Serum magnesium levels may be impacted by neurohormonal activation, renal function, and diuretics. The clinical profile and prognostic significance of serum magnesium level concentration in patients hospitalized for heart failure (HF) with reduced ejection fraction is unclear. In this retrospective analysis of the placebo group of the Efficacy of Vasopressin Antagonism in Heart Failure Outcome Study with Tolvaptan trial, we evaluated 1,982 patients hospitalized for worsening HF with ejection fractions ≤40%. Baseline magnesium levels were measured within 48 hours of admission and analyzed as a continuous variable and in quartiles. The primary end points of all-cause mortality (ACM) and cardiovascular mortality or HF rehospitalization were analyzed using Cox regression models. Mean baseline magnesium level was 2.1 ± 0.3 mg/dl. Compared with the lowest quartile, patients in the highest magnesium level quartile were more likely to be older, men, have lower heart rates and blood pressures, have ischemic HF origin, and have higher creatinine and natriuretic peptide levels (all p <0.003). During a median follow-up of 9.9 months, every 1-mg/dl increase in magnesium level was associated with higher ACM (hazard ratio [HR] 1.77; 95% confidence interval [CI] 1.35 to 2.32; p <0.001) and the composite end point (HR 1.44; 95% CI 1.15 to 1.81; p = 0.002). However, after adjustment for known baseline covariates, serum magnesium level was no longer an independent predictor of either ACM (HR 0.94, 95% CI 0.69 to 1.28; p = 0.7) or the composite end point (HR 1.01, 95% CI 0.79 to 1.30; p = 0.9). In conclusion, despite theoretical concerns, baseline magnesium level was not independently associated with worse outcomes in this cohort. Further research is needed to understand the importance of serum magnesium levels in specific HF patient populations.

Despite the well-established benefits of mineralocorticoid receptor agonists (MRAs) in heart failure with reduced ejection fraction, safety concerns remain in patients with concomitant diabetes mellitus (DM) because of common renal and electrolyte abnormalities in this population. We analyzed all-cause mortality and composite cardiovascular mortality and HF hospitalization over a median 9.9 months among 1,998 patients in the placebo arm of the Efficacy of Vasopressin Antagonism in Heart Failure Outcome Study With Tolvaptan (EVEREST) trial by DM status and discharge MRA use. Of the 750 patients with DM, 59.2% were receiving MRAs compared with 62.5% in the non-DM patients. DM patients not receiving MRAs were older, more likely to be men, with an ischemic heart failure etiology and slightly worse renal function compared with those receiving MRAs. After adjustment for baseline risk factors, among DM patients, MRA use was not associated with either mortality (hazard ratio [HR] 0.93; 95% confidence interval [CI] 0.75 to 1.15) or the composite end point (HR 0.94; 95% CI 0.80 to 1.10). Similar findings were seen in non-DM patients (mortality [HR 1.01; 95% CI 0.84 to 1.22] or the composite end point [HR 0.98; 95% CI 0.85 to 1.13] [p >0.43 for DM interaction]). In conclusion, in-hospital initiation of MRA therapy was low (15% to 20%), and overall discharge MRA use was only 60% (with regional variation), regardless of DM status. There does not appear to be clear, clinically significant in-hospital hemodynamic or even renal differences between those on and off MRA. Discharge MRA use was not associated with postdischarge end points in patients hospitalized for worsening heart failure with reduced ejection fraction and co-morbid DM. DM does not appear to influence the effectiveness of MRA therapy.