title: Electrocardiographic imaging of cardiac resynchronization therapy in heart failure: observation of variable electrophysiologic responses.
abstract: BACKGROUND
  Cardiac resynchronization therapy (CRT) for congestive heart failure patients with delayed left ventricular (LV) conduction is clinically beneficial in approximately 70% of patients. Unresolved issues include patient selection, lead placement, and efficacy of LV pacing alone. Being an electrical approach, detailed electrical information during CRT is critical to resolving these issues. However, electrical data from patients have been limited because of the requirement for invasive mapping.
  
  
  OBJECTIVE
  The purpose of this study was to provide observations and insights on the variable electrophysiologic responses of the heart to CRT using electrocardiographic imaging (ECGI).
  
  
  METHODS
  ECGI is a novel modality for noninvasive epicardial mapping. ECGI was conducted in eight patients undergoing CRT during native rhythm and various pacing modes.
  
  
  RESULTS
  In native rhythm (six patients), ventricular activation was heterogeneous, with latest activation in the lateral LV base in three patients and in the anterolateral, midlateral, or inferior LV in the remainder of patients. Anterior LV was susceptible to block and slow conduction. Right ventricular pacing improved electrical synchrony in two of six patients. LV pacing in three of four patients involved fusion with intrinsic excitation resulting in electrical resynchronization similar to biventricular pacing. Although generally electrical synchrony improved significantly with biventricular pacing, it was not always accompanied by clinical benefit.
  
  
  CONCLUSIONS
  Results suggest that (1) when accompanied by fusion, LV pacing alone can be as effective as biventricular pacing for electrical resynchronization; (2) right ventricular pacing is not effective for resynchronization; and (3) efficacy of CRT depends strongly on the patient-specific electrophysiologic substrate.
authors.affiliation: Cardiac Bioelectricity Research and Training Center, Case Western Reserve University, Cleveland, Ohio, USA.
authors.forename: Ping
authors.initials: P
authors.lastname: Jia
authors.forename: Charulatha
authors.initials: C
authors.lastname: Ramanathan
authors.forename: Raja N
authors.initials: RN
authors.lastname: Ghanem
authors.forename: Kyungmoo
authors.initials: K
authors.lastname: Ryu
authors.forename: Niraj
authors.initials: N
authors.lastname: Varma
authors.forename: Yoram
authors.initials: Y
authors.lastname: Rudy
mesh_terms: D000368:Aged; D002304:Cardiac Pacing, Artificial; D004562:Electrocardiography / Q000379:methods*; D004594:Electrophysiology; D004867:Equipment Design; D005260:Female; D006329:Heart Conduction System / Q000502:physiology*; D006333:Heart Failure / Q000503:physiopathology* / Q000628:therapy*; D006352:Heart Ventricles / Q000503:physiopathology; D006801:Humans; D008297:Male