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19-01-2012 | Cardiology | Article

Serum potassium in MI patients should be lower than currently recommended


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MedWire News: Research suggests that the serum potassium levels in patients admitted to hospital with acute myocardial infarction (AMI) should be maintained within a lower range than is recommended by current guidelines.

The findings suggest that AMI inpatients who have a postadmission serum potassium level between 3.5 and 4.5 mEq/L are less likely to die than those with higher or lower potassium levels. However, current guidelines endorse maintaining serum potassium levels between 4.0 and 5.0 mEq/L or, in some cases, 4.5 and 5.5 mEq/L, note Abhinav Goyal (Emory Schools of Public Health and Medicine, Atlanta, Georgia, USA) and colleagues in JAMA.

They conducted a retrospective cohort study of 38,689 patients with biomarker-confirmed AMI who were admitted to hospital between January 2000 and December 2008. In-hospital serum potassium measurements were taken for all patients.

Overall, 2679 (6.9%) patients died during hospitalization.

The findings revealed a U-shaped relationship between mean postadmission serum potassium level and in-hospital mortality, which persisted after multivariate adjustment.

The mortality rate was comparable between the reference groups, with postadmission potassium levels of 3.5 to less than 4.0 mEq/L, and patients with levels of 4.0 to less than 4.5 mEq/L.

But the risk for mortality doubled for patients with postadmission potassium of 4.5 to less than 5.0 mEq/L, at 10%, and was even greater at higher potassium levels, at 25% for patients with a potassium level of 5.0 to less than 5.5 mEq/L, and 61% for patients with a level of 5.5 mEq/L or greater.

Of note, mortality was also significantly higher among patients with a potassium level of less than 3.5 mEq/L, at 11%, than the reference group.

Of the 38,689 patients with AMI, 1707 (4.4%) experienced an episode of ventricular fibrillation, ventricular flutter, or cardiac arrest during hospitalization.

After adjusting for covariates including potassium level at admission, the rates of ventricular arrhythmia or cardiac arrest were higher among those with the very lowest and highest mean postadmission levels (<3.0 mEq/L and ≥5.0 mEq/L) than in the reference group.

"Maintaining serum potassium levels between 3.5 and 4.5 mEq/L may be more advisable than the 4.0 to 5.0 mEq/L range currently recommended by practice guidelines in patients with AMI," write the authors.

"These [current] 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."

The authors point out that their findings apply solely to patients with AMI and cannot be extrapolated to patients with other cardiac conditions, including heart failure. They say that studies similar to theirs should be replicated in the heart failure population.

In a related commentary, editorialists Benjamin Scirica and David Morrow from the Harvard Medical School in Boston, Massachusetts, USA write: "It remains clinically reasonable to avoid significant hypokalemia (<3.5 mEq/L) in patients post-AMI, particularly with significant, sustained, ventricular ectopy or other high-risk features."

By Piriya Mahendra

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