Patients with heart failure who have low to low-normal serum potassium levels (less than 4 mEq/L) are at increased risk of death compared with peers who have levels between 4 and 5.5 mEq/L, according to an article in the June issue of European Heart Journal.

The study, which was conducted at University of Alabama at Birmingham (USA), is the first to look directly at the long-term effect of low potassium levels in a population of propensity-matched heart failure patients.

Investigators studied 1,187 pairs of patients - half with low potassium and half with normal levels - who were balanced in all measured baseline covariates. They were enrolled in the Digitalis Investigation Group, a large clinical trial of heart failure patients conducted in 302 centers in the United States and Canada from 1991 to 1993. The study was funded by a grant from the National Heart, Lung and Blood Institute, one of the National Institutes of Health.

“Our findings showed that heart failure patients with low to low-normal (less than 4 mEq/L) potassium levels were more likely to die than those with higher levels (4 to 5.5 mEq/L) of potassium,” said Ali Ahmed, MD, associate professor of medicine in the Division of Gerontology, Geriatrics and Palliative Care and director, Geriatric Heart Failure Clinics, at UAB and the study’s lead investigator. “These patients were not significantly more likely to be hospitalized than the higher potassium group, suggesting that most low potassium associated deaths were sudden deaths due to ventricular arrhythmias.”

“It would appear that the threshold for low potassium, 3.5 mEq/L, needs to be raised for chronic heart failure and that any of these patient with a potassium level less than 4 mEq/L should be considered as having low potassium and thus at increased risk of death,” said Ahmed.

Of particular concern for clinicians, according to Ahmed, is the link between low potassium and diuretics. Diuretics are a common medication for patients with heart failure, and are known to cause low potassium.

“Our findings suggest that low potassium levels in patients with chronic heart failure should be corrected and potassium should be maintained above 4 mEq/L,” said Ahmed. “However, whether this should be maintained using potassium supplements or an aldosterone antagonist such as spironolactone is currently unknown. Spironolactone reduces mortality in heart failure patients, and also raises potassium levels. Potassium supplements, on the other hand, are commonly used, and yet their long-term effects on outcomes are unknown.”