Prognostic Effect of Renal Function in Ambulatory Patients With Heart Failure and Reduced Ejection Fraction: The Kidney Is a Marker of Cardiac Function

Abstract

Background: Chronic kidney disease is a frequent comorbidity in heart failure (HF), associated with increased mortality. The impact of temporal evolution of kidney function in HF prognosis is largely unknown. We evaluated the effect of renal function over time in all-cause mortality among ambulatory patients with HF. Methods: We retrospectively analyzed data from 560 patients with HF with left ventricular systolic dysfunction followed for a median of 25.1 months at an outpatient clinic. Demographics and comorbidities were collected at baseline. Creatinine values were abstracted from records at each clinical visit. Kidney function was assessed by estimated glomerular filtration rate (eGFR) and was categorized into 3 classes. Extended Cox models were performed to study the association between time-varying eGFR and death. Results: Patients' mean age was 67.5 +/- 13.9 years, 67.0% were men, 46.1% had ischemic etiology, the majority had moderate-to-severe left ventricular systolic dysfunction, and 45.9% had chronic kidney disease at baseline. The eGFR declined approximately 9.0 mL/min/1.73 m(2) over 5 years. In crude analysis, time-varying eGFR had a significant dose-dependent association with death (hazard ratio [HR] = 1.34, 95% confidence interval [CI]: 1.03-1.75 for eGFR between 30 and 60 mL/min/1.73 m(2); HR - 1.55, 95% CI: 1.11-2.17 for < 30 mL/min/1.73 m2). The prognostic value of time-varying eGFR was totally explained by baseline comorbidities, indicators of HF severity and drugs (adjusted HR = 1.11, 95% CI: 0.83-1.48; HR = 1.19, 95% CI: 0.79-1.80, for eGFR 30-60 and < 30 mL/min/m(2), respectively). Conclusions: Time-varying kidney function is not independently related to poor prognosis in HF. Rather than directly affecting survival, renal impairment is probably a surrogate marker of HF severity.