Pathology of cardiovascular interventions and surgery

MINI-SYMPOSIUM: CARDIOVASCULAR PATHOLOGY

Pathology of cardiovascular interventions and surgery*

tissue, and complications related to the procedure. The pathologist needs to be well informed of the clinical history, which should include a detailed description of any explanted prosthesis or device. Each report prepared by the pathologist should convey a comprehensive clinical-pathologic discussion to provide useful information to the physicians treating the patient, including cardiologists and cardiovascular surgeons.

Alice Y Li Kelsey B Law

Keywords aneurysms; angioplasty; coronary artery disease; endomyocardial biopsies; endovascular repair; prosthetic vascular grafts; stem cells; stents; ventricular assist devices

Katharine RB Phillips Harriet Nwachukwu Jagdish Butany Avrum I Gotlieb

Atherosclerosis A thorough understanding of the pathogenesis of the atherosclerotic plaque is essential in interpreting plaque findings in numerous cardiovascular interventions and clinical conditions. A useful way to describe pathogenesis is as a series of three clinicopathological stages that can be identified over the course of the growth of the human plaque: (i) a plaque initiation and formation stage, (ii) a plaque adaptation stage, and (iii) a clinical stage.1 In these stages, many biologically active molecules regulate the function of the cells of the arterial wall as they interact with the wall itself, and with the constituents and physical forces of the blood stream. These molecules may demonstrate atheroprotective and/or atherogenic properties depending on local and systemic conditions.

Abstract This review describes the histopathology of cardiovascular tissue in patients who have undergone interventions and/or surgery, primarily on coronary arteries, aortas arteries, cardiac biopsies and excisions, and explanted devices. The tissue, prosthesis and/or devices are submitted for surgical pathology or autopsy examination. The anatomic pathologist must provide comprehensive reports on the gross and microscopic findings of the biopsied or explanted specimen, including the condition of any existing prosthesis, the state of the normal and/or diseased host

*

Excludes valve replacement surgery, heart valve repair and cardiac tumour resection. Alice Y Li BSC is at the Department of Pathology, University Health Network. She is also at Department of Laboratory Medicine and Pathobiology, University of Toronto, Canada. Conflict of interest: none. Funding source: none.

Stage I: plaque initiation and formation Injury is considered to be the earliest event in pathogenesis with injury to the endothelium leading to endothelial cell (EC) dysfunction, disruption of endothelial integrity and/or loss of ECs. The state of the endothelial surface should be commented on in pathology reports. Injury may be due to several conditions including hyperlipidaemia, hypertension, microorganisms, toxins, immunologic events, and haemodynamic shear stress, especially at branch points and curves. Intimal lesions initially occur at vascular sites predisposed to atherosclerotic plaque formation. The presence of subendothelial smooth muscle cells (SMCs), in an intimal cell mass (eccentric intimal thickening, intimal cushion) at branch points and other sites is a predisposing condition for plaque formation since it provides a readily available source of SMCs. Human atherosclerotic lesions tend to occur at sites where shear stresses are low but fluctuate rapidly, such as at bifurcations and branch points.2 Since the location of the plaque is important in pathogenesis, this should be identified in pathology reports. Low shear has been shown to induce expression of cell adhesion molecules on the surface of ECs to promote monocyte attachment, such as vascular cell adhesion molecule (VCAM). The leukocytes first roll along the endothelium mediated by P-selectin and E-selectin and then adhere due to chemokine induced EC activation and integrin interactions with cell adhesion molecules.3 The leukocytes penetrate the endothelial barrier at interendothelial sites, regulated by platelet EC adhesion molecule (PECAM, CD31). Haemodynamic forces induce gene expression of several biologically active molecules in ECs that are likely to promote atherosclerosis, including fibroblast growth factor-2 (FGF-2), tissue factor (TF), plasminogen activator (PA), and endothelin. However, shear stress also

Kelsey B Law Undergraduate student is at the Department of Pathology, University Health Network. She is also at Department of Laboratory Medicine and Pathobiology, University of Toronto, Canada. Conflict of interest: none. Funding source: none. Katharine RB Phillips BSC is at the Department of Pathology, University Health Network. She is also at Department of Laboratory Medicine and Pathobiology, University of Toronto, Canada. Conflict of interest: none. Funding source: none. Harriet Nwachukwu Undergraduate student is at the Department of Pathology, University Health Network. She is also at Department of Laboratory Medicine and Pathobiology, University of Toronto, Canada. Conflict of interest: none. Funding source: none. Jagdish Butany MBBS is at the Department of Pathology, University Health Network. He is also at Department of Laboratory Medicine and Pathobiology, University of Toronto, Canada. Conflict of interest: none. Funding source: none. Avrum I Gotlieb MDCM FRCPC is at the Department of Pathology, University Health Network. He is also at Department of Laboratory Medicine and Pathobiology, University of Toronto, Canada and MaRS Centre, Toronto Medical Discovery Tower, 101 College Street, East Tower Room 3-311, Toronto, Ontario M5G 1L7, Canada. Conflict of interest: none. Funding source: none.

