RELATION OF PACE MAPPING QRS CONFIGURATION AND CONDUCTION DELAY TO VENTRICULAR-TACHYCARDIA REENTRY CIRCUITS IN HUMAN INFARCT SCARS

Objectives. This study sought to determine the relation of the paced Q RS configuration and conduction delay during pace mapping to reentry c ircuit sites in patients,vith ventricular tachycardia late after myoca rdial infarction. Background. The QRS configuration produced by ventri cular pacing during sinus rhythm (pace mapping) can locate focal idiop athic ventricular tachycardias during catheter mapping, but postinfarc tion reentry circuits may be relatively large and contain regions of s low conduction. We hypothesized that for postinfarction ventricular ta chycardia, 1) pacing during sinus rhythm at reentry circuit sites dist ant from the exit from the scar would produce a QRS configuration diff erent from the tachycardia; and 2) a stimulus to QRS delay during pace mapping may be a useful guide to reentry circuit slow conduction zone s. Methods. Catheter mapping and ablation were performed in 18 consecu tive patients with ventricular tachycardia after myocardial infarction . At 85 endocardial sites in 13 patients, 12-lead electrocardiograms ( ECGs) were recorded during pace mapping, and participation of each sit e in a reentry circuit was then evaluated by entrainment techniques du ring induced ventricular tachycardia or by application of radiofrequen cy current. Results. Pace maps resembled tachycardia at <30% of likely reentry circuit sites identified by entrainment criteria and at only 1 (9%) of 11 sites where radiofrequency current terminated tachycardia . Analysis of the stimulus to QRS interval during entrainment with con cealed fusion shelved that the conduction time from the pacing site to the exit from the scar was longer at sites where the pace map did not resemble tachycardia. Evidence of slow conduction during pace mapping , with a stimulus to QRS interval >40 ms was observed at greater than or equal to 70% of reentry circuit sites. Conclusions. At many sites i n postinfarction ventricular reentry circuits, the QRS configuration d uring pace mapping does not resemble the ventricular tachycardia QRS c omplex, consistent with relatively large reentry circuits or regions o f functional conduction block during ventricular tachycardia. A stimul us to QRS delay during pace mapping is consistent with slow conduction and may aid in targeting endocardial sites for further evaluation dur ing tachycardia.