Long-Term Potassium Monitoring and Dynamics in Heart Failure and Risk of Mortality

BACKGROUND: The prognostic value of long-term potassium monitoring and dynamics in heart failure has not been characterized completely. We sought to determine the association between serum potassium values collected at follow-up with all-cause mortality in a prospective and consecutive cohort of patients discharged from a previous acute heart failure admission. METHODS: Serum potassium was measured at every physician-patient encounter, including hospital admissions and ambulatory settings. The multivariable-adjusted association of serum potassium with mortality was assessed by using comprehensive state-of-the-art regression methods that can accommodate time-dependent exposure modeling. RESULTS: The study sample included 2164 patients with a total of 16 116 potassium observations. Mean potassium at discharge was 4.3 +/- 0.48 mEq/L. Hypokalemia (<3.5 mEq/L), normokalemia (3.5-5.0 mEq/L), and hyperkalemia (>5 mEq/L) were observed at the index admission in 77 (3.6%), 1965 (90.8%), and 122 (5.6%) patients, respectively. At a median follow-up of 2.8 years (range, 0.03-12.8 years), 1090 patients died (50.4%). On a continuous scale, the multivariable-adjusted association of potassium values and mortality revealed a nonlinear association (U-shaped) with higher risk at both ends of its distribution (omnibus P=0.001). Likewise, the adjusted hazard ratios for hypokalemia and hyperkalemia, normokalemia as reference, were 2.35 (95% confidence interval, 1.40-3.93; P=0.001) and 1.55 (95% confidence interval, 1.11-2.16; P=0.011), respectively (omnibus P=0.0003). Furthermore, dynamic changes in potassium were independently associated with substantial differences in mortality risk. Potassium normalization was independently associated with lower mortality risk (P=0.001). CONCLUSIONS: Either modeled continuously or categorically, serum potassium levels during long-term monitoring were independently associated with mortality in patients with heart failure. Likewise, persistence of abnormal potassium levels was linked to a higher risk of death in comparison with patients who maintained or returned to normal values.