Critical and acute limb ischemia: an overview

Pressure-Induced Microvascular Reactivity With Whole Foot Loading Is Unique Across the Human Foot Sole

BACKGROUND

Foot sole plantar pressure generates transient but habitual cutaneous ischemia, which is even more exacerbated in atypical gait patterns. Thus, adequate post-occlusive reactive hyperaemia (PORH) is necessary to maintain skin health. Plantar pressure regional variance during daily tasks potentially generates region-specific PORH, crucial for ischemic defence.

AIMS

The current work investigated regional PORH across the human foot sole resulting from stance-like loading.

MATERIALS & METHODS

A loading device equipped with an in-line laser speckle contrast imager measured blood flux before, during, and after whole-foot loading for 2 and 10 min durations at 15% and 50% body weight. Flux was compared between six regions: the heel, lateral arch, medial arch, and fifth, third, and first metatarsals (MT).

RESULTS

Baseline flux was significantly greater in the 1MT and 3MT than all other regions. Loading occluded the heel, 5MT and 3MT more than all other regions. Regional PORH peak, time to peak, area under the curve, and recovery rate were ranked between regions.

DISCUSSION

The 3MT, followed by 5MT, overall had the strongest PORH response, suggesting a heightened protection against ischemia compared to other regions.

CONCLUSION

This work highlights regional variations within a healthy foot, providing a framework for future ulcer risk assessments and interventions to preserve foot health.

Autologous Bone Marrow Stem Cells in Patients With Critical Limb Ischaemia not Eligible for Revascularization: A Single Centre Experience

We evaluated the use of autologus bone marrow stem cells transplantation in patients with critical limb ischaemia (CLI) not eligible for revascularization. Eighty consecutive patients candidate to amputation were enrolled in a single-centre retrospective study. The primary endpoint was defined as the amputation-free rate from stem cells transplantation. Secondary endpoints were the evaluation of transcutaneous oximetry and its predictive potential for probability of amputation and the evaluation of rest pain. Ankle brachial index, transcutaneous oxygen (TcpO2) and radiological imaging were performed at the enrolment and during the follow-up times. All patients were treated with auto transplant of bone marrow stem cells. Two patients died due to acute renal and acute respiratory failures. 19 patients were amputated from the thigh or leg. In total, 59 of 80 patients intended to thigh amputation saved the limb, preserving the plantar support. TcpO2 was found a predictive metric with an AUC equal to .763, and a threshold for a risk of amputation of 10% and 5% at the values ≤22.7 and ≤26.9 mmHg, respectively. Auto transplant of bone marrow stem cells seems to be a safe and an efficient option for CLI not eligible to revascularizzation.

Endovascular Revascularization and Outcomes of Critical Limb-Threatening Ischemia in Trinidad and Tobago: The EVENT Pilot Study-Challenges in a Limited-Resource, Caribbean Setting

INTRODUCTION

This retrospective study investigated major adverse limb events (MALE) and mortality outcomes in critical limb-threatening ischemia (CLTI) patients with tissue loss after an endovascular revascularization-first (EVR-1st) strategy.

METHODS

MALE and mortality were assessed in 157 consecutive patients with CLTI and tissue loss from June 2019 to June 2022 at the Eric Williams Medical Sciences Complex, Trinidad and Tobago.

RESULTS

157 patients underwent the EVR-1st strategy, of whom 20 were pivoted to immediate surgical revascularization (SR). Of the remaining 137 patients, successful EVR was achieved in 112, giving a procedural success of 82% and an all-comer overall success of 71%. The mortality and MALE rates were 2.7% and 8.9% at 2 years, respectively. Males and patients with previous major amputations were at significantly higher risk for MALE (p values of 0.016 and 0.018, respectively). There was a statistically significant difference in successful EVR for both Rutherford-Baker (RB) 5 (minor) and RB 6 (major) classifications: 63 (56%) vs. 5 (20%) and 49 (44%) vs. 20 (80%), both with a p value of 0.01. There were no differences in successful EVR amongst Wound, Ischemia, Foot Infection (WIfI) clinical stages. There were no differences in successful EVR amongst the Trans-Atlantic Inter-Society Consensus (TASC II) classifications.

CONCLUSIONS

This study may prove clinically informative and applicable for an EVR-1st management strategy for high-risk patients with CLTI in a limited-resource, Caribbean setting.

TRIAL REGISTRATION NUMBER

NCT05547022 (retrospectively registered).

Percutaneous thrombectomy or ultrasound-accelerated thrombolysis for initial management of acute limb ischaemia

BACKGROUND

Acute limb ischaemia (ALI), the sudden and significant reduction of blood flow to the limb, is considered a vascular emergency. In the general population, the incidence is estimated as 14 per 100,000. Prognosis depends on the time it takes to diagnose the condition and begin appropriate treatment. Standard initial interventional treatments include conventional open surgery and endovascular interventions such as catheter-directed thrombolysis (CDT). Percutaneous interventions, such as percutaneous thrombectomy (PT, including mechanical thrombectomy or pharmomechanical thrombectomy) and ultrasound-accelerated thrombolysis (USAT), are also performed as alternative endovascular techniques. The proposed advantages of PT and USAT include reduced time to revascularisation and when combined with catheter-directed thrombolysis, a reduction in dose of thrombolytic agents and infusion time. The benefits of PT or USAT versus open surgery or thrombolysis alone are still uncertain. In this review, we compared PT or USAT against standard treatment for ALI, in an attempt to determine if any technique is comparatively safer and more effective.

