Annals of Vascular Surgery
Volume 23, Issue 5 , Pages 569-576, September 2009

Percutaneous Transluminal Angioplasty of Lower Limb Arteries Causes a Systemic Inflammatory Response

Vascular Surgery Department, Hammersmith Hospital, London, UK

published online 21 May 2009.

Article Outline

Background

Percutaneous transluminal angioplasty (PTA) of a lower limb arterial segment is a well-established treatment for suitable lesions for critical or noncritical lower limb ischemia. Our aim was to define the inflammatory response after PTA by measuring inflammatory markers.

Methods

Twenty-five patients having PTA were compared with 20 patients having angiography alone. Interleukin-6 (IL-6), IL-8, IL-10, and tumor necrosis factor-α (TNF-α) were measured sequentially. The difference between postprocedure and preprocedure baseline levels were compared statistically between angiography alone and PTA. Patients were followed up to 1 year after the procedure, and the failure rate of PTA was noted.

Results

IL-6 and TNF-α were significantly higher in PTA patients at 1 hr after PTA (p < 0.05), and the IL-6 level only was significantly higher at 24 hr post-PTA (p < 0.05) compared to angiography alone (Mann-Whitney test). IL-8 and IL-10 levels did not differ significantly in the PTA group. At 1 year after the procedure, 45% of PTAs had failed. There was no statistically significant correlation between failed PTA and inflammatory response.

Conclusion

PTA appears to cause a significant inflammatory response compared to angiography alone. This demonstrates a systemic manifestation of localized ischemia/reperfusion injury. Further investigation of the inflammatory response due to ischemia/reperfusion injury and its correlation with restenosis is recommended.

 

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Introduction 

Ischemic diseases remain a major source of morbidity and mortality around the world. In particular, atherosclerotic peripheral vascular disease (PVD) has become one of the most significant health problems in the Western world. Intermittent claudication (IC) is the most common and early symptom. By late middle age approximately 5% of men and women in the United Kingdom will demonstrate symptoms of IC,1, 2 and about 50,000 patients in England and Wales are admitted to hospital each year because of severe disabling disease.3 The main aim of the clinicians who treat ischemic diseases is to restore blood flow to the ischemic areas, to recover function. Percutaneous transluminal angioplasty (PTA) is now an established method for treatment of peripheral arterial disease in the lower limbs,4 but restenosis remains a frequent complication to angioplasty and decreases the long-term patency. The restenosis rate at 6-12 months in the iliac arteries is around 20% and that in the femoropopliteal arteries is 30-50%.5, 6, 7

Now it has become apparent that restoring blood flow to these ischemic areas paradoxically results in further injury to those areas, and this process has been called reperfusion injury. Ischemia/reperfusion injury (IRI) is now a major problem encountered in many aspects of medical and surgical practices and has been the subject of intensive research. IRI is a dynamic process that involves multiple organ systems in various clinical states including transplantation, trauma, and surgery. Research into this field has identified key molecular and signaling players that mediate, modulate, or augment cellular, tissue, and organ injury during this disease process. Further elucidation of the molecular mechanisms should provide the rationale to identify much needed novel therapeutic options to prevent or ameliorate organ damage due to ischemia and reperfusion in the clinics.8 IRI is a known clinical event in patients who undergo revascularization procedures in the form of either angioplasty or bypass operations to restore the blood flow to the limb distal to the arterial occlusion.9 Reperfusion itself causes further significant metabolic abnormalities, which add to considerable morbidity and mortality.10 The severity of IRI ranges from minor symptoms to acute tubular necrosis and even sudden cardiac arrhythmias and death. The exact mechanisms responsible for these events are still unclear.

The mechanisms of restenosis are complex and incompletely understood. Several factors, such as tissue factor and thrombin, involved in thrombosis are also of importance in the development of restenosis.11, 12 Inflammation plays a critical role in restenosis,13 atherosclerosis,14 and thrombosis.15 Elevated levels of C-reactive protein (CRP), a marker of systemic inflammation, predict future risk of symptomatic peripheral arterial disease.16 Fibrinogen, an acute-phase protein as well as a component of the coagulation cascade, and CRP are associated with restenosis after PTA in the iliac and femoropopliteal arteries.6, 17 Effective medical treatment to prevent restenosis and improve patency after PTA is still elusive.

The aims of this prospective clinical study were to characterize the systemic inflammatory response due to IRI caused by successful peripheral revascularization by PTA by investigating plasma levels of interleukin-6 (IL-6), IL-8, IL-10, and tumor necrosis factor-α (TNF-α) in peripheral venous blood and their significance for later restenosis of PTA.

