title: Sinus bradycardia during hypothermia in comatose survivors of out-of-hospital cardiac arrest - a new early marker of favorable outcome?
abstract: BACKGROUND
  Bradycardia is a common finding in patients undergoing therapeutic hypothermia (TH) following out-of-hospital cardiac arrest (OHCA), presumably as a normal physiological response to low body temperature. We hypothesized that a normal physiological response with sinus bradycardia (SB) indicates less neurological damage and therefore would be associated with lower mortality.
  
  
  METHODS
  We studied 234 consecutive comatose survivors of OHCA with presumed cardiac etiology and shockable primary rhythm, who underwent a full 24-h TH-protocol (33°C) at a tertiary heart center (years: 2004-2010). Primary endpoint was 180-day mortality; secondary endpoint was favorable neurological outcome (180-day cerebral performance category: 1-2).
  
  
  RESULTS
  SB, defined as sinus rhythm <50 beats per minute during TH, was present in 115 (49%) patients. Baseline characteristics including sex, witnessed arrest, bystander cardiopulmonary resuscitation and time to return of spontaneous circulation were not different between SB- and no-SB patients. However, SB-patients were younger, 57±14 vs. 63±14 years, p<0.001 and less frequently had known heart failure (7% vs. 20%, p<0.01). Patients experiencing SB during the hypothermia phase of TH had a 17% 180-day mortality rate compared to 38% in no-SB patients (p<0.001), corresponding to a 180-day hazard ratio (HRadjusted=0.45 (0.23-0.88, p=0.02)) in the multivariable analysis. Similarly, SB during hypothermia was directly associated with lower odds of unfavorable neurological outcome (ORunadjusted=0.42 (0.23-0.75, p<0.01).
  
  
  CONCLUSIONS
  Sinus bradycardia during therapeutic hypothermia is independently associated with a lower 180-day mortality rate and may thus be a novel, early marker of favorable outcome in comatose survivors of OHCA.
authors.affiliation: Department of Cardiology 2142, The Heart Centre, Copenhagen University Hospital, Rigshospitalet, Denmark. Electronic address: jakob@jht.dk.
authors.forename: Jakob Hartvig
authors.initials: JH
authors.lastname: Thomsen
authors.affiliation: Department of Cardiology 2142, The Heart Centre, Copenhagen University Hospital, Rigshospitalet, Denmark.
authors.forename: Christian
authors.initials: C
authors.lastname: Hassager
authors.affiliation: Department of Cardiology 2142, The Heart Centre, Copenhagen University Hospital, Rigshospitalet, Denmark.
authors.forename: John
authors.initials: J
authors.lastname: Bro-Jeppesen
authors.affiliation: Department of Cardiology 2142, The Heart Centre, Copenhagen University Hospital, Rigshospitalet, Denmark.
authors.forename: Helle
authors.initials: H
authors.lastname: Søholm
authors.affiliation: Department of Anesthesia and Intensive Care, Helsingborg Hospital, Helsingborg, Sweden.
authors.forename: Niklas
authors.initials: N
authors.lastname: Nielsen
authors.affiliation: Department of Thoracic Anesthesiology, The Heart Centre, Copenhagen University Hospital, Rigshospitalet, Denmark.
authors.forename: Michael
authors.initials: M
authors.lastname: Wanscher
authors.affiliation: Department of Cardiology 2142, The Heart Centre, Copenhagen University Hospital, Rigshospitalet, Denmark.
authors.forename: Lars
authors.initials: L
authors.lastname: Køber
authors.affiliation: Department of Cardiology 2142, The Heart Centre, Copenhagen University Hospital, Rigshospitalet, Denmark.
authors.forename: Steen
authors.initials: S
authors.lastname: Pehrson
authors.affiliation: Department of Cardiology 2142, The Heart Centre, Copenhagen University Hospital, Rigshospitalet, Denmark.
authors.forename: Jesper
authors.initials: J
authors.lastname: Kjaergaard
mesh_terms: D000328:Adult; D000368:Aged; D001919:Bradycardia / Q000453:epidemiology*; D003128:Coma / Q000209:etiology* / Q000401:mortality; D003718:Denmark; D005260:Female; D006801:Humans; D007036:Hypothermia, Induced / Q000009:adverse effects*; D008297:Male; D008875:Middle Aged; D058687:Out-of-Hospital Cardiac Arrest / Q000150:complications / Q000401:mortality* / Q000628:therapy*; D017063:Outcome Assessment, Health Care; D015995:Prevalence; D012189:Retrospective Studies; D015996:Survival Rate
keywords: Out-of-hospital cardiac arrest; Outcome; Prognostic factor; Sinus bradycardia; Target temperature management; Therapeutic hypothermia