Blog | Thursday, January 12, 2012

QD: News Every Day--Goldilocks offers insight for potassium blood levels after heart attack

There's a lower risk of death among hospitalized heart attack patients who maintained blood potassium levels between 3.5 and 4.5 mEq/L compared to lower or higher levels, a retrospective study concluded.

Applying the Goldilocks rule, not too much and not too little seems to just right for acute myocardial infarction [AMI] patients. But two clinical practice guidelines (here and here) recommend maintaining serum potassium levels between 4.0 and 5.0 mEq/L in patients after a heart attack.

The study authors commented that up to now, "Potassium homeostasis [equilibrium] is critical to prevent adverse events in patients with cardiovascular disease. Several studies have demonstrated a relationship between low serum potassium levels, usually less than 3.5 mEq/L, and the risk of ventricular arrhythmias in patients with acute myocardial infarction [AMI; heart attack]. On the basis of these studies, experts and professional societies have recommended maintaining potassium levels between 4.0 and 5.0 mEq/L, or even 4.5 to 5.5 mEq/L, in AMI patients.

However, most prior studies were conducted before the routine use of beta-blockers, reperfusion therapy, and early invasive management, the authors noted in the Jan. 11 issue of the Journal of the American Medical Association.

A retrospective cohort study included 38,689 patients with biomarker-confirmed AMI admitted to 67 U.S. hospitals between January 2000 and December 2008. All patients had in-hospital serum potassium measurements and were categorized by average postadmission serum potassium level.

Of all patients, 1,707 (4.4%) 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 to 4.0 mEq/L) only for the lowest and highest average postadmission potassium levels (less than 3.0 mEq/L and 5.0 mEq/L or greater).

Of the study patients, 2,679 (6.9%) died during hospitalization. There was a U-shaped relationship between mean postadmission serum potassium level and in-hospital mortality, according to the study.

Compared to patients with potassium blood levels of 3.5 to 4.0 mEq/L (mortality rate, 4.8%), mortality was comparable for patients with postadmission potassium levels of 4.0 to less than 4.5 mEq/L (mortality rate, 5%; odds ratio (OR), 1.19 (95% confidence interval [CI], 1.04 to 1.36). Mortality was twice as great for potassium levels of 4.5 to less than 5.0 mEq/L (mortality rate, 10%; multivariable-adjusted OR, 1.99; 95% CI, 1.68 to 2.36), and was even greater at higher potassium levels. Similarly, mortality rates were higher for potassium levels of less than 3.5 mEq/L.

"In conclusion, our large study of patients with AMI challenges current clinical practice guidelines that endorse maintaining serum potassium levels between 4.0 and 5.0 mEq/L," the authors concluded. "These guidelines are based on small, older studies that focused only on ventricular arrhythmias (and not mortality) and were conducted before the routine use of beta-blockers, reperfusion therapy, and early invasive management in AMI patients."

An accompanying editorial noted the report doesn't establish treating hypokalemia alters outcome. However, a randomized, controlled trial is unlikely, so based on current knowledge, the inexpensive and relatively low-risk repletion of potassium for levels of less than 3.5 mEq/L remains reasonable, but repletion for higher levels than this "do not appear justified."