Mortality and Serum Potassium Levels

For patients with cardiovascular disease, maintaining stable levels of potassium is important in preventing adverse events. Studies have found an association between low serum potassium levels, defined as <3.5 mEq/L, and the risk of ventricular arrhythmias in patients with acute myocardial infarction (AMI). Professional societies recommend maintaining potassium levels between 4.0 and 5.0 mEq/L or 4.5 to 5.5 mEq/L in patients with AMI. The previous studies, however, were conducted prior to the routine use of beta-blockers, reperfusion therapy, and early invasive management in eligible AMI patients; the studies were small and focused on the outcome of postinfarction ventricular arrhythmias, which occur less frequently with the available AMI treatments. Therefore, according to researchers, there is a need for current data that define the optimal range of serum potassium levels with respect to mortality and other clinical outcomes in patients with AMI. The researchers recently conducted a retrospective cohort study to (1) characterize the distribution and trend of serum potassium levels during hospitalization in patients with AMI; (2) determine the relationship between serum potassium levels and in-hospital mortality; and (3) evaluate the relationship between potassium levels and ventricular arrhythmias or cardiac arrest in patients with AMI. They reported study results in the Journal of the American Medical Association [2012;307(2):157-164]. Data from the Cerner Health Facts database representing 67 US hospitals and 38,689 patients with AMI hospitalized between January 1, 2000, and December 31, 2008, were used in the study. The primary outcome was in-hospital mortality, documented in the Health Facts database. Secondary outcomes were the composite of ventricular fibrillation or flutter, or cardiac arrest during hospitalization (both documented by International Classification of Diseases, Ninth Revision, Clinical Modification codes). All patients had in-hospital potassium measurements and were classified by potassium serum levels: <3.0, 3.0 to <3.5, 3.5 to <4.0, 4.0 to <4.5, 4.5 to <5.0, 5.0 to <5.5, and ≥5.5 mEq/L. There was a U-shaped relationship between in-hospital mortality and mean postadmission potassium level. Compared with the reference group (3.5-<4.0 mEq/L; mortality rate 4.8%; 95% confidence interval [CI], 4.4%-5.1%), mortality was comparable for patients with a mean postadmission potassium level of 4.0 to <4.5 mEq/L (5.0%; 95% CI, 4.7%-5.3%), multivariable adjusted odds ratio (OR), 1.19; 95% CI, 1.04-1.36. Mortality was twice as great for potassium levels of 4.5 to <5.0 mEq/L (10.0%; 95% CI, 9.1%-10.9%) (multivariable adjusted OR, 1.99; 95% CI, 1.68-2.36), and was even greater at higher potassium levels. In addition, mortality rates were higher for potassium levels >3.5 mEq/L. In contrast, rates of ventricular fibrillation or cardiac arrest were higher only among patients with potassium levels <3.0 mEq/L and at levels ≥5.0 mEq/L. In summary, the researchers noted that “among inpatients 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.”