Technique for quantifying and qualifying debris captured in embolic protection filters

Abstracts

Background: Quality and quantity of the content retained in embolic protection filters (EPFs) used in percutaneous transluminal angioplasty and stenting may possibly indicate the importance of EPFs in the management of carotid stenosis. Objectives: To analyze the content retained by EPFs in patients undergoing percutaneous transluminal angioplasty and stenting of the internal carotid artery using a new technique for qualitative and quantitative analysis. Methods: Material captured in 10 EPFs during percutaneous transluminal angioplasty and stenting in high-surgical-risk patients was examined to determine a qualitative and quantitative microscopic analysis. Digital photographs of the hematoxylin-eosin stained slides were analyzed using the Axio Vision LE Release 4.1 software in order to calculate the particles area in micra/square meter (µm²). Results: Histopathological examination identified particulate debris in 100% of the filters including predominantly blood residues, cholesterol crystals, and calcium Quantity of captured fragments was significant (mean of 1,570,310 µm²) with a wide range of these values. Conclusions: Significant quantity of fragments of atheromatous plaques is retained by EPFs and the wide range in the quantity of the retained debris can be associated with the lesion severity; therefore new studies using standardized technique for quantifying these fragments and for better understanding their real clinical meaning are necessary.

Carotid artery; carotid stenosis; percutaneous transluminal angioplasty and stenting; embolic protection filters

Contexto: A qualidade e a quantidade de partículas coletadas em filtros de proteção cerebral (FPC) durante angioplastia transluminal percutânea com stent (ATPS) podem esclarecer a importância desses dispositivos no tratamento de estenoses carotídeas. Objetivos: Analisar o conteúdo retido por FPC em pacientes submetidos a ATPS de artéria carótida interna com nova técnica de análise qualiquantitativa. Métodos: O material coletado em 10 FPC durante ATPS da bifurcação da carótida em pacientes com alto risco cirúrgico foi submetido a análise microscópica qualiquantitativa. Fotografias digitais das lâminas com material corado com hematoxilina e eosina foram analisadas com o programa Axio Vision LE Release 4.1, que calculou a área das partículas em micrômetros/metro quadrado (µm²). Resultados: O exame histopatológico evidenciou material em 100% dos filtros consistindo predominantemente de restos hemáticos, cristais de colesterol e cálcio. A área média de fragmentos coletados foi expressiva (1.570.310 µm²), e houve ampla variância desses valores. Conclusões: Os FPC coletam quantidade importante de fragmentos de placas de ateroma, e a grande variância nas quantidades de material coletado pode estar associada com a gravidade da lesão, motivo pelo qual se tornam relevantes estudos que utilizem técnica padronizada para a quantificação desses fragmentos e para a compreensão de seu real significado clínico.

Artéria carótida; estenose carotídea; angioplastia transluminal percutânea com stent; filtros de proteção cerebral

ORIGINAL ARTICLE

Technique for quantifying and qualifying debris captured in embolic protection filters

Gabriel Santos Novaes; Álvaro Razuk Filho; Geanete Pozzan; Andrea Reis; Alexandre Fioranelli; Valter Castelli Jr.; Walter Khegan Karakhanian; Roberto Augusto Caffaro

Chair of Vascular Surgery, Department of Surgery, Faculdade de Ciências Médicas da Santa Casa de São Paulo (FCMSCSP), São Paulo, SP, Brazil

Correspondence

Abstract

Background: Quality and quantity of the content retained in embolic protection filters (EPFs) used in percutaneous transluminal angioplasty and stenting may possibly indicate the importance of EPFs in the management of carotid stenosis.

Objectives: To analyze the content retained by EPFs in patients undergoing percutaneous transluminal angioplasty and stenting of the internal carotid artery using a new technique for qualitative and quantitative analysis.

Methods: Material captured in 10 EPFs during percutaneous transluminal angioplasty and stenting in high-surgical-risk patients was examined to determine a qualitative and quantitative microscopic analysis. Digital photographs of the hematoxylin-eosin stained slides were analyzed using the Axio Vision LE Release 4.1 software in order to calculate the particles area in micra/square meter (&microm²).

