External validation of the OAC3-PAD risk score after endovascular revascularisation

Background: The OAC(3)-PAD bleeding risk score was developed to assess the bleeding risk in patients with peripheral arterial disease (PAD), however its performance in patients treated exclusively with endovascular revascularisation has not yet been tested. We aimed to externally validate the bleeding risk score for this patient cohort. Patients and methods: A retrospective observational study, analysing the data of all PAD patients successfully treated with endovascular revascularisation in a single centre within a five-year period. The performance of the Cox proportional hazards (CPH) model, upon which the OAC(3)-PAD bleeding risk score is based, was tested using calibration methods, discrimination, and a scaled Brier score for overall performance. The OAC(3)-PAD bleeding risk score was calculated for all patients, classifying them into the four respective risk groups. Kaplan-Meier curves were plotted for all risk groups and discrimination was tested using log-rank tests. Results: While discrimination of the CPH model was adequate, calibration of the model was poor and the scaled Brier score was 3.27% (95% CI 0.65%-4.40%). Of the 1,434 patients, 33 (2.3%) experienced a major bleeding event. The frequency of bleeding was 0.4% in the low risk group (3/736 patients), 0.8% in the low-to-moderate risk group (2/243 patients), 5.8% in the moderate-to-high risk group (15/258 patients), and 6.6% in the high risk group (13/197 patients). The OAC(3)-PAD score successfully discriminated each of the two lower bleeding risk groups from one of the two higher risk groups, but failed to discriminate among the two lower risk groups and the two higher risk groups, respectively. Conclusions: Although the OAC(3)-PAD score did not stratify patients into the four respective risk groups, it allowed discrimination between the low risk patients and the high risk patients. It could therefore become a useful tool for predicting major bleeding events in patients with PAD after endovascular revascularisation.