title: A novel method for determining the phase of T-wave alternans: diagnostic and therapeutic implications.
abstract: BACKGROUND
  T-wave alternans (TWA) has been implicated in the pathogenesis of ventricular arrhythmias and sudden cardiac death. However, to estimate and suppress TWA effectively, the phase of TWA must be accurately determined.
  
  
  RESULTS
  We developed a method that computes the beat-by-beat integral of the T-wave morphology, over time points within the T-wave with positive alternans. Then, we estimated the signed derivative of the T-wave integral sequence, which allows the classification of each beat to a binary phase index. In animal studies, we found that this method was able to accurately identify the T-wave phase in artificially induced alternans (P<0.0001). The coherence of the phase increased consistently after acute ischemia induction in all body-surface and intracardiac leads (P<0.0001). Also, we developed a phase-resetting detection algorithm that enhances the diagnostic utility of TWA. We further established an algorithm that uses the phase of TWA to deliver appropriate polarity-pacing pulses (all interventions compared with baseline, P<0.0001 for alternans voltage; P<0.0001 for K(score)), to suppress TWA. Finally, we demonstrated that using the phase of TWA we can suppress spontaneous TWA during acute ischemia; 77.6% for alternans voltage (P<0.0001) and 92.5% for K(score) (P<0.0001).
  
  
  CONCLUSIONS
  We developed a method to quantify the temporal variability of the TWA phase. This method is expected to enhance the utility of TWA in predicting ventricular arrhythmias and sudden cardiac death and raises the possibility of using upstream therapies to abort a ventricular tachyarrhythmia before its onset.
authors.affiliation: Cardiovascular Research Center.
authors.forename: Omid
authors.initials: O
authors.lastname: Sayadi
authors.forename: Faisal M
authors.initials: FM
authors.lastname: Merchant
authors.forename: Dheeraj
authors.initials: D
authors.lastname: Puppala
authors.forename: Theofanie
authors.initials: T
authors.lastname: Mela
authors.forename: Jagmeet P
authors.initials: JP
authors.lastname: Singh
authors.forename: E Kevin
authors.initials: EK
authors.lastname: Heist
authors.forename: Chris
authors.initials: C
authors.lastname: Owen
authors.forename: Antonis A
authors.initials: AA
authors.lastname: Armoundas
mesh_terms: D000200:Action Potentials; D000465:Algorithms; D000818:Animals; D001145:Arrhythmias, Cardiac / Q000175:diagnosis* / Q000209:etiology / Q000503:physiopathology; D002304:Cardiac Pacing, Artificial; D004195:Disease Models, Animal; D004562:Electrocardiography; D022062:Electrophysiologic Techniques, Cardiac; D006329:Heart Conduction System / Q000503:physiopathology*; D008297:Male; D017202:Myocardial Ischemia / Q000150:complications / Q000503:physiopathology; D011237:Predictive Value of Tests; D012815:Signal Processing, Computer-Assisted; D013552:Swine; D013997:Time Factors
keywords: alternans; arrhythmia (heart rhythm disorders); defibrillators, implantable; pacing