Optimal potassium level after MI differs from guidelines, study finds

Post-myocardial infarction inpatients with blood potassium levels between 3.5 and 4.5 mEq/L had a lower mortality risk than those with levels higher or lower than this range, a new study found.
Current guidelines recommend maintaining serum potassium levels between 4.0 and 5.0 mEq/L in acute myocardial infarction (AMI) patients, but most studies on which the guidelines are based occurred before the routine use of beta-blockers, reperfusion therapy and early invasive management for eligible patients, the study authors noted. Those previous studies also focused on ventricular arrhythmias, not mortality, they said.
For their retrospective cohort study, the researchers examined data from 38,689 patients with AMI confirmed by biomarkers, who were admitted to 67 U.S. hospitals from 2000 through 2008. All patients had serum potassium measured in the hospital and were categorized by mean level after admission as <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 or ≥5.5 mEq/L.
Researchers found a U-shaped relationship between mean post-admission potassium level and in-hospital mortality. Nearly 7% of study patients (n=2,679, or 6.9%) died during hospitalization. Compared with the reference group (3.5 to <4.0 mEq/L; mortality rate, 4.8%), the group with levels of 4.0 to <4.5 mEq/L had similar mortality (5.0%). Patients with levels of 4.5 to <5.0 mEq/L had double the mortality rate (10%), and mortality was even higher for those at 5.0 mEq/L or higher.
Mortality rates were also higher for patients with potassium levels <3.5 mEq/L. However, rates of ventricular arrhythmias or cardiac arrest were higher (compared to the reference group) only for those with the lowest and highest average potassium levels (i.e, <3.0 mEq/L and ≥5.0 mEq/L). The study was published in the Jan. 11 Journal of the American Medical Association.
The findings "challenge current clinical practice guidelines" and suggest the optimal range of potassium levels in AMI patients is between 3.5 and 4.5 mEq/L, while levels greater than 4.5 mEq/L "should probably be avoided," the authors wrote. Editorialists largely agreed, saying potassium repletion for levels lower than 3.5 mEq/L "remains reasonable," while repletion for levels between 3.5 mEq/L and 4.0 mEq/L doesn't seem justified—and neither does targeting levels above 4.5 mEq/L.