title: Detection of T-wave alternans using an implantable cardioverter-defibrillator.
abstract: BACKGROUND
  Microvolt T-wave alternans (TWA) increases acutely prior to ventricular tachycardia (VT) or ventricular fibrillation (VF) in computer simulations and animal models, suggesting that TWA may provide a warning for VT/VF in patients with an implantable cardioverter-defibrillator (ICD).
  
  
  OBJECTIVE
  The purposes of this study were to develop a method for analyzing TWA recorded from ICD electrograms (EGMs) and to evaluate the degree of concordance between EGM TWA and TWA recorded from the surface ECG.
  
  
  METHODS
  We developed a software program to measure EGM TWA in the frequency domain and then used simulated EGMs to determine the effects of ICD signal processing, electrical noise, and variation in the EGM fiducial point on the recorded amplitude and K score (signal-to-noise ratio) of TWA. We then applied this method to analyze TWA simultaneously using both surface ECGs and ICD EGMs during incremental pacing in 25 ICD patients. Pacing modes and EGM sources were varied in repeated trials. EGMs with dynamic range adjusted to achieve a large T wave were telemetered to a digital Holter recorder and measured offline. ECG TWA was analyzed using a commercial system. A positive (+) ECG test had sustained alternans >or=1.9 microV with K score >or=3. Stored EGMs were reviewed for VT/VF during a 6-month follow-up period.
  
  
  RESULTS
  Simulations demonstrated that the EGM method accurately identified TWA >or=10 microV. Overall, 10 (40%) patients had at least one ECG TWA+ test and 15 patients (60%) had no ECG TWA+ tests. The maximum value of TWA was greater in EGMs than in ECGs (median 64 microV vs 2.2 microV, P <.0001). EGM TWA was greater in ECG TWA+ tests than in ECG TWA- tests (169 +/- 175 microV vs 71 +/- 61 microV, P <.001). Using a sustained EGM TWA threshold of 30 microV, EGM TWA was concordant with ECG TWA in 63 (84%) of 75 analyzed tests (P <.0001) and predicted ECG TWA results with 85% sensitivity and 84% specificity. Both ECG and EGM TWA predicted VT/VF during follow-up (ECG: P = .006; EGM: P = .035).
  
  
  CONCLUSIONS
  The amplitude of TWA is at least 10 times greater on ICD EGMs than on surface ECGs. EGM and ECG TWA have substantial concordance and comparable predictive value for spontaneous VT/VF. These observations support the hypothesis that ECG and EGM TWA detect the same electrical alternans phenomenon.
authors.affiliation: Cedars Sinai Medical Center, Los Angeles, California 90048, USA.
authors.forename: Offir
authors.initials: O
authors.lastname: Paz
authors.forename: Xiaohong
authors.initials: X
authors.lastname: Zhou
authors.forename: Jeff
authors.initials: J
authors.lastname: Gillberg
authors.forename: Hsiang-Jer
authors.initials: HJ
authors.lastname: Tseng
authors.forename: Eli
authors.initials: E
authors.lastname: Gang
authors.forename: Charles
authors.initials: C
authors.lastname: Swerdlow
mesh_terms: D000368:Aged; D017147:Defibrillators, Implantable; D015716:Electrocardiography, Ambulatory; D005260:Female; D005500:Follow-Up Studies; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D015203:Reproducibility of Results; D017180:Tachycardia, Ventricular / Q000175:diagnosis* / Q000503:physiopathology / Q000628:therapy