The observational study, published in the January 11 issue of JAMA, included 38,689 patients with biomarker-confirmed acute myocardial infarction (AMI), or heart attack, admitted to 67 U.S. hospitals between January 2000 and December 2008.
Researchers found that patients hospitalized after a heart attack with blood potassium levels between 3.5 and less than 4.5 mEq/L (milliEquivalents per liter) had a lower risk of death than patients with potassium levels that were higher or lower than this range.
Generally, the normal range for serum (blood) potassium is considered to be 3.5-5.0 mEq/L. However, in patients with AMI, clinical practice guidelines recommend maintaining a potassium value greater than 4.0 mEq/L (usually 4.0-5.0 mEq/L) in an effort to avoid ventricular arrhythmias.
“These guidelines are based on studies from the 1980s and early 1990s, a period in which beta-blockers and early reperfusion therapy were not yet standard of care,” says lead investigator Abhinav Goyal, MD, MHS, assistant professor of medicine (cardiology) at Emory University School of Medicine and faculty member in the Department of Epidemiology at Emory’s Rollins School of Public Health.
“In the current treatment era, ventricular arrhythmias in AMI patients are much less common than they were 20 years ago, so we decided to use current data and take a fresh look at the relationship between potassium levels and more relevant outcomes in AMI patients, particularly mortality, which prior investigations were too underpowered to study.”
The Emory study suggests that hospital mortality rates are twice as high in AMI patients with potassium levels of 4.5-5.0 mEq/L (the “upper third” of what is considered a “normal” potassium range of 3.5-5.0 mEq/L) compared to patients with potassium levels of 3.5 to <4.5 mEq/L (“lower and middle thirds” of the “normal” potassium range). At the same time, ventricular fibrillation / cardiac arrest rates did not increase significantly until potassium levels decreased below 3.0 mEq/L.
“Our large study of patients with AMI challenges current clinical practice guidelines and suggests that potassium levels greater than 4.5 mEq/L are associated with increased mortality and should probably be avoided,” says Goyal.
“Although our findings are observational, they suggest that it might be reasonable to amend the guidelines to recommend maintaining a potassium range between 3.5-4.5 mEq/L in most AMI patients.”
Goyal says the gold standard approach to determining the optimal potassium range in AMI patients would be to conduct a randomized, controlled trial but that is unlikely due to the high cost and regulatory burden associated with it.
Of the study patients, 2,679 (6.9 percent) died during hospitalization. The researchers found that compared with the reference group (3.5-<4.0 mEq/L; mortality rate, 4.8 percent), mortality was comparable for patients with postadmission potassium levels of 4.0 to less than 4.5 mEq/L (5.0 percent). Mortality was twice as great for potassium levels of 4.5 to less than 5.0 mEq/L (10.0 percent), and was even greater at higher potassium levels. Similarly, mortality rates were higher for potassium levels of less than 3.5 mEq/L.
Of the 38,689 patients with AMI, 1,707 (4.4 percent) had an episode of ventricular fibrillation, ventricular flutter or cardiac arrest during hospitalization. Rates of ventricular arrhythmias or cardiac arrest were higher (compared with the reference group, 3.5 <4.0 mEq/L) only for the lowest and highest average postadmission potassium levels (<3.0 mEq/L and 5.0 mEq/L or greater).
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