Successful transseptal catheter electrical ablation of sustained ventricular tachycardia of possible intramuscular origin.

Low-energy electrical ablation at 100 joules was attempted via a catheter in a patient with sustained ventricular tachycardia (VT) refractory to drug therapy. The patient was a 17-year-old woman who had undergone complete surgical correction of a double outlet right ventricle at the age of 9. The first episode of VT appeared at the age of 17. It was refractory to procainamide and lidocaine and it was sustained until termination with direct countershock. Two different QRS morphologies of VT were documented in the electrophysiologic study and one was identical to the VT observed in the clinical course. Conventional drug therapy failed to prevent induction of VT and catheter electrical ablation was attempted. The earliest activation site during the clinical episode of VT was localized to the right ventricular side of the interventricular septum (site 14-15), but pacing from this site resulted in a slightly different QRS morphology from that of VT. At the left ventricular side of this site (site 2), pacing during VT resulted in a QRS morphology identical to that of VT but the electrogram of this site did not precede the onset of the surface QRS complex. From these findings, the origin of VT was considered to be in the muscular layer of the interventricular septum. The method of transseptal shock using two catheters was applied and direct countershock at 100 joules successfully ablated the VT.