title: Body surface projection of action potential duration alternans: a combined clinical-modeling study with implications for improving T-wave alternans detection.
abstract: BACKGROUND
  Action potential duration alternans (APDA) can vary regionally in magnitude and phase. The influence of APDA heterogeneity on T-wave alternans (TWA) has not been defined.
  
  
  OBJECTIVE
  Our objectives were: (1) to determine how APDA affects the magnitude and spatial distribution of TWA, and (2) to optimize electrocardiographic (ECG) lead configuration accordingly to improve TWA detection.
  
  
  METHODS
  Global, regional, and discordant APDA were simulated in a 257-node heart model. Using a forward solution, body surface potentials were derived at 300 points on the thorax and TWA was computed at each point. In 22 patients with cardiomyopathy (left ventricular ejection fraction 28% +/- 6%), TWA was measured from a 114-electrode body surface map using the spectral method during atrial pacing at 110 beats/min.
  
  
  RESULTS
  An increase in global APDA from 4 to 12 ms resulted in an increase in maximum TWA from 10 to 30 microV. TWA magnitude varied with the size and location of the alternating myocardium, but was largest with discordant APDA compared with regional or global APDA. Irrespective of the location or phase of APDA, TWA was largest over the precordium and correlated with T-wave amplitude in the simulation (R(2) = 0.56 +/- 0.24, P <.01) and clinical study (R(2) = 0.45 +/- 0.23, P <.02). A novel lead configuration (12 precordial leads + limb leads) significantly improved maximum TWA detection compared with the conventional 12-lead ECG+ Frank lead configuration.
  
  
  CONCLUSIONS
  TWA magnitude is dependent on the interaction of concordant and discordant alternating sources within the heart. Maximum TWA consistently localizes to the precordium and a novel lead configuration using 12 precordial leads improves TWA quantification.
authors.affiliation: Division of Cardiology, University Health Network, Toronto, Canada.
authors.forename: Raja J
authors.initials: RJ
authors.lastname: Selvaraj
authors.forename: Adrian M
authors.initials: AM
authors.lastname: Suszko
authors.forename: Anandaraja
authors.initials: A
authors.lastname: Subramanian
authors.forename: Dhinesh
authors.initials: D
authors.lastname: Sivananthan
authors.forename: Ann
authors.initials: A
authors.lastname: Hill
authors.forename: Kumaraswamy
authors.initials: K
authors.lastname: Nanthakumar
authors.forename: Vijay S
authors.initials: VS
authors.lastname: Chauhan
mesh_terms: D000200:Action Potentials; D018780:Body Surface Potential Mapping; D009202:Cardiomyopathies / Q000175:diagnosis / Q000503:physiopathology*; D004562:Electrocardiography; D004699:Endocardium; D006329:Heart Conduction System / Q000503:physiopathology*; D006801:Humans; D008954:Models, Biological; D010496:Pericardium; D013223:Statistics as Topic; D013318:Stroke Volume; D013997:Time Factors; D016277:Ventricular Function, Left