OBJECTIVES

To assess the safety and effectiveness of percutaneous thrombectomy or ultrasound-accelerated thrombolysis for the initial management of acute limb ischaemia in adults.

SEARCH METHODS

The Cochrane Vascular Information Specialist searched the Cochrane Vascular Specialised Register, CENTRAL, MEDLINE, Embase, CINAHL, the World Health Organization (WHO) International Clinical Trials Registry Platform, and ClinicalTrials.gov to 3 March 2021. We searched reference lists of relevant studies and papers.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) that compared PT (any modality, including mechanical thrombectomy (aspiration, rheolysis, rotation) or pharmomechanical thrombectomy) or USAT with open surgery, thrombolysis alone, no treatment, or another PT modality for the treatment of ALI.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected the studies, assessed risk of bias, extracted data, performed data analysis, and assessed the certainty of evidence according to GRADE. Outcomes of interest were primary patency, amputation rate, major bleeding, clinical success, secondary patency, and adverse effects.

MAIN RESULTS

We included one RCT in this review. This study had a total of 60 participants and compared USAT with standard treatment (CDT). The study included 32 participants in the CDT group and 28 participants in the USAT group. We found no evidence of a difference between USAT and CDT alone for the following evaluated outcomes: amputation rate (risk ratio (RR) 1.14, 95% confidence interval (CI) 0.17 to 7.59); major bleeding (RR 1.71, 95% CI 0.31 to 9.53); clinical success (RR 1.00, 95% CI 0.94 to 1.07); and adverse effects (RR 5.69, 95% CI 0.28 to 113.72). We rated the certainty of the evidence as very low for these outcomes. We downgraded the certainty of the evidence for amputation rate, major bleeding, clinical success, and adverse effects by two levels due to serious limitations in the design (there was a high risk of bias in critical domains) and by two further levels due to imprecision (a small number of participants and only one study included). The study authors reported 30-day patency, but did not report primary and secondary patency separately. The patency rate in the successfully lysed participants was 71% (15/21) in the USAT group and 82% (22/27) in the CDT group. The study authors did not directly report secondary patency, which is patency after secondary procedures, but they did report on secondary procedures. Secondary procedures were subdivided into embolectomy and bypass grafting. Embolectomy was performed on 14% (4/28) of participants in the USAT group versus 3% (1/32) of participants in the CDT group. Bypass grafting was performed on 4% (1/28) of participants in the USAT group versus 0% in the CDT group. As we did not have access to the specific participant data, it was not possible to assess these outcomes further. We did not identify studies comparing the other planned interventions.

AUTHORS' CONCLUSIONS

There is insufficient evidence to assess the safety and effectiveness of USAT versus CDT alone for ALI for our evaluated outcomes: amputation rate, major bleeding, clinical success, and adverse effects. Primary and secondary patency were not reported separately. There was no RCT evidence for PT. Limitations of this systematic review derive from the single included study, small sample size, short clinical follow-up period, and high risk of bias in critical domains. For this reason, the applicability of the results is limited. There is a need for high-quality studies to compare PT or USAT against open surgery, thrombolysis alone, no treatment, or other PT modalities for ALI. Future trials should assess outcomes, such as primary patency, amputation rate, major bleeding, clinical success, secondary patency, and adverse effects.

Viabahn-Assisted Extra-Arterial Bypass Combined With Surgical Arterial Endarterectomy as a Salvage Technique to Treat Critical Limb Ischemia

BACKGROUND

Revascularization of patients with critical limb ischemia (CLI) is always challenging because of long occlusive arterial lesions with severe calcification and poor general condition. Here we describe a novel hybrid technique to treat a CLI patient.

METHODS

The patient was a 60-year-old male with left foot ulcer. Preoperative scan showed long calcific and occlusive lesions running from the left proximal common femoral artery to P1 of the popliteal artery (PA). Surgical endarterectomy was performed on the proximal femoral artery. Then, retrograde PA access was achieved to protect the vital collateral artery at the proximal PA. When the retrograde V18 guidewire failed to advance because of severe occlusion in the middle one-third of the SFA, we punctured the artery with the V18 guidewire, and manually introduced it into the lumen of the proximal SFA. Three Viabahn stent grafts were successively implanted, parts of which were situated outside the SFA.

RESULTS

Computed tomography 1 week after surgery showed patent blood flow to the left toes. Good recovery was observed during a 1-year follow up, the toe wound healed after amputation, and no rest pain recurred. Ultrasound showed 60% stenosis in the PA stent, while the other stents were patent. The anklebrachial index of the left limb was 0.48.

CONCLUSIONS

This case illustrates successful use of Viabahn-assisted extra-arterial bypass combined with surgical arterial endarterectomy to salvage the limb after CLI. This novel technique might be an alternative in carefully selected patients.

