Outcomes and Patterns Related to Magnesium in Acute Heart Failure: A Population-Based Study

<h2>Abstract</h2><h3>Background</h3> The significance of magnesium as a treatment or prognostic factor in heart failure (HF) remains uncertain despite frequent use. We evaluated the frequency and outcomes of magnesium testing, hypomagnesemia and intravenous (IV) replacement in a large population-based cohort. <h3>Methods</h3> This retrospective cohort study used linked administrative data (April 2012-March 2020). Patients with a primary diagnosis of HF in the emergency department (ED) or hospital were included. Outcomes included all-cause and cause-specific death and hospitalization. Secondary outcomes included ED visits and physicians claims. We also examined rates of serum magnesium testing and hypomagnesemia. <h3>Results</h3> Among 78,957 acute HF episodes (in 42,763 patients), 58.7% included serum magnesium testing. Of those tested, serum magnesium levels were <0.75 mmol/L in 31.7%, between 0.75 - 0.95 mmol/L in 56.8% and >0.95 mmol/L in 11.5%. Magnesium levels (per 0.02 mmol/L increase) were independently associated with mortality when <0.70 mmol/L (hazard ratio [HR] 0.99; 95% confidence interval [CI] 0.98-0.99; <i>P<</i>0.001) or >0.86 mmol/L (HR 1.04; 95% CI 1.03-1.04; <i>P<</i>0.001)]. IV magnesium was administered to 13.7% (n=6333) of tested patients, including 29.7% without hypomagnesemia. After multivariable adjustment, IV magnesium was associated with a higher short-term mortality (HR 1.66; 95% CI 1.4-1.96; <i>P<</i>0.0001) and hospitalization risk (HR 1.36; 95% CI 1.13-1.63; <i>P<</i>0.001). <h3>Conclusions</h3> Serum magnesium testing is common in patients presenting to the ED or hospital with HF, and low or high magnesium is associated with worse outcomes. Replacement with IV magnesium was associated with worse outcomes even after adjustment, warranting further study.