title: Vectorcardiography as a tool for easy optimization of cardiac resynchronization therapy in canine left bundle branch block hearts.
abstract: BACKGROUND
  In cardiac resynchronization therapy (CRT), optimization of left ventricular (LV) stimulation timing is often time consuming. We hypothesized that the QRS vector in the vectorcardiogram (VCG) reflects electric interventricular dyssynchrony, and that the QRS vector amplitude (VAQRS), halfway between that during left bundle branch block (LBBB) and LV pacing, reflects optimal resynchronization, and can be used for easy optimization of CRT.
  
  
  RESULTS
  In 24 canine hearts with LBBB (12 acute, 6 with heart failure, and 6 with myocardial infarction), the LV was paced over a wide range of atrioventricular (AV) delays. Surface ECGs were recorded from the limb leads, and VAQRS was calculated in the frontal plane. Mechanical interventricular dyssynchrony (MIVD) was determined as the time delay between upslopes of LV and right ventricular pressure curves, and systolic function was assessed as LV dP/dtmax. VAQRS and MIVD were highly correlated (r=0.94). The VAQRS halfway between that during LV pacing with short AV delay and intrinsic LBBB activation accurately predicted the optimal AV delay for LV pacing (1 ms; 95% CI, -5 to 8 ms). Increase in LV dP/dtmax at the VCG predicted AV delay was only slightly lower than the highest observed LV dP/dtmax (-2.7%; 95% CI, -3.6 to -1.8%). Inability to reach the halfway value of VAQRS during simultaneous biventricular pacing (53% of cases) was associated with suboptimal hemodynamic response, which could be corrected by sequential pacing.
  
  
  CONCLUSIONS
  The VAQRS reflects electric interventricular dyssynchrony and accurately predicts optimal timing of LV stimulation in canine LBBB hearts. Therefore, VCG may be useful as a reliable and easy tool for individual optimization of CRT.
authors.affiliation: Department of Physiology, Department of Cardiology, Cardiovascular Research Institute Maastricht, Maastricht University Medical Center, Maastricht, The Netherlands. c.vandeursen@maastrichtuniversity.nl
authors.forename: Caroline J M
authors.initials: CJ
authors.lastname: van Deursen
authors.forename: Marc
authors.initials: M
authors.lastname: Strik
authors.forename: Leonard M
authors.initials: LM
authors.lastname: Rademakers
authors.forename: Arne
authors.initials: A
authors.lastname: van Hunnik
authors.forename: Marion
authors.initials: M
authors.lastname: Kuiper
authors.forename: Liliane
authors.initials: L
authors.lastname: Wecke
authors.forename: Harry J G M
authors.initials: HJ
authors.lastname: Crijns
authors.forename: Kevin
authors.initials: K
authors.lastname: Vernooy
authors.forename: Frits W
authors.initials: FW
authors.lastname: Prinzen
mesh_terms: D000818:Animals; D002037:Bundle-Branch Block / Q000503:physiopathology / Q000628:therapy*; D058406:Cardiac Resynchronization Therapy / Q000379:methods*; D004195:Disease Models, Animal; D004285:Dogs; D005260:Female; D006329:Heart Conduction System / Q000503:physiopathology*; D008297:Male; D015203:Reproducibility of Results; D014672:Vectorcardiography; D016277:Ventricular Function, Left / Q000502:physiology*