title: High amplitude T-wave alternans precedes spontaneous ventricular tachycardia or fibrillation in ICD electrograms.
abstract: BACKGROUND
  T-wave alternans (TWA) increases acutely prior to ventricular tachycardia (VT) or fibrillation (VF) in animal studies, suggesting that it may provide a warning for VT/VF in implantable cardioverter defibrillator (ICD) patients. Clinically, measurement of surface ECG TWA requires preprocessing the input signal to reduce noise and/or analyzing more sinus beats than are recorded in ICDs as pre-onset, stored intracardiac electrograms (EGMs) before VT/VF. Our objective was to measure TWA from the few sinus EGMs stored in ICDs before spontaneous VT/VF in humans.
  
  
  OBJECTIVE
  The purpose of this study was to evaluate the technical feasibility of measuring TWA from pre-onset ICD EGMs and to measure EGM TWA before spontaneous VT/VF in humans.
  
  
  METHODS
  We developed a method to measure EGM TWA as a simple average (AVE) of peak-to-peak alternans. Using simulation, we determined the effect of ICD signal processing on EGM TWA for durations comparable to those in pre-onset EGMs. We then applied this method to pre-onset ICD EGMs that preceded 101 episodes of sustained VT/VF in 10 patients. In 6 of these patients, EGM recordings in atrial pacing and sinus rhythm provided control data.
  
  
  RESULTS
  In simulation, the AVE method discriminated input TWA differences > or = 15 microV. In patients, EGM TWA was 78 +/- 62 microV prior to VT/VF vs. 13 +/- 10 microV in control recordings (p< .0001). Eighty percent of pre-onset measurements exceeded 30 microV, while 95% of control measurements were less than 30 microV.
  
  
  CONCLUSIONS
  A simple averaging method can measure TWA preceding VT/VF in stored ICD EGMs. Pilot data indicate that high-amplitude EGM TWA usually precedes spontaneous VT/VF and is infrequent in control recordings. They provide a rationale for developing ICD technology to measure EGM TWA continuously, both to warn patients and to initiate pacing algorithms to prevent VT/VF.
authors.affiliation: Cedars Sinai Medical Center, Los Angeles, CA Medtronic Inc., Minneapolis, MN, USA. swerdlow@ucla.edu
authors.forename: Charles D
authors.initials: CD
authors.lastname: Swerdlow
authors.forename: Xiaohong
authors.initials: X
authors.lastname: Zhou
authors.forename: Olga
authors.initials: O
authors.lastname: Voroshilovsky
authors.forename: Athula
authors.initials: A
authors.lastname: Abeyratne
authors.forename: Jeff
authors.initials: J
authors.lastname: Gillberg
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D017147:Defibrillators, Implantable; D004562:Electrocardiography; D005240:Feasibility Studies; D005260:Female; D006329:Heart Conduction System; D006801:Humans; D008297:Male; D008875:Middle Aged; D017180:Tachycardia, Ventricular / Q000175:diagnosis / Q000503:physiopathology*; D014693:Ventricular Fibrillation / Q000175:diagnosis / Q000503:physiopathology*