Therapeutic Use of Microbubbles and Ultrasound in Acute Peripheral Arterial Thrombosis: A Systematic Review

Catheter-directed thrombolysis (CDT) for acute peripheral arterial occlusion is time consuming and carries a risk of major hemorrhage. Contrast-enhanced sonothrombolysis (CEST) might enhance outcomes compared with standard CDT. In the study described here, we systematically reviewed all in vivo studies on contrast-enhanced sonothrombolysis in a setting of arterial thrombosis. A systematic search of the PubMed, Embase, Cochrane Library and Web of Science databases was conducted. Two reviewers independently performed the study selection, quality assessment and data extraction. Primary outcomes were recanalization rate and thrombus weight. Secondary outcome was any possible adverse event. The 35 studies included in this review were conducted in four different (pre)clinical settings: ischemic stroke, myocardial infarction, (peripheral) arterial thrombosis and arteriovenous graft occlusion. Because of the high heterogeneity among the studies, it was not possible to conduct a meta-analysis. In almost all studies, recanalization rates were higher in the group that underwent a form of CEST. One study was terminated early because of a higher incidence of intracranial hemorrhage. Studies on CEST suggest that adding microbubbles and ultrasound to standard intra-arterial CDT is safe and might improve outcomes in acute peripheral arterial thrombosis. Further research is needed before CEST can be implemented in daily practice.

Anatomical study and branching point of neurovascular structures at the medial side of the ankle

Nerve entrapment and blood circulation impairment associated with the medial side of the ankle are not uncommon. The purpose of this study was to describe the anatomical basis of neurovascular structures of the medial ankle which comprised the number, origin, branching pattern, and branching point. Forty feet of fresh cadavers were examined by using 2 reference lines: the malleolar-calcaneal (MC) and navicular-calcaneal (NC) axes. We recorded number, origin, length of the 2 axes, the locations and widths of neurovascular structures on MC and NC axes, the branching point of neurovascular structures, and the branching pattern of neurovascular structures was recorded and was separated into 5 types. The posterior tibial nerve (PTN) bifurcated to plantar and calcaneal nerves and branched proximally to the tarsal tunnel (TT). The posterior tibial artery bifurcated to plantar and calcaneal arteries and branched inferiorly to PTN and within the TT. The calcaneal nerves and arteries had more variation of number and origin. The most common branching point of calcaneal nerves and arteries is within the TT, except the medial calcaneal nerve. It branched proximally to the TT. The anatomical knowledge from this study is important for the diagnosis and treatment of clinicians.

Comparison of Long Term Outcomes After Endovascular Treatment Versus Bypass Surgery in Chronic Limb Threatening Ischaemia Patients with Long Femoropopliteal Lesions

OBJECTIVE

There are currently two treatments available for patients with chronic limb threatening ischaemia (CLTI): open surgical bypass (OSB) and percutaneous transluminal angioplasty with/without stenting (PTA/S). The aim of this study was to compare short and long term outcomes between PTA/S and OSB in CLTI patients with long (GLASS grade III and IV) femoropopliteal disease.

METHODS

This was a two centre retrospective study including all consecutive patients with CLTI undergoing first time lower extremity intervention at two distinct vascular surgical centres. Between 1 January 2012 and 1 January 2018, 1 545 CLTI consecutive limbs were treated for femoropopliteal GLASS grade III and IV lesions at two vascular surgical centres. Using covariables from baseline and angiographic characteristics, a propensity score was calculated for each limb. Thus, comparable patient cohorts (235 in PTA/S and 235 in OSB group) were identified for further analysis. The primary outcomes were freedom from re-intervention in the treated extremity and major amputation. Secondary outcomes were all hospital complications among the two patient groups.

RESULTS

Total overall complication rates were significantly higher in the OSB group (20.42% vs. 5.96%, p < .001), especially wound infection/seroma rate that required prolonged hospitalisation and further treatment (7.65% vs. 0%, p < .001). After the median follow up of 61 months, re-intervention rates were significantly higher in the PTA/S group (log rank test, 44.68% vs. 29.79%, p = .002), but there was no significant difference in terms of major amputation rates between the two group of patients (log rank test, PTA/S 27.23% vs. OSB 22.13%, p = .17).

CONCLUSION

Bypass surgery seems to be superior to PTA/S for GLASS grade III and IV femoropopliteal lesions in patients with CLTI in terms of long term re-intervention rates, but with considerably higher rates of post-operative complications. A larger cohort of patients in currently ongoing randomised trials, as well as prospective cohort studies are necessary to confirm these findings.

Injectable pre-cultured tissue modules catalyze the formation of extensive functional microvasculature in vivo

Revascularization of ischemic tissues is a major barrier to restoring tissue function in many pathologies. Delivery of pro-angiogenic factors has shown some benefit, but it is difficult to recapitulate the complex set of factors required to form stable vasculature. Cell-based therapies and pre-vascularized tissues have shown promise, but the former require time for vascular assembly in situ while the latter require invasive surgery to implant vascularized scaffolds. Here, we developed cell-laden fibrin microbeads that can be pre-cultured to form primitive vascular networks within the modular structures. These microbeads can be delivered in a minimally invasive manner and form functional microvasculature in vivo. Microbeads containing endothelial cells and stromal fibroblasts were pre-cultured for 3 days in vitro and then injected within a fibrin matrix into subcutaneous pockets on the dorsal flanks of SCID mice. Vessels deployed from these pre-cultured microbeads formed functional connections to host vasculature within 3 days and exhibited extensive, mature vessel coverage after 7 days in vivo. Cellular microbeads showed vascularization potential comparable to bulk cellular hydrogels in this pilot study. Furthermore, our findings highlight some potentially advantageous characteristics of pre-cultured microbeads, such as volume preservation and vascular network distribution, which may be beneficial for treating ischemic diseases.