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Methods 

Patients 

This is an observational prospective study. During April 2004 to December 2005 consecutive patients admitted to the Vascular Surgery Department for either lower limb diagnostic angiography or angioplasty of a defined lesion were approached and recruited into the study. Two groups were defined: group-1 (control group) had diagnostic angiography alone and group-2 (study group) had angioplasty/stent of lower limb arterial segment. The Hammersmith Hospital ethics committee approved the study, and all patients gave written informed consent to participate.

Patients undergoing angioplasty of bypass grafts or redo angioplasty or surgery and those with recent (<6 weeks) myocardial infarction, unstable angina, stroke, or congestive heart failure, as well as those with renal or liver impairment and warfarin therapy, were excluded from the study.

The criteria for femoral angiography with or without angioplasty for lower limb revascularization in our hospital are severe debilitating IC and/or critical ischemia (i.e., ischemic rest pain with or without tissue loss). IC and critical ischemia were defined according to the criteria proposed by the Society for Vascular Surgery and International Society for Cardiovascular Surgery (SVS/ISCVS).18

Blood Samples 

Peripheral venous blood was obtained at three time points as follows:

Sample 1 (S1): Before the angiogram or angioplasty

Sample 2 (S2): 1hr after the angiogram or angioplasty

Sample 3 (S3): 24hr after the angiogram or angioplasty

Peripheral venous blood was drawn from antecubital vein by venepuncture using a 21-gauge needle directly into a vacutainer (Becton Dickinson, Franklin Lakes, NJ). Blood (9mL) was taken in two 4.5mL K3 ethylenediaminetetraacetic acid (EDTA) vacutainers. Plasma samples were centrifuged at 3,000rpm for 20min at 10°C, and then supernatant plasma was separated immediately and stored at -70°C for subsequent batched analysis.

Interventional Protocol 

Angiography and/or angioplasty were performed in the angiography suite by an interventional vascular radiologist. An ipsilateral antegrade or contralateral retrograde percutaneous puncture of the femoral artery was performed. Patients received 5,000 U of heparin intra-arterially before angioplasty. Technical success was defined as angioplasty resulting in <30% residual stenosis after dilatation. Hemodynamic improvement was defined as an increase in ankle/brachial pressure index (ABPI) >0.10.4 Clinical examination and ABPI were performed before and after angioplasty.

Plasma Analysis for IL-6, IL-8, IL-10, and TNF-α 

Plasma analysis was carried out using the standard enzyme-linked immunosorbent assay (ELISA) technique by a single operator. R&D Systems (Oxford, UK) supplied ELISA kits. The assay employed the quantitative sandwich enzyme immunoassay technique as described elsewhere. Adult reference ranges for all assays had been established previously in the authors' laboratory.

Statistical Analysis 

Descriptive statistics are shown as median with interquartile range (IQR). Differences in plasma levels between preprocedure (S1) and 1hr postprocedure (S2), i.e., D1=S2 - S1, and between S3 and S1, i.e., D2=S3 - S1, were calculated. The significance of these differences (D1, D2) was investigated between the femoral angiogram alone and the femoral angioplasty groups. A nonparametric Mann-Whitney U-test was used, and significance was accepted at p<0.05. Data were analyzed with the help of a medical statistician. The statistical package used was STATA, version 8.0 (StataCorp, College Station, TX).

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Results 

Baseline Demographics 

Baseline characteristics of patients across both groups are described in Table I.

Table I. Baseline demographics across the three groups
Femoral angiogram onlyIliofemoral angioplastyp∗ (Kruskall-Wallis or χ2 test)
Patients/limbs (n)2520
Mean age±SD (years)68.2±11.769.3±6.60.443
Sex ratio (F:M)9:166:140.903
Diabetes mellitus10 (40%)9 (45%)0.939
Hypertension13 (52%)12 (60%)0.770
Current smoking10 (40%)12 (60%)0.416
Aspirin use17 (68%)20 (100%)0.532
Statin use17 (68%)20 (100%)0.344
Critical ischemia8 (32%)7 (35%)0.015
ABPI of treated limb (mean±SD)0.65±0.160.48±0.190.0001
Baseline IL-6 (mean±SD)14.11±29.1114.60±25.580.353
Baseline IL-8 (mean±SD)35.48±70.6720.55±24.550.458
Baseline IL-10 (mean±SD)9.37±8.697.24±11.290.665
Baseline TNF-α (mean±SD)6.05±4.795.73±6.890.125
Location of lesion and angioplasty-CIA or EIA, 11CFA, 1
SFA, 8
Use of stent-CIA, 3

ABPI, ankle-brachial pressure index (highest of three peripheral arterial pressures); SD, standard deviation; CIA, common iliac artery; EIA, external iliac artery; CFA, common femoral artery; SFA, superficial femoral artery.