DIAGNOSTIC HISTOPATHOLOGY 16:1

17

Ó 2009 Published by Elsevier Ltd.

MINI-SYMPOSIUM: CARDIOVASCULAR PATHOLOGY

induces gene expression of agents that are considered antiatherogenic, including nitric oxide synthase (NOS) and plasminogen activator inhibitor-1 (PAI-1).2 Increased lipid entry and subsequent accumulation depend on disruption of the integrity of the endothelial barrier through cell dysfunction, disruption of cellecell adhesion junctions, and/or cell loss. Low density lipoproteins (LDL) carry lipids into the intima which lead to lipid oxidation. Monocytes/macrophages adhere to activated ECs and transmigrate into the intima also bringing in lipids. Some macrophages become foam cells, due in part to the uptake of oxidized LDL via scavenger receptors. These cells undergo necrosis, release lipids and incite further inflammation. A change in the types and quantity of matrix proteins and proteoglycans synthesized by intimal SMCs enhances binding of lipids. These proteoglycans such as chrondroitin sulphate rich proteoglycans have a high binding affinity for lipoproteins. Versican and biglycan are thus thought to promote atherosclerosis while decorin may be protective. Macrophages secrete cytokines, including monocyte chemoattractant protein-1 (MCP-1) and growth factors, thereby promoting further accumulation of both macrophages and SMCs. Oxidized lipoproteins and macrophage derived reactive oxygen species induce tissue damage. Monocyte/macrophages synthesize platelet derived growth factor (PDGF), FGF, tumour necrosis factor (TNF), interleukin-1 (IL-1), IL-6, interferon-g (IFN-g), and transforming growth factor-b (TGF-b), each of which can modulate the growth of SMCs and ECs. The cytokines IL-1 and TNF stimulate ECs to produce platelet-activating factor (PAF), tissue factor (TF), and PAI. TF expression, an important initiator of the coagulation cascade, is also upregulated by oxidized lipids, thus several conditions promote the transformation of the normal anticoagulant vascular surface to a procoagulant endothelium. Thrombi may develop on the damaged prothrombotic intimal surface.4 Numerous biologically active molecules are released from adherent and activated platelets.5 PDGF, accelerates SMC proliferation, TGF-b enhances the secretion of matrix components and thrombin and adenine diphosphate (ADP) and thromboxane promote further platelet activation resulting in enhanced thrombus growth. Since thrombosis also initiates fibrinolysis and inhibitory factors in the coagulation pathway, the thrombus may alternatively lyse. Organization of the thrombus and incorporation into the plaque may occur in part by TGF-b which regulates secretion of collagen, matrix proteins, and differentiation of SMCs into myofibroblasts. Further growth of the thrombus is now a balance between pro- and anti-thrombotic processes. The histopathology of the plaque should be described and the extent of thrombosis reported. The deep part of the thickened intima is poorly nourished. Hypoxia promotes HIF-1a translocation to the nucleus of SMCs and macrophages, which binds to the promoter specific hypoxia response element, leading to the transcriptional activation of VEGF and other target genes. Some macrophages and SMCs undergo ischaemic necrosis, as well as apoptosis. Cell death is also promoted by proteolytic enzymes released by macrophages and by tissue damage caused by oxidized LDL and other reactive oxygen species. VEGF initiates plaque angiogenesis with new vessels forming from the vasa vasorum, therefore establishing permanency to the plaque.

