title: QRS axis and the benefit of cardiac resynchronization therapy in patients with mildly symptomatic heart failure enrolled in MADIT-CRT.
abstract: BACKGROUND
  Mildly symptomatic heart failure (HF) patients derive substantial clinical benefit from cardiac resynchronization therapy with defibrillator (CRT-D) as shown in MADIT-CRT. The presence of QRS axis deviation may influence response to CRT-D. The objective of this study was to determine whether QRS axis deviation will be associated with differential benefit from CRT-D.
  
  
  METHODS
  Baseline electrocardiograms of 1,820 patients from MADIT-CRT were evaluated for left axis deviation (LAD: quantitative QRS axis -30 to -90) or right axis deviation (RAD: QRS axis 90-180) in left bundle branch block (LBBB), right bundle branch block (RBBB), and nonspecific interventricular conduction delay QRS morphologies. The primary endpoints were the first occurrence of a HF event or death and the separate occurrence of all-cause mortality as in MADIT-CRT.
  
  
  RESULTS
  Among LBBB patients, those with LAD had a higher risk of primary events at 2 years than non-LAD patients (20% vs 16%; P = 0.024). The same was observed among RBBB patients (20% vs 10%; P = 0.05) but not in IVCD patients (22% vs 23%; P = NS). RAD did not convey any increased risk of the primary combined endpoint in any QRS morphology subgroup. When analyzing the benefit of CRT-D in the non-LBBB subgroups, there was no significant difference in hazard ratios for CRT-D versus ICD for either LAD or RAD. However, LBBB patients without LAD showed a trend toward greater benefit from CRT therapy than LBBB patients with LAD (HR for no LAD: 0.37, 95% CI: 0.26-0.53 and with LAD: 0.54, 95% CI: 0.36-0.79; P value for interaction = 0.18).
  
  
  CONCLUSIONS
  LAD in non-LBBB patients (RBBB or IVCD) is not associated with an increased benefit from CRT. In LBBB patients, those without LAD seem to benefit more from CRT-D than those with LAD.
authors.affiliation: Cardiology Division of the Department of Medicine, University of Rochester Medical Center, Rochester, New York 14642, USA. Andrew_Brenyo@urmc.rochester.edu
authors.forename: Andrew
authors.initials: A
authors.lastname: Brenyo
authors.forename: Mohan
authors.initials: M
authors.lastname: Rao
authors.forename: Alon
authors.initials: A
authors.lastname: Barsheshet
authors.forename: David
authors.initials: D
authors.lastname: Cannom
authors.forename: Aurelio
authors.initials: A
authors.lastname: Quesada
authors.forename: Scott
authors.initials: S
authors.lastname: McNitt
authors.forename: David T
authors.initials: DT
authors.lastname: Huang
authors.forename: Arthur J
authors.initials: AJ
authors.lastname: Moss
authors.forename: Wojciech
authors.initials: W
authors.lastname: Zareba
mesh_terms: D000200:Action Potentials; D000368:Aged; D002037:Bundle-Branch Block / Q000175:diagnosis / Q000209:etiology / Q000401:mortality / Q000503:physiopathology / Q000628:therapy*; D002170:Canada; D058406:Cardiac Resynchronization Therapy / Q000009:adverse effects / Q000401:mortality; D058409:Cardiac Resynchronization Therapy Devices; D016009:Chi-Square Distribution; D004562:Electrocardiography; D005060:Europe; D005260:Female; D006329:Heart Conduction System / Q000503:physiopathology*; D006333:Heart Failure / Q000150:complications / Q000175:diagnosis / Q000401:mortality / Q000503:physiopathology / Q000628:therapy*; D006801:Humans; D053208:Kaplan-Meier Estimate; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D018579:Patient Selection; D016016:Proportional Hazards Models; D018570:Risk Assessment; D012307:Risk Factors; D012720:Severity of Illness Index; D013318:Stroke Volume; D013997:Time Factors; D016896:Treatment Outcome; D014481:United States; D016277:Ventricular Function, Left; D020257:Ventricular Remodeling