Magnesium Prophylaxis for the Prevention of New-Onset Atrial Fibrillation in Critically Ill Patients

This trial is testing whether giving intravenous magnesium to critically ill patients in the ICU can prevent them from developing a new irregular heart rhythm called atrial fibrillation, which is a common and dangerous complication in this setting. **You may be eligible if...** - You are 18 years or older - You have been admitted to an ICU and are receiving breathing support (non-invasive ventilation or a breathing tube expected for more than 24 hours) or are on medications to support your heart or blood pressure - OR you have experienced a cardiac arrest - Your heart is being continuously monitored **You may NOT be eligible if...** - You have already been in the ICU receiving these interventions for more than 18 hours before enrolment - You already have atrial fibrillation - You are on oral or IV amiodarone (a heart rhythm drug) - You are unlikely to survive more than 24 hours, or you are in palliative care - You have had cardiac surgery - You need magnesium for another reason (e.g., preeclampsia or severe asthma) - You are on dialysis - You are pregnant Talk to your doctor to see if this trial is right for you.