Short-term prognosis of normalising serum potassium following an episode of hypokalaemia in patients with chronic heart failure

Abstract

Background/ aim: It is well known that patients with chronic heart failure and hypokalaemia have increased mortality risk. We investigated the impact of normalising serum potassium following an episode of hypokalaemia on short-term mortality among patients with chronic heart failure. Methods and results: We identified 1673 patients diagnosed with chronic heart failure who had a serum potassium measurement under 3.5 mmol/l within 14 days and one year after initiated medical treatment with both loop diuretics and angiotensin-converting enzyme inhibitors or angiotensin-II receptor blockers. A second serum potassium measurement was required 8-30 days after the episode of hypokalaemia. All-cause mortality and cardiovascular mortality was examined within 90 days from the second serum potassium measurement. Mortality was examined according to six predefined potassium groups derived from the second measurement:<3.5 mmol/l (n = 302), 3.5-3.7 mmol/l (n = 271), 3.8-4.1 mmol/l (n = 464), 4.2-4.4 mmol/l (n = 270), 4.5-5.0 mmol/l (n = 272), and 5.1-8.0 mmol/l (n = 94). We used Cox regression to estimate both all-cause mortality risk and cardiovascular mortality, with serum potassium at 3.8-4.1 mmol/l as reference. After 90 days, the all-cause mortality in the six groups was 29.5%, 22.1%, 20.3%, 24.8%, 23.5% and 43.6%, respectively. In multivariable adjusted analysis, patients with serum potassium <3.5 mmol/l (hazard ratio: 1.51; 95% confidence interval: 1.13-2.02) and serum potassium 5.1-8.0 mmol/l (hazard ratio: 2.18; 95% confidence interval: 1.50-3.17) had an increased risk of all-cause mortality compared to the reference. After 90 days, the cardiovascular mortality in the six groups was 19.2%, 17.7%, 14.4%, 18.9%, 18.8% and 34.0%, respectively. In multivariable adjusted analysis, patients with serum potassium 5.1-8.0 mmol/l (hazard ratio: 2.32; 95% confidence interval: 1.51-3.56) had an increased risk of cardiovascular mortality compared to the reference, while serum potassium <3.5 mmol/l (hazard ratio: 1.37; 95% confidence interval: 0.97-1.95) had a trend toward increased risk of cardiovascular mortality compared to the reference. Conclusion: Patients with chronic heart failure and hypokalaemia, who after 8-30 days remained hypokalaemic, had a significantly higher 90-day all-cause mortality risk compared to patients in the reference group (3.8-4.1 mmol/l). Patients with chronic heart failure and hypokalaemia, who after 8-30 days had the serum potassium level increased to a level within 5.1-8.0 mmol/l, had both a significantly higher 90-day all-cause mortality risk and cardiovascular mortality risk compared to patients in the reference group (3.8-4.1 mmol/l).