DIAGNOSTIC HISTOPATHOLOGY 16:1

The fibroinflammatory lipid plaque is formed, with a central necrotic core and a fibrous cap which separates the necrotic core from the blood in the lumen. The distribution of inflammatory cell infiltration, lipids and SMC and matrix is heterogeneous within the plaque. TGF-b regulates the plaque by increasing several types of collagen, fibronectin and proteoglycans. It inhibits proteolytic enzymes that promote matrix degradation and enhances expression of protease inhibitors. This may reflect a dual effect of TGF-b in promoting plaque growth but also being beneficial by promoting fibrous cap formation and thus plaque stability.6 The expression of human leukocyte antigen-DR (HLA-DR) antigens on both ECs and SMCs in plaques suggests immunological activation, perhaps in response to IFN-g released by activated T cells present in the plaque. Antibodies to oxidized LDL have been identified in the plaque. Stage II: adaptation stage As the plaque encroaches upon the lumen, the wall of the artery undergoes remodelling to maintain the original lumen size, likely regulated by haemodynamic shear stress, TGF-b and metalloproteinases (MMP) and their inhibitors (TIMP). Once a plaque encroaches upon about half the lumen, compensatory remodelling can no longer maintain normal patency, and the lumen of the artery becomes stenotic. Thus it is important to comment on lumen size in the pathology assessment, however without perfusion, fixation can only provide an approximation of the true value. Haemodynamic shear stress regulates the expression of a variety of genes that encode for proteins that promote remodelling such as MMPs, collagens, bFGF, TGF-b and inflammatory mediators. SMC turnover characterized by proliferation and apoptosis, and matrix synthesis and degradation modulate remodelling of the vessel and the plaque.7 This compensatory remodelling is useful because it maintains patency and blood flow in the lumen; however it may delay clinical diagnosis of atherosclerosis since the plaque may be ‘‘clinically silent’’ without demonstrating any symptoms. Even though the plaque is small, plaque rupture with catastrophic results may occur at this stage, as noted below. Stage III: clinical stage Plaque growth continues as the plaque encroaches on the lumen.8 Haemorrhage into a plaque due to leakage from the small fragile vessels of neovascularization may not necessarily result in actual rupture of the plaque but may still increase plaque size. Complications develop in the plaque, including surface erosion, ulceration, fissure formation, calcification, and aneurysm formation.9 It is important to record these complications in the microscopic evaluation of the plaque. Calcification is driven by chondrogenesis and osteogenesis, regulated in part by TGF-b, osteogenic progenitor cells and bone forming proteins. Activated mast cells are found at sites of erosion and may release proinflammatory mediators and cytokines. Continued plaque growth leads to severe stenosis or occlusion of the lumen. Plaque rupture through the fibrous cap leads to thrombosis and occlusion precipitating acute myocardial infarction. Endothelial erosion, ulceration, fistula; thin fibrous cap; decreased SMCs in cap; inflammation; macrophages and SMC foam cells; haemodynamic shear stress; imbalance in matrix synthesis/degradation; and

18

Ó 2009 Published by Elsevier Ltd.

MINI-SYMPOSIUM: CARDIOVASCULAR PATHOLOGY

nodular calcification are all risk factors for plaque rupture. Research to identify reliable biomarkers of impending plaque rupture has not been successful to date.

The interaction of the stent with the underlying atherosclerotic artery must be well described.19 Stents with thinner struts are endothelialized rapidly and cause less vessel-wall injury. Stent struts lacking neointimal coverage promote platelet-rich thrombi. Even within the same stent, some struts may show neointimal growth, while others remain bare and are a nidus for mural thrombosis.20 The middle section of the stent is the most common location for deficient neointimal coverage.20 Thus sampling from proximal and distal ends and middle portions is required. The useful drugs tested appear to not prevent but delay healing of the stented artery.19 The effects of the drugs on the cell biology of vascular cells are an important consideration and should be determined in the evaluation of the tissue.21 Nonerodable polymers when applied thinly without defect or cracking cause less inflammation and perform better.22 Reduced inflammation occurs when biodegradable polymers degrade and leave a BMS. However, when a durable polymer carrier is used to control drug elution, the polymer remains and has the potential to lead to later unwanted effects. It is for these reasons that a complete description and characterization of the stent are required in the pathological assessment of the case including type, model, drug and elution profile. Late stent thrombosis has emerged as a concern.23,24 DES stents have been reported to have delayed re-endothelialization when compared to BMS while showing less neointimal thickening. Pathologic studies of patients dying from late DES thrombosis demonstrate delayed arterial healing, characterized by persistent fibrin deposition and poor endothelialization. Other risk factors for late stent thrombosis include ostial or bifurcation stenting, malapposition/incomplete apposition of struts, and strut penetration into a necrotic core of the atherosclerotic plaque. The timing of late stent thrombosis in BMS was significantly earlier than those in DES. Lipophilic drugs such as sirolimus and paclitaxel are likely to persist longer when the struts are located in the necrotic core as this area is avascular. Arterial branch points may also predispose towards thrombosis by inducing flow disturbances and changes in shear stress.25 Heavily calcified plaques may prevent uniform strut deployment leading to malapposition and flow disturbances that could influence the pattern of arterial healing through shear stress induced growth stimuli. It is important to assess the extent of stent apposition.19 At pathological examination, it is not possible to determine whether the incomplete apposition identified is acquired or due to incomplete stent expansion during the index procedure. It appears that lack of strut apposition to the vessel wall delays arterial healing because these struts remain uncovered and promote thrombosis. Late malapposition is associated with the presence of thrombus between stent strut and the underlying plaque. Non-erodable polymers have been reported to induce granulomatous and hypersensitivity reactions, especially in Cypher stents in humans.26 In five cases, four with Cypher and one with Taxus, the Cypher stents show the presence of the inflammatory cells throughout the whole stent, whereas in the one case involving a Taxus stent, only focal eosinophilic infiltrate and some lymphocytes around occasional stent struts were reported.

