Park, Jae Y

Background: It is known that hypokalemia, hypocalcemia and hypomagnesemia cause a prolonged QTc interval and are associated with an increased risk of ventricular arrhythmias. However, there are limited data on optimal serum electrolytes for patients admitted to the coronary care unit (CCU). Objective: Here, we aimed to evaluate the relationship between serum potassium, ionized calcium and magnesium levels and in-hospital mortality in the CCU setting. Methods: This retrospective cohort study included 8,498 consecutive patients admitted to the CCU at an academic tertiary medical center from 2004 through 2013. The mean of serum electrolytes was categorized as <3.5, 3.5-<4.0, 4.0-<4.5 (reference), 4.5-<5.0, and ≥5.0 mEq/L for potassium; <4.4, 4.4-<4.6, 4.6-<4.8, 4.8-<5.0 (reference), and ≥5.0 mg/dL for ionized calcium; and <1.8, 1.8-<2.0, 2.0-<2.2 (reference), 2.2-<2.4, and ≥2.4 mg/dL for magnesium. Multivariate logistic regression analysis was used to determine the association between the mean of serum electrolytes and in-hospital mortality. Results: Of the 8,498 patients, 599 (7%) died during hospitalization. Relationship between mean serum potassium (U-shaped), ionized calcium (inverted J-shape) and magnesium (J-shaped) and in-hospital mortality was present in Figure. Serum potassium levels <3.5, 4.5-<5.0 and ≥5.0 mEq/L were independently associated with an increased risk of in-hospital mortality (adjusted OR 1.7 95% CI 1.1-2.5, OR 1.7 95% CI 1.3-2.2, and OR 3.4 95% CI 2.4-4.8, respectively), compared to the reference group. As for serum ionized calcium, the levels of <4.4, 4.4-<4.6, and 4.6-<4.8 mg/dL independently increased risk of mortality (adjusted OR 3.0 95% CI 2.3-4.0, OR 2.0 95% CI 1.5-2.6, and OR 1.4 95% CI, 1.1-1.8, respectively). As for serum magnesium, an only level above 2.4 mg/dL was associated with an increased mortality risk (OR 1.6 95% CI, 1.1-2.2). Conclusions: In the CCU setting, serum potassium 3.5-<4.5 mEq/L, ionized calcium ≥5.0 mg/dL and magnesium <2.4 mg/dL are associated with the lowest in-hospital mortality. These findings do not support supratherapeutic repletion of potassium and magnesium.