Left Ventricular Resynchronization Is Mandatory for Response to Cardiac Resynchronization Therapy

BACKGROUND: Recent studies have demonstrated that a positive response to cardiac resynchronization therapy (CRT) is related to the presence of preimplantation left ventricular (LV) dyssynchrony. The time course and the extent of LV resynchronization after CRT implantation and their relationship to response are currently unknown. METHODS AND RESULTS: One hundred consecutive patients scheduled for implantation of a CRT device were prospectively included if they met the following criteria: New York Heart Association class III to IV, LV ejection fraction < or = 35%, QRS duration > 120 ms, and LV dyssynchrony (> or = 65 ms) on color-coded tissue Doppler imaging. Immediately after CRT implantation, LV dyssynchrony was reduced from 114+/-36 to 40+/-33 ms (P<0.001), which persisted at the 6-month follow-up (35+/-31 ms; P<0.001 versus baseline; P=0.14 versus immediately after implantation). At the 6-month follow-up, 85% of patients were classified as responders to CRT (defined as > 10% reduction in LV end-systolic volume). Immediately after implantation, the responders to CRT demonstrated a significant reduction in LV dyssynchrony from 115+/-37 to 32+/-23 ms (P<0.001). The nonresponders, however, did not show a significant reduction in LV dyssynchrony (106+/-29 versus 79+/-44 ms; P=0.08). If the extent of acute LV resynchronization was < 20%, response to CRT at the 6-month follow-up was never observed. Conversely, 93% of patients with LV resynchronization > or = 20% responded to CRT. CONCLUSIONS: LV resynchronization after CRT is an acute phenomenon and predicts response to CRT at 6-month follow-up in patients with echocardiographic evidence of LV dyssynchrony at baseline.