Percutaneous coronary interventions Percutaneous coronary intervention (PCI), introduced by Andreas Grutzig in 1977, has changed the care of patients with ischaemic heart disease.10 Using this catheter-based approach to revascularize coronary arteries that are significantly compromised by atherosclerotic plaques has resulted in improved clinical outcomes in high-risk patients with acute coronary syndromes and STelevation myocardial infarction.11 Whether there is a beneficial role in treatment of patients with non-acute coronary artery disease is still not settled.12 Thus pathology reports must include details of clinical events, including use of anti-platelet and anticoagulation drugs, laboratory tests and investigations which should be correlated with pathology findings. PCI is now carried out almost exclusively with the insertion of a stent, a tubular scaffold device designed to restore blood flow through a stenotic artery. Originally bare metal stents (BMS) were utilized. Currently however, most deployed stents are drug eluting in nature. The stent must have sufficient radial strength to keep open the diseased atherosclerotic artery. In doing so, the stent induces stress fields on the artery wall which have been implicated in promoting vascular injury resulting in restenosis. Currently, drug-eluting stents (DES) are considered the standard of care for the treatment of coronary artery disease following PCI.13 The first two DES approved in the USA were the Cordis CypherÔ Coronary Sirolimus-Eluting Stent in April 2003 and Boston Scientific TaxusÔ Express2Ô Paclitaxel-Eluting Coronary Stent in March 2004. In pathological evaluation, there is a need to focus on four major features of DES: the stent platform itself, the polymer carrier, the drug and the interaction of the stent with the arterial wall, especially with the atherosclerotic plaque. The initial clinical trials carried out to evaluate the safety and effectiveness of these first two DES involved patients with focal atherosclerotic coronary lesions. Most patients had single vessel disease, with a vessel diameter between 2.5 and 3.5 mm and lesion lengths in the range of 12e30 mm.14 In the past several years, however, DES have been used to treat a wider range of patients, including those with multiple-vessel disease,15 bifurcation lesions,16 saphenous vein graft lesions, chronic total occlusions and unprotected left main coronary lesions. In pathology evaluation, information on these complex lesions must be documented through the clinical history, imaging investigations, and gross and microscopic descriptions of the histopathology. The least successful way of examining a stented vessel segment is gross dissection and removal of stent struts from the vessel wall with subsequent processing of the remaining tissue, with or without decalcification. This results in much artifactual destruction of the vascular wall and loss of intraluminal tissue.17 Alternately, the stented segment may be plastic embedded and then sectioned to provide an excellent preservation of stent and vessel wall. A method for the dissolution of most metallic stents from vascular segments has been recently described which is fast, cost-effective, and allows examination of the entire stented vascular segment.18

DIAGNOSTIC HISTOPATHOLOGY 16:1

19

Ó 2009 Published by Elsevier Ltd.

MINI-SYMPOSIUM: CARDIOVASCULAR PATHOLOGY

Saphenous vein graft stents

the intima of vein grafts due to vessel-wall injury and endothelial denudation leading to platelet and leukocyte adhesion. There are different surgical techniques for preserving vein grafts so it is important for the pathologist to report the technique used to harvest the vein. Graft-artery anastomosis must be examined carefully since early graft closure may occur due to compression which occurs when part of the coronary wall is everted or compressed by suturing during construction of the graft/ artery anastomosis. By one year, SVGs show intimal thickening composed of numerous smooth muscle cells within a loose matrix of collagen, proteoglycans and glycoproteins.28 Some of the thickening may be due to organizing or organized thrombi. The intimal thickening varies along the length of the graft and from graft to graft in the same patient. Atherosclerosis does develop in the SBVG and should be described in reports.

Percutaneous interventions in saphenous vein grafts (SVGs) have a worse long-term clinical outcome compared with stenting of native coronary arteries. SVGs often show thrombotic and necrotic composition of the plaque with plaque protrusion through the stent wires. Stent placement may easily fracture the fragile media in the SVG with subsequent neointimal proliferation. Since medial fracture and neointimal inflammatory cell density, especially close to stent wires, correlate with increased neointimal thickness, descriptions in reports need to include comments on these features.

