title: Cardiac resynchronization therapy and AV optimization increase myocardial oxygen consumption, but increase cardiac function more than proportionally.
abstract: BACKGROUND
  The mechanoenergetic effects of atrioventricular delay optimization during biventricular pacing ("cardiac resynchronization therapy", CRT) are unknown.
  
  
  METHODS
  Eleven patients with heart failure and left bundle branch block (LBBB) underwent invasive measurements of left ventricular (LV) developed pressure, aortic flow velocity-time-integral (VTI) and myocardial oxygen consumption (MVO2) at 4 pacing states: biventricular pacing (with VV 0 ms) at AVD 40 ms (AV-40), AVD 120 ms (AV-120, a common nominal AV delay), at their pre-identified individualised haemodynamic optimum (AV-Opt); and intrinsic conduction (LBBB).
  
  
  RESULTS
  AV-120, relative to LBBB, increased LV developed pressure by a mean of 11(SEM 2)%, p=0.001, and aortic VTI by 11(SEM 3)%, p=0.002, but also increased MVO2 by 11(SEM 5)%, p=0.04. AV-Opt further increased LV developed pressure by a mean of 2(SEM 1)%, p=0.035 and aortic VTI by 4(SEM 1)%, p=0.017. MVO2 trended further up by 7(SEM 5)%, p=0.22. Mechanoenergetics at AV-40 were no different from LBBB. The 4 states lay on a straight line for Δexternal work (ΔLV developed pressure × Δaortic VTI) against ΔMVO2, with slope 1.80, significantly >1 (p=0.02).
  
  
  CONCLUSIONS
  Biventricular pacing and atrioventricular delay optimization increased external cardiac work done but also myocardial oxygen consumption. Nevertheless, the increase in cardiac work was ~80% greater than the increase in oxygen consumption, signifying an improvement in cardiac mechanoenergetics. Finally, the incremental effect of optimization on external work was approximately one-third beyond that of nominal AV pacing, along the same favourable efficiency trajectory, suggesting that AV delay dominates the biventricular pacing effect - which may therefore not be mainly "resynchronization".
authors: International Centre for Circulatory Health, National Heart and Lung Institute, Imperial College London, UK.
authors: Andreas
authors: A
authors: Kyriacou
authors: International Centre for Circulatory Health, National Heart and Lung Institute, Imperial College London, UK.
authors: Punam A
authors: PA
authors: Pabari
authors: International Centre for Circulatory Health, National Heart and Lung Institute, Imperial College London, UK.
authors: Jamil
authors: J
authors: Mayet
authors: International Centre for Circulatory Health, National Heart and Lung Institute, Imperial College London, UK.
authors: Nicholas S
authors: NS
authors: Peters
authors: International Centre for Circulatory Health, National Heart and Lung Institute, Imperial College London, UK.
authors: D Wyn
authors: DW
authors: Davies
authors: International Centre for Circulatory Health, National Heart and Lung Institute, Imperial College London, UK.
authors: P Boon
authors: PB
authors: Lim
authors: International Centre for Circulatory Health, National Heart and Lung Institute, Imperial College London, UK.
authors: David
authors: D
authors: Lefroy
authors: International Centre for Circulatory Health, National Heart and Lung Institute, Imperial College London, UK.
authors: Alun D
authors: AD
authors: Hughes
authors: International Centre for Circulatory Health, National Heart and Lung Institute, Imperial College London, UK.
authors: Prapa
authors: P
authors: Kanagaratnam
authors: International Centre for Circulatory Health, National Heart and Lung Institute, Imperial College London, UK. Electronic address: d.francis@imperial.ac.uk.
authors: Darrel P
authors: DP
authors: Francis
authors: International Centre for Circulatory Health, National Heart and Lung Institute, Imperial College London, UK.
authors: Zachary I
authors: ZI
authors: Whinnett
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001283:Atrioventricular Node / Q000502:physiology*; D002037:Bundle-Branch Block / Q000378:metabolism / Q000503:physiopathology; D058406:Cardiac Resynchronization Therapy / Q000379:methods*; D005260:Female; D006329:Heart Conduction System / Q000502:physiology; D006333:Heart Failure / Q000378:metabolism / Q000503:physiopathology / Q000628:therapy*; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009200:Myocardial Contraction / Q000502:physiology*; D009206:Myocardium / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology*; D016277:Ventricular Function, Left / Q000502:physiology
keywords: Biventricular pacing; Myocardial oxygen consumption; Optimization