ALTERNATION OF QRS MORPHOLOGY AND EFFECT OF RADIOFREQUENCY ABLATION IN IDIOPATHIC VENTRICULAR-TACHYCARDIA

We performed electrophysiological studies in 13 patients with idiopath ic VT and attempted radiofrequency (RF) catheter ablation in 4 of them . Results: VT was induced by programmed stimulation in all patients an d 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 o bserved. Transient entrainment was achieved in all patients by rapid p acing from the right ventricular outflow tract so reentry was consider ed the underlying mechanism of VT. The site of earliest activation (EA S) during VT was located at the apicoposterior portion of the left ven tricular septum amd used as the target site for RF catheter ablation. Spikelike presystolic activity was detected 20-40 msec prior to the la rge deflection of the local electrogram in four patients. VT was termi nated by a few seconds of RF current in all four patients, but subsequ ently new VTs with a slightly different morphology were induced in thr ee 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 fin dings at the time of catheter ablation suggest that an alternative pat hway or multiple exits may be present in some patients with idiopathic VT, because the change in VT morphology was associated with a shift o f the EAS.