Saphenous vein bypass grafts At autopsy care must be taken to avoid injury to saphenous vein bypass grafts (SVBG) or internal mammary artery (IMA) grafts as they are removed from the surface of the heart. These may be embedded in fibrous tissue and adhesions to adjacent structures may result in damage to the grafts. The ascending aorta is left in continuity with the heart to enable in situ examination of the proximal anastomoses of the vein grafts to the aortic orifice. Twists and excessive tautness in the course of the grafts between aorta and distal anastomosis should be noted. SVBGs may be visualized by postmortem radiographs using bariumegelatin mixture.27 These are radiographed before injecting the coronary arteries to study the native coronary arteries distal to the grafts as well as at the coronary/graft anastomosis.27 Injecting the grafts may dislodge thrombi and other material on the luminal surface and is a drawback of this technique. Measurements of lumen diameters may be made from the radiographs. Where an IMA is anastomosed to the left coronary system, the internal mammary artery is injected at the point where it was severed during removal of the heart. If the vessels are not injected, it is best to fix the opened heart in 10% buffered formaldehyde overnight prior to dissecting the grafts and native arteries. The grafts and native arteries may then be removed from the heart and cut at 5 mm intervals to determine the extent of luminal narrowing, the presence or absence of thrombi, and/or the extent of atherosclerosis in vein or IMA grafts and coronary arteries, especially at the anastomosis site. Anastomotic sites are sectioned in different ways depending on whether the connection is end-to-end or end-to-side in order to capture the common lumen at the anastomosis. Fresh or healed tears and/or dissections should be carefully looked for and described since coronary plaques may detach during the surgical procedure. Autopsy examination requires a careful examination and reporting of specific features that may occur at different times post surgery. Early graft closure within the first few days following aorto-coronary saphenous vein bypass surgery may be due to mechanical problems, and/or faulty surgical technique, especially at the distal anastomosis. A careful review of the operating report and discussion with the surgeon is required. Inadequate size of the distal coronary vessels results in poor runoff promoting low flow conditions and predisposing thrombosis. The extent of SVBG damage occurring at the time of the surgical harvesting and implantation should be assessed. A comment on the extent of inflammation, necrosis and thrombosis should be made in a semi-quantitative fashion. A layer of platelets, fibrin, erythrocytes, and polymorphonuclear leukocytes is observed in

DIAGNOSTIC HISTOPATHOLOGY 16:1

Prosthetic vascular grafts Carotid polytetrafluorethylene bypass is only carried out in selective cases29 because of the thrombogenic potential of the (PTFE) graft surface in comparison with that of carotid endartectomy (CEA) which gives excellent long-term results for standard lesions. In patients with extensive atherosclerotic lesions, presence of a thick plaque on the common carotid artery leaves a step at the proximal end of the endarterectomy which could cause embolism and restenosis. In addition, extended open endarterectomy creates a long endarterectomized thrombogenic zone. In these cases, prosthetic carotid bypass (PCB) grafting is the simplest and safest modality. Treatment alternative for atheromatous stenosis associated with kink of the internal carotid artery is eversion CEA. Most residual stenosis after eversion CEA are located in the common carotid artery. Recurrent stenosis after CEA and repeat CEA with patch angioplasty should be assessed in relation to atherosclerotic progression. In most cases, CEA failure was due to either the difficulty associated with treatment of massive calcified lesions of the common or the internal carotid artery or perforation of the arterial wall during endarterectomy of transmural atherosclerotic lesions. Autologous greater saphenous vein has been considered by many surgeons as the material of choice for this type of procedure. However, adequate length to avoid aneurysms, absence of valves, diameter >4 mm and excellent vein wall texture are essential for success. PTFE is adequate for carotid bypass and could be used routinely when this technique is indicated. Measurement of the graft length should be accurate so that the distal anastomosis can be made without tension or kink after clamp removal. Implantation of both ends of the bypass graft on a non-diseased artery is also important in order to avoid residual stenosis. The PTFE graft is stiffer than the carotid artery to which it is anastomosed, and the diameter of the internal carotid artery is between 3.5 and 4.5 mm, significantly less than the smallest non-thrombogenic PTFE graft (6 mm) available. Using end-to-end anastomosis with an oversized PTFE graft is not ideal.30 However, an end-to-side anastomosis is easier to construct in high carotid lesions and to avoid the risk of anastomotic stenosis. Plaques extending on the posterior wall of the internal carotid artery can lead to dissection

20

Ó 2009 Published by Elsevier Ltd.

MINI-SYMPOSIUM: CARDIOVASCULAR PATHOLOGY

or plaque disruption. Placement of a clip close to the heel of the anastomosis prevents a cul-de-sac which results in turbulence, thrombosis and embolization, and converts the end-to-side anastomosis into a hemodynamically improved end-to-end anastomosis. These anastomoses need to be well described and studied by the pathologist. Different materials can be used for bypass grafting including autologous and homologous grafts from the saphenous vein or the human umbilical vein as well as prosthetic graft materials such as PTFE or polyester (DacronÒ) grafts.31 Autologous vein grafts when suitable veins exist are superior to prosthetic graft materials in bypass surgery. Comparison of gelatin-coated DacronÒ vs. collagen-coated DacronÒ grafts showed no difference between the groups. Heparin-bonded DacronÒ also showed no difference to bare DacronÒ graft material. Synthetic vascular graft infection is one of the most serious complications in vascular surgery and is not uncommon.32,33 Several options have been proposed to treat this problem, including using allo- and auto-grafts, and more recently, Rifampicin-bounded and Silver-coated synthetic vascular grafts.

and followed with connective tissue, larger injuries, on the other hand, cannot be sufficiently sealed by connective tissue. These areas are most prone to pseudoaneurysm formation.

