title: Serum potassium levels, cardiac arrhythmias, and mortality following non-ST-elevation myocardial infarction or unstable angina: insights from MERLIN-TIMI 36.
abstract: BACKGROUND
  In acute coronary syndrome (ACS), potassium levels <3.5 mEq/L are associated with ventricular arrhythmias. Current guidelines therefore recommend a potassium target >4.0 mEq/L in ACS. Our study evaluated the association between potassium levels, cardiac arrhythmias, and cardiovascular death in patients with non-ST-segment elevation myocardial infarction or unstable angina.
  
  
  METHODS
  Potassium levels were measured in 6515 patients prior to randomization to receive either ranolazine or a placebo in the MERLIN-TIMI 36 trial. A seven-day continuous electrocardiographic assessment was obtained to determine the incidence of non-sustained ventricular tachycardia (NSVT) and ventricular pauses. The association between potassium levels and cardiovascular death was evaluated using a Cox proportional hazards regression model with multivariable adjustment.
  
  
  RESULTS
  NSVT lasting for at least eight consecutive beats occurred more frequently at potassium levels <3.5 mEq/L than at potassium levels ⩾5 mEq/L (10.1 vs. 4.5%, p=0.03 for trend), whereas the inverse pattern was observed for ventricular pauses >3 s, which occurred more frequently at potassium levels ⩾5 mEq/L than at potassium levels <3.5 mEq/L (5.9 vs. 2.0%, p=0.03 for trend). There was a U-shaped relationship between the potassium level at admission and both early and late risk of cardiovascular death. Compared with patients with potassium levels of 3.5 to <4 mEq/L, a potassium level <3.5 mEq/L was associated with an increased risk of cardiovascular death at day 14 (2.4 vs. 0.8%, HRadj3.1, p=0.02) and at one year (6.4 vs. 3.0%, HRadj2.2, p=0.01). The risk of cardiovascular death at one year was also significantly increased at potassium levels ⩾4.5 mEq/L and a similar trend was noted at potassium levels ⩾5 mEq/L.
  
  
  CONCLUSIONS
  The lowest risk of cardiovascular death was observed in patients with admission potassium levels between 3.5 and 4.5 mEq/L. Both lower and higher levels of potassium were associated with tachyarrhythmias and bradyarrhythmias, suggesting a potential mechanistic explanation for the increased risk of cardiovascular death at the extremes of potassium homeostasis.
authors.affiliation: 1 TIMI Study Group, Division of Cardiology, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, USA.
authors.forename: Ravi B
authors.initials: RB
authors.lastname: Patel
authors.affiliation: 1 TIMI Study Group, Division of Cardiology, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, USA.
authors.forename: Sara
authors.initials: S
authors.lastname: Tannenbaum
authors.affiliation: 2 Hospital Clinico San Carlos, Spain.
authors.forename: Ana
authors.initials: A
authors.lastname: Viana-Tejedor
authors.affiliation: 1 TIMI Study Group, Division of Cardiology, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, USA.
authors.forename: Jianping
authors.initials: J
authors.lastname: Guo
authors.affiliation: 1 TIMI Study Group, Division of Cardiology, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, USA.
authors.forename: KyungAh
authors.initials: K
authors.lastname: Im
authors.affiliation: 1 TIMI Study Group, Division of Cardiology, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, USA.
authors.forename: David A
authors.initials: DA
authors.lastname: Morrow
authors.affiliation: 1 TIMI Study Group, Division of Cardiology, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, USA.
authors.forename: Benjamin M
authors.initials: BM
authors.lastname: Scirica
mesh_terms: D000368:Aged; D000789:Angina, Unstable / Q000150:complications / Q000378:metabolism / Q000401:mortality*; D001145:Arrhythmias, Cardiac / Q000175:diagnosis / Q000453:epidemiology*; D002317:Cardiovascular Agents / Q000627:therapeutic use; D004562:Electrocardiography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D000072658:Non-ST Elevated Myocardial Infarction / Q000150:complications / Q000378:metabolism / Q000401:mortality*; D011188:Potassium / Q000097:blood*; D000069458:Ranolazine / Q000627:therapeutic use
chemical_list: D002317:Cardiovascular Agents; D000069458:Ranolazine; D011188:Potassium
keywords: Arrhythmias; acute coronary syndrome; cardiovascular death; myocardial infarction; potassium levels; ventricular tachycardia