Long-Term Survival of Patients With Left Bundle Branch Block Who Are Hypo-Responders to Cardiac Resynchronization Therapy.

Guidelines support cardiac resynchronization therapy with a defibrillator (CRT-D) in mild heart failure (HF) patients with left bundle branch block (LBBB). However, not all patients demonstrate echocardiographic or clinical response to CRT-D. We aimed to evaluate the long-term outcomes of echocardiographic hypo-responders and clinical hypo-responders to CRT-D with LBBB in the Multicenter Automatic Defibrillator Implantation Trial with Cardiac Resynchronization Therapy. Five-hundred thirty-four patients with LBBB in the CRT-D arm were followed for 5.6 years (median). Clinical hypo-response was defined as HF event in the first year after CRT-D implantation. Echocardiographic hypo-response was defined as ≤35% reduction (median) in left ventricular end-systolic volume 1 year after CRT-D implantation without evidence of clinical hypo-response. Echocardiographic and clinical response was observed in 257 patients (48%). Two-hundred fifty patients (47%) were echocardiographic hypo-responders and 27 patients (5%) were clinical hypo-responders. Echocardiographic hypo-responders had increased risk of all-cause mortality compared with echocardiographic + clinical responders (hazard ratio [HR] 2.85, 95% confidence interval [CI]: 1.37 to 5.94, p = 0.005). Clinical hypo-responders had increased risk of mortality compared with echocardiographic + clinical responders (HR 7.49, 95% CI: 2.88 to 19.48, p <0.0001) and compared with echocardiographic hypo-responders (HR 2.63, 95% CI: 1.17 to 5.92, p = 0.020). In conclusion, during long-term follow-up, patients with mild HF and LBBB who have echocardiographic hypo-response to CRT, with or without clinical signs of worsening HF, have increased risk of mortality. This study emphasizes the prognostic significance of echocardiographic assessment of left ventricular volume after CRT implantation in LBBB patients with mild HF.