General and Disease-Specific Factors Associated with Patient-Reported Outcomes Among Patients with Peripheral Artery Disease: Key Considerations for Understanding Minimum Important Improvement and Defining Success in Clinical Registries
Chloe A. Powell, Gloria Y. Kim, Bryan Aaron, Stephanie Otto, Ashley Duby, Katherine A. Gallagher, Mary E. Byrnes, Matthew A. Corriere
University of Michigan, Ann Arbor, MI
Background: Patient-reported outcomes (PRO) have been championed for assessment of peripheral artery disease (PAD) outcomes. Limited evidence exists regarding factors associated with PRO that may affect their sensitivity to change with interventions. We performed a prospective, cross-sectional study to evaluate how patient-level factors are associated with a validated PAD-specific health related quality of life (QOL) instrument, the VascuQol-6.
Methods: Patients were recruited from a diagnostic vascular unit based on referral for ankle brachial index (ABI). PAD symptoms were assessed using the San Diego Claudication Questionnaire. Neuropathy screening used the Michigan Neuropathy Screening Instrument (MNSI). PAD-specific QOL was assessed using the VascuQol-6, and potential for a minimally important difference (MID) increase was defined based on a score ≥23, indicating lack of room for a MID increase ≥1.4 based on published literature. Factors associated with QOL were evaluated using confidence intervals, Wilcoxon scores, and linear models.
Results: 87 patients were recruited and participated. Mean age was 68.3±11.5 years; 42% of participants were women. Comorbid conditions included diabetes (24.4%), current smoking (26.7%) and peripheral neuropathy (46.0%). Mean ABI was 0.74±0.27 and mean TBI was 0.48±0.23. PAD symptoms were classified as claudication in 47.1%, critical limb threatening ischemia (CLTI) in 27.6%, and asymptomatic in 25.3%. Among symptomatic patients, 51% had multi-level symptoms, 32% had calf symptoms only, 11% had buttock symptoms only, and 6% had thigh symptoms only. Seven patients (8.0%) had VascuQol-6 scores indicating no potential for MID increase, and these patients were older than those who did have potential for MID increase (76.7±6.1 vs. 67.3±11.8 years; P=0.032)(Figure). Patients with multi-level symptoms had lower scores (13.4±3.9; 90% CI 12.1-14.8) versus those with no symptoms (17.7±4.8; 90% CI 16.4-19.1), calf symptoms (16.8±4.0; 90% CI 15.0-18.6) (P=0.008). In multivariable models QOL was associated with minimum ABI (P=0.027), symptom anatomic level (P=0.001) and age (P=0.001), but not symptom category (P=0.46). No associations between QOL and smoking status, diabetes, neuropathy, or bilateral versus unilateral symptoms were observed.
Conclusions: PAD-specific QOL instruments are associated with factors related and unrelated to PAD. Higher scores among older participants may impart ceiling effects that limit potential for improvement in this subgroup, while patients with multi-level symptoms may have greater potential gains from PAD treatment. Future work following this cohort will explore changes in QOL over time and associations with treatment interventions, adverse events, and patient-level factors. 
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