Manchester researchers contribute to new major study assessing potassium in cardiac surgery patients

Results from a major research trial reveal patients who have heart bypass surgery receive no benefit from taking high doses of expensive potassium supplements.

Findings from the TIGHT K Trial were presented for the first time at the European Society of Cardiology Congress (ESC) in London and published in the Journal of the American Medical Association.

Researchers at Manchester University NHS Foundation Trust’s (MFT) Manchester Heart Institute, which brings together cardiology services across multiple sites at MFT, were authors on the study. The Trust was also a major recruiting site, with 150 patients joining the trial between November 2020 and November 2023.

Funded by the British Heart Foundation, the TIGHT K Trial aimed to discover if potassium supplements would reduce atrial fibrillation (AF), an abnormal heart rhythm that occurs in one in three patients after ‘coronary artery bypass graft’ heart surgery.

AF after cardiac surgery is associated with poorer outcomes for patients. Many doctors give patients extra potassium, an important mineral in the blood vital for normal heart function, with the aim of preventing AF. However, there has never been any evidence of its effectiveness, until this research.

Overall, 1,690 patients from 23 centres in the UK and Germany were split into two groups. One group received potassium supplements with the aim of keeping their blood potassium levels at the high end of normal; this required lots of supplement doses. The other group only got supplements when their levels dropped below the normal range, which required much fewer supplements. 

The study found that the risk of getting AF was no greater when lower potassium concentrations were targeted. The findings will impact on patients globally, sparing them unnecessary side effects of taking potassium, such as gastrointestinal symptoms (constipation, irritable bowel syndrome, nausea, gas, bloating and diarrhoea).

1.5 million people have cardiac surgery worldwide per year and heart bypass surgery is the most common type of surgery – at MFT, approximately 650 patients undergo heart bypass surgery each year.

Dr Niall Campbell, Consultant Cardiologist at the Manchester Heart Institute, and one of the study’s lead authors said: “Before the study results were available, we did not know whether giving higher potassium doses was beneficial. Now the findings are available, all of our patients can now benefit from this scientific knowledge that high doses of potassium are unnecessary, and we can be confident that they are receiving the most appropriate doses. This will also provide significant cost savings for the NHS.

“This was a collaborative effort from all members of the research team, and I want to recognise the dedication of our team in Manchester, helping to successfully contribute to this important research study.

I am also extremely grateful to all our patients who kindly agreed to participate in the TIGHT K Trial.  It is only through their contribution high quality research that benefits future generations can take place.

Following surgery, study participants wore a heart rhythm monitor for five days. The results were then analysed in an independent data analysis centre (called a core laboratory) based at Wythenshawe Hospital for all 23 centres involved in the study in the UK and Germany.

 

Keith Pearce, Consultant Cardiac Physiologist, Wythenshawe Hospital, who led the independent Core Laboratory at MFT and is also one of the study’s authors said: “This work is a testament to the quality of our healthcare scientists and cardiac scientists in our Core Laboratory within the Manchester Heart Institute at MFT. Our team provided heart rhythm analyses for all 23 centres, and it was a great honour for our unit to be chosen for such an important study. This is work that will have a lasting impact on patients around the world.”

The London School of Hygiene and Tropical Medicine Clinical Trials Unit supported and collaborated with MFT on the study – contributing to the design and running of the study as well as analysing the data.

Professor Ben O’Brien from the Berlin Heart Institute, who presented the findings at the ESC Congress, said: “We learned that the group who had fewer doses of potassium got the same amount of heart rhythm problems as the group who got more doses. When patients got less potassium, it saved money (£87 per patient). Potassium supplementation is also associated with other risks and can be unpleasant for patients to receive. Our results indicate that it is now time to abandon the widespread practice of maintaining high-normal potassium levels after coronary artery bypass grafting.”

Dr Sonya Babu-Narayan, Associate Medical Director at the British Heart Foundation, which funded the research, said: “This international trial shows the power of collaboration across borders to answer important medical questions. The results reveal that many patients could be spared potassium supplementation when recovering from coronary artery bypass surgery.

Preventing the over-use of potassium supplementation could also save money for the NHS at a time when every penny counts. Around 13,000 people have coronary artery bypasses in the UK each year. Small amounts safely saved per patient here can add up to large amounts being used more effectively elsewhere in the health service.

The manuscript in the Journal of the American Medical Association can be found on the JAMA Network website.