SLR - March 2020 - Hyun W. Shim

Quantitative Evaluation of Post-Intervention Foot Blood Supply in Patients with Peripheral Artery Disease by Computed Tomography Perfusion

Reference: Gao P, Li Z, Jin L, Li L, Zhao W, Zhang W, Sun Y, Zhao Y, Cui J, Li M. Quantitative Evaluation of Post-Intervention Foot Blood Supply in Patients with Peripheral Artery Disease by Computed Tomography Perfusion. Journal of Vascular Surgery. 2020 Jan 19; 71 (1).

Scientific Literature Review
 
Reviewed By: Hyun W. Shim, DPM
Residency Program: Temple University Hospital – Philadelphia, PA

Podiatric Relevance: Peripheral arterial disease is a common disorder encountered by Podiatric surgeons. Performing surgeries on patients with compromised vascular status carries the risk of non-healing surgical sites which may have detrimental outcomes. The ankle brachial index (ABI) is commonly used tool for assessing peripheral arterial disease. However, its use is limited for patients with arterial calcification, due to false elevation.  Computed tomography angiogram (CTA) is used to examine lumens and blood vessel walls but cannot assess tissue perfusion. Perfusion computed tomography (perfusion CT) is commonly used for diagnosis of cerebral/myocardial ischemia but rarely used for lower extremities. The purpose of the study was to quantitatively assess the blood supply in the foot post-intervention using perfusion CT.

Methods: This was a single center, prospective cohort study with IRB approval. Nineteen patients who underwent endovascular procedures from 1/2018 – 11/2018 were included in the study. Further inclusion criteria include pre-operative and post-operative ABI, CTA with confirmed vascular stenosis of > 70 percent.  Exclusion criteria include renal insufficiency, history of chronic heart failure, cardiac history, and contrast hypersensitivity. Perfusion CT was performed on both limbs, pre-operatively and three days post-operatively. Four regions of interest (ROI) on the foot were identified and are as follows: dorsal aspect, heel, cross section of the forefoot, and plantar foot. Variables compared include blood flow, mean transit time (MTT), and time to peak (TTP). Blood flow measures the blood volume flowing through the local tissue, MTT measures the circulation time from arteriole to the veins, and TTP measures time from initial enhancement to peak enhancement of the ROI.  

Results: Post-intervention ABI showed improvement on the diseased limb, with increase in the value from 0.41 to 0.76 post-operatively. Post-operative perfusion CT showed improvement in the variables measured. Tissue perfusion measuring blood flow, MTT, and TTP showed improvement. Mean blood flow to ROI showed increased by 24.01 mL/100 g•min, MTT was shortened by 3.89 seconds, and TTP was shortened by 12.24 seconds.

Conclusions: The purpose of the study was to quantitatively evaluate blood supply in the foot post-endovascular procedure using perfusion CT. It is a diagnostic method which can provide anatomic and functional information by evaluating local tissue blood supply, without overtreating or undertreating a patient. Utilization of perfusion CT has its advantages over any other diagnostic tools. In regards to hardware, it has a wider detector, allowing scans of both feet at one axis. In regards to software, it uses a perfusion analysis algorithm, preventing excessive use of contrasts, and has higher patient satisfaction.  Authors believe that utilization of perfusion CT can establish appropriate amputation range in limb gangrene and assess severity of ischemia with severe arterial calcification. The study does show that the utilization of perfusion CT can be an acceptable non-invasive form of assessing the degree of PAD without relying on ABI, which can be inaccurate, or waiting for patients to obtain an angiogram. By use of this diagnostic tool, it can provide patients with appropriate treatment options in a reasonable timeframe.  

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