title: Short-term hemodynamic effects of cardiac resynchronization therapy in patients with heart failure, a narrow QRS duration, and no dyssynchrony.
abstract: BACKGROUND
  Cardiac resynchronization therapy produces both short-term hemodynamic and long-term symptomatic/mortality benefits in symptomatic heart failure patients with a QRS duration >120 ms. This is conventionally believed to be due principally to relief of dyssynchrony, although we recently showed that relief of external constraint to left ventricular filling may also play a role. In this study, we evaluated the short-term hemodynamic effects in symptomatic patients with a QRS duration <120 ms and no evidence of dyssynchrony on conventional criteria and assessed the effects on contractility and external constraint.
  
  
  RESULTS
  Thirty heart failure patients (New York Heart Association class III/IV) with a left ventricular ejection fraction < or =35% who were in sinus rhythm underwent pressure-volume studies at the time of pacemaker implantation. External constraint, left ventricular stroke work, dP/dtmax, and the slope of the preload recruitable stroke work relation were measured from the end-diastolic pressure-volume relation before and during delivery of biventricular and left ventricular pacing. The following changes were observed during delivery of cardiac resynchronization therapy: Cardiac output increased by 25+/-5% (P<0.05), absolute left ventricular stroke work increased by 26+/-5% (P<0.05), the slope of the preload recruitable stroke work relation increased by 51+/-15% (P<0.05), and dP/dtmax increased by 9+/-2% (P<0.05). External constraint was present in 15 patients and was completely abolished by both biventricular and left ventricular pacing (P<0.05).
  
  
  CONCLUSIONS
  Cardiac resynchronization therapy results in an improvement in short-term hemodynamic variables in patients with a QRS <120 ms related to both contractile improvement and relief of external constraint. These findings provide a potential physiological basis for cardiac resynchronization therapy in this patient population.
authors.affiliation: Department of Cardiovascular Medicine, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK. L.K.Williams@bham.ac.uk
authors.forename: Lynne K
authors.initials: LK
authors.lastname: Williams
authors.forename: Susan
authors.initials: S
authors.lastname: Ellery
authors.forename: Kiran
authors.initials: K
authors.lastname: Patel
authors.forename: Francisco
authors.initials: F
authors.lastname: Leyva
authors.forename: Robert A
authors.initials: RA
authors.lastname: Bleasdale
authors.forename: Thanh T
authors.initials: TT
authors.lastname: Phan
authors.forename: Berthold
authors.initials: B
authors.lastname: Stegemann
authors.forename: Vince
authors.initials: V
authors.lastname: Paul
authors.forename: Paul
authors.initials: P
authors.lastname: Steendijk
authors.forename: Michael
authors.initials: M
authors.lastname: Frenneaux
mesh_terms: D000328:Adult; D000368:Aged; D002302:Cardiac Output; D002304:Cardiac Pacing, Artificial / Q000379:methods; D004562:Electrocardiography / Q000379:methods; D005260:Female; D006333:Heart Failure / Q000503:physiopathology* / Q000628:therapy*; D006439:Hemodynamics / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D013997:Time Factors; D016277:Ventricular Function, Left / Q000502:physiology; D055815:Young Adult