Peripheral Vascular Disease Workup

Routine blood tests may be indicated in the evaluation of patients with suspected serious compromise of vascular flow to an extremity. Complete blood count (CBC), blood urea nitrogen (BUN), creatinine, and electrolyte studies help evaluate for signs of end-organ injury and for factors that might lead to worsening of peripheral perfusion. Risk factors for the development of vascular disease (lipid profile, coagulation tests) can also be evaluated, though not necessarily in the emergency department (ED) setting.

Elevated levels of inflammatory blood markers such as D dimer, C-reactive protein, interleukin-6, and homocysteine have been linked to decreased lower extremity tolerance of exercise. ^[10] Higher levels of activity in daily life have been shown to decrease these levels. ^[11] The applicability to practice in emergency medicine is not clear, but it is unlikely to be of clinical significance.

See also guidelines from the American Heart Association and American College of Cardiology (AHA/ACC)  ^[12] and the Canadian Cardiovascular Society (CCS). ^[13]

Plain films are of little use in the setting of peripheral vascular disease (PVD).

The criterion standard for intraluminal obstruction has always been arteriography, though it is both potentially risky and often unobtainable in the emergency setting. The delay associated with obtaining arteriography in the setting of obvious limb ischemia can delay definitive treatment to deleterious effect. If time allows, arteriography can prove useful in discriminating thrombotic disease from embolic disease.

Doppler ultrasonographic studies are useful as primary noninvasive studies to determine flow status. Upper extremities are evaluated over the axillary, brachial, ulnar, and radial arteries. Lower extremities are evaluated over the femoral, popliteal, dorsalis pedis, and posterior tibial arteries. Note the presence of Doppler signal and the quality of the signal (ie, monophasic, biphasic, triphasic). The presence of distal flow does not exclude emboli or thrombi because collateral circulation may provide these findings.

Magnetic resonance imaging (MRI) may be of some clinical benefit by virtue of its high visual detail. Plaques are imaged easily, as is the difference between vessel wall and flowing blood. MRI also has the benefits of angiography, providing even higher detail and capable of replacing traditional arteriography. The utility of MRI is limited in the emergency setting, often because of the location of the device and the technical skill required to interpret the highly detailed images.

Computed tomography (CT) can be of use to the emergency physician in  that it does not have the time and availability constraints that MRI does. Although noncontrast studies can be useful for imaging calcification and arteriosclerosis, contrast studies are most useful for imaging arterial insufficiency. Renal function should be confirmed before contrast administration; PVD often coexists with risk factors for contrast-induced renal failure. High-definition CT studies in patients who exhibit symptoms of PVD can be of benefit in guiding treatment decisions and modalities. ^[14]

CT angiography (CTA) and magnetic resonance angiography (MRA) represent significant developments in axial imaging of PVD. Benefits of CTA include rapid noninvasive acquisition, wide availability, high spatial resolution, and the ability to generate isotropic datasets on 64-detector-row and higher CT scanners; drawbacks include the exposure to iodinated contrast and ionizing radiation. Benefits of MRA include high diagnostic accuracy and the avoidance of exposure to ionizing radiation; drawbacks include limited availability and increased cost. ^[15]

Molecular imaging with radionuclide-based approaches may potentially provide a novel noninvasive assessment of biologic processes in PVD, such as angiogenesis and atherosclerosis. ^[16]

See also guidelines from the American Heart Association and American College of Cardiology (AHA/ACC) ^[12]  and the Canadian Cardiovascular Society (CCS). ^[13]

Ankle-brachial index

The ankle-brachial index (ABI) is a useful test for comparing pressures in the lower extremity with pressures in the upper extremity. Blood pressure normally is slightly higher in the lower extremities than in the upper. Comparison to the contralateral side may suggest the degree of ischemia.

The ABI is obtained by applying blood pressure cuffs to the calf and the upper arm. The blood pressure is measured, and the systolic ankle pressure is divided by the systolic brachial pressure. Normal ABI is higher than 1; a value less than 0.95 is considered abnormal. This test can be influenced by arteriosclerosis and small-vessel disease (eg, diabetes), which reduce its reliability. Progressive peripheral arterial disease (PAD), indicated by an ABI decline of more than 0.15, has been associated with increased cardiovascular disease risk. ^[17]

A retrospective study found that the combination of the ABI and percentage of mean arterial pressure (%MAP) improves the diagnostic sensitivity for PAD versus ABI alone in those with an ABI above 0.90. ^[18]  Analysis was based on medical records from 114 patients (215 limbs) with a diagnosis of PAD based on multiple detector computed tomography angiography (MDCTA). Among the findings were the following ^[18] :

• Improved sensitivity from a combination of an ABI < 0.90 and a %MAP ≥42.5% as diagnostic criteria for PAD versus ABI alone
• Significantly higher PAD risk in individuals with both an ABI < 0.90 and an ABI >0.90 with a %MAP ≥42.5% compared to patients who have ABI >0.90 with a %MAP < 42.5%
• Improved sensitivity and specificity from a combination of an ABI ≤0.90 and a %MAP ≥42.5% than when using a low or borderline ABI

Transcutaneous oximetry

Transcutaneous oximetry affords assessment of impaired flow secondary to both microvascular and macrovascular disruption. Its use is increasing, especially in the realm of wound care and patients with diabetes. Transcutaneous oximetry has not been studied extensively in emergent occlusion.

Electrocardiography

An electrocardiogram (ECG) may be obtained to look for evidence of dysrhythmia, prior cardiac injury, or even acute myocardial infarction.

See also guidelines from the American Heart Association and American College of Cardiology (AHA/ACC) ^[12] and the Canadian Cardiovascular Society (CCS). ^[13]

Carotid artery reactivity

A novel procedure that assesses endothelial function appears to have the potential to predict cardiovascular (CV) events in patients with peripheral arterial disease (PAD). ^[19]  In a study of 172 patients with PAD who underwent carotid artery reactivity, 82 showed carotid constriction and 90 showed carotid dilation. There were more CV events seen in the carotid constriction group than those in the carotid dilation group; moreover, there was a four-fold higher risk for higher CV events and a two-fold higher risk for clinical deterioration even when adjusted for other risk factors. ^[19]