Thymosin‑β 4 induces angiogenesis in critical limb ischemia mice via regulating Notch/NF‑κB pathway

Thymosin‑β 4 (Tβ4) has been reported to exert a pro‑angogenic effect on endothelial cells. However, little is known on the role and underlying mechanisms of Tβ4 on critical limb ischemia (CLI). The present study aimed therefore to investigate the mechanisms and pro‑angiogenic effects of Tβ4 in CLI mice. Tβ4 overexpression lentiviral vector was first transfected into HUVEC and CLI mice model, and inhibitors of Notch pathway (DAPT) and NF‑κB pathway (BMS) were also applied to HUVEC and CLI mice. Subsequently, MTT, tube formation and wound healing assays were used to determine the cell viability, angiogenesis and migratory ablity of HUVEC, respectively. Western blotting, reverse transcription, quantitative PCR, immunofluorescence and immunohistochemistry were used to detect the expression of the angiogenesis‑related factors angiopoietin‑2 (Ang2), TEK receptor tyrosine kinase 2 (tie2), vascular endothelial growth factor A (VEGFA), CD31 and α‑smooth muscle actin (α‑SMA) and the Notch/NF‑κB pathways‑related factors NOTCH1 intracellular domain (N1ICD), Notch receptor 3 (Notch3), NF‑κB and p65 in HUVEC or CLI mice muscle tissues. The results demonstrated that Tβ4 not only enhanced the cell viability, angiogenesis and migratory ability of HUVEC but also promoted the expression of Ang2, tie2, VEGFA, N1ICD, Notch3, NF‑κB, and phosphorylated (p)‑p65 in HUVEC. In addition, Tβ4 promoted the expression of CD31, α‑SMA Ang2, tie2, VEGFA, N1ICD and p‑p65 in CLI mice muscle tissues. Treatment with DAPT and BMS had opposite effects of Tβ4, whereas Tβ4 reversed the effect of DAPT and BMS. The findings from the present study suggested that Tβ4 may promote angiogenesis in CLI mice via regulation of Notch/NF‑κB pathways.

ROS-responsive capsules engineered from EGCG-Zinc networks improve therapeutic angiogenesis in mouse limb ischemia

The successful treatment of limb ischemia requires that promote angiogenesis along with microenvironment improvement. Zinc ions have been reported to stimulate angiogenesis, but application was limited to the toxicity concerns. We hypothesized that zinc based metal-EGCG capsule (EGCG/Zn Ps) can achieve sustained release Zn²⁺ resulting in reduced toxicity and improve angiogenesis as well as the improvement of microenvironment by ROS scavenging of EGCG. The surface morphology, zeta potential, infrared absorbance peaks and zinc ion release profile of the EGCG/Zn Ps were measured. In vitro, EGCG/Zn showed significantly antioxidant, anti-inflammatory and induced cell migration effect. In addition, EGCG/Zn Ps enabled the sustained release of zinc ions, which reduced cytotoxicity and enhanced the secretion of vascular endothelial growth factor (VEGF) in vitro and in vivo. In mouse models of limb ischemia, EGCG/Zn Ps promoted angiogenesis and cell proliferation in ischemic tissues. Moreover, EGCG/Zn Ps group exhibited the most significant recovery of limb ischemic score, limb temperature and blood flow than other groups. In conclusion, EGCG/Zn Ps is a safe and promising approach to combine the merit of Zn²⁺ and EGCG, thus enabling the direct application to limb ischemia.

•

Metal-polyphenol networks have been firstly applied in the Limb ischemic disease.

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EGCG improve the microenvironment of ischemic whereas Zinc exerts angiogenic property.

•The slowly release of zinc ions were achieved, resulting in better biocompatibility.

Through Thick or Thin: Disparities in Perioperative Anticoagulant Use in Trauma Patients

Although vascular surgery guidelines recommend immediate anticoagulation for acute occlusion of a peripheral artery, it is unclear whether trauma surgeons follow this practice. A survey regarding the use of perioperative anticoagulation was sent to surgeons who perform their own peripheral arterial repairs after traumatic injury to define contemporary practice patterns. This survey demonstrated minimal consensus opinion regarding the management of extremity vascular injuries, strongly suggesting the need for a consensus conference, meta-analysis, and prospective studies to guide further care.

A prothrombotic state and denser clot formation in patients following acute limb ischemia of unknown cause

INTRODUCTION

Fibrin clot structure differs between healthy individuals and those following thromboembolic events. Dense and poorly lysable fibrin clots have also been reported in peripheral artery disease. We studied fibrin clot properties and its determinants in individuals with a history of acute lower limb ischemia (ALI) of unknown cause.

MATERIALS AND METHODS

In this case-control study, we enrolled 43 patients who experienced ALI of unknown cause, and two age-and sex-matched reference groups: (1) patients with cryptogenic non-lacunar stroke (n = 43) and (2) individuals without any history of thromboembolism (n = 43, control group). Plasma fibrin clot properties, along with thrombin generation and fibrinolysis markers were assessed following ≥3 months of anticoagulation.

