New endpoint for ablation of ventricular tachycardia: change in QRS morphology with pacing at protected isthmus as index of isthmus block.

INTRODUCTION

Endpoints confirming block in the critical isthmus in sinus rhythm and with pace mapping have not been established.

METHODS AND RESULTS

A 44-year-old man with a history of Tetralogy of Fallot presented with recurrent ventricular tachycardia (VT). Entrainment mapping was consistent with a macroreentrant circuit rotating in a clockwise fashion under the pulmonic valve. After termination of the VT in a critical isthmus located on the conal free wall, a pace map proximal to the site of successful ablation was consistent with a change in QRS morphology. This change in QRS morphology suggested critical isthmus block and successful ablation, which was confirmed by noninducibility with programmed stimulation.

CONCLUSION

Evidence of conduction block can be used as an additional endpoint for successful ablation of VT.