Aortic aneurysms Aortic aneurysms can be classified by location or by pathology (Table 1). There are four types according to location: aortic root aneurysm (or aneurysm of the sinus of valsalva), thoracic aortic aneurysm (ascending, aortic arch, descending), abdominal aortic aneurysm, and thoraco-abdominal aortic aneurysm. Approximately 80% of aortic aneurysms occur between the renal arteries and the aortic bifurcation. When classified according to pathology, there are two types of aortic aneurysms: true and false aneurysms. True aneurysms are generally bound by complete but thinned and stretched out vessel walls with no leakage. They may be further sub-classified into saccular, fusiform and dissecting (or aortic dissections). A saccular aneurysm is a sac-like bulge of part of the circumference of the artery wall and a fusiform aneurysm is a spindle-shaped generalized dilation of the wall. A dissecting aneurysm is a separation of the inner layers of the aortic wall, creating a double-lumen vessel. The entry and exit sites must be identified and acute and/or chronic pathology clearly described. False aneurysms are ‘‘holes’’ in the vessel wall lined by a part of the vessel wall and/or only by the peri-vascular tissues with the surrounding tissue becoming fibrotic.

Arteriovenous shunts Arteriovenous (AV) shunts provide long-term vascular access for haemodialysis in patients with end-stage renal failure. The most common forms of vascular access are autologous fistulas and synthetic grafts made with materials such as PTFE or polyester (DacronÒ) (Figure 1). Regardless of the type of graft, the main cause of graft explantation is graft wall destruction and subsequent pseudoaneurysm formation as a result of repetitive needle punctures during dialysis. True aneurysms are less common, but are also observed. Aside from needle trauma, aneurysms may also form as a result of infection/inflammatory processes and iatrogenic causes. The pathology of aneurysm formation has been previously described. Small needle injuries are first sealed by fibrin plugs

Pathogenesis An aortic aneurysm is characterized by thinning of the media, coupled with destruction of smooth muscle cells, collagen and elastin. Both atherosclerosis and hypertension are commonly associated with aortic aneurysms, and cigarette smoking and advancing age are risk factors.34e36 Some medial thinning occurs with advancing age in most aortas.37 There is often significant transmural infiltration of the aortic wall of the aneurysm by macrophages, B and T cells, which then secrete cytokines

aeb Surgically resected arteriovenous shunt with a vein graft. a This image shows the AV shunt (arrows) with an ellipse of skin overlying it. The central part shows an area of ulceration (*). b Microscopic section shows the ulceration of the underlying graft (V) and thrombus (T) (Movat pentachrome, original magnification 25). Figure 1

DIAGNOSTIC HISTOPATHOLOGY 16:1

21

Ó 2009 Published by Elsevier Ltd.

MINI-SYMPOSIUM: CARDIOVASCULAR PATHOLOGY

characterized by a mutation in fibrillin-1, while there is a defect in collagen synthesis in the EhlerseDanlos syndrome. Dissecting aneurysms are also associated with bicuspid aortic valves in about 2% of cases. Extrinsic factors such as trauma and infection may also lead to aortic aneurysms, specifically false aneurysms. Physical injury to the chest or abdomen (blunt injury) may weaken the aorta, making it susceptible to false aneurysm formation. Thus a clinical history of trauma should be commented upon. Bacterial infections can lead to mycotic aneurysms, a rare type of aortic aneurysms which requires histopathological identification of the organisms.

Classification of aortic aneurysms By Location C Aortic root aneurysm (or aneurysm of the sinus of valsalva) C Thoracic aortic aneurysm (ascending, aortic arch, descending) C Abdominal aortic aneurysm C Thoraco-abdominal aortic aneurysm By Pathology C True Aneurysm B Saccular: usually atherosclerotic B Fusiform: usually with aortopathy, inflammation, genetic disease B Dissection: idiopathic, post-traumatic C

Clinical manifestations Aneurysms are often asymptomatic until they become large or rupture (Figure 3) and are often incidental findings when patients undergo procedures for other reasons. Others are found when the patients present with non-specific symptoms. Chest and back pain are two common clinical manifestations of large aortic aneurysms. There may also be compression of nerve roots in the region of the aneurysm, leading to leg pain and numbness. Thrombo-emboli which form in the aneurysms may lead to stroke, myocardial infarction, peripheral and/or bowel ischaemia. Aortic aneurysms that are smaller than 5.5 cm in diameter usually do not rupture, and thus are rarely repaired. However, these individuals must be closely monitored with follow-up ultrasonography and CT scans, as they continue to grow. When the diameter is greater than 5.5 cm, the risk of rupture increases significantly, and the lesion is often treated prophylactically with surgical or endovascular repair. Treatment of a ruptured aneurysm has a much higher failure rate than repairing unruptured aneurysms, with the mortality rate for patients with ruptured aortic aneurysms at 80%.39 Autopsies done in these cases require very careful examination of the aortic aneurismal wall in order to identify and characterize the site of rupture.

