title: CRT improves the exercise capacity and functional reserve of the failing heart through enhancing the cardiac flow- and pressure-generating capacity.
abstract: BACKGROUND
  While information on how cardiac resynchronisation therapy (CRT) affects cardiac performance at rest is readily available, the mechanisms whereby CRT alters cardiac function during maximal exercise are unclear.
  
  
  OBJECTIVE
  We examined the medium-term effects of CRT on cardiac and physical functional reserve of patients with severe heart failure (CHF) and prolonged QRS duration.
  
  
  METHODS
  Seventeen consecutive patients with severe CHF (NYHA III-IV) and widened QRS underwent maximal cardiopulmonary exercise testing with non-invasive central haemodynamic measurements before and 6-8 weeks after CRT pacemaker implantation.
  
  
  RESULTS
  After CRT there were significant increases in exercise cardiac output by 19.3% (P=0.0048) from 9.5+/-3.4 l min(-1), peak mean arterial blood pressure by 14.1% (P=0.0001) from 91.3+/-13.6 mm Hg, and peak cardiac power output by 37.2% (P=0.0008) from 1.92+/-0.74 W. There were no significant changes in these variables at rest. Exercise duration (+42.3%, P=0.0002), NYHA functional class (P=0.0001) and SF-36 symptom score (P=0.0006) were also significantly improved. Powerful surrogate indicators of prognosis were also significantly improved with CRT: peak O(2) consumption (+20.9%, P=0.0007), VE/VCO(2) slope (-20.0%, P=0.005) and circulatory power (+42.0%, P=0.0012).
  
  
  CONCLUSIONS
  In this cohort of patients, post-implant CRT significantly improved the flow-, pressure- and power-generating capacity of the failing hearts. This may be causally related to the improvements observed in exercise capacity, functional class and symptom scores.
authors.affiliation: Molecular Cardiovascular Medicine, University of Leeds, Leeds General Infirmary, Great George Street, Leeds LS1 3EX, UK.
authors.forename: D
authors.initials: D
authors.lastname: Schlosshan
authors.forename: D
authors.initials: D
authors.lastname: Barker
authors.forename: C
authors.initials: C
authors.lastname: Pepper
authors.forename: G
authors.initials: G
authors.lastname: Williams
authors.forename: C
authors.initials: C
authors.lastname: Morley
authors.forename: L-B
authors.initials: LB
authors.lastname: Tan
mesh_terms: D000368:Aged; D002302:Cardiac Output; D002304:Cardiac Pacing, Artificial; D005080:Exercise Test; D017079:Exercise Tolerance; D005260:Female; D005500:Follow-Up Studies; D006305:Health Status Indicators; D006333:Heart Failure / Q000503:physiopathology* / Q000628:therapy*; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D010101:Oxygen Consumption; D010138:Pacemaker, Artificial; D011446:Prospective Studies; D011788:Quality of Life; D014655:Vascular Resistance