Potassium levels outside recommended range heighten mortality risk after acute MI

Issue: April 2012

Patients hospitalized after acute MI who had serum potassium levels of 3.5 mEq/L to 4.5 mEq/L had a lower risk for death compared with patients who had potassium levels that were higher or lower than this range, researchers reported in a new study.

“Our large study of patients with acute MI challenges current clinical practice guidelines that endorse maintaining serum potassium levels between 4 mEq/L and 5 mEq/L. 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 acute MI patients,” Abhinav Goyal, MD, MHS, of Emory Rollins School of Public Health in Atlanta, and colleagues wrote in the Journal of the American Medical Association.

Researchers conducted a retrospective cohort study to determine the relationship between serum potassium levels and in-hospital mortality in acute MI patients. The study included 38,689 patients with biomarker-confirmed acute MI who were admitted to 67 US hospitals from 2000 to 2008. All patients had in-hospital serum potassium measurements and were categorized by average postadmission serum potassium level.

Study results

Overall, 6.9% of patients died during hospitalization. Mortality was comparable for patients with postadmission potassium levels of 4 mEq/L to 4.5 mEq/L (5%) compared with a reference group with levels of 3.5 mEq/L to 4 mEq/L (4.8%). Among patients with potassium levels of 4.5 mEq/L to 5 mEq/L, mortality was twice as high, at 10%.

Of the more than 38,000 patients studied, 4.4% experienced an episode of ventricular fibrillation, ventricular flutter or cardiac arrest during hospitalization for acute MI. Rates of ventricular arrhythmias or cardiac arrest were higher only for patients with the highest (≥5 mEq/L) and lowest (<3 mEq/L) postadmission potassium levels compared with the reference group.

“Our data suggest that the optimal range of serum potassium levels in acute MI patients may be between 3.5 mEq/L and 4.5 mEq/L and that potassium levels of greater than 4.5 mEq/L are associated with increased mortality and should probably be avoided,” the researchers concluded.

Establishing optimal potassium levels

These data “cannot establish that treatment of hypokalemia alters outcome,” Benjamin M. Scirica, MD, MPH, and David A. Morrow, MD, MPH, of Brigham and Women’s Hospital and Harvard Medical School, wrote in an accompanying editorial.

“However, as noted by the authors, an adequately sized randomized trial of potassium repletion in acute MI is unlikely to be ever performed and, thus, decisions about care must be formulated on the basis of best available information,” Scirica and Morrow said. “Given that it is an inexpensive and relatively low-risk intervention, repletion of potassium for levels of less than 3 mEq/L remains reasonable. However … viewed together with previous smaller studies, potassium repletion for concentrations of 3.5 mEq/L to 4 mEq/L and routinely targeting levels greater than 4.5 mEq/L do not appear justified.”

For more information:

Disclosure: The researchers report no relevant financial disclosures.

Follow CardiologyToday.com on Twitter.