title: Exercise testing for non-invasive assessment of atrial electrophysiological properties in patients with persistent atrial fibrillation.
abstract: OBJECTIVE
  Experimental studies suggest that the autonomic nervous system modulates atrial refractoriness and conduction velocity in atrial fibrillation (AF). These modulatory effects are, however, difficult to assess in the clinical setting. This study sought to non-invasively characterize in patients with persistent AF, the influence of autonomic modulation induced by exercise on atrial fibrillatory rate as marker of atrial refractoriness and to identify clinical and electrocardiographic predictors of atrial rate response.
  
  
  RESULTS
  In 24 patients (16 males, mean age 60 +/- 13 years) with persistent AF (16 +/- 25 months), continuous ECGs were recorded during bicycle exercise testing. Fibrillatory rate (in fibrillations per minute, fpm) was assessed at baseline and immediately after termination of exercise with spatiotemporal QRST cancellation and time-frequency analysis. Ventricular response was characterized by time-domain HRV indices. Exercise had no influence on mean fibrillatory rate (409 +/- 42 vs. 414 +/- 43 fpm, P = NS). Seven patients responded to exercise with an increase in fibrillatory rate (26 +/- 10 fpm, P < 0.001 and three with a decrease (-21 +/- 8 fpm, P < 0.001), while the remaining 14 patients did not show a response. Responders' HRV indices changed in response to exercise similarly to that of non-responders. Their baseline fibrillatory rate was, however, lower than that of non-responders (387 +/- 18 vs. 425 +/- 48 fpm, P = 0.028). No other clinical or echocardiographic variable was associated with fibrillatory rate response. Twelve weeks after cardioverson, responders were more likely to remain in sinus rhythm than non-responders (88 vs. 46 %, P = 0.04).
  
  
  CONCLUSIONS
  Exercise-induced autonomic activation produces changes in atrial electrophysiological properties that can be detected by time-frequency analysis. Higher baseline fibrillatory rates are associated with an impaired atrial response to exercise that suggests advanced electrical remodelling and reduced sensitivity to autonomic stimuli.
authors.affiliation: Department of Cardiology, Otto-von-Guericke University, University Hospital, Leipziger Str. 44, 39120 Magdeburg, Germany.
authors.forename: Oliver
authors.initials: O
authors.lastname: Husser
authors.forename: Daniela
authors.initials: D
authors.lastname: Husser
authors.forename: Martin
authors.initials: M
authors.lastname: Stridh
authors.forename: Leif
authors.initials: L
authors.lastname: Sörnmo
authors.forename: Valentina D A
authors.initials: VD
authors.lastname: Corino
authors.forename: Luca T
authors.initials: LT
authors.lastname: Mainardi
authors.forename: Federico
authors.initials: F
authors.lastname: Lombardi
authors.forename: Helmut U
authors.initials: HU
authors.lastname: Klein
authors.forename: S Bertil
authors.initials: SB
authors.lastname: Olsson
authors.forename: Andreas
authors.initials: A
authors.lastname: Bollmann
mesh_terms: D001281:Atrial Fibrillation / Q000175:diagnosis*; D016275:Atrial Function; D003936:Diagnosis, Computer-Assisted / Q000379:methods*; D004562:Electrocardiography / Q000379:methods*; D005080:Exercise Test / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012008:Recurrence; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity