New Endpoint for Ablation of Ventricular Tachycardia: Change in QRS Morphology with Pacing at Protected Isthmus as Index of Isthmus Block

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. (J Cardiovasc Electrophysiol, Vol. 21, pp. 320-324, March 2010).