RESULTS

Compared with the control group, the ALI group exhibited more compact plasma fibrin clots (13.4% lower permeability [K_s], p = .001), decreased formed clot lysis (12.5% lower D-D_rate, p = .001) and unaltered clot lysis potential, along with enhanced thrombin generation potential (49% higher peak thrombin concentration, p < .0001). There were no differences in these variables between ALI and stroke patients. Patients with ALI had slightly higher α₂-antiplasmin and lower plasminogen activator inhibitor 1 levels compared with the stroke and control groups (all p < .01).

CONCLUSIONS

Patients who experienced ALI of unknown cause display a prothrombotic fibrin clot phenotype, including increased clot density and hypofibrinolysis associated with higher thrombin generation, which might suggest potential benefits from prolonged anticoagulation in this disease.

Evaluation of skeletal muscle perfusion in a canine hind limb ischemia model using CT perfusion imaging

PURPOSE

To evaluate skeletal muscle perfusion in a canine hind limb ischemia model using CT perfusion imaging (CTPI).

METHODS

Twelve beagles underwent embolization at the branch of the left deep femoral artery. The right hind limbs were used as controls. CTPI was performed immediately after embolization. The perfusion parameters of the regions of interest (ROI), including blood volume (BV), blood flow (BF), mean transit time (MTT) and permeability (PMB), were obtained in both the lateral and posterior hind limb muscle groups.

RESULTS

After embolization, the BV, BF and PMB values in the lateral muscles of the left hind limbs were significantly lower than those in the right hind limbs (P > 0.05), and the MTT was significantly prolonged (P > 0.05). The values for BV, BF, MTT and PMB in the posterior muscles of the left hind limbs were not significantly different from those in the right hind limbs (P > 0.05). The values for BV, BF and PMB in the lateral muscles of the left hind limbs were significantly lower than those in the posterior muscles of the left hind limbs (P > 0.05).

CONCLUSION

CTPI could be used to evaluate skeletal muscle perfusion in a canine model, which may have clinical relevance in lower limb ischemia and vascular reconstruction.

Evaluation of skeletal muscle perfusion in canine hind limb ischemia model using color-coded digital subtraction angiography

OBJECTIVE

To evaluate perfusion alterations in skeletal muscle in a canine hind limb ischemia model using color-coded digital subtraction angiography (CC-DSA).

METHODS

Twelve beagles underwent embolization at the branch of their left deep femoral artery. Right hind limbs were used as the control group. Angiography was performed before and immediately after embolization. Upon CC-DSA analysis, time to peak (TTP) was measured before embolization in both sides of the beagles' hind limbs at the middle iliac artery, and the distant, middle and proximal femoral artery. Regions of interest (ROI) peak and ROI peak time were symmetrically computed in proximal and distal thigh muscles before and immediately after embolization. The data were analyzed and compared using the Wilcoxon signed rank test.

RESULTS

Before embolization, ROI peak in the proximal thigh was lower than in the ipsilateral distal thigh, whereas ROI peak time in the proximal thigh was longer than in the distal thigh. In the iliac femoral artery, there was no significant difference in ROI peak, ROI peak time, or TTP between right and left sides. After embolization, ROI peaks in proximal and distal skeletal muscles of the left hind limb were significantly lower than on the contralateral side. ROI peak time was significantly longer in the left proximal and left distal thigh compared to the contralateral side. There were no significant changes in ROI peak or ROI peak time in the right proximal and right distal thigh compared to pre-embolization values. Changes in ROI peak and ROI peak time were larger in the left proximal than in the left distal thigh.

CONCLUSION

CC-DSA provided real-time measurement of changes in vascular hemodynamics and skeletal muscle perfusion without increasing X-ray usage or contrast agent dose.

Color-coded Digital Subtraction Angiography for Assessing Acute Skeletal Muscle Ischemia-Reperfusion Injury in a Rabbit Model

RATIONALE AND OBJECTIVES

This paper describes an ongoing investigation of imaging and characterization of ischemia-reperfusion (IR) and investigated the use of color-coded digital subtraction angiography (DSA) to assess reperfusion injury or potential injury.

METHODS

New Zealand white rabbits were subjected to right hindlimb ischemia (IR, n = 24) or sham operation (control, n = 6). After 3 hours, the IR rabbits underwent reperfusion and were assessed at 0, 6, 12, or 24 hours (n = 6 each). DSA of the bilateral vastus lateralis muscle of each animal was performed. The maximum contrast enhancement value of a consistent region of interest in the right and left hind limbs (peak enhancement-R/L) was determined. Associations between the relative ratio of the peak right limb to the peak left limb (peak-R/L) and the following blood indicators of IR injury were analyzed: lactic dehydrogenase (LDH), creatine kinase (CK), malondialdehyde (MDA), and superoxide dismutase (SOD).

RESULTS

Serum LDH, CK, and MDA values in each IR group were significantly higher than those of the control group and were positively associated with the IR interval, whereas SOD was significantly lower and negatively associated. The mean peak-R/L decreased linearly with the IR interval from 1.07 ± 0.01 in the control group, and 0.93 ± 0.06, 0.79 ± 0.05, 0.65 ± 0.04, and 0.47 ± 0.04 at 0, 6, 12, and 24 hours in the IR groups. The coefficients of correlation between the peak-R/L and LDH, CK, MDA, SOD serum levels were -0.885, -0.908, -0.541, and 0.832, respectively.

