title: Frequency analysis of atrial action potential alternans: a sensitive clinical index of individual propensity to atrial fibrillation.
abstract: BACKGROUND
  Few clinical indices identify the propensity of patients to atrial fibrillation (AF) when not in AF. Repolarization alternans has been shown to indicate AF vulnerability, but is limited in its sensitivity to detect changes in action potential (AP) duration (APD), which may be subtle. We hypothesized that spectral analysis would be a more sensitive and robust marker of AP alternans and thus a better clinical index of individual propensity to AF than APD alternans.
  
  
  RESULTS
  In 31 patients (12 persistent AF, 15 paroxysmal AF, 4 controls with no AF), we recorded left (n=27) and right (n=6) atrial monophasic APs during incremental pacing from cycle length 500 ms (120 beats per minute) to AF onset. Alternans was measured by APD and spectral analysis. At baseline pacing (median cycle length [1st, 3rd quartiles], 500 ms [500, 500]), APD alternans was detected in only 7 of 27 AF patients (no controls), whereas spectral AP alternans was detected in 18 of 27 AF patients (no controls; P=0.003); AP alternans was more prevalent in persistent than paroxysmal AF, and absent in controls (P=0.018 APD; P=0.042 spectral). Spectral AP alternans magnitude at baseline was highest in persistent AF, with modest rate-dependent amplification, followed by paroxysmal AF, with marked rate dependence, and undetectable in controls until just before induced AF.
  
  
  CONCLUSIONS
  Spectral AP alternans near baseline rates can identify patients with, versus those without, clinical histories and pathophysiological substrates for AF. Future studies should examine whether the presence of spectral AP alternans during sinus rhythm may obviate the need to actually demonstrate AF, such as on ambulatory ECG monitoring.
authors.affiliation: University of California-San Diego and Veterans Affairs Medical Center, San Diego, CA.
authors.forename: Gautam G
authors.initials: GG
authors.lastname: Lalani
authors.forename: Amir A
authors.initials: AA
authors.lastname: Schricker
authors.forename: Paul
authors.initials: P
authors.lastname: Clopton
authors.forename: David E
authors.initials: DE
authors.lastname: Krummen
authors.forename: Sanjiv M
authors.initials: SM
authors.lastname: Narayan
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D001281:Atrial Fibrillation / Q000503:physiopathology*; D022062:Electrophysiologic Techniques, Cardiac; D005260:Female; D006329:Heart Conduction System / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D011446:Prospective Studies; D012307:Risk Factors
keywords: action potential duration; action potentials; alternans; atrial fibrillation; spectral analysis