title: Site-specific differences in latency intervals during biventricular pacing: impact on paced QRS morphology and echo-optimized V-V interval.
abstract: OBJECTIVE
  To investigate differences in latency intervals during right ventricular (RV) pacing and left ventricular (LV) pacing from the (postero-)lateral cardiac vein in cardiac resynchronization therapy (CRT) patients and their relationship to echo-optimized interventricular (V-V) intervals and paced QRS morphology.
  
  
  METHODS
  We recorded digital 12-lead electrocardiograms in 40 CRT patients during RV, LV, and biventricular pacing at three output settings. Stimulus-to-earliest QRS deflection (latency) intervals were measured in all leads. Echocardiographic atrioventricular (AV) and V-V optimization was performed using aortic velocity time integrals.
  
  
  RESULTS
  Latency intervals were longer during LV (34 ± 17, 29 ± 15, 28 ± 15 ms) versus RV apical pacing (17 ± 8, 15 ± 8, 13 ± 7 ms) for threshold, threshold ×3, and maximal output, respectively (P < 0.001), and shortened with increased stimulus strength (P < 0.05). The echo-optimized V-V interval was 58 ± 31 ms in five of 40 (12%) patients with LV latency ≥ 40 ms compared to 29 ± 20 ms in 35 patients with LV latency < 40 ms (P < 0.01). During simultaneous biventricular pacing, four of five (80%) patients with LV latency ≥ 40 ms exhibited a left bundle branch block (LBBB) pattern in lead V(1) compared to three of 35 (9%) patients with LV latency < 40 ms (P < 0.01). After optimization, all five patients with LV latency ≥ 40 ms registered a dominant R wave in lead V(1) .
  
  
  CONCLUSIONS
  LV pacing from the lateral cardiac vein is associated with longer latency intervals than endocardial RV pacing. LV latency causes delayed LV activation and requires V-V interval adjustment to improve hemodynamic response to CRT. Patients with LV latency ≥ 40 ms most often display an LBBB pattern in lead V(1) during simultaneous biventricular pacing, but a right bundle branch block after V-V interval optimization.
authors.affiliation: Arrhythmia Service and Division of Cardiology, Tampa General Hospital and University of South Florida, Tampa, Florida 33606, USA. bherweg@tampabay.rr.com
authors.forename: Bengt
authors.initials: B
authors.lastname: Herweg
authors.forename: Rias
authors.initials: R
authors.lastname: Ali
authors.forename: Arzu
authors.initials: A
authors.lastname: Ilercil
authors.forename: Chris
authors.initials: C
authors.lastname: Madramootoo
authors.forename: Ray
authors.initials: R
authors.lastname: Cutro
authors.forename: Mark W
authors.initials: MW
authors.lastname: Weston
authors.forename: S Serge
authors.initials: SS
authors.lastname: Barold
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002037:Bundle-Branch Block / Q000000981:diagnostic imaging / Q000503:physiopathology* / Q000628:therapy; D058406:Cardiac Resynchronization Therapy; D015150:Echocardiography, Doppler; D004562:Electrocardiography; D005260:Female; D006333:Heart Failure / Q000000981:diagnostic imaging / Q000503:physiopathology* / Q000628:therapy; D006352:Heart Ventricles / Q000000981:diagnostic imaging / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D016896:Treatment Outcome