Results: Histopathological examination identified particulate debris in 100% of the filters including predominantly blood residues, cholesterol crystals, and calcium Quantity of captured fragments was significant (mean of 1,570,310 &microm²) with a wide range of these values.

Conclusions: Significant quantity of fragments of atheromatous plaques is retained by EPFs and the wide range in the quantity of the retained debris can be associated with the lesion severity; therefore new studies using standardized technique for quantifying these fragments and for better understanding their real clinical meaning are necessary.

Keywords: Carotid artery, carotid stenosis, percutaneous transluminal angioplasty and stenting, embolic protection filters.

Introduction

Endarterectomy is the treatment of choice for carotid artery stenosis in selected patients.^1-5 However, percutaneous transluminal angioplasty and stenting (PTAS) has been increasingly accepted as an alternative for the open surgery in cases of high surgical risk and occlusive cardiovascular disease.⁶

The success of PTAS has been widely questioned due to the high rates of neurologic events related to distal embolization caused by the release of particles during stent placement.⁷ Although not all released particles are clinically important, there is evidence showing that the size of these particles seems to be the most important factor in this phenomenon.^8-11

Bosiers et al.¹² demonstrated late events related to the type of stent used (open or closed mesh); on the other hand, it has been shown that there is more release of particles during dilatation after stent placement,¹³ which led to the development of protection systems that prevent these particles from entering the brain blood flow.^14-16

Among these devices, the embolic protection filters (EPFs) developed to capture the macroscopic particles are the most widely used nowadays, and several studies have shown lower rates of neurologic events when these devices are used in PTAS.^17-19

The objective of the present study is to present a reproducible technique for the qualitative and quantitative analysis of fragments of atheromatous plaques of the carotid bifurcation collected by EPFs.

Méthod

In the present study, we present 10 prospective procedures of PTAS using EPF in the carotid artery. These procedures were conducted in the course of Vascular Surgery of the School of Medicine of Santa Casa de São Paulo (FCMSCSP) and strictly complied with the criteria for indication of such treatment, that is, high surgical risk, hostile neck, and high carotid bifurcation. Only patients with atherosclerotic carotid stenosis were included.

The group of patients who underwent the surgical procedures included five men and five women whose mean age was 61.4±8.7 years (42 to 73 years), and five of them had symptoms.

Before the surgical procedure, the patients were evaluated using diagnostic cerebral digital subtraction angiography (Integris V3000, Phillips^®) involving the aortic arch and all bifurcations of the carotid and intracranial arteries with the purpose of classifying the lesions with carotid artery stenosis.²⁰ The lesions treated were classified according to the angiographic categories A (two cases), B (six cases), and C (two cases) suggested by Wholey et al.²⁰

After the study project was approved by the Research Ethics Committee of the FCMSCSP, the material collected by the EPFs used in the angioplasties was analyzed considering the effects of this study.

PTAS and EPF: The procedures were conducted by assistant professors of Vascular Surgery in the angiography room, Department of Radiology of the FCMSCSP using the device Integris V 3000 (Phillips^®) and the patients received general anesthesia. Before the procedure, a dose of 100 mg of acetylsalicylic acid (ASA) was administered.

After puncture of the femoral artery, which was used as the arterial access, the patients received systemic heparin at doses of 100 U/kg. The surgeons used 7F or 8F guide catheters (Boston Scientific^®) or Shuttle Select long guiding sheath (Cook Medical^®), which received continuous flow of physiologic solution containing heparin during the whole procedure.

The EPF used was FilterWire EZ (Embolic Protection System, Boston Scientific^®), composed of a radiopaque spring coil tip, followed by nosecone, 110-micron-pore polyurethane filter with radiopaque nitinol loop, suspension arm, and polytetrafluoroethylene (PTFE) coated wire 0.014". The one size (3.2F) silicon-coated nosecone is safely inserted into 3.5 to 5.5 mm diameter landing zone enabling easy access to the lesions. The microporosity of the filter allows continuous blood flow at the same time as it enables efficient capture of embolic particles. The suspended nitinol filter loop provides up to 360º apposition in straight or tortuous anatomy.