False Aneurysm B Post-traumatic: e.g. blunt or surgical trauma B Infection: e.g. mycotic aneurysms

Table 1

resulting in the activation of many proteases, including matrix metalloproteinases. By degrading collagen and elastin, these proteases weaken the vessel wall and promote aneurysm formation and progression. The pathologist must provide a full microscopic description of the aneurysm wall, the luminal thrombus and both diseased and normal aortic tissue away from the aneurysm. There is a genetic component to this disease. Approximately 20% of patients who suffer from thoracic aortic aneurysms have one or more first-degree relatives who also suffer from this disease. Thoracic aortic aneurysms and dissecting aneurysms are strongly associated with genetic disorders such as Marfan syndrome and EhlerseDanlos syndrome, both of which are connective tissue disorders38 (Figure 2). Marfan syndrome is

aec Chronic dissection with features consistent with Marfan syndrome. a Surgically excised segments of ascending aortic tissue showing separation of the adventitia (*), thrombus, and a false lumen (FL). b Extensive medial changes with fragmented elastic tissue, markedly increased pools of mucopolysaccharides (white arrow), and areas of smooth muscle cell proliferation (black arrow) (Movat pentachrome, original magnification 50). c Microscopic section of the junctional area of the true and false lumen with the false lumen showing significant fibrocellular proliferation (arrow head) and a large pool of mucopolysaccharides (arrow) (Movat pentachrome, original magnification 16). Adv: adventitia, M: media, I: intima, TL: true lumen. Figure 2

DIAGNOSTIC HISTOPATHOLOGY 16:1

22

Ó 2009 Published by Elsevier Ltd.

MINI-SYMPOSIUM: CARDIOVASCULAR PATHOLOGY

aeb A ruptured saccular aneurysm in the thoracic aorta. The aneurysm measures 12  6  6 cm with the total rupture site being 4.5 cm long. a Gross section showing the aneurysm (*) surrounded by atherosclerotic plaque (black arrow) and a haematoma (white arrow). N: normal, smooth aorta. b Transverse section indicating the ‘‘shoulder’’ or neck of the aneurysm (curved arrow) and the rupture site (arrow head). TL: true lumen, white arrow: periaortic haematoma. Figure 3

Treatment procedures Currently, there are two procedures for patients with aortic aneurysms: open surgical and endovascular interventions. Pathology reports require a complete history of the intervention including clinical complications if they occur. Surgical repair has been the traditional mode of treatment. The aneurysm is opened, much of the thrombus evacuated, and a synthetic graft is sewn in place at the two ends. The aorta is closed around the graft. There are risks associated with this procedure to many organs, including the heart, brain, lungs, and kidneys, especially as these patients often have several comorbidities. Open surgical repair is also associated with a relatively high operative mortality rate of 2e5% as well as significant morbidity. Endovascular repair is normally performed under radiographic control by a vascular surgeon or interventional radiologist and involves the threading of a stent from the femoral artery to just beyond the aneurysmal region of the aorta (Figure 4). The stent is fixed to the inner vessel wall above the level of the aneurysm to help support the blood vessel and the stent. Several stents currently being used for abdominal aortic aneurysm repair include the Cook Zenith Device, the Gore Excluder Device, and the Medtronic Talent Device. In experienced hands, this procedure is faster than the open surgical repair, and offers a shorter recovery time with fewer complications. However, long-term

outcomes are not known and several devices have failed or been taken off the market after being used for a few months. Many patients must undergo re-interventions at a later time due to complications such as endoleaks, migration of the graft within the aortic sac due to the downward forces from blood flow, and stent-graft fatigue, which is characterized by changes in the mechanical nature of the device. Thus, great care is required when examining the endovascular graft in situ at autopsy. Measurements of stent location as well as the extent and description of luminal thrombi are required. Stenting has also been performed for other types of aortic aneurysms aside from abdominal aortic aneurysm, but less is known about the success of these procedures. There have been several studies comparing the two procedures, including the EndoVascular Aneurysm Repair (EVAR) trials40 and the Dutch Randomised Endovascular Aneurysm Management (DREAM) trials.41 Both EVAR-142 and DREAM43 trials have shown that compared to open repair, endovascular repair is associated with reduced peri-operative morbidity, shorter initial hospital stay and reduced overall recovery time. Notably, there was no significant difference in overall mortality rates after 2 years. The EVAR-1 and DREAM trials also show that endovascular repair is not cost-effective. This is primarily due to the current cost of endografts, the complications related to the procedure, and the need for long-term surveillance. However, with the future development of less expensive and improved endografts, this procedure may become more cost-effective.

