On the basis of small studies with surrogate outcomes, current practice guidelines for managing ST-elevation myocardial infarction (STEMI) recommend maintaining a potassium level greater than 4.0 mEq/L. To explore the association of potassium levels with mortality, investigators used the Cerner Health Facts database to conduct a retrospective cohort study involving 38,689 patients with biomarker-confirmed acute MI and one or more serum potassium level measurements during hospitalization (mean number of measurements, 5.9). Mean admission potassium level was 4.2 mEq/L, and levels remained fairly constant during hospitalization.
In-hospital mortality was 6.9%. Mortality was lowest (4.8%) in patients with postadmission potassium levels of 3.5 to <4.0 mEq/L and similar (5.0%) in patients with postadmission potassium levels of 4.0 to <4.5 mEq/L. However, in-hospital mortality was twice that rate (10%) in patients with postadmission potassium levels of 4.5 to <5.0 mEq/L and continued to rise with higher potassium levels. In-hospital mortality was also significantly increased (13%) at potassium levels less than 3.5 mEq/L. The U-shaped association persisted after multivariable adjustment and did not differ between patients who received potassium supplementation during hospitalization and those who did not. In-hospital ventricular fibrillation or cardiac arrest occurred in 1707 patients (4.4%); rates of these events were relatively flat across a wide range of potassium levels and were substantively increased only in patients with the lowest or highest mean potassium levels (<3 or 
5.0 mEq/L).
Comment: These findings confirm that hypokalemia is associated with worse outcome in patients with acute myocardial infarction; moreover, they reveal a similar adverse effect of hyperkalemia. As editorialists note, the fact that mortality was not affected by potassium supplementation suggests that potassium level may be a marker of severity of illness or of other underlying conditions. Nonetheless, a serum potassium target somewhat lower and narrower than that currently recommended for these patients seems reasonable.
— Joel M. Gore, MD
Published in Journal Watch Cardiology February 8, 2012