None of the patients underwent pre-dilatation. A Carotid Wallstent^® closed-cell self-expandable stent with a 5-French sheath made of the metal alloy Elgiloy^®, composed of nickel (20%), molybdenum (7%), magnesium (2%), iron, carbon, and beryllium, with density of 8.30 g/cm was placed.³ Post-dilatation was performed using a Gazelle or Ultrasoft balloon catheter (Boston Scientific^®), whose sizes were 5.0 mm x 20 mm, 5.5 mm x 20 mm, or 6.0 mm x 20 mm.

Analysis of material collected by the EPFs: After TPAS using EPF, the filters were withdrawn and opened for macroscopic assessment of their inner part. Clots adhered to the mesh of the filter were not considered as macroscopic particles. Next, the filters were closed and stored in a 10% formol solution and sent to the Department of Pathology of the FCMSCSP, where they were opened once more and washed using formol solution. Particles were cytocentrifugated using a Hermle Z300 centrifuge, and the remaining material was placed on slides and stained with hematoxylin and eosin.

The slides were examined using a Zeiss Axioskop 40 microscope, with a 10 times magnification factor, and pictures of the cluster of particles placed on the slide were taken using a Sony digital camera, model DSC-S85 with 4 Mp at 1280 x 960 resolution.

The pictures of each slide were analyzed using the Axio Vision LE Release 4.1 computer program designed to enable the identification of the morphologic characteristics of the material analyzed and to calculate the area of the particles in micrometers per square meter (&microm²). Blood cells found in the samples were not considered for measuring purposes.

Results

Ao exame, após a abertura dos filtros, foram identificadas partículas macroscópicas em dois (20,0%) deles (Figura 1).

After hematoxylin-eosin staining, we could carry out a qualitative evaluation of the composition of the particles captured by the filters using optical microscopy. The particles were made of blood residues, calcium, and cholesterol crystals in all filters examined (Figure 2). The presence of calcium and cholesterol crystals is due to the fragmentation of the atheromatous plaques.

In the quantitative analysis, the calculation of the area of the particles captured by the filters performed using the Axio Vision LE Release 4.1 computer program (Figure 3) resulted in values ranging from 2,480.33 to 13,568,860.21 &microm², with the mean value of 1,570,310 &microm² and significantly large variance (F = 0.003; SD = 4,223,240 &microm².

Discussion

The material captured by the EPFs in this series consisted of atheromatous particles released by the rupture of the atheromatous plaques during angioplasty, confirming the histological findings of other studies.^17,21,22 DeRubertis et al.²¹ found a very small amount of calcium in the material collected and reported important platelet activity in the material collected from symptomatic patients. A better understanding of the composition of the atheromatous plaque and the particles generated during TPAS, which is allowed by the analysis of the material collected by the EPF, might eventually lead the the development of strategies aimed at reducing neurologic events during and after the treatment of carotid stenosis.

The capture of the macroscopic material (20%) was quite lower than the 60.3⁶ and 69%¹⁸ reported in the literature. Sprouse et al.⁶ used five different filters and, without analyzing microscopic factors of the material collected, concluded that the EPFs are needless in angioplasties, since they cannot prevent macroembolization in 40% of the cases. Our collection of macroscopic material using EPFs was only slightly higher than the 19% reported by DeRubertis et al.²¹, highlighting the fact that we used the same filter in all cases.

DeRubertis et al.²¹ collected microscopic material in 77% of the filters studied; used and compared different filters and analyzed the time line of the use of these devices and concluded that the effective collection of microscopic particles is directly dependent on the type of filter used and on the learning curve, which had been previously suggested by Cremonesi et al.¹⁷

Our results evidenced that 100% of the EPFs captured debris of a mean area of 1,570,310 &microm² (from 2,480.33 to 13,568,860.21 &microm²), and this large variance seems to be related to the severity of the lesions, since larger debris were more frequent among patients with more severe angiographic lesions (Wholey's category C²⁰).

