Tight K is the first appropriately powered non-inferiority multicentre randomised trial of a strategy of 'relaxed' potassium supplementation versus a strategy of 'tight' potassium supplementation, which is defined as standard of care. The routine maintenance of serum [K+] ≥4.5 mEq/L is of unproven efficacy, may be unpleasant or hazardous for patients, and is costly. The findings will have important consequences for patients and clinicians, regardless of whether or not potassium supplementation is found to be non-inferior for the prevention of AF after cardiac surgery. A survey of practice patterns in Europe and North America suggests that there is genuine equipoise, with 67% of caregivers practising in Europe reporting that their institution has a protocol for maintaining high-normal serum potassium levels after cardiac surgery. So one in three do not.

The Tight K Trial will set out to test the hypothesis that AF after cardiac surgery will be no more common after CABG surgery when serum potassium levels are maintained ≥3.6 mEq/L as when they are maintained ≥4.5 mEq/L.

Inclusion criteria

1. Scheduled to have isolated CABG surgery
2. Patient in sinus rhythm

Exclusion criteria

1. Age less than 18 years
2. Previous history of Atrial Fibrillation, Atrial Flutter and/or Atrial Tachyarrhythmia
3. Pre-operative high-degree atrioventricular (AV) block (defined as Mobitz type 2 second degree AV block or complete heart block)
4. Pre-operative serum [K+] greater than 5.5 mEq/L
5. Current or previous use of medication for the purposes of cardiac rhythm management
6. Dialysis-dependent end-stage renal failure
7. Concurrent patient involvement in another clinical study assessing cardiac rhythm post-operative interventions
8. Unable to provide informed consent

If you are a patient interested in taking part in the study, you can contact the research team at your local hospital to discuss this further.