title: The paced electrocardiogram cannot be used to identify left and right ventricular pacing sites in cardiac resynchronization therapy: validation by cardiac computed tomography.
abstract: OBJECTIVE
  Paced electrocardiogram characteristics to confirm left ventricular (LV) and right ventricular (RV) pacing sites in cardiac resynchronization therapy (CRT) have not been validated with accurate knowledge of pacing lead positions. We aimed to evaluate the ability of the paced QRS morphology to differentiate between various LV and RV lead positions using cardiac computed tomography (CT) as the reference for LV and RV pacing site.
  
  
  RESULTS
  Ninety-seven CRT patients were included. The QRS morphology was evaluated during forced LV-only and RV-only pacing. Pacing lead positions were assessed in a standard LV 16-segment model and a simplistic RV 6-segment model using cardiac CT. Ten patients with LV lead displacement or a LV pacing site outside the non-apical free wall were excluded from the analysis of the LV paced QRS complex. Pacing within the LV free wall was associated with a superior and a right-axis deviation (P = 0.02 and 0.04, respectively). Pacing from basal LV segments mainly produced a late (V5 or later) precordial QRS transition as compared with mid-LV pacing (P = 0.001). No significant associations were found between RV pacing site and QRS axis or precordial transition. Different QRS morphologies were observed during single-chamber pacing from identical LV or RV myocardial segments.
  
  
  CONCLUSIONS
  Weak associations exist between LV and RV pacing sites and the paced QRS axis. None of the paced QRS characteristics can be used to reliably confirm specific LV and RV pacing sites in CRT patients.
authors.affiliation: Department of Cardiology, Aarhus University Hospital, Skejby, Brendstrupgaardsvej 100, Aarhus N DK-8200, Denmark a.sommer@dadlnet.dk.
authors.forename: Anders
authors.initials: A
authors.lastname: Sommer
authors.affiliation: Department of Cardiology, Aarhus University Hospital, Skejby, Brendstrupgaardsvej 100, Aarhus N DK-8200, Denmark.
authors.forename: Mads Brix
authors.initials: MB
authors.lastname: Kronborg
authors.affiliation: Department of Cardiology, Aarhus University Hospital, Skejby, Brendstrupgaardsvej 100, Aarhus N DK-8200, Denmark.
authors.forename: Christoffer Tobias
authors.initials: CT
authors.lastname: Witt
authors.affiliation: Department of Cardiology, Aarhus University Hospital, Skejby, Brendstrupgaardsvej 100, Aarhus N DK-8200, Denmark.
authors.forename: Bjarne Linde
authors.initials: BL
authors.lastname: Nørgaard
authors.affiliation: Department of Cardiology, Aarhus University Hospital, Skejby, Brendstrupgaardsvej 100, Aarhus N DK-8200, Denmark.
authors.forename: Jens Cosedis
authors.initials: JC
authors.lastname: Nielsen
mesh_terms: D000368:Aged; D058406:Cardiac Resynchronization Therapy; D058409:Cardiac Resynchronization Therapy Devices; D015331:Cohort Studies; D004562:Electrocardiography; D005260:Female; D006333:Heart Failure / Q000628:therapy*; D006352:Heart Ventricles / Q000000981:diagnostic imaging*; D006801:Humans; D008297:Male; D008875:Middle Aged; D014057:Tomography, X-Ray Computed
keywords: Cardiac computed tomography; Cardiac resynchronization therapy; Electrocardiogram; Left ventricular pacing site; Right ventricular lead position