The percentage of filters that collected microscopic material for analysis (100%) was higher than that reported by other authors, which ranged from 77.0²¹ to 83.7%.¹⁷

There are not standardized methods to determine the amount or size of the debris collected using EPFs in the different studies, but the large variance of values found in our study confirms other findings,^17,19,21,23 which stimulates the interest in better understanding it in terms of the clinical and angiographic characteristics of the patients with carotid stenosis.

It is important to highlight, however, that, in the other studies that analyzed the material collected using EPF, the samples were studied by means of scanning electronic microscopy,^17-19,21 which is a more expensive and more often unavailable technique. Considering that the results of our study are not completely different from the findings of other researchers, the use of optical microscopy for the analysis of material collected using EPFs seems to be as efficient as the use of scanning electronic microscopy, with the advantage of being less expensive and more easily available, allowing the technique to be repeated more easily and in a quicker manner, which, on its turn, may even help to understand the occasional correlations between this material collected using EPFs and the prevention of neurologic events after TPAS.

It seems that clinical factors represented by associated comorbidities may be predictive of the larger or smaller size of the particles collected using EPFs, although they cannot predict the absence of these particles in EPFs used during TPAS.⁶ The presence, amount or size of these particles do not have a predictive value for new ischemic lesions after TPAS using EPFs.²²

There is a theory according to which the characteristics of the lesion with stenosis may determine its tendency to originate emboli and, therefore, its potential to cause a stroke. In this sense, the amount of particles captured would be associated with the severity of the lesion with stenosis.²⁴ However, there are few studies approaching this association, even tough it has been found that arteries with more severe lesions may be more susceptible to histological lesions caused by EPFs.^18,24

Our findings allow us to corroborate the recommendations according to which EPFs should be used more carefully in more severe lesions, mainly in those excessively pointed or in those requiring excessive strength to insert the device.¹⁹ Lesions > 2 cm are also associated with a three times higher probability of neurologic complications,²⁰ which is also a warning regarding the special care and the higher learning curve of the use of TPAS performed with EPFs. Angiographic examination to determine the severity of the lesion with stenosis before revascularization of the carotid artery is a mandatory procedure.

It has already been shown that the type of mesh used is responsible for the higher rate of late complications in the symptomatic population, which is not true for asymptomatic patients.¹² Studies focused on the use of EPFs^7,21 could not replicate these differences, reporting homogeneous results for patients with and without neurologic symptomatology, both in terms of the progress of therapeutic peri- and post-intervention and the characteristics of the material collected.

We believe that the studies on the material collected using EPFs according to the required careful procedures and adequate techniques and materials during TPAS still may provide valuable information for the understanding of the mechanisms that lead to embolization and neurologic events in these procedures. The technique used in this study evidenced the large amount of material collected by the protection filters, which, therefore, did not enter the intracranial blood flow, confirming the potential of such protection system to reduce neurologic complications during the treatment of carotid artery stenosis.

Conclusion

The present study enables us to conclude that the method used for the qualitative and quantitative assessment of the particles captured by EPFs is effective, less expensive and more easily and quickly available, and it will allow for the analysis and correlation to clinical and anatomical data.

