Relationship between sinus rhythm activation and the reentrant ventricular tachycardia isthmus.

Background: In canine hearts with inducible reentry, the isthmus tends to form along an axis from the area of last to first activity during sinus rhythm. It was hypothesized that this phenomenon could be quantified to predict reentry and the isthmus location.
Methods and Results: An in situ canine model of reentrant ventricular tachycardia occurring in the epicardial border zone was used in 54 experiments (25 canine hearts in which primarily long monomorphic runs of figure-8 reentry were inducible, 11 with short monomorphic or polymorphic runs, and 18 lacking inducible reentry). From the sinus rhythm activation map for each experiment, the linear regression coefficient and slope were calculated for the activation times along each of 8 rays extending from the area of last activation. The slope of the regression line for the ray with greatest regression coefficient (called the primary axis) was used to predict whether or not reentry would be inducible (correct prediction in 48 of 54 experiments). For all 36 experiments with reentry, isthmus location and shape were then estimated on the basis of site-to-site differences in sinus rhythm electrogram duration. For long and short runs of reentry, estimated isthmus location and shape partially overlapped the actual isthmus (mean overlap of 71.3% and 43.6%, respectively). On average for all reentry experiments, a linear ablation lesion positioned across the estimated isthmus would have spanned 78.2% of the actual isthmus width.
Conclusions: Parameters of sinus rhythm activation provide key information for prediction of reentry inducibility and isthmus location and shape.