title: Iterative cardiac output measurement for optimizing cardiac resynchronization therapy: a randomized, blinded, crossover study.
abstract: BACKGROUND
  Many invasive and noninvasive methods have been proposed for guiding optimal programming of cardiac resynchronization therapy (CRT) devices. However, results are not satisfying. Preliminary results suggest that cardiac output (CO) measurements using inert gas rebreathing (IGR) might be an eligible method to tailor atrioventricular (AV) and ventriculo-ventricular (VV) programming. The aims of the present study were: (1) to evaluate whether an optimization of CRT can be obtained by noninvasive CO measurements and (2) to evaluate whether acute hemodynamic improvements obtained by this approach relate into increase in cardiac exercise capacity.
  
  
  METHODS
  In 24 patients on CRT, iterative VV- and AV-delay optimization was done using the IGR method. This blinded, randomized, crossover study compared the responses to optimization during two periods: a 4-week optimized and a 4-week standard programming. Exercise capacity after optimization was assessed after each period by New York Heart Association (NYHA) classification, a 6-minute walking test, and quality of life (QoL) questionnaire.
  
  
  RESULTS
  CO could be determined by IGR in all patients. The NYHA class decreased by 17.8% (2.8 ± 0.3 vs 2.3 ± 0.4, P < 0.001), the mean (± standard deviation) distance walked in 6 minutes was 9.3% greater after optimization (456 ± 140 m vs 417 ± 134 m, P < 0.001), and the QoL improved by 14.5% (41.8 ± 10.4 vs 36.5 ± 9.5, P < 0.001). The portion of responders to CRT increased from 66.5% to 87.5%.
  
  
  CONCLUSIONS
  CRT optimization by iterative CO measurements leads to an increase in CO and an improvement of exercise capacity. Our results suggest that this method might become an important additive tool to adjust CRT programming.
authors.affiliation: West-German Heart Centre Essen, Department of Cardiology, University of Duisburg-Essen, Hufelandstrasse 55, Essen, Germany. nico.reinsch@uk-essen.de
authors.forename: Nico
authors.initials: N
authors.lastname: Reinsch
authors.forename: Thomas
authors.initials: T
authors.lastname: Konorza
authors.forename: Dagmar
authors.initials: D
authors.lastname: Woydowski
authors.forename: Heike
authors.initials: H
authors.lastname: Bruck
authors.forename: Michaela
authors.initials: M
authors.lastname: Volsek
authors.forename: Thomas
authors.initials: T
authors.lastname: Müller-Tasch
authors.forename: Till
authors.initials: T
authors.lastname: Neumann
authors.forename: Raimund
authors.initials: R
authors.lastname: Erbel
authors.forename: Heinrich
authors.initials: H
authors.lastname: Wieneke
mesh_terms: D000368:Aged; D002302:Cardiac Output; D058406:Cardiac Resynchronization Therapy / Q000379:methods*; D058409:Cardiac Resynchronization Therapy Devices; D018592:Cross-Over Studies; D015444:Exercise; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011788:Quality of Life; D013318:Stroke Volume; D016138:Walking