References

• 1. Barnett HJ, Taylor DW, Eliasziw M, et al. Benefit of carotid endarterectomy in patients with symptomatic moderate or severe stenosis. North American Symptomatic Carotid Endarterectomy Trial Collaborators. N Engl J Med. 1998;339:1415-25.
• 2. Beneficial effect of carotid endarterectomy in symptomatic patients with high grade carotid stenosis. North American Symptomatic Carotid Endarterectomy Trial Collaboration. N Engl J Med. 1991;325:445-53.
• 3. MRC European Carotid Surgery Trial: Interim results for symptomatic patients with severe (70-99%) or with mild (0-29%) carotid stenosis. The European Carotid Surgery Trialists Collaborative Group. Lancet. 1991;337:1235-43.
• 4. Endarterectomy for moderate symptomatic carotid stenosis: interim results from de MRC European Carotid Surgery Trial. Lancet. 1996;347:1591-3.
• 5. Randomized trial of endarterectomy for recently symptomatic carotid stenosis: Final results of the MRC European Carotid Surgery Trial (ECST). Lancet. 1998;351:1379-87.
• 6. Sprouse LR 2nd, Peeters P, Bosiers M. The capture of visible debris by distal cerebral protection filters during carotid artery stenting: Is it predictable? J Vasc Surg. 2005;41:950-5.
• 7. Yadav IS, Wholey MH, Kuntz RE, et al. Protected carotid-artery stenting versus endarterectomy in high risk patients. N Engl J Med. 2004;351:1493-501.
• 8. Crawley F, Clifton A, Buckenham T, Loosemore T, Taylor RS, Brown MM. Comparison of hemodynamic cerebral ischemia and microembolic signals detected during carotid endarterectomy and carotid angioplasty. Stroke. 1997;28:2460-4.
• 9. Manninen HI, Rasanen HT, Vanninen RL, Vainio P, Hippeläinen M, Kosma VM. Stent placement versus percutaneous transluminal angioplasty of human carotid arteries in cadaver in situ: distal embolization and findings at intravascular. Radiology. 1999;212:483-92.
• 10. Parodi JC, Ferreira LM, Sicard G, La Mura R, Fernandez S. Cerebral protection during carotid stenting using flow reversal. J Vasc Surg. 2005;41:416-22.
• 11. Rapp JH, Wakil L, Sawhney RS, et al. Subclinical embolization after carotid artery stenting: new lesions of diffusion-weighted magnetic resonance imaging occur postprocedure. J Vasc Surg. 2007;45:867-72.
• 12. Bosiers M, de Donato G, Deloose K, et al. Does free cell area influence the outcome in carotid artery stenting? Eur J Vasc Edovasc Surg. 2007;33:135-41.
• 13. Burton KR, Lindsay TE. Assessment of short-term outcomes for protected carotid angioplasty with stents using recent evidence. J Vasc Surg. 2005;42:1094-100.
• 14. Mellière D. [Carotid surgery: assessment and current problems]. J Mal Vasc. 1993;18:176-85.
• 15. Ohki T, Marin NL, Lyon RT, et al. Ex vivo human carotid artery bifurcation stenting: Correlation of lesion characteristics with embolic potential. J Vasc Surg. 1998;27:463-71.
• 16. Theron J, Courtheoux P, Alachkar F, Bouvard G, Maiza D. New triple coaxial catheter system for carotid angioplasty with cerebral protection. Am J Neuroradiol. 1990;11:869-74.
• 17. Angelini A, Reimers B, Della Barbera M, et al. Cerebral protection during carotid artery stenting: collection and histopathologic analysis of embolized debris. Stroke. 2002;33:456-61.
• 18. Cremonesi A, Manetti R, Setacci F, Setacci C, Castriota F. Protected carotid stent: Clinical advantages and complications of embolic protection devices in 442 consecutive patients. Stroke. 2003;34:1936-41.
• 19. Reimers B, Corvaja N, Moshiri S, et al. Cerebral protection with filter devices during carotid artery stenting. Circulation. 2001;104:12-5.
• 20. Wholey MH, Wholey M, Mathias K, et al. Global experience in cervical carotid artery stent placement. Catheter Cardiovasc Intervent. 2000;50:160-7.
• 21. DeRubertis BG, Chaer RA, Gordon R, et al. Determining the quantity and character of carotid artery embolic debris by electron microscopy and energy dispersive spectroscopy. J Vasc Surg. 2007;45:716-25.
• 22. Maleux G, Demaerel P, Verbeken E. Cerebral ischemia after filter-protected carotid artery stenting is common and cannot be predicted by the presence of substantial amount of debris captured by the filter device. Am J Neuroradiol. 2006;27:1830-3.
• 23. Whitlow PL, Lylyk P, Londero H, et al. Carotid artery stenting protected with an emboli containment system. Stroke. 2002;33:1308-14.
• 24. Müller-Hülsbeck S, Stolzmann P, Liess C, et al. Vessel wall damage caused by cerebral protection devices: Ex vivo evaluation in porcine carotid arteries. Radiology. 2005;235:454-60.

Publication Dates

• Publication in this collection
  26 Mar 2010
• Date of issue
  Dec 2009

History

• Received
  18 Feb 2009
• Accepted
  04 Nov 2009