Abstract
Cardiac resynchronization therapy (CRT) using biventricular (BiV) pacing has been developed to restore synchrony and improve cardiac performance in patients with heart failure. It has been clinically beneficial in 65% to 70% of patients. Being an electrical (pacing) approach, detailed electrical information during CRT is critical in understanding its mechanism and clinical outcome. However, electrical data from patients have been limited because of the requirement for invasive mapping. Electrocardiographic imaging provides the necessary tool to noninvasively obtain this information. We applied electrocardiographic imaging to 8 patients undergoing CRT during their native rhythm and various (single-ventricular and BiV) pacing modes with the following observations: (1) native rhythm activation was heterogeneous with latest activation in lateral left ventricular (LV) base (3 of 6 patients) or in anterolateral, midlateral, or inferior LV; (2) when accompanied by fusion, LV pacing was as effective as BiV; (3) right ventricular pacing was not effective for resynchronization; (4) efficacy of CRT depended strongly on patient-specific electrophysiologic substrate.