title: Optimisation of atrioventricular delay during exercise improves cardiac output in patients stabilised with cardiac resynchronisation therapy.
abstract: BACKGROUND
  Atrioventricular (AV) delay in cardiac resynchronisation therapy (CRT) recipients are typically optimised at rest. However, there are limited data on the impact of exercise-induced changes in heart rate on the optimal AV delay and left ventricular function.
  
  
  RESULTS
  The authors serially programmed AV delays in 41 CRT patients with intrinsic sinus rhythm at rest and during two stages of supine bicycle exercise with heart rates at 20 bpm (stage I) and 40 bpm (stage II) above baseline. The optimal AV delay during exercise was determined by the iterative method to maximise cardiac output using Doppler echocardiography. Results were compared to physiological change in PR intervals in 56 normal controls during treadmill exercise. The optimal AV delay was progressively shortened (p<0.05) with escalating exercise level (baseline: 123±26 ms vs. stage I: 102±24 ms vs stage II: 70±22 ms, p<0.05). AV delay optimisation led to a significantly higher cardiac output than without optimisation did during stage I (6.2±1.2 l/min vs. 5.2±1.2 l/min, p<0.001) and stage II (6.8±1.6 l/min vs. 5.9±1.3 l/min, p<0.001) exercise. A linear inverse relationship existed between optimal AV delays and heart rates in CRT patients (AV delay=241-1.61×heart rate, R2=0.639, p<0.001) and healthy controls (R2=0.646, p<0.001), but the slope of regression was significantly steeper in CRT patients (p<0.001).
  
  
  CONCLUSIONS
  Haemodynamically optimal AV delay shortened progressively with increasing heart rate during exercise, which suggests the need for programming of rate-adaptive AV delay in CRT recipients.
authors: Division of Cardiology, S.H. Ho Cardiovascular Disease and Stroke Centre, Prince of Wales Hospital, The Chinese University of Hong Kong, Hong Kong. jingpingsun6@yahoo.com
authors: Jing Ping
authors: JP
authors: Sun
authors: Alex Pui-Wai
authors: AP
authors: Lee
authors: Richard A
authors: RA
authors: Grimm
authors: Ming-Jui
authors: MJ
authors: Hung
authors: Xing Sheng
authors: XS
authors: Yang
authors: David
authors: D
authors: Delurgio
authors: Angel R
authors: AR
authors: Leon
authors: John D
authors: JD
authors: Merlino
authors: Cheuk-Man
authors: CM
authors: Yu
mesh_terms: D000328:Adult; D000368:Aged; D001283:Atrioventricular Node / Q000502:physiology*; D001642:Bicycling / Q000502:physiology; D002302:Cardiac Output / Q000502:physiology*; D058406:Cardiac Resynchronization Therapy / Q000379:methods*; D016022:Case-Control Studies; D004562:Electrocardiography; D015444:Exercise / Q000502:physiology*; D005260:Female; D006333:Heart Failure / Q000503:physiopathology / Q000628:therapy*; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged