Serum Potassium Levels and Mortality in Acute Myocardial Infarction
What is the association between average serum potassium during hospitalization and the outcome of patients with acute myocardial infarction (AMI)?
The authors retrospectively evaluated the outcome of 38,689 patients in the Cerner Health Facts database, who were hospitalized with biomarker-confirmed AMI, to 67 US hospitals from 2000-2008. All patients had in-hospital serum potassium measurements and were categorized by mean postadmission serum potassium level (<3.0, 3.0-<3.5, 3.5-<4.0, 4.0-<4.5, 4.5-<5.0, 5.0-<5.5, and >5.5 mEq/L). Hierarchical logistic regression was used to determine the association between potassium levels and outcomes after adjusting for patient- and hospital-level factors.
There was a U-shaped relationship between mean postadmission serum potassium level and in-hospital mortality that persisted after multivariable adjustment for multiple factors. The mortality among the reference group with potassium (K) levels of 3.5-<4.0 mEq/L was 4.8% (95% confidence interval [CI], 4.4%-5.2%), and was similar in those with postadmission potassium of 4.0-<4.5 mEq/L (5.0%; 95% CI, 4.7%-5.3%; adjusted OR, 1.19 [95% CI, 1.04-1.36]). Mortality increased with an increase in serum potassium (K 4.5-<5.0 mEq/L, mortality 10.0%; adjusted OR, 1.99; 95% CI, 1.68-2.36; K 5-<5.5 mEq/L, mortality 24.8%, adjusted OR, 3.27; 95% CI, 2.52-4.24; K >5.5 mEq/L mortality 61.4%, adjusted OR, 6.44; 95% CI, 4.27-9.70). A lesser degree of increase in mortality was observed with decreasing average potassium levels (K <3 mEq/L, mortality 46.2%, adjusted OR, 8.11; 95% CI, 2.69-24.2; K 3-<3.5 mEq/L, mortality 11.4, adjusted OR, 1.45; 95% CI, 1.06-1.99). Rates of ventricular fibrillation or cardiac arrest were higher only among patients with potassium levels of <3.0 mEq/L and at levels of 5.0 mEq/L or greater.
The authors concluded that among patients hospitalized with AMI, the lowest mortality was observed in those with postadmission serum potassium levels between 3.5 and <4.5 mEq/L compared with those who had higher or lower potassium levels.
The authors evaluated a large database and demonstrated a U-shaped relationship between average serum potassium and mortality in patients with AMI. There was a disconnect between occurrence of cardiac arrest or ventricular fibrillation and total mortality at both extremes, and an increase in cardiac arrests or ventricular fibrillation was seen only with extreme levels of serum potassium. This raises concern about residual confounding and reverse causality, the elegant analytical design notwithstanding. Although prior guidelines are based on a small body of observational data, it may be premature to change current practice without randomized data.
Keywords: Myocardial Infarction, Potassium, Hospital Mortality, Biological Markers, Ventricular Fibrillation, Hypokalemia, Cardiovascular Diseases, Heart Arrest, Confidence Intervals, Logistic Models
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