title: Shorter AV delays provide improved echocardiographic hemodynamics during exercise in patients receiving cardiac resynchronization therapy.
abstract: BACKGROUND
  Although atrial ventricular (AV) intervals are often optimized at rest in patients receiving cardiac resynchronization therapy (CRT), there are limited data on the impact of exercise on optimal AV interval.
  
  
  METHODS
  In 15 patients with CRT, AV intervals were serially programmed while patients were supine and at rest, and during exercise with heart rates that averaged 20 and 40 beats per minute above their resting rates. Echocardiographic Doppler images were acquired at each programmed AV interval and each rate. Three independent echocardiographic criteria were retrospectively used to determine each patient's optimal AV interval as a function of exercise-induced increased heart rates: the duration of left ventricular filling, stroke volume, and a clinical assessment of left ventricular function.
  
  
  RESULTS
  A negative correlation between the optimal AV interval and heart rate was observed across all patients using all three independent criterion: the maximum left ventricular filling time (slope =-0.77, intercept = 151.9, r = 0.55, P < 0.001), maximum stroke volume (slope =-0.93, intercept = 183.3, r = 0.50, P = 0.002), or the subjective clinical assessment (slope =-1.06, intercept = 182.0, r = 0.72, P < 0.001). Consistent trends were observed between all three parameters for 12 out of the 15 patients.
  
  
  CONCLUSIONS
  These results suggest that in patients indicated for CRT, rate-adaptive functions may be useful to shorten AV intervals with increased rate, in order to maximize left ventricular filling, stroke volume, and clinical left ventricular function. Further studies are necessary to determine the clinical impact of these rate-adaptive algorithms.
authors.affiliation: Department of Cardiovascular Medicine, The Cleveland Clinic, Cleveland, Ohio 44195, USA. grimmr@ccf.org
authors.forename: Richard A
authors.initials: RA
authors.lastname: Grimm
authors.forename: Jing Ping
authors.initials: JP
authors.lastname: Sun
authors.forename: Deborah
authors.initials: D
authors.lastname: Agler
authors.forename: Ben
authors.initials: B
authors.lastname: Fitzgerald
authors.forename: Bruce
authors.initials: B
authors.lastname: Wilkoff
authors.forename: Kathryn
authors.initials: K
authors.lastname: Hilpisch
authors.forename: George
authors.initials: G
authors.lastname: Perlic
authors.forename: Edward
authors.initials: E
authors.lastname: Chinchoy