Blood Factors and Peripheral Arterial Disease Outcomes

BACKGROUND:

The pathophysiology of functional impairment in patients with lower extremity peripheral arterial disease (PAD) is not well understood. Although lower ankle brachial index (ABI) levels are associated with greater functional impairment, one study suggests that the ABI improves to a greater degree than functional impairment after lower extremity revascularization. A meta-analysis of exercise studies in intermittent claudication demonstrated no significant association between improved walking ability after exercise and change in calf blood flow or ABI. Thus, characteristics in addition to ABI appear to influence walking ability in PAD.

It has been hypothesized that chronic inflammation is a biological mechanism underlying the decline in physical function that occurs with aging. It was recently reported that higher levels of D-dimer (fibrin degradation product) and high-sensitivity C-reactive protein (hsCRP) are associated with greater objectively assessed functional limitations in persons with PAD, but functional limitations refer to specific abilities, such as objectively measured walking speed or balance, which are distinct from disability. Furthermore, functional limitations may not fully explain disability.

DESIGN NARRATIVE:

The prospective study assessed associations between hemostatic and inflammatory blood factors and progression of lower extremity arterial ischemia and cardiovascular events in 346 men and women with lower extremity peripheral arterial disease (PAD) and 203 men and women without PAD.The study was ancillary to an NHLBI funded prospective study of functional and cardiovascular outcomes in men and women with PAD, the Walking and Leg Circulation Study (WALCS). The blood factors under study which included fibrinogen, PAI-1, TPA antigen, d-dimer, prothrombin 1.2, and C-reactive protein (CRP), were associated with progression of coronary atherosclerosis in proposed models of the pathogenesis of coronary atherosclerosis, but were not well studied in PAD.

There were two specific aims. The first was to determine whether higher baseline blood factor levels were associated with a) progression of lower extremity arterial ischemia (decline in ankle brachial index >= 0.15, lower extremity gangrene, ulcer, revascularization, or amputation); b) functional decline over a 48 month follow-up. The second aim was to determine whether higher baseline blood factor levels were associated with new cardiovascular events over a 48 month follow-up. The hypothesis was that higher blood factor levels at baseline would be associated with PAD progression, functional decline, and higher rates of cardiovascular morbidity and mortality

Pilot data from the Cardiovascular Health Study (CHS) showed that relative risks of fibrinogen, D-dimer and CRP levels for cardiovascular events were highest for events occurring more proximate to baseline blood factor measurements. Therefore, the study also sought to determine whether blood factor levels measured at the most recent examination prior to cardiovascular events or PAD progression were higher than the levels that did not immediately precede cardiovascular events or PAD progression. The hypothesis was tested that blood factor levels at the most recent examination prior to cardiovascular events or PAD progression would be higher than blood factor levels that did not immediately precede cardiovascular events.