Narrowed sinus rhythm electrograms in the zone of uniform slow conduction are helpful to identify VT isthmus location, shape, and orientation.

Abstract

Background: Although the sinus rhythm uniform slow conduction zone is an indicator of the reentrant ventricular tachycardia (VT) sources, it cannot alone be used for delineation.

Objective: Utilize substrate mapping to determine VT isthmus characteristics.

Methods: In 31 canine postinfarction experiments, an infarct and border zone formed in the anterior left ventricle following LAD coronary artery ligation. In each experiment, 3-5 days postinfarction, sustained monomorphic reentrant VT was reproducibly inducible via premature electrical stimulation. Epicardial bipolar electrograms were acquired using multielectrode grids. The isthmus location, shape, and orientation was determined from VT activation mapping. Sinus rhythm electrograms were marked for activation time and duration, and mapped. The VT isthmus was prognosticated from the sinus rhythm maps via the following paradigm: 1. Locate the late activation region. 2. Determine and outline the border of the largest area of narrowed electrograms (≲40msec) nearest the late activation region. 3. Ascertain the direction of uniform slow conduction in the narrowed electrogram region. 4. Draw lateral isthmus boundaries symmetric to the uniform slow conduction direction there.

Results: At the VT isthmus versus periphery, sinus rhythm electrograms are narrower (p<0.02) and activation time differences trend greater with less variability (p∼0.1). Overlap of predicted versus actual VT isthmus location was 57.9±23.6%, with a centroids difference of 7.60±6.29mm, and a divergence in exit angle of 18.0±9. 5°.

Conclusion: Narrowed electrogram duration near sinus rhythm late activation sites, along with uniform slow conduction, are indicative of VT isthmus location, and activation wavefront exit direction can be discerned from activation maps.