title: Myocardial injury secondary to ICD shocks: insights from patients with lead fracture.
abstract: BACKGROUND
  Patients who receive appropriate implantable cardioverter defibrillator (ICD) shocks have a subsequent adverse prognosis. Most data suggest that patients with inappropriate ICD shocks also have a subsequent adverse prognosis, although this is more controversial. The shocks may be an epiphenomenon, that is, a marker of underlying disease progression; however, it cannot be excluded that shocks cause direct myocardial damage. This latter question is difficult to clarify as the arrhythmia provoking the shock can also cause troponin release. Inappropriate shocks secondary to lead fracture are an ideal situation to examine this question; any troponin release in an otherwise well and hemodynamically stable patient, is likely due directly to the shocks.
  
  
  METHODS
  All patients with Fidelis lead fracture admitted to our institution with inappropriate shocks were included in this study. Troponin (I or T) was considered positive if the level was above the 99th percentile reference cutoff.
  
  
  RESULTS
  Elevated troponin levels were recorded in 16 of 22 patients (73%). Patients with elevated troponin received a higher number of shocks (20.3 ± 30.1 vs 5.3 ± 4.8, P = 0.07) compared with patients with normal troponin. Very elevated troponin levels (>0.8 mcg/L) were seen in five of 22 (22%) patients. The mean peak troponin level for these five patients was 7.06 ± 8.56 mcg/L; two patients had troponin levels that would be expected from a medium-sized myocardial infarction or severe myocarditis.
  
  
  CONCLUSIONS
  Troponin elevation occurred in the majority of our patients after inappropriate ICD discharges secondary to lead fracture. This indicates that ICD shocks can cause myocardial injury.
authors.affiliation: Division of Cardiology, Department of Medicine, University of Ottawa Heart Institute, Ottawa, Ontario, Canada.
authors.forename: Raed Abu
authors.initials: RA
authors.lastname: Sham'a
authors.forename: Pablo
authors.initials: P
authors.lastname: Nery
authors.forename: Mouhannad
authors.initials: M
authors.lastname: Sadek
authors.forename: Derek
authors.initials: D
authors.lastname: Yung
authors.forename: Calum
authors.initials: C
authors.lastname: Redpath
authors.forename: Mark
authors.initials: M
authors.lastname: Perrin
authors.forename: Bradley
authors.initials: B
authors.lastname: Sarak
authors.forename: David
authors.initials: D
authors.lastname: Birnie
mesh_terms: D000328:Adult; D015415:Biomarkers / Q000097:blood; D017147:Defibrillators, Implantable / Q000009:adverse effects*; D004556:Electric Injuries / Q000097:blood / Q000209:etiology*; D004567:Electrodes, Implanted / Q000009:adverse effects*; D004868:Equipment Failure; D005260:Female; D006335:Heart Injuries / Q000097:blood / Q000209:etiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009203:Myocardial Infarction / Q000097:blood / Q000175:diagnosis / Q000209:etiology*; D009864:Ontario; D012189:Retrospective Studies; D014336:Troponin / Q000097:blood*
chemical_list: D015415:Biomarkers; D014336:Troponin
keywords: ICD leads; implantable cardioverter defibrillator; inappropriate shocks; lead fracture; troponin