title: Electrophysiologic substrate and intraventricular left ventricular dyssynchrony in nonischemic heart failure patients undergoing cardiac resynchronization therapy.
abstract: BACKGROUND
  Electrocardiographic imaging (ECGI) is a method for noninvasive epicardial electrophysiologic mapping. ECGI previously has been used to characterize the electrophysiologic substrate and electrical synchrony in a very heterogeneous group of patients with varying degrees of coronary disease and ischemic cardiomyopathy.
  
  
  OBJECTIVE
  The purpose of this study was to characterize the left ventricular electrophysiologic substrate and electrical dyssynchrony using ECGI in a homogeneous group of nonischemic cardiomyopathy patients who were previously implanted with a cardiac resynchronization therapy (CRT) device.
  
  
  METHODS
  ECGI was performed during different rhythms in 25 patients by programming their devices to biventricular pacing, single-chamber (left ventricular or right ventricular) pacing, and native rhythm. The electrical dyssynchrony index (ED) was computed as the standard deviation of activation times at 500 sites on the LV epicardium.
  
  
  RESULTS
  In all patients, native rhythm activation was characterized by lines of conduction block in a region with steep activation-recovery interval (ARI) gradients between the epicardial aspect of the septum and LV lateral wall. A native QRS duration (QRSd) >130 ms was associated with high ED (≥30 ms), whereas QRSd <130 ms was associated with minimal (25 ms) to large (40 ms) ED. CRT responders had very high dyssynchrony (ED = 35.5 ± 3.9 ms) in native rhythm, which was significantly lowered (ED = 23.2 ± 4.4 ms) during CRT. All four nonresponders in the study did not show significant difference in ED between native and CRT rhythms.
  
  
  CONCLUSIONS
  The electrophysiologic substrate in nonischemic cardiomyopathy is consistent among all patients, with steep ARI gradients co-localizing with conduction block lines between the epicardial aspect of the septum and the LV lateral wall. QRSd wider than 130 ms is indicative of substantial LV electrical dyssynchrony; however, among patients with QRSd <130 ms, LV dyssynchrony may vary widely.
authors.affiliation: Cardiac Bioelectricity and Arrhythmia Center (CBAC), Washington University, St. Louis, Missouri 63130-4899, USA.
authors.forename: Subham
authors.initials: S
authors.lastname: Ghosh
authors.forename: Jennifer N A
authors.initials: JN
authors.lastname: Silva
authors.forename: Russell M
authors.initials: RM
authors.lastname: Canham
authors.forename: Tammy M
authors.initials: TM
authors.lastname: Bowman
authors.forename: Junjie
authors.initials: J
authors.lastname: Zhang
authors.forename: Edward K
authors.initials: EK
authors.lastname: Rhee
authors.forename: Pamela K
authors.initials: PK
authors.lastname: Woodard
authors.forename: Yoram
authors.initials: Y
authors.lastname: Rudy
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D018780:Body Surface Potential Mapping; D058406:Cardiac Resynchronization Therapy; D002648:Child; D022062:Electrophysiologic Techniques, Cardiac; D005260:Female; D006333:Heart Failure / Q000503:physiopathology* / Q000628:therapy*; D006801:Humans; D008297:Male; D008875:Middle Aged