Skip Potassium After Cardiac Surgery

LONDON — Potassium supplementation does not alter the risk for postoperative atrial fibrillation in patients who have undergone cardiac surgery, contrary to expectations and popular clinical practice, new trial results demonstrate.

The widespread practice of giving patients potassium after bypass heart surgery even though their blood levels are within the normal range can be abandoned, said Benjamin O Brien, MD, PhD, director of the Clinic for Cardioanesthesiology and Intensive Care Medicine at Charité Hospital in Berlin, Germany.

Results from the randomized TIGHT-K trial that assessed two levels of potassium supplementation were presented at .

In the tight-control group, supplementation was provided to maintain high-normal levels of potassium (> 4.5 mEq/L). In the relaxed-control group, supplementation was provided only when potassium levels fell below the low-normal threshold (< 3.6 mEq/L).

Trial Upending Popular Practice

The multinational trial involved 23 centers in Germany and the United Kingdom. All 1690 participants enrolled were scheduled to undergo a coronary artery bypass graft procedure, but O Brien said he considers the results of TIGHT-K to be broadly applicable.

There is no physiological basis to expect a different result in patients undergoing different types of cardiac surgery, he said.

The primary endpoint was clinically and electrocardiography confirmed new-onset atrial fibrillation that occurred in the 5 days after the bypass procedure.

For the primary atrial fibrillation endpoint, event rates were similar in the tight-control and the relaxed-control groups (26.2% vs 27.8%); the 1.7% difference did not approach statistical significance (P = .44). The difference in dysrhythmias other than atrial fibrillation, although numerically lower in the tight-control group, was also not significant (19.1% vs 21.1%; P = .26).

There were no significant differences in several secondary endpoints, including length of hospital stay and in-patient mortality, but cost, a prespecified secondary endpoint, was approximately $120 lower per patient in the relaxed-control group than in the tight-control group (P < .001).

Lowering Cost Across Cardiac Surgeries

During the 5-day follow-up, median potassium levels were higher in the tight-control group. Levels in both groups fell gradually, but essentially in parallel, over the study period, so median potassium levels were always higher in the tight-control group than in the relaxed-control group. At the end of the observation period, mean potassium levels were 4.34 mEq/L in the tight-control group and 4.08 mEq/L in the relaxed-control group.

Prior to the development of atrial fibrillation, participants in the tight-control group received a medium of seven potassium administrations (range, 4 12), whereas those in the relaxed-control group received a medium of zero.

There were no significant differences in episodes in any subgroup evaluated, including those divided by age, sex, baseline left ventricular ejection fraction, and the absence or presence of beta blockers or loop diuretics. A per-protocol analysis also failed to show any advantage for tight potassium control.

Atrial fibrillation occurs in about one third of patients after bypass surgery, as it does after many types of cardiac surgery. Institutions often have strategies in place to reduce the risk after cardiac surgery, and potassium supplementation is one of the most common, despite the lack of supportive evidence, O Brien said.

Narrow Window for Optimal Potassium Levels

The difference in potassium levels between the tight-control group and the relaxed-control group were modest in this study, said Subodh Verma, MD, a cardiac surgeon at St Michael’s Hospital and professor at the University of Toronto.

However, this is unavoidable and central to the question being posed, O’Brien pointed out. Because of the risks for both hypokalemia and hyperkalemia, the window for safe supplementation is short. Current practice is to achieve high-normal levels to reduce atrial fibrillation, but TIGHT-K demonstrates this has no benefit.

The conclusion of TIGHT-K is appropriate, said Faiez Zannad, MD, PhD, professor of therapeutics in the Division of Cardiology at the University of Lorraine in Nancy, France, who praised the design and conduct of the study.

He acknowledged an unmet need for effective methods to reduce the risk for atrial fibrillation after cardiac surgery, but the ESC invited discussant said it is now necessary to look at other strategies. Several are under current evaluation, such as supplementary magnesium and the use of sodium-glucose contransporter-2 inhibitors, he reported.

Although Zannad encouraged more studies of methods to reduce atrial fibrillation risk after cardiac surgery, he said that TIGHT-K has answered the question of whether potassium supplementation is beneficial.

Potassium supplementation should no longer be offered, he said, which will “reduce healthcare costs and decrease patient risk from an unnecessary intervention.”