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LONDON -- Keeping potassium levels high after cardiac surgery in hopes of preventing post-surgical atrial fibrillation (Afib) didn't work, a randomized clinical trial showed.

New-onset Afib after isolated coronary artery bypass grafting (CABG) occurred in 26.2% of patients supplemented at a tight potassium threshold of 4.5 mEq/L and 27.8% of patients at a more relaxed supplementation threshold of 3.6 mEq/L.

The risk difference of 1.7% (95% CI -2.6 to 5.9) fell well within the noninferiority margin, Benjamin O'Brien, MD, PhD, of Charité Universitätsmedizin Berlin, reported at the European Society of Cardiology (ESC) meeting.

"There's a widespread practice of routinely and proactively or even aggressively supplementing potassium to achieve a high normal level after heart bypass surgery," he said at an ESC press conference. A practice pattern survey suggested that about two-thirds of U.K. centers maintain tight potassium control after cardiac surgery, as do about one-third of U.S. centers.

However, that common practice had been built on no solid trial evidence, O'Brien noted. "We believe that on the findings of our trial, that can now be abandoned. Abandoning this will decrease patient risk from an unnecessary intervention and reduce healthcare cost."

Cost emerged as the only significant outcome difference between treatment arms. Purchasing and administering potassium cost an average $111.89 less per patient in the relaxed arm (P<0.001).

Post-operative Afib affects about one in three patients after CABG, "and it's associated with morbidity, mortality -- both long and short term -- and also length of stay and cost of care," O'Brien noted. "And because it's so frequent and impactful, there are many interventions to try and prevent it, but most of them have no evidence to support them."

Realizing this, his group set out to provide the evidence base. Their TIGHT K trial included 1,690 adults (mean age 65, 15% females) who were in sinus rhythm at randomization and scheduled at 23 cardiac centers in the U.K. and Germany for CABG surgery with no additional cardiac or vascular procedure during the same operation. Exclusion criteria included history of Afib, atrial flutter, or atrial tachyarrhythmia; preoperative high-degree atrioventricular block; current or previous use of cardiac rhythm management medication; a preoperative serum potassium concentration greater than 5.5 mEq/L; or dialysis-dependent kidney failure.

Randomization worked to keep potassium at the upper end of normal for the tight control group, resulting in higher serum potassium and a median seven times (some in excess of 40) potassium was administered prior to first post-operative Afib episode compared with an average of zero in the relaxed group who were dosed only if hypokalemic.

Primary outcome events were validated by a blinded event validation committee and were assessed in the first 120 hours after CABG or until hospital discharge.

No secondary outcomes showed an impact of the potassium strategy, including occurrence of at least one Afib episode detected by any means or by ambulatory heart rhythm monitor alone, non-Afib dysrhythmias, in-patient mortality, or length of stay.

Limitations included the open-label design and "markedly higher" nonadherence in the tight group, "despite it being the perceived standard of care," the researchers noted. "In this group, potassium supplementation occurred less consistently when serum potassium concentration was just narrowly below the threshold at approximately 4.3 or 4.4 mEq/L. However, findings did not change in additional sensitivity analyses."

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