title: Implantable cardioverter-defibrillator shocks increase T-wave alternans.
abstract: BACKGROUND
  While implantable defibrillator shocks save lives, shock can lead to ventricular arrhythmias. However, the mechanism of shock-related proarrhythmia remains unclear. We evaluated the impact of ICD shock on repolarization instability, a factor associated with ventricular arrhythmogenesis.
  
  
  RESULTS
  Sixty-five patients with ICDs underwent ambulatory ECG monitoring during defibrillation testing 3 months postimplant. TWA was analyzed continuously in the time domain during baseline, sedated, and post-shock states. RR, QRS, and QT intervals and catecholamines were also measured continuously. Adequate pre- and post-shock Holter data were recorded in 55 patients, 48 male, mean 64 +/- 12 years, 50 with coronary disease, 48 with prior spontaneous or induced arrhythmia. TWA significantly increased after shock, from 9.6 +/- 0.5 to 11.9 +/- 0.6 microV, as did QRS duration, epinephrine, and norepinephrine levels, compared with sedated and baseline states. RR intervals decreased minimally. TWA changes with shock were not associated with RR or QRS duration changes, but were associated with changes in epinephrine.
  
  
  CONCLUSIONS
  ICD shock, even in the sedated state, increases repolarization instability as measured by TWA, an effect mediated in part by sympathetic stimulation. This association between shock and TWA may have important mechanistic and clinical implications for optimization of defibrillation therapy.
authors.affiliation: Department of Medicine, Yale University School of Medicine New Haven, Connecticut, USA. rachel.lampert@yale.edu
authors.forename: Rachel
authors.initials: R
authors.lastname: Lampert
authors.forename: Robert
authors.initials: R
authors.lastname: Soufer
authors.forename: Craig A
authors.initials: CA
authors.lastname: McPherson
authors.forename: William P
authors.initials: WP
authors.lastname: Batsford
authors.forename: Stephanie
authors.initials: S
authors.lastname: Tirado
authors.forename: Christine
authors.initials: C
authors.lastname: Earley
authors.forename: Anna
authors.initials: A
authors.lastname: Goldberg
authors.forename: Vladimir
authors.initials: V
authors.lastname: Shusterman
mesh_terms: D017147:Defibrillators, Implantable / Q000009:adverse effects*; D004554:Electric Countershock / Q000009:adverse effects*; D015716:Electrocardiography, Ambulatory; D005260:Female; D006333:Heart Failure / Q000517:prevention & control*; D006801:Humans; D008297:Male; D008875:Middle Aged; D018570:Risk Assessment / Q000379:methods*; D012307:Risk Factors; D014693:Ventricular Fibrillation / Q000175:diagnosis* / Q000209:etiology* / Q000517:prevention & control