Mild hyperkalemia and outcomes in chronic heart failure: a propensity matched study.

Background: Compared with serum potassium levels 4-5.5 mEq/L, those <4 mEq/L have been shown to increase mortality in chronic heart failure (HF). Expert opinions suggest that serum potassium levels >5.5 mEq/L may be harmful in HF. However, little is known about the safety of serum potassium 5-5.5 mEq/L.

Methods: Of the 7788 chronic HF patients in the Digitalis Investigation Group trial, 5656 had serum potassium 4-5.5 mEq/L. Of these, 567 had mild hyperkalemia (5-5.5 mEq/L) and 5089 had normokalemia (4-4.9 mEq/L). Propensity scores for mild hyperkalemia were used to assemble a balanced cohort of 548 patients with mild hyperkalemia and 1629 patients with normokalemia. Cox regression models were used to estimate hazard ratios (HR) and 95% confidence intervals (CI) for association between mild hyperkalemia and mortality during a median follow-up of 38 months.

Results: All-cause mortality occurred in 36% and 38% of matched patients with normokalemia and mild hyperkalemia respectively (HR, 1.07; 95% CI, 0.90-1.26; P=0.458). Unadjusted, multivariable-adjusted, and propensity-adjusted HRs for mortality associated with mild hyperkalemia were 1.33 (95% CI, 1.15-1.52; P<0.0001), 1.16 (95% CI, 1.01-1.34; P=0.040) and 1.13 (95% CI, 0.98-1.31; P=0.091) respectively. Mild hyperkalemia had no association with cardiovascular or HF mortality or all-cause or cardiovascular hospitalization.

Conclusion: Serum potassium 4-4.9 mEq/L is optimal and 5-5.5 mEq/L appears relatively safe in HF. Despite lack of an intrinsic association , the bivariate association of mild-hyperkalemia with mortality suggests that it may be useful as a biomarker of poor prognosis in HF.