Incomplete Follow-Up and Competing Risks as Sources of Bias in Vascular Surgical Investigations

Background/Objectives: The aim of the study was to determine whether incomplete follow-up and competing events may be associated with the clinical course in peripheral artery disease (PAD) patients after treatment and with known risk factors, such as chronic limb threatening ischemia (CLTI). Methods: In this retrospective, observatory study patients hospitalized with PAD were included, treated by endovascular or open-surgical means and followed-up. The primary outcome was reintervention free survival (RFS), secondary outcomes and competing events were major amputation and death. The follow-up index (FUI) was determined in each patient. Results: The FUI depended significantly on disease stage (CLTI) and tendentially on age. Independently from disease stage, patients with FUI<0.5 had a shorter RFS. When FUI and competing events were considered using the Fine-Gray regression analysis, CLTI and anterior tibial artery state were associated with the RFS, while FUI, CLTI and common femoral artery state were associated with major amputation free survival. Conclusions: Incomplete follow-up is associated with progressed PAD and itself may mask a worse outcome, such as reintervention, restenosis, major amputation or death. Competing events should also be considered possible bias sources. Therefore, FUI and competing events should be reported and conclusions drawn cautiously in clinical studies, being it observatory or randomized prospective ones.