ABSTRACT
Scar-related ventricular tachycardia is the result of re-entry from fixed or functional unidirectional block, where regions of slow conduction result from viable myocardial interspersed within areas of fibrosis. With extensive postmyocardial infarct scar, antiarrhythmic usage, and rapid ventricular tachycardia where QRS onset may be subjective and difficult to discern, these criteria have limited discriminatory value. Multiple electrocardiogram criteria have been proposed and evaluated to suggest epicardial exit sites. In general, the further the site of origin is from the conduction system, the wider the QRS complex. The original approach to catheter ablation of ventricular tachycardia was aimed at mimicking surgical subendocardial resection and encircling ventriculotomy. Ablation across dense scar can be performed with the goal of transecting a critical isthmus. Pace mapping can be used to estimate the exit morphology produced from an electrogram of interest. Correlation with the targeted ventricular tachycardia exit sites may help localize channels of slow conduction.
