 9.3 +/- 5.2 months.

CONCLUSION

RF catheter ablation seems useful and safe for idiopathic VT. The alternation of QRS morphology and the findings at the time of catheter ablation suggest that an alternative pathway or multiple exists may be present in some patients with idiopathic VT, because the change in VT morphology was associated with a shift of the EAS.