Utility of superb microvascular imaging for assessment of foot perfusion in patients with critical limb ischemia

Abstract

Abstract Background Recently, an increasing attention has been paid to foot microcirculation in critical limb ischemia (CLI). Although skin perfusion pressure (SPP) is the most frequently used marker of microcirculation, SPP is often unmeasurable at the most ischemic site in the foot. A new ultrasound technique (superb micro-vascular imaging [SMI]) allows the detection of extremely low velocity flows and enables the quantitative verification as vascular index (VI). We examined the diagnostic value of SMI-based VI in assessing foot perfusion when planning endovascular treatment (EVT). Methods Consecutive 50 patients with CLI were enrolled. All cases underwent EVT for superficial femoral arteries. SMI-based VI of plantar, dorsal, medial heel, lateral heel and toe's area were obtained before and after EVT, and those were compared with SPP (plantar and dorsal) or ankle-brachial index (ABI) representing macrocirculation. Results Based on the six angiosomes concept, SMI enabled to visualize microcirculation in all subjects, but SPP was not feasible in 13% of all subjects at the most ischemic site. After EVT, ABIs were significantly increased from 0.64±0.19 to 0.85±0.27 (P=0.0003). Plantar SPP also increased from 39.6±20.4 mmHg to 58.5±27.1 mmHg (p=0.002). SMI-based VI significantly increased in each sites based on the six angiosomes concept. Of note, plantar SMI-based VI significantly increased from 5.1±3.2% to 10.6±6.6% (p<0.0001), suggesting improvement of foot perfusion. Plantar SMI-based VI was well correlated with plantar-SPP both before and after EVT (p=0.002, r=0.663). Plantar VI was also informative in showing a rapid improvement of foot perfusion during EVT. Conclusion SMI enabled to visualize the foot microcirculation on the basis of angiosomes concept. SMI has potential as an alternative to SPP. Funding Acknowledgement Type of funding source: Public grant(s) – National budget only. Main funding source(s): Grant-in -Aid for Scientific Reseach, Japan