CONCLUSIONS

Color-coded DSA may be used for monitoring the dynamics of skeletal muscle IR injury.

Acute Limb Ischemia Therapies: When and How to Treat Endovascularly

Acute limb ischemia is an emergent limb and life-threatening condition with high morbidity and mortality. An understanding of the presentation, clinical evaluation, and initial workup, including noninvasive imaging evaluation, is critical to determine an appropriate management strategy. Modern series have shown endovascular revascularization for acute limb ischemia to be safe and effective with success rates approaching surgical series and with similar, or even decreased, perioperative morbidity and mortality. A thorough understanding of endovascular techniques, associated pharmacology, and perioperative care is paramount to the endovascular management of patients presenting with acute limb ischemia. This article discusses the diagnosis and strategies for endovascular treatment of acute limb ischemia.

Long-term outcomes in patients with critical limb ischemia and heart failure with preserved or reduced ejection fraction

The impact of heart failure (HF) on long-term survival in patients with critical limb ischemia (CLI) has not been well described. Outcomes stratified by left ventricular ejection fraction (EF) are also unknown. A single center retrospective chart review was performed for patients who underwent treatment for CLI from 2006 to 2013. Baseline demographics, procedural data and outcomes were analyzed. HF diagnosis was based on appropriate signs and symptoms as well as results of non-invasive testing. Among 381 CLI patients, 120 (31%) had a history of HF and 261 (69%) had no history of heart failure (no-HF). Within the HF group, 74 (62%) had HF with preserved ejection fraction (HFpEF) and 46 (38%) had HF with reduced ejection fraction (HFrEF). The average EF for those with no-HF, HFpEF and HFrEF were 59±13% vs 56±9% vs 30±9%, respectively. The likelihood of having concomitant coronary artery disease (CAD) was lowest in the no-HF group (43%), higher in the HFpEF group (70%) and highest in the HFrEF group (83%) ( p=0.001). Five-year survival was on average twofold higher in the no-HF group (43%) compared to both the HFpEF (19%, p=0.001) and HFrEF groups (24%, p=0.001). Long-term survival rates did not differ between the two HF groups ( p=0.50). There was no difference in 5-year freedom from major amputation or freedom from major adverse limb events between the no-HF, HFpEF and HFrEF groups, respectively. Overall, the combination of CLI and HF is associated with poor 5-year survival, independent of the degree of left ventricular systolic dysfunction.

Distributed vasculogenesis from modular agarose-hydroxyapatite-fibrinogen microbeads

Critical limb ischemia impairs circulation to the extremities, causing pain, disrupted wound healing, and potential tissue necrosis. Therapeutic angiogenesis seeks to repair the damaged microvasculature directly to restore blood flow. In this study, we developed modular, micro-scale constructs designed to possess robust handling qualities, allow in vitro pre-culture, and promote microvasculature formation. The microbead matrix consisted of an agarose (AG) base to prevent aggregation, combined with cell-adhesive components of fibrinogen (FGN) and/or hydroxyapatite (HA). Microbeads encapsulating a co-culture of human umbilical vein endothelial cells (HUVEC) and fibroblasts were prepared and characterized. Microbeads were generally 80-100µm in diameter, and the size increased with the addition of FGN and HA. Addition of HA increased the yield of microbeads, as well as the homogeneity of distribution of FGN within the matrix. Cell viability was high in all microbead types. When cell-seeded microbeads were embedded in fibrin hydrogels, HUVEC sprouting and inosculation between neighboring microbeads were observed over seven days. Pre-culture of microbeads for an additional seven days prior to embedding in fibrin resulted in significantly greater HUVEC network length in AG+HA+FGN microbeads, as compared to AG, AG+HA or AG+FGN microbeads. Importantly, composite microbeads resulted in more even and widespread endothelial network formation, relative to control microbeads consisting of pure fibrin. These results demonstrate that AG+HA+FGN microbeads support HUVEC sprouting both within and between adjacent microbeads, and can promote distributed vascularization of an external matrix. Such modular microtissues may have utility in treating ischemic tissue by rapidly re-establishing a microvascular network.

STATEMENT OF SIGNIFICANCE

Critical limb ischemia (CLI) is a chronic disease that can lead to tissue necrosis, amputation, and death. Cell-based therapies are being explored to restore blood flow and prevent the complications of CLI. In this study, we developed small, non-aggregating agarose-hydroxyapatite-fibrinogen microbeads that contained endothelial cells and fibroblasts. Microbeads were easy to handle and culture, and endothelial sprouts formed within and between microbeads. Our data demonstrates that the composition of the microbead matrix altered the degree of endothelial sprouting, and that the addition of hydroxyapatite and fibrinogen resulted in more distributed sprouting compared to pure fibrin microbeads. The microbead format and control of the matrix formulation may therefore be useful in developing revascularization strategies for the treatment of ischemic disease.

