Objective Measures for Evaluating Critical Limb Ischemia

In the January issue of Vascular Disease Management, Marianne Brodmann, MD, comments on noninvasive and minimally invasive testing in the treatment of critical limb ischemia (CLI). Dr. Brodmann clearly points out the attributes and the limitations of many of the commonly utilized studies in the evaluation of patients presenting with CLI. Clinicians clearly need objective tests that can better determine who should have intervention and to determine the subsequent adequacy of intervention or surgery. Dr. Brodmann highlights the limitations of many of the present diagnostic tools. These studies are not able to determine adequacy of perfusion at the capillary level on a completely reproducible basis and some do not show the degree of improvement for up to 1 day post intervention. 

Knowing when to intervene, and determining when an intervention has adequately achieved the successful intended result, has been elusive. Clinical parameters and angiographic results are the determinants utilized by most practitioners today. Tissue blush is often cited at the time of intervention as a measure of success. Unfortunately clinical parameters are not always objective and may at times lead to treatments that aren’t needed or failure to treat further when initial therapy isn’t adequate. Angiography is the present “gold standard” but it can’t adequately assess capillary perfusion in an affected area. 

Dr. Brodmann points out the limitations of ABIs (ankle brachial indices), which are limited to assessing the macrovascular flow and are inaccurate in cases where there is significant dystrophic vascular calcification. Toe brachial indices are superior to ABIs in assessing macrovascular circulation as there is often sparing of calcification of the pedal vessels. Toe brachial indices should be utilized more frequently in CLI assessment and in CLI research protocols.

Lower-extremity arterial duplex studies allow imaging and flow evaluation, but they are suboptimal in assessing calcified infrapopliteal vessels and do not assess true tissue perfusion. Despite these limitations, arterial duplex studies are reliable in determining arterial patency and remain cornerstones in guiding therapeutic decisions.

Tissue perfusion assessment in CLI has been most commonly performed invasively by flourescin angiography and noninvasively by TCOM (transcutaneous oxygen measurement) or by subcutaneous laser Doppler (skin perfusion pressure). Unfortunately, although these newer studies are helpful, they are not easily reproducible and often do not immediately reflect perfusion changes. These studies are often difficult to measure post intervention because of ulcers, nonhealing wounds, and infection.

Dr. Brodmann mentions the possible utilization in the future of angiographic functional imaging which is still in its infancy. At present it is clear that angiographic functional imaging can result in great images. At present there is no data to suggest clear clinical utility. 

Critical limb ischemia is a disabling and deadly disease process that is finally getting the attention that it deserves. At present, there are no clear diagnostic, therapeutic, or follow-up guidelines to direct appropriate therapy. Although great strides are being made in crossing and treating obstructive lesions in patients with CLI, we still lack appropriate objective measures to determine when to intervene, what constitutes adequate intervention, and what should prompt repeat intervention. For now, clinical judgement, despite its many limitations, must serve as our guide in directing therapy.