∗Chi-squared test used for categorical data and Kruskall-Wallis for continuous data.

Outcome after Angioplasty 

The technical success immediately after angioplasty was 100%, and there were no major complications. Patients were followed up until 1 year after the procedure. Routine follow-up at 6 weeks, 3 months, 6 months, and 1 year was planned. At all the follow-up visits clinical history, examination with ABPI measurement, and lower limb arterial duplex were performed. Failure of the procedure was defined as no symptomatic improvement or worsening of symptoms associated with decreased ABPIs, and arterial duplex showing >50% luminal diameter reduction at the site of the angioplastied segment was taken as evidence of restenosis.

At 6 months postprocedure 45% (9/20) of angioplasties had failed, and at 1 year 40% (8/20) of angioplasty patients were dead. Cause of death was ischemic heart disease or major cerebral vascular accident (CVA).

Inflammatory Markers: Graphical Representation 

Absolute values of IL-6, IL-8, IL-10, and TNF-α are shown in Fig. 1, Fig. 2, Fig. 3, Fig. 4, where the x axis represents sample timing (S1, S2, and S3), the y axis shows median levels of the measured marker, and the secondary y axis shows absolute levels of the measured marker, with boxes representing the IQR and whiskers representing the range of data distribution.

Statistical Significance 

Plasma levels of IL-6 and TNF-α were significantly higher at 1hr postangioplasty compared to angiogram alone (p=0.041 and 0.006, respectively; Table II). Plasma levels of IL-8 and IL-10 did not show such a significant response at 1hr postangioplasty. Only IL-6 remained significantly higher at 24hr postangioplasty (p=0.013, Table III). IL-8, IL-10, and TNF-α did not show such a significant response at 24hr postangioplasty. None of the inflammatory markers was a predictor of later restenosis after angioplasty.

Table II. Comparison of differences between baseline and 1hr postprocedure relative to angiogram for plasma levels of IL-6, IL-8, IL-10, and TNF-α
Procedure and markerMedian difference from baseline to 1hr postprocedure (IQR)Mann-Whitney U-test p relative to angiogram
IL-6
Angiogram0 (-0.3 to 1.4)-
Angioplasty1.7 (-0.1 to 11.1)0.041
IL-8
Angiogram1.0 (-3.7 to 6.2)-
Angioplasty6.8 (0.6–15.8)0.057
IL-10
Angiogram-0.3 (-2.2 to 0)-
Angioplasty0 (-0.6 to 0)0.201
TNF-α
Angiogram0 (-1.2 to 1.2)-
Angioplasty2.0 (0.6-2.9)0.006
Table III. Comparison of differences between baseline and 24hr postprocedure relative to angiogram for plasma levels of IL-6, IL-8, IL-10, and TNF-α
ProcedureMedian difference from baseline to 24hr postprocedure (IQR)Mann-Whitney U-test p relative to angiogram
IL-6
Angiogram0 (-3.8 to 2.6)-
Angioplasty5.6 (0.8-16.2)0.013
IL-8
Angiogram0.4 (-1.1 to 4.6)-
Angioplasty1.7 (-3.2 to 17.8)0.891
IL-10
Angiogram0 (-1.0 to 2.3)-
Angioplasty0.3 (0-5.7)0.281
TNF-α
Angiogram0 (-1.0 to 1.7)-
Angioplasty0.4 (-0.4 to 4.0)0.205

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Discussion 

Vascular injury induced by angioplasty may lead to neointimal hyperplasia mediated by platelet deposition, proliferation and migration of vascular smooth muscle cells (VSMCs), and synthesis and deposition of extracellular matrix. Inflammatory processes play a critical role in the vascular response to injury.13 Inflammation can cause local thrombosis, which can amplify inflammation.19 VSMCs not only produce procoagulants but can also undergo inflammatory activation. Thrombin stimulation causes VSMC production of IL-6, which in turn induces CRP.20

