TUESDAY, Jan. 10 (HealthDay News) -- Heart attack patients whose blood potassium levels are within a certain range are less likely to die than those with levels of the mineral below or above that range, says a new study that challenges current recommendations for potassium levels in heart attack patients.

Researchers looked at data from nearly 39,000 heart attack patients admitted to 67 U.S. hospitals between 2000 and 2008. Of those patients, nearly 7 percent died while they were hospitalized.

The death rate for patients with blood potassium levels of between 3.5 and less than 4 mEq/L (milliEquivalents per liter) was 4.8 percent, about the same as the 5 percent death rate among those with levels of 4 mEq/L to less than 4.5 mEq/L.

But mortality rose to 10 percent for those with levels of 4.5 to less than 5 mEq/L, and was even higher for those with levels greater than 5 mEq/L, the investigators found.

Patients with potassium levels of less than 3.5 mEq/L also had a higher death rate than those with levels of between 3.5 and less than 4.5 mEq/L, Dr. Abhinav Goyal, of the Emory Rollins School of Public Health in Atlanta, and colleagues, reported in the study published in the Jan. 11 issue of the Journal of the American Medical Association.

Currently, professional societies and experts recommend that potassium levels in heart attack patients should be maintained between 4.0 and 5.0 mEq/L or even 4.5 to 5.5 mEq/L, the researchers noted.

"In conclusion, our large study of patients with AMI [acute myocardial infarction, or heart attack] challenges current clinical practice guidelines that endorse maintaining serum potassium levels between 4.0 and 5.0 mEq/L," the study authors wrote.

The 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, treatments to quickly clear blockages and restore blood flow, and other treatment advances, the researchers said.

"Our data suggest that the optimal range of serum potassium levels in AMI patients may be between 3.5 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 study authors noted.

In an accompanying editorial, Dr. Benjamin Scirica and Dr. David Morrow of Brigham and Women's Hospital and Harvard Medical School wrote that proving maintaining certain potassium levels prevents deaths would require a clinical trial that randomly assigns patients to different treatments, which is unlikely to ever be done.

"Thus, decisions about care must be formulated on the basis of best available information," the editorialists wrote.

Given that it is inexpensive and relatively low-risk, it's "reasonable" to avoid abnormally low potassium levels of less than 3.5 mEq/L in heart attack patients.

"However, based on the report by Goyal [and colleagues], viewed together with previous smaller studies . . . routinely targeting levels greater than 4.5 mEq/L, do not appear justified."

More information

The U.S. National Heart, Lung, and Blood Institute has more about heart attack.