Heart surgery - TIGHT-K

The clinical question

Atrial fibrillation (AF) is an abnormal heart rhythm that causes your heart to beat irregularly and too fast. Around one in three people who have coronary artery bypass surgery (CABG) develop AF afterwards, and this is linked to having a longer hospital stay and worse outcomes. It has been thought that giving people extra potassium after heart surgery, even when the levels of potassium in the blood are in the normal range, might help prevent AF. Many people have therefore been given extra potassium after their CABG surgery, aiming to keep their blood potassium levels in a high-normal range.

But there are downsides to giving potassium. Potassium supplements have a bitter, unpleasant taste, making it difficult for people to take them. The alternative – giving potassium through a vein – can have side effects and is time consuming for the clinical care team. Importantly, there is also no good evidence that keeping blood potassium levels in a high normal range prevents AF. That’s why Professor Benjamin O’Brien, Professor of Perioperative Medicine at Queen Mary, University of London and Director of Cardiac Anesthesiology and Intensive Care Medicine at Deutsches Herzzentrum der Charité, Berlin, Germany, designed and led the BHF-funded TIGHT K trial.

What did the study involve?

Between October 2020 and November 2023, the TIGHT-K trial recruited 1690 patients having CABG surgery at 23 centres in the UK and Germany. To be eligible for the trial, potential participants did not have a history of atrial fibrillation or any other heart rhythm disturbance.

Participants were assigned to receive either:

• Extra potassium when their blood potassium levels dropped below a level at the higher end of the 'normal range' [4.5mEq/l - tight control group] or
• Extra potassium only when their blood potassium levels dropped below the bottom end of the 'normal range' [3.6 mEq/l - relaxed control group]

The trial participants were given extra potassium according to the group they were in for 5 days after their CABG surgery or until they were discharged from hospital, whichever came sooner.

To detect all episodes of AF, participants wore a portable heart monitor during their hospital stay. After discharge, the rhythm strip from the heart monitor was sent to a central laboratory to be analysed by a team that did not know which group the participants were in. The researchers also recorded whether AF had been detected by the clinical care team in the 5 days after the CABG procedure.

What did the study show?

• The trial showed that the risk of developing AF after CABG was similar in both the relaxed-control and tight-control groups.
• In other words, similar numbers of people in the relaxed control group (who got fewer doses of potassium and had lower potassium levels) and in the tight control group developed AF after their CABG surgery (27.8% [231 people] in the relaxed control group developed AF versus 26.2% [219 people] in the tight control group).
• The researchers also checked for any other heart rhythm problems and there was no difference between groups.
• There was no difference in the number of people who died after surgery between the relaxed and tight control groups or in the time people had to spend in hospital.
• The only significant difference between the groups was in the cost of purchasing and giving potassium, which was four times higher in the tight control group.

Why is the study important?

The TIGHT K trial showed that potassium supplements do not help to prevent AF in people who’ve had CABG surgery, as long as potassium levels are kept within the normal range.

On presenting the results of TIGHT K at the 2024 European Society of Cardiology Congress in London, UK, Professor O’Brien concluded: “There’s a widespread practice of routinely and proactively, or even aggressively, supplementing potassium to achieve a high-normal level after heart bypass surgery, and we believe that [based] on the findings of our trial, that can now be abandoned."

Study details

"The TIGHT-K STUDY. Arrhythmias on the cardiac intensive care unit - does maintenance of high- normal serum potassium levels matter?" 
Award reference: CS/18/3/34063
Principal Investigator: Professor Benjamin O’Brien, Queen Mary, University of London
Trial registration number: NCT04053816

Publication details

Potassium Supplementation and Prevention of Atrial Fibrillation After Cardiac Surgery: The TIGHT K Randomized Clinical Trial. JAMA. 2024;332(12):979-988. doi:10.1001/jama.2024.17888.