IL-6, IL-8, and TNF-α are potent proinflammatory mediators, whereas IL-10 is pleiotropic but has predominantly anti-inflammatory activity.21 These cytokines have not been studied in the context of IRI due to peripheral revascularization. They have been shown to potentially play a major role in distant organ damage following repair of abdominal aortic aneurysm (AAA) subsequently leading to multiorgan failure (MOF).22 Norwood et al.23 showed that ischemia and reperfusion during AAA repair were associated with a marked increase in IL-6 concentration in the portal vein, suggesting that IL-6 was produced by the gastrointestinal tract. IL-8 levels were shown to be increased after exercise in patients with stable PVD.24 IL-8 is associated with severe injury, a possible marker of MOF and potent neutrophil chemotaxin.25 TNF-α is a potent chemoattractant that stimulates the production of other cytokines and free radicals. It is also a key mediator in proapoptotic pathways.26

In our study baseline characteristics of patients in the two groups did not differ significantly except the presence of low ABPI in angioplasty group patients. Patients with advanced lower limb ischemia have a higher inflammatory state,27 but in our study both groups of patients had similar baseline inflammatory markers. The reason for this remains unknown. Our results suggest that peripheral revascularization in the form of angioplasty causes a significant inflammatory response. Angioplasty appears to cause a significant systemic inflammatory response both immediately and 24hr after the procedure as demonstrated by increased levels of IL-6 and TNF-α (Table II, Table III, Fig. 1, Fig. 4). IL-8 has a very short plasma half-life, which may be responsible for the nonsignificant change in its plasma level. IL-10 is an anti-inflammatory mediator, which requires significantly large trauma or insult for its release to counteract an inflammatory response. This may explain its levels in this study.

Currently, peripheral arterial angioplasty with best medical therapy is the established treatment of choice for suitable cases of critical or noncritical limb ischemia.4 Angioplasty has obvious benefits over surgical revascularization and has significant benefits to patients, especially the cardioprotective effects of the resulting increased exercise tolerance. A recent study demonstrated a medium-term improvement in the resting procoagulant and hypofibrinolytic state, which may translate into a reduction in morbidity and mortality from thrombotic vascular events in this group of patients.28 Despite the obvious benefits of angioplasty, it is still associated with an inflammatory response as demonstrated in our study; and the long-term implications of this on future patency of angioplasty are still to be investigated. Angioplasty is also associated with transient IRI; even though IRI is a known event following revascularization, its pathogenesis is still poorly understood, its treatment is currently highly unsatisfactory, and there are no current national guidelines available. Partly this is because of the incomplete understanding of the exact mechanism of IRI and partly because there is only a narrow window of clinical opportunity following the insult when the treatment can be delivered effectively.

The transient rise of these inflammatory mediators may have clinical relevance, especially in high-risk patients such as those with renal failure. The long-term effect of this inflammatory response in the angioplasty group of patients is unknown, but it may have a significant relation to the long-term patency of angioplastied lesions. Clinically relevant restenosis has been correlated with an inflammatory response following coronary angioplasty in recent studies.29 IL-10 and TNF-α have been shown to be risk markers for early restenosis after percutaneous coronary intervention.30, 31, 32 The correlation between inflammation and restenosis of peripheral arterial angioplasty is far from clear. A recent study demonstrated a borederline correlation between restenosis of angioplastied femoropopliteal segment and increased CRP postangioplasty.33 Future study to check the long-term patency of angioplasty or grafts in patients who demonstrate maximum inflammatory response is recommended. Also active coated stents with properties of anticoagulation, antiproliferation, and anti-inflammation may be a way to prevent restenosis. The role of free radical scavengers like allopurinol is currently being evaluated to study their effects in patients who undergo angioplasty for peripheral arterial occlusive disease.

The degree of ischemia was more severe in the group of patients who underwent PTA, based on ABPI and, to some extent, the presence of critical limb ischemia. The inflammatory response demonstrated by the angioplasty group may have relation to the presence or degree of ischemia prior to the angioplasty. This is one limitation of our study. Our subgroup analysis showed no significant difference in the measured inflammatory markers between critically ischemic patients requiring angioplasty compared to the noncritically ischemic group requiring angioplasty.

In conclusion, we observed a significant inflammatory response after PTA. The biochemical markers, before and after angioplasty, were not related to restenosis. Interleukins and TNF-α could causally be involved in atherothrombosis after angioplasty. Limitations of our study were a small group of heterogeneous patients with some large outliers in inflammatory markers after angioplasty. Thus, due caution should be taken in interpreting the results. Future studies are needed to delineate the molecular mechanisms behind these observations and their involvement in thrombosis and restenosis. If these pathways are further defined, improved treatment strategies, including antithrombotic treatments, statins, and antioxidants, could be tailored to modulate postprocedural inflammation.

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PII: S0890-5096(09)00050-8

doi:10.1016/j.avsg.2009.02.004

Annals of Vascular Surgery
Volume 23, Issue 5 , Pages 569-576, September 2009

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