title: Clinical feasibility of exercise-based A-V interval optimization for cardiac resynchronization: a pilot study.
abstract: BACKGROUND
  One-third of eligible patients fail to respond to cardiac resynchronization therapy (CRT). Current methods to "optimize" the atrio-ventricular (A-V) interval are performed at rest, which may limit its efficacy during daily activities. We hypothesized that low-intensity cardiopulmonary exercise testing (CPX) could identify the most favorable physiologic combination of specific gas exchange parameters reflecting pulmonary blood flow or cardiac output, stroke volume, and left atrial pressure to guide determination of the optimal A-V interval.
  
  
  METHODS
  We assessed relative feasibility of determining the optimal A-V interval by three methods in 17 patients who underwent optimization of CRT: (1) resting echocardiographic optimization (the Ritter method), (2) resting electrical optimization (intrinsic A-V interval and QRS duration), and (3) during low-intensity, steady-state CPX. Five sequential, incremental A-V intervals were programmed in each method. Assessment of cardiopulmonary stability and potential influence on the CPX-based method were assessed.
  
  
  RESULTS
  CPX and determination of a physiological optimal A-V interval was successfully completed in 94.1% of patients, slightly higher than the resting echo-based approach (88.2%). There was a wide variation in the optimal A-V delay determined by each method. There was no observed cardiopulmonary instability or impact of the implant procedure that affected determination of the CPX-based optimized A-V interval.
  
  
  CONCLUSIONS
  Determining optimized A-V intervals by CPX is feasible. Proposed mechanisms explaining this finding and long-term impact require further study.
authors.affiliation: Aurora Cardiovascular Services, Aurora Sinai/Aurora St. Luke's Medical Centers, University of Wisconsin School of Medicine and Public Health, Milwaukee, Wisconsin.
authors.forename: Indrajit
authors.initials: I
authors.lastname: Choudhuri
authors.forename: Dean
authors.initials: D
authors.lastname: MacCarter
authors.forename: Rachael
authors.initials: R
authors.lastname: Shaw
authors.forename: Steve
authors.initials: S
authors.lastname: Anderson
authors.forename: John
authors.initials: J
authors.lastname: St Cyr
authors.forename: Imran
authors.initials: I
authors.lastname: Niazi
mesh_terms: D000368:Aged; D058406:Cardiac Resynchronization Therapy; D003131:Combined Modality Therapy; D005081:Exercise Therapy; D005240:Feasibility Studies; D005260:Female; D006333:Heart Failure / Q000628:therapy*; D006801:Humans; D008297:Male; D010865:Pilot Projects
keywords: A-V interval; cardiac resynchronization therapy; cardiopulmonary exercise; enhanced optimization; heart failure