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

ImportanceThe significance of magnesium as a treatment or prognostic factor is unknown in heart failure despite its frequent use. ObjectiveTo assess the frequency and outcomes of magnesium testing, hypomagnesemia and intravenous (IV) replacement in a large population-based cohort. Design, Setting, and ParticipantsRetrospective cohort study using linked administrative data from April 2012 - March 2020. Patients with primary diagnosis of HF in the emergency department or hospital were included and the rates and outcomes of magnesium testing, hypomagnesemia and IV replacement were assessed. Main Outcome(s) and Measure(s)The primary clinical outcomes included all-cause and cause specific death and hospitalization. Secondary outcomes included emergency department visits and physicians claims. Other outcomes included factors and rates of serum magnesium testing and hypomagnesemia. ResultsOf 78,957 acute heart failure episodes (in 42,763 patients), 58.7% included a serum magnesium measurement. Of the patients who were 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); p<0.001] or >0.86 mmol/L [HR 1.04 (95% CI 1.03-1.04); p<0.001]. IV magnesium was given to 13.7% (n=6,333) of those who were tested (29.7% of whom did not have hypomagnesemia); after multivariable adjustment, receiving IV magnesium was associated with a higher short term mortality [HR 1.66 (95% CI 1.4-1.96); p<0.0001] and hospitalization risk [HR 1.36 (95% CI 1.13-1.63); p<0.001]. Conclusions and RelevanceSerum 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, a finding which warrants further study.