Renal function in patients with mechanical prosthetic valves : Long-term effects of anticoagulation and over-anticoagulation with warfarin.

Background: Warfarin-related nephropathy (WRN) is a complication of warfarin over-anticoagulation that is associated with acute and/or chronic renal dysfunction and increased mortality. The long-term effects of warfarin on renal function has not been adequately studied in patients with a mechanical prosthetic valve (MPV).

Aim: To study the time-dependent effects of over-anticoagulation on renal function in patients with a MPV.

Methods: A total of 193 patients who underwent MPV implantation and were followed up in this study were eligible for inclusion. Time above therapeutic international normalized ratio (INR) range (TATR) was calculated by dividing the number of INR measurements above target in a year by the total number of INR measurements within a year. Patients were divided into quartiles according to average TATR at 60 months.

Results: At 60 months more patients within the 4th quartile had a ≥20% reduction in the estimated glomerular filtration rate (eGFR, 25.0%, p = 0.04) and chronic kidney disease (CKD, 33.0%, p = 0.07) compared to patients within the 1st quartile. High TATR remained a significant determinant for reduction in eGFR (odds ratio OR: 7.50, 95% confidence interval CI:1.55-36.32) and CKD (OR:5.15, 95% CI: 1.26-20.62) after adjusting for other variables. Longitudinal analysis revealed that the change in eGFR was related to the duration of warfarin use (p < 0.001) and the interaction between the duration of warfarin use and TATR (p = 0.03). Similar findings were observed in patients without CKD at baseline, but not in those with CKD before the index operation.

Conclusion: Anticoagulation over targeted INR values is associated with a steeper decline in eGFR and an increased frequency of CKD in patients with a MPV.