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

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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.