Indocyanine Green Angiography Evaluated for Use in CLI Patients

February 7, 2013—An early quantitative evaluation of indocyanine green angiography (ICGA) in patients with critical limb ischemia concluded that ICGA provides rapid visual and quantitative information about regional foot perfusion. The study by Jonathan D. Braun, MD, et al was recently published online ahead of print in the Journal of Vascular Surgery and was presented in June during the Rapid Session at the 2012 Vascular Annual Meeting of the Society of Vascular Surgery in National Harbor, Maryland.

In the Journal of Vascular Surgery, the investigators stated that they believe this is the first report describing quantification of foot perfusion before and after lower extremity revascularization for severe limb ischemia. They advised that further study is warranted to help define the utility of this intriguing new technology to assess perfusion, response to revascularization, and potentially, to predict likelihood of wound healing.

In comments to Endovascular Today, investigator Joseph L. Mills, MD, of the University of Arizona, discussed the ways in which the concept of CLI has evolved since it was first published, referencing the global epidemic of diabetes and the increasingly aging population as the major causes.

"Forty years ago, when the term was first defined, patients were most often nondiabetic smokers with ischemic rest pain or gangrene," Dr. Mills explained. "They fit into a pure ischemia model. Diabetics were actually excluded from the original definition of CLI published in 1982 because of the confounding effects of neuropathy and infection. 

“Patients now most commonly present with a diabetic foot ulcer and a broad spectrum of ischemia,” he continued. “Infection seems to be synergistic with ischemia; that is, PAD plus infection triples the odds of limb amputation in a patient with diabetes.”

In the background to the study, the investigators described the ways in which cases requiring lower extremity revascularization are increasingly complex. For instance, traditional means of evaluating perfusion before and after revascularization are often limited by the presence of medial calcinosis, open wounds, previous toe or forefoot amputations, and infection. Dr. Mills pointed out that in such patients, measurement of perfusion status at baseline and reassessment after vascular intervention, when needed, is extremely important in amputation prevention efforts.

As summarized in the Journal of Vascular Surgery, this study evaluated the initial application of ICGA to patients with severe lower extremity ischemia to develop quantitative, reproducible parameters to assess perfusion. ICGA uses a charge-coupled device camera, a laser, and intravenous contrast to visually assess skin surface perfusion.

From January 2011 to April 2012, the investigators performed ICGA within 5 days of 31 revascularization procedures in patients with Rutherford class 5 and 6 ischemia. They also compared ICGA before and after revascularization in a subset of 13 patients. Multiple quantitative parameters were evaluated to assess perfusion.

“We sought to determine if ICGA could better assess perfusion in a group of patients at high risk for amputation and also whether it could document the level of perfusion benefit achieved by endovascular or open revascularization," said Dr. Mills. “We have developed methods to quantify perfusion in such patients, perhaps for the first time. ICGA also appears to be beneficial in identifying patients with regional perfusion abnormalities (eg, heel ulcer in renal failure patient with palpable dorsalis pedis pulse) and may prove extremely valuable in further delineating the angiosome concept of revascularization.”

The investigators reported that 24 patients underwent ICGA associated with 31 revascularization procedures (26 endovascular, four open, one hybrid) for 26 lower limb wounds; 92% were diabetic and 20% were dialysis-dependent. In 50% of these patients, it was not possible to measure the ankle-brachial index because of medial calcinosis. Paired analysis of ingress (increase in pixel strength [PxS]), ingress rate (slope of increase in PxS), curve integral (area under the curve in PxS over time), end intensity (PxS at end of study), egress (decrease in PxS from maximum), and egress rate (slope of decrease in PxS) increased significantly (P < .05) after revascularization.

Dr. Mills concluded, “We believe careful application and further development of this technology will be clinically useful in assessing baseline perfusion status, predicting the likelihood of wound healing, and determining the perfusion response to targeted revascularization.”