A propensity-matched study of the association of low serum potassium levels and mortality in chronic heart failure

Abstract

Potassium homeostasis is essential for normal myocardial function, and low serum potassium may cause fatal arrhythmias. However, the association of low potassium and long-term mortality and morbidity in heart failure (HF) is largely unknown. We studied 6845 HF patients in the Digitalis Investigation Group trial with serum potassium levels < or =5.5 mEq/L. Of these, 1189 had low potassium (<4 mEq/L). Propensity scores for low potassium were calculated for each patient and were used to match 1187 low-potassium patients with 1187 normal-potassium (4-5.5 mEq/L) patients. Effects of low potassium on outcomes were assessed using matched Cox regression analyses. All-cause mortality occurred in 379 (rate, 1103/10 000 person-years) normal-potassium and 441 (rate, 1330/10 000 person-years) low-potassium patients, respectively, during 3437 and 3315 years of follow-up [hazard ratio (HR), 1.25; 95% confidence interval (CI), 1.07-1.46; P = 0.006]. Cardiovascular mortality occurred in 297 (864/10 000 person-years) normal-potassium and 356 (1074/10 000 person-years) low-potassium patients (HR, 1.27; 95% CI, 1.06-1.51; P = 0.009). Cardiovascular hospitalization occurred in 610 (rate, 2553/10 000 person-years) normal-potassium and 637 (rate, 2855/10 000 person-years) low-potassium patients (HR, 1.13; 95% CI, 0.99-1.29; P = 0.082). In a cohort of ambulatory chronic systolic and diastolic HF patients who were balanced in all measured baseline covariates, serum potassium <4 mEq/L was associated with increased mortality, with a trend towards increased hospitalization.