Magnesium levels and intravenous (IV) replacement were associated with outcomes in patients presenting with heart failure (HF). In this population-based retrospective cohort study published in Canadian Journal of Cardiology, linked administrative data from April 2012 to March 2020 were analyzed, including patients with a primary diagnosis of HF in the emergency department (ED) or hospital.

A total of 78,957 acute HF episodes across 42,763 patients were evaluated. Serum magnesium testing was performed in 58.7% of episodes. Among those tested, 31.7% had levels <0.75 mmol/L, 56.8% had levels between 0.75-0.95 mmol/L, and 11.5% had levels >0.95 mmol/L.
Magnesium levels were independently associated with mortality at both low (<0.70 mmol/L; hazard ratio [HR] 0.99; 95% confidence interval [CI] 0.98-0.99; P<0.001) and high (>0.86 mmol/L; HR 1.04; 95% CI 1.03-1.04; P<0.001) ranges.

Intravenous magnesium was administered in 13.7% of tested patients, including 29.7% without hypomagnesemia. After multivariable adjustment, IV magnesium was associated with higher short-term mortality (HR 1.66; 95% CI 1.40-1.96; P<0.0001) and hospitalization risk (HR 1.36; 95% CI 1.13-1.63; P<0.001).

Serum magnesium testing was common in patients presenting with HF, and both low and high magnesium levels were associated with worse outcomes. IV magnesium was associated with higher mortality and hospitalization, warranting further study.