A propensity-matched study of low serum potassium and mortality in older adults with chronic heart failure

Abstract

Objective Most HF patients are older adults, yet the associations of low serum potassium and outcomes in these patients are unknown. We studied the effect of low serum potassium in a propensity-matched population of elderly HF patients. Methods Of the 7788 patients in the Digitalis Investigation Group trial, 4036 were ≥ 65 years. Of these, 3598 had data on baseline serum potassium and 324 with potassium ≥ 5 mEq/L were excluded. Remaining patients were categorized into low (< 4 mEq/L; n = 590) and normal (4–4.9 mEq/L; n = 2684) potassium groups. Propensity scores for low-potassium, calculated for each patient, were used to match 561 low-potassium and 1670 normal-potassium patients. Association of low potassium and outcomes were assessed using matched Cox regression analyses. Results Patients had a mean (± SD) age of 72 (± 6) years, 29% were women and 12% were non-whites. Of the 561 low-potassium patients, 500 had low-normal (3.5–3.9 mEq/L) potassium. All-cause mortality occurred in 37% (rate, 1338/10,000 person-years) normal-potassium and 43% (rate, 1594/10,000 person-years) low-potassium patients (hazard ratio {HR} for low-potassium, 1.22; 95% confidence interval {CI}, 1.04–1.44; p = 0.014). Low-normal (3.5–3.9 mEq/L) potassium levels had a similar association with mortality (HR, 1.19, 95% CI, 1.00–1.41, p = 0.049). Low (HR, 1.10; 95% CI, 0.96–1.25; p = 0.175) or low-normal (HR = 1.09, 95% CI = 0.95–1.25, p = 0.229) serum potassium levels were not associated with all-cause hospitalization. Conclusions In a propensity-matched population of elderly ambulatory chronic HF patients, well-balanced in all measured baseline covariates, low and low-normal serum potassium were associated with increased mortality but had no association with hospitalization.