Hypoxic preconditioning-induced autophagy enhances survival of engrafted endothelial progenitor cells in ischaemic limb

Recent clinical studies have suggested that endothelial progenitor cells (EPCs) transplantation provides a modest benefit for treatment of the ischaemic diseases such as limb ischaemia. However, cell‐based therapies have been limited by poor survival of the engrafted cells. This investigation was designed to establish optimal hypoxia preconditioning and evaluate effects of hypoxic preconditioning‐induced autophagy on survival of the engrafted EPCs. Autophagy of CD34⁺VEGFR‐2⁺EPCs isolated from rat bone marrow increased after treatment with 1% O₂. The number of the apoptotic cells in the hypoxic cells increased significantly after autophagy was inhibited with 3‐methyladenine. According to balance of autophagy and apoptosis, treatment with 1% O₂ for 2 hrs was determined as optimal preconditioning for EPC transplantation. To examine survival of the hypoxic cells, the cells were implanted into the ischaemic pouch of the abdominal wall in rats. The number of the survived cells was greater in the hypoxic group. After the cells loaded with fibrin were transplanted with intramuscular injection, blood perfusion, arteriogenesis and angiogenesis in the ischaemic hindlimb were analysed with laser Doppler‐based perfusion measurement, angiogram and the density of the microvessels in histological sections, respectively. Repair of the ischaemic tissue was improved significantly in the hypoxic preconditioning group. Loading the cells with fibrin has cytoprotective effect on survival of the engrafted cells. These results suggest that activation of autophagy with hypoxic preconditioning is an optimizing strategy for EPC therapy of limb ischaemia.

Nanoparticular delivery system for a secretoneurin derivative induces angiogenesis in a hind limb ischemia model

Common therapeutic strategies for peripheral arterial disease often fail to re-establish sufficient blood flow within legs and feet of patients for avoiding critical limb ischemia, what is characterized by a substantial risk for amputation. The neuropeptide secretoneurin induces angiogenesis in models of limb and myocardial ischemia and might be a promising tool in the treatment of patients without the option of revascularization therapy for severe ischemia. Within this manuscript, the biologically active part of secretoneurin was identified, modified by induction of a cysteine residue to gain higher stability against enzymatic degradation and further packed into S-protected thiolated chitosan nanoparticles, which enable intra-muscular application of secretoneurin. Secretoneurin nanoparticles restored blood flow in a mouse hind limb ischemia model within one week, whereas control particles did not. In vitro testing also revealed the angiogenic, antiapoptotic and proliferative effects of the new secretoneurin derivate, as tested in primary human umbilical vein endothelial cells. With the work from this study we provide a new promising tool for treatment of peripheral arterial disease.

Matrix metalloproteinases and risk stratification in patients undergoing surgical revascularisation for critical limb ischaemia

Critical limb ischaemia (CLI) is the most advanced form of peripheral artery disease (PAD) and it is often associated with foot gangrene, which may lead to major amputation of lower limbs, and also with a higher risk of death due to fatal cardiovascular events. Matrix metalloproteinases (MMPs) seem to be involved in atherosclerosis, PAD and CLI. Aim of this study was to evaluate variations in MMP serum levels in patients affected by CLI, before and after lower limb surgical revascularisation through prosthetic or venous bypass. A total of 29 patients (7 females and 22 males, mean age 73·4 years, range 65-83 years) suffering from CLI and submitted to lower extremity bypass (LEB) in our Institution were recruited. Seven patients (group I) underwent LEB using synthetic polytetrafluoroethylene (PTFE) graft material and 22 patients (group II) underwent LEB using autogenous veins. Moreover, 30 healthy age-sex-matched subjects were also enrolled as controls (group III). We documented significantly higher serum MMPs levels (P < 0·01) in patients with CLI (groups I and II) with respect to control group (group III). Finally, five patients with CLI (17·2%) showed poor outcomes (major amputations or death), and enzyme-linked immunosorbent assay (ELISA) test showed very high levels of MMP-1 and MMP-8. MMP serum levels seem to be able to predict the clinical outcomes of patients with CLI.

Nonoperative Management of Acute Upper Limb Ischemia

BACKGROUND

Acute upper limb ischemia (AULI) is an uncommon emergency warranting immediate evaluation and treatment. The role of nonsurgical therapies including endovascular techniques, thrombolytics, and anticoagulation remains undefined. The authors systematically reviewed the current literature on the nonsurgical treatment of acute ischemia of the upper extremity.

METHODS

A PubMed and Embase search was conducted, and articles were screened using predetermined criteria. Data collected included patient demographics, cause of upper limb ischemia, type of nonsurgical treatment used, treatment outcomes, and complications. Patients were divided into 4 treatment groups: catheter embolectomy, catheter-directed thrombolysis, endovascular stenting, and anticoagulation/medical therapy alone.

RESULTS

Twenty-three retrospective studies met the search criteria. Of 1326 reported occlusions, 92% (1221) were attributed to thromboembolic disease. The second most common cause was iatrogenic (1.5%). Overall limb salvage rates were excellent with catheter embolectomy (862 of 882 cases, 97.7%) and catheter-directed thrombolysis (110 of 114 cases, 96.5%). Limb salvage rates were also high with anticoagulation/medical therapy (158 of 165 cases, 95.8%), but poor functional outcomes were more often reported.

