PURPOSE: Left ventricular (LV) electrical activation pattern could determine optimal LV lead placement site during cardiac resynchronization therapy (CRT) device implant. We sought to determine the feasibility of using EnSite NavX™ electroanatomic mapping system (St. Jude Medical Inc., St. Paul, MN) to assess LV electrical activation during CRT implant.

METHODS: Patients (n = 32; NYHA III, LVEF%, QRSd >120 ms) underwent NavX™ mapping during CRT implant. Left bundle branch block (LBBB) was present during sinus rhythm in group A (n = 17), whereas LBBB was induced by permanent RV apical pacing in group B (n = 15). Following coronary sinus (CS) cannulation, a coil tip 0.014-in. guidewire was introduced into all available CS branches as a mapping electrode. Each patient's unipolar activation map was successfully constructed within 10 min, using the onset of surface QRS as reference.

RESULTS: LV activation patterns were complex and varied in both groups. Earliest activation was usually apical, but latest activation was more heterogenous. The lateral or posterolateral branches were the sites of latest activation in 47 % of group A and 73 % of group B. An LV lead positioned conventionally by a physician blinded to the mapping data was concordant with the latest activated segment in 18 % of group A and none of group B patients.

CONCLUSIONS: Electroanatomic mapping of the CS tributaries is feasible and clinically practicable. Mapping revealed heterogenous conduction patterns that vary between patients in each group and between groups. An LV lead empirically placed in a lateral branch rarely paces the optimal, latest activated vein segment.