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Study challenges potassium guidelines in acute MI

Reuters Health • The Doctor's Channel Daily Newscast

NEW YORK (Reuters Health) – Data released online today in the Journal of the American Medical Association challenge current guidelines for maintaining potassium levels immediately after a heart attack.

Clinical practice guidelines from major medical societies call for potassium to be kept above 4.0 mEq/L (usually 4.0 to 5.0 mEq/L) in this setting, to avoid ventricular arrhythmias.

But a report from Dr. Abhinav Goyal of Emory University in Atlanta, Georgia, and colleagues suggests serum potassium should be maintained at 3.5 to 4.5 mEq/L after acute myocardial infarction (MI), because levels above that are associated with increased mortality.

In an editorial, Dr. Benjamin Scirica and Dr. David Morrow of Brigham and Women’s Hospital in Boston say potassium repletion for concentrations of 3.5 to 4.0 mEq/L and routinely targeting levels greater than 4.5 mEq/L “do not appear justified,” based on this study and previous smaller ones.

In an email to Reuters Health, Dr. Goyal noted that current guidelines on potassium in acute MI are based on studies from the 1980’s and early 1990’s, before beta-blockers and early reperfusion therapy were standard of care.

“In the current treatment era, ventricular arrhythmias in acute MI patients are much less common than they were 20 years ago; therefore, we thought it would be important to take a fresh look at the relationship between potassium levels and more relevant outcomes (particularly mortality, which prior investigations were too underpowered to study),” Dr. Goyal said.

Using the Cerner Health Facts database, the researchers analyzed nearly 39,000 patients treated for acute MI at U.S. hospitals between 2000 and 2008. The total included 2,679 (6.9%) who didn’t survive to discharge.

On multivariate analysis, mortality was twice as high in patients with average postadmission potassium levels of 4.5 to 5.0 mEq/L as in patients with potassium levels of 3.5 to <4.5 mEq/L (i.e., the lower and middle thirds of the “normal” potassium range).

Mortality rates rose from 4.8% when the mean postadmission potassium level was 3.5 to <4.0 mEq/L, to 5.0% with a mean level of 4.0 to <4.5 mEq/L, 10% with levels of 4.5 to <5.0 mEq/L, and 24% in those with levels of 5.0 to <5.5 mEq/L.

Rates of ventricular arrhythmias or cardiac arrest were flat as potassium levels rose from 3.0 to 5.0 mEq/L; higher rates were observed only for potassium levels at or above 5.0 mEq/L, or below 3.0 mEq/L, according to the authors.

“Ventricular fibrillation/cardiac arrest rates did not increase significantly until potassium levels decreased below 3.0 mEq/L,” Dr. Goyal reported.

“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 and 4.5 mEq/L in most acute MI patients,” Dr. Goyal told Reuters Health.

“Even though our study did not look at potassium treatment per se, perhaps we also might also need to rethink the common practice (supported by existing guidelines) of routinely giving potassium supplementation to acute MI patients with potassium levels between 3.5 and <4.0 mEq/L, with the intent of increasing their potassium levels to 4.0 mEq/L or greater,” Dr. Goyal added.

“Our data suggest that this may not be sound practice, because of the potential risk of ‘overcorrecting’ potassium levels and increasing them to 4.5 mEq/L or greater — a range that was associated with harm in our study,” the researcher said.

SOURCE:

Serum Potassium Levels and Mortality in Acute Myocardial Infarction

JAMA 2012;307:157-164,195-196.