CONCLUSIONS

High-quality evidence to guide the nonsurgical treatment of AULI is lacking. Retrospective studies support the utility of catheter-based embolectomy and thrombolysis for distal ischemia. Whether a surgical or nonsurgical approach is taken, anticoagulation therapy remains a mainstay of both treatment and prevention of AULI. Because AULI patients often have underlying cardiac and/or systemic disease, a multidisciplinary approach is essential to minimize complications and prevent future occurrences.

Endothelial sprouting and network formation in collagen- and fibrin-based modular microbeads

A modular tissue engineering approach may have advantages over current therapies in providing rapid and sustained revascularization of ischemic tissue. In this study, modular protein microbeads were prepared from pure fibrin (FIB) and collagen-fibrin composites (COL-FIB) using a simple water-in-oil emulsification technique. Human endothelial cells and fibroblasts were embedded directly in the microbead matrix. The resulting microbeads were generally spheroidal with a diameter of 100-200μm. Cell viability was high (75-80% viable) in microbeads, but was marginally lower than in bulk hydrogels of corresponding composition (85-90% viable). Cell proliferation was significantly greater in COL-FIB microbeads after two weeks in culture, compared to pure FIB microbeads. Upon embedding of microbeads in a surrounding fibrin hydrogel, endothelial cell networks formed inside the microbead matrix and extended into the surrounding matrix. The number of vessel segments, average segment length, and number of branch points was higher in FIB samples, compared to COL-FIB samples, resulting in significantly longer total vessel networks. Anastomosis of vessel networks from adjacent microbeads was also observed. These studies demonstrate that primitive vessel networks can be formed by modular protein microbeads containing embedded endothelial cells and fibroblasts. Such microbeads may find utility as prevascularized tissue modules that can be delivered minimally invasively as a therapy to restore blood flow to ischemic tissues.

STATEMENT OF SIGNIFICANCE

Vascularization is critically important for tissue engineering and regenerative medicine, and materials that support and/or promote neovascularization are of value both for translational applications and for mechanistic studies and discovery-based research. Therefore, we fabricated small modular microbeads formulated from pure fibrin (FIB) and collagen-fibrin (COL-FIB) containing endothelial cells and supportive fibroblasts. We explored how cells encapsulated within these materials form microvessel-like networks both within and outside of the microbeads when embedded in larger 3D matrices. FIB microbeads were found to initiate more extensive sprouting into the surrounding ECM in vitro. These results represent an important step towards our goal of developing injectable biomaterial modules containing preformed vascular units that can rapidly restore vascularization to an ischemic tissue in vivo.

Matrix metalloproteinase 10 is associated with disease severity and mortality in patients with peripheral arterial disease

OBJECTIVE

Peripheral arterial disease (PAD) is associated with poor prognosis in terms of cardiovascular (CV) morbidity and mortality. Matrix metalloproteinases (MMPs) contribute to vascular remodeling by degrading extracellular matrix components and play a role in atherosclerosis as demonstrated for MMP-10 (stromelysin-2). This study analyzed MMP-10 levels in PAD patients according to disease severity and CV risk factors and evaluated the prognostic value of MMP-10 for CV events and mortality in lower limb arterial disease after a follow-up period of 2 years.

METHODS

MMP-10 was measured by enzyme-linked immunosorbent assay in 187 PAD patients and 200 sex-matched controls.

RESULTS

PAD patients presented with increased levels of MMP-10 (702 ± 326 pg/mL control vs 946 ± 473 pg/mL PAD; P < .001) and decreased levels of tissue inhibitor of matrix metalloproteinase 1 (312 ± 117 ng/mL control vs 235 ± 110 ng/mL PAD; P < .001) compared with controls. Among PAD patients, those with critical limb ischemia (n = 88) showed higher levels of MMP-10 (1086 ± 478 pg/mL vs 822 ± 436 pg/mL; P < .001) compared with those with intermittent claudication (n = 99), whereas the MMP-10/tissue inhibitor of matrix metalloproteinase 1 ratio remained similar. The univariate analysis showed an association between MMP-10, age (P = .015), hypertension (P = .021), and ankle-brachial index (P = .006) in PAD patients that remained significantly associated with PAD severity after adjustment for other CV risk factors. Patients with the highest MMP-10 tertile had an increased incidence of all-cause mortality and CV mortality (P < .03).

CONCLUSIONS

Our results suggest that MMP-10 is associated with severity and poor outcome in PAD.

Clinical Predictors of Long-Term Outcomes in Patients With Critical Limb Ischemia Who have Undergone Endovascular Therapy

Clinical predictors of long-term outcomes in patients with critical limb ischemia (CLI) treated with endovascular therapy (EVT) remain unclear. In this study, clinical predictors of long-term outcomes in EVT-treated patients with CLI were investigated. In this prospective, observational study, we analyzed a total of 253 Taiwanese patients with CLI with 314 limbs who underwent EVT between 2005 and 2012. Cox models were used to estimate hazard ratios of death, limb loss, and sustained clinical success (SCS). Multivariate analysis showed that age, atrial fibrillation (AF), end-stage renal disease (ESRD), and albumin were significant predictors of mortality. Patients with coronary artery disease and low albumin levels had a significant risk of major limb amputation, while AF, ESRD, and albumin were significant, independent predictors of SCS. In addition to previously reported predictors, we showed that AF and malnutrition can be used to predict long-term outcome in EVT-treated patients with CLI.