The Misleading QRS Morphology of Scar-Related Ventricular Tachycardia.

Background: The QRS morphology of ventricular tachycardia (VT) reflects the re-entry circuit exit location and helps guide mapping for radiofrequency ablation (RFA). It can be misleading, however, particularly in structural heart disease.

Objective: The aim of this study was to assess the relation of the site where RFA terminated VT to the location of the exit predicted by the VT QRS morphology.

Methods: This study included 64 scar-related re-entrant left ventricular VTs (57.9% ischemic cardiomyopathy) with an identified region where RFA terminated the VT; a previously reported electrocardiogram algorithm that uses the QRS vector to predict the VT exit region on the American Heart Association 17-segment left ventricular model was applied. QRS discordant VTs were defined as having the RFA termination site outside of the predicted exit region. Entrainment and pace mapping (PM) data were also analyzed to assess possible reasons for discrepancies.

Results: The QRS morphology was discordant with the termination region in 57 (89%) VTs. Two types of discordance were seen. In 22 (34.4%), the termination region was remote from the circuit exit. In 32 (50%), the termination site was in the VT re-entry circuit exit, but the QRS suggested a different exit region. Analysis of voltage maps and PM suggested that the QRS vector was often altered by scar.

Conclusions: For scar-related VTs, the exit predicted from a vector-based QRS algorithm often differs from the location where ablation terminates the VT. This is an important consideration for use of the QRS to guide VT ablation strategies. PM can potentially assist in recognizing this discrepancy and warrants study.