Lower Limb Ischemia: A Novel Method for Diagnosing Severity

The Consequences of Ischemia

Despite global and domestic advances in vascular surgery, the number of patients with critical lower limb ischemia remains significant. Diseases causing occlusion of lower limb arteries are among the most common reasons for primary disability. The amputation rate in the natural course of critical ischemia reaches 20%, particularly when open or endovascular reconstructions are not feasible. This is often due to the choice of surgical strategy, a conservative treatment approach, and the insufficient accuracy of current diagnostic methods for assessing ischemia severity. One method to increase limb salvage rates is fluorescence diagnostics using Indocyanine Green.

Diagnostic Tools for Ischemia

To diagnose the degree of ischemia, besides initial examination and patient history, a physician may prescribe ultrasound Doppler scanning (USD) to assess the anatomy of affected arteries and blood flow characteristics, or computed tomographic angiography (CT angiography). This article focuses on a method employed by the Russian "MARS" video fluorescence diagnostic system, used to evaluate the need for surgical intervention, perform post-operative analysis, and determine further treatment tactics. The equipment is installed at the "Diabetic Foot" department of the National Medical Research Center for Endocrinology of the Russian Ministry of Health. The center's physicians have mastered and implemented this blood flow assessment technique using the "MARS" software capabilities.

The "MARS" Video Fluorescence Diagnostic System

When a contrast agent (Indocyanine Green – ICG) is administered intravenously, vessels become visually accessible under laser light in the near-infrared spectrum; this process is called fluorescence. The physician identifies areas with varying degrees of blood supply. However, visual assessment alone may be insufficient for deciding on surgical intervention or tracking dynamic changes. In such cases, quantitative parameters of fluorescence intensity are needed.

Quantitative assessment of blood supply in patients with clinical lower limb ischemia provides an objective understanding of arterial status.

The parameters T_start and T_max on the X-axis indicate the time to fluorescence onset and the time to peak (maximum) fluorescence in the region of interest after ICG injection. In medical terms, lower T_start and T_max values indicate better blood supply in these zones. The maximum fluorescence intensity is denoted as I_max and represented on the graph as the peak of each curve. The greater the brightness of the highlighted area, the higher this value. Conversely, dark areas, a prolonged time to peak fluorescence, and a significant difference between fluorescence onset and peak time may indicate blood supply issues.

Fluorescence angiography is considered an alternative method for assessing lower limb ischemia severity and offers several significant advantages over other standard methods (ABI – ankle-brachial index, TBI – toe-brachial index, TcPO2 – transcutaneous oximetry).

For example, a reduction in the time to peak fluorescence after revascularization, compared to the pre-operative value, would indicate positive dynamics in the limb's condition. This is clearly demonstrated on the graph and reflected in numerical data thanks to the "MARS" software functionality. Another important advantage is the physician's ability to either perform the analysis immediately at the patient's bedside or analyze a video file recorded on the device's memory without time constraints.

In-depth research on fluorescence diagnostics in patients with critical lower limb ischemia was conducted by endocrinologist Zerа Nusredovna Dzhemilova at the Diabetic Foot department of the Diabetes Institute, NMRC for Endocrinology. You can learn about her work and findings regarding this technology in the overview video about the "MARS" system on our YouTube channel.

It is crucial to note that besides performing the fluorescence diagnostic procedure correctly, the data obtained via the software must also be interpreted accurately. Proper interpretation of the fluorescence protocol enables:

• Determining the severity level in patients with lower limb ischemic lesions during monitoring.
• Making decisions regarding surgical intervention and, in some cases, avoiding limb amputation.
• Tracking dynamic changes following lower limb revascularization procedures.

Undoubtedly, fluorescence diagnostics has already gained recognition among many specialists, not only in endocrinology. It is also gratifying that the "MARS" equipment is currently available for purchase and trialing. If you have such a need or any questions about the presented medical equipment, please contact us at kriptomed.com.

1) Screen image from the "MARS" system monitor showing fluorescence with Indocyanine Green dye.

2) “MARS" Video Fluorescence Diagnostic System

3) Graph axes: Vertical Y-axis – Brightness (relative units), Horizontal X-axis – Time (seconds)