Optimized Left Ventricular Endocardial Stimulation Is Superior to Optimized Epicardial Stimulation in Ischemic Patients With Poor Response to Cardiac Resynchronization Therapy

OBJECTIVES: The purpose of this study was to identify the optimal pacing site for the left ventricular (LV) lead in ischemic patients with poor response to cardiac resynchronization therapy (CRT). BACKGROUND: LV endocardial pacing may offer benefit over conventional CRT in ischemic patients. METHODS: We performed cardiac magnetic resonance, invasive electroanatomic mapping (EAM), and measured the acute hemodynamic response (AHR) in patients with existing CRT systems. RESULTS: vs. baseline) (11.81 -7.2 to 44.6 vs. 6.55 -11.0 to 19.7; p = 0.025). This was associated with a similar first ventricular depolarization (Q-LV) (75 ms 13 to 161 ms vs. 75 ms 25 to 129 ms; p = 0.354), shorter stimulation-QRS duration (15 ms 7 to 43 ms vs. 19 ms 5 to 66 ms; p = 0.010) and shorter paced QRS duration (149 ms 95 to 218 ms vs. 171 ms 120 to 235 ms; p < 0.001). The mean best achievable AHR was higher with endocardial pacing (25.64 ± 14.74% vs. 12.64 ± 6.76%; p = 0.044). Furthermore, AHR was significantly greater pacing the same site endocardially versus epicardially (15.2 ± 10.7% vs. 7.6 ± 6.3%; p = 0.014) with a shorter paced QRS duration (137 ± 22 ms vs. 166 ± 30 ms; p < 0.001) despite a similar Q-LV (70 ± 38 ms vs. 79 ± 34 ms; p = 0.512). Lack of capture due to areas of scar (corroborated by EAM and cardiac magnetic resonance) was associated with a poor AHR. CONCLUSIONS: In ischemic patients with poor CRT response, biventricular endocardial pacing is superior to epicardial pacing. This may reflect accessibility to sites that cannot be reached via coronary sinus anatomy and/or by access to more rapidly conducting tissue. Furthermore, guidance to the optimal LV pacing site may be aided by modalities such as cardiac magnetic resonance to target delayed activating sites while avoiding scar.