Serum potassium levels provide prognostic information in symptomatic heart failure beyond traditional clinical variables

Abstract

Aims: Despite of recent advances in the pharmacological treatment, heart failure (HF) maintains significant morbidity and mortality rates. While serum potassium disorders are common and associated with adverse outcomes, the exact recommended potassium level for patients with HF are not entirely established. We aimed to investigate the prognostic role of potassium levels on a cohort of patients with symptomatic chronic HF.

Methods and results: Patients with symptomatic chronic HF were identified at the referral to 6 min walking test (6MWT) and were prospectively followed up for cardiovascular events. Clinical and laboratorial data were retrospectively obtained. The primary endpoint was the composite of cardiovascular death, hospitalization due to HF, and heart transplantation. The cohort included 178 patients with HF with the mean age of 51 ± 12.76 years, 39% were female, 85% of non-ischaemic cardiomyopathy, and 38% had New York Heart Association Class III with a relatively high Meta-Analysis Global Group in Chronic Heart Failure (MAGGIC) score (12.91 ± 6.6). The mean left ventricular ejection fraction was 39.98 ± 15.79%, and the mean 6MWT distance was 353 ± 136 m. After a median follow-up of 516 days, there were 22 major cardiovascular events (4 cardiovascular deaths, 13 HF admissions, and 5 heart transplants). Patients were stratified according to cut-point level of serum potassium of 4.7 mmol/L to predict combined cardiac events based on receiver operating characteristic analysis. Individuals with higher potassium levels had worse renal function (glomerular filtration rate, K ≤ 4.7: 102.8 ± 32.2 mL/min/1.73 m² vs. K > 4.7: 85.42 ± 36.2 mL/min/1.73 m² , P = 0.004), higher proportion of New York Heart Association Class III patients (K ≤ 4.7: 28% vs. K > 4.7: 48%, P = 0.0029), and also higher MAGGIC score (K ≤ 4.7: 12.08 ± 5.7 vs. K > 4.7: 14.9 ± 7.9, P = 0.0089), without significant differences on the baseline pharmacological HF treatment. Both potassium levels [hazard ratio (HR) 4.26, 95% confidence interval (CI) 1.59-11.421, P = 0.003] and 6MWT distance (HR 0.99, 95% CI 0.993-0.999, P = 0.01) were independently associated with the primary outcome. After adjustments for MAGGIC score and 6MWT distance, potassium levels > 4.7 mmol/L maintained a significant association with outcomes (HR 3.57, 95% CI 1.305-9.807, P = 0.013). Patients with K > 4.7 mmol/L were more likely to present clinical events during the follow-up (log rank = 0.005). Adding potassium levels to the model including 6MWT and MAGGIC significantly improved the prediction of events over 2 years (integrated discrimination index 0.105, 95% CI 0.018-0.281, P = 0.012 and net reclassification index 0.447, 95% CI 0.077-0.703, P = 0.028).

Conclusions: Potassium levels were independently associated with worse outcomes in patients with chronic symptomatic HF, also improving the accuracy model for prognostic prediction when added to MAGGIC score and 6MWT distance. The potassium levels above 4.7 mmol/L might identify those patients at an increased risk of cardiovascular events.

Keywords: Heart failure; Physical capacity; Potassium; Prognosis; Renal function.