Magnesium Supplementation and Tachyarrhythmias: A Nonrandomized Clinical Trial.

Magnesium supplementation showed no evidence of effect on the occurrence of tachyarrhythmia in ICU patients with hypomagnesemia.

• The primary outcome was ventricular or supraventricular tachyarrhythmia in the 24 hours after magnesium testing.
• Risk difference for tachyarrhythmia was 0.1% (95% CI, -4.2 to 6.9).
• This null finding was true across all cutoff levels evaluated, ranging from 1.6 mg/dL to 2.0 mg/dL.
• A fuzzy regression discontinuity design was used to allow for plausible causal inference, comparing individuals just either side of the eligibility cutoff for magnesium supplementation.

Magnesium supplementation was not associated with a reduction in hypotension in ICU patients.

• Hypotension was a prespecified secondary outcome measured in the 24 hours after magnesium testing.
• Risk difference for hypotension was 1.2% (95% CI, -0.9 to 17.7), indicating no significant beneficial effect.
• The wide confidence interval includes zero, consistent with no effect.

Magnesium supplementation was not associated with a reduction in mortality in ICU patients.

• Death was a prespecified secondary outcome.
• Risk difference for death was 1.4% (95% CI, -0.6 to 5.3), indicating no significant beneficial effect.
• The confidence interval crosses zero, consistent with no effect on mortality.

The study included a large cohort of ICU patients from 93 ICUs across the US and Europe over nearly two decades.

• A total of 478,901 twenty-four-hour treatment windows from 171,727 ICU admissions were included.
• Data were collected between 2003 and 2022 from 93 ICUs across the US and Europe.
• A total of 72,767 admitted patients (42.4%) were female, 98,960 (57.6%) were male, and the mean (SD) age was 63 (16) years.
• Data were analyzed from August to October 2025.

A fuzzy regression discontinuity design was used to address confounding by indication and other biases inherent in conventional observational studies of magnesium supplementation.

• Conventional observational studies of this question are described as being at risk of confounding by indication and other biases.
• The design compared individuals just either side of the eligibility cutoff for magnesium supplementation.
• This comparison was performed across a range of treatment cutoffs in current use, ranging from 1.6 mg/dL to 2.0 mg/dL.
• The authors describe this quasi-experimental study design as one that 'plausibly allows for causal inference.'

The evidence base for the common practice of magnesium supplementation for tachyarrhythmia prevention and the specific treatment thresholds used is described as limited.

• Magnesium supplementation is stated to be regularly given to acutely ill patients with serum levels below the standard reference range, primarily for prevention of tachyarrhythmias such as atrial fibrillation.
• The authors note that 'the evidence for this practice and the specific treatment thresholds used is limited.'
• Treatment cutoffs evaluated ranged from 1.6 mg/dL to 2.0 mg/dL, reflecting variation in current institutional practice.