title: Can body surface microvolt T-wave alternans distinguish concordant and discordant intracardiac alternans?
abstract: BACKGROUND
  There is convincing experimental evidence that cellular action potential duration (APD) alternans is arrhythmogenic but its relationship with body surface microvolt T-wave alternans (MTWA) remains unclear. We investigated the relationship between MTWA and APD alternans induced by alternating cycle length (CL) pacing in a pig model.
  
  
  METHODS
  In 10 pigs, catheters in the right atrium (RA) and right (RV) and left ventricle (LV) allowed pacing and recording of monophasic action potentials (MAP). During RA pacing at stable 500-ms CL, LV was paced at alternating CL (505 ms and 495 ms). Changing the alternating LV (A-LV) pacing delay changes the size of the region with alternating ventricular activation. Spectral analysis of intracardiac MAP was correlated with body surface MTWA. In a similar setup (during alternating pacing in RV and LV), we investigated concordant versus discordant APD alternans.
  
  
  RESULTS
  Pacing the LV with subtle alternating cycle lengths at short A-LV delay leads to broad QRS (97 ± 10 ms), body surface MTWA (mean Valt 4.2 ± 1.8 µV), and positive RR-interval alternans. At longer A-LV delay, not resulting in QRS widening (68 ± 5 ms), body surface RR alternans was absent but MTWA remained detectable and was even more pronounced (8.7 ± 5.1 µV, P < 0.01). During both concordant and discordant pacing MTWA was present. The precordial leads were better for detecting discordant APD alternans (8.0 ± 2.9 µV and 12.8 ± 4.52 µV, P = 0.02).
  
  
  CONCLUSIONS
  MTWA is a potent technique to detect subtle and isolated intracardiac APD alternans that is artificially induced by alternating pacing. In the same model, discordant activation alternans can only be discriminated from concordant when using a quantifying approach of MTWA analysis.
authors.affiliation: Department of Cardiovascular Diseases, Division of Experimental Cardiology, University of Leuven, Campus Gasthuisberg, Herestraat, Leuven, Belgium.
authors.forename: Vincent
authors.initials: V
authors.lastname: Floré
authors.forename: Piet
authors.initials: P
authors.lastname: Claus
authors.forename: Rolf
authors.initials: R
authors.lastname: Symons
authors.forename: Godfrey L
authors.initials: GL
authors.lastname: Smith
authors.forename: Karin R
authors.initials: KR
authors.lastname: Sipido
authors.forename: Rik
authors.initials: R
authors.lastname: Willems
mesh_terms: D000465:Algorithms; D000818:Animals; D001145:Arrhythmias, Cardiac / Q000175:diagnosis* / Q000503:physiopathology*; D018780:Body Surface Potential Mapping / Q000379:methods*; D003936:Diagnosis, Computer-Assisted / Q000379:methods*; D003937:Diagnosis, Differential; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013552:Swine
keywords: T-wave alternans; action potential duration alternans