Aortic dissections Most aortic dissections result from intimal tears which permit blood to flow between the intima and media. While the majority of patients have no underlying diseases, there is an association with bicuspid aortic valves and Marfan syndrome. There are now several ways to classify dissecting aneurysms. Here, we draw attention to the Stanford classification system which classifies dissecting aneurysms according to the site of primary tear. Specifically, Type A dissecting aneurysms involve the ascending aorta, while Type B aneurysms do not and are instead found distal to the subclavian artery in the thoracic descending aorta. This classification system is often preferred by physicians as

Figure 4 Medtronic TalentÒ aortic stent in a severely atherosclerotic aorta. When fully deployed, the ‘open cage’ end (arrow) of the graft rests beyond the aneurysm and anchors the stent in place. The stented graft lies across the aneurysm with its lower end in the common iliac artery (i). In this image, the stent has been moved to show the aneurysm (*) with the probe (P) holding the stent in place.

DIAGNOSTIC HISTOPATHOLOGY 16:1

23

Ó 2009 Published by Elsevier Ltd.

MINI-SYMPOSIUM: CARDIOVASCULAR PATHOLOGY

catheter with attached cutting pinchers, also called a ‘bioptome’ (commonly the Stanford Bioptome), through a sheath which is first advanced into a vein or artery. To perform a biopsy on the right-side of the heart, clinicians prefer a right internal jugular vein approach, although the left internal jugular vein, subclavian and femoral veins are also used. To carry out left sided heart biopsies, the femoral and brachial arteries are typically used. Originally introduced in 1962, the cardiac bioptome is inserted into a large vein or artery using a cutdown technique. The procedure became more widely accepted in the early 1970s when design modifications allowed for percutaneous insertion of the bioptome under local anaesthesia and a more rapid procedure.47 The majority of EMBs are taken from the right interventricular septum, although the left ventricle may occasionally be sampled when the suspected condition is thought to be isolated to the left side of the heart. Some centres have begun deliberate sampling of the right ventricular outflow tract and right ventricular apex to improve the likelihood of diagnosing arrhythmogenic right ventricular cardiomyopathy (ARVC) changes on EMB; however, a higher rate of complications is associated with these procedures. As a result of requiring central venous or arterial access and having to advance cutting pincers into the heart under 2-dimensional imaging guidance, procedural complications can and do arise.

a way to determine whether immediate surgical repair is necessary. Type A dissecting aneurysms are more severe than Type B aneurysms, often leading to poor perfusion of the brain and coronary arteries, thus requiring immediate open surgical repair. Surgical repair involves resectioning the affected areas and replacement with a prosthetic graft. The aortic valve may also require repair or replacement depending on the extent of injury. Endovascular repair of entry tears in the ascending aorta is more difficult due to the close proximity of coronary ostia. The strategy for repairing acute dissecting aneurysms not involving the ascending aorta (Type B) is less clear. These often lead to poor perfusion of the spinal cord, bowel, liver, kidneys and legs and this must be identified by examining aortic branches carefully and the target organs for evidence of ischaemia. Surgical intervention is reserved for complicated patients at high risk for, or presenting with, aortic rupture.

Endomyocardial biopsy Endomyocardial biopsy (EMB) is widely used as a means of monitoring allograft rejection following heart transplantation (Figure 5) and to investigate non-transplant related pathologies which cannot be diagnosed on the basis of clinical findings alone (Figure 6, Table 2). The standardized nomenclature used in the diagnosis of heart rejection has been recently revised.44 Current advances in effectiveness of immunosuppression regimens and reduction in incidence and severity of acute rejection suggest that the role of EMBs in the first year after transplantation for clinical surveillance needs to be reconsidered.45 Disease recurrence in the graft heart has been observed in eosinophilic cardiomyopathy, giant cell myocarditis, sarcoidosis and light-chain amyloidosis, and biopsy is useful in monitoring possible recurrence.46 Heart tissue samples are obtained by percutaneous insertion of a biopsy

Indications EMBs are performed when a comprehensive work-up including a detailed history, physical exam, blood work, selected laboratory studies, ECG, chest X-ray, transthoracic echocardiogram and cardiac catheterization fails to establish the aetiology of a cardiomyopathy. Based on the clinical information obtained, the pathologist can differentiate between possible etiologies by means of histological, immunohistochemical, electron microscopy and molecular analysis of biopsy tissue (Table 3).

a Routine post-transplant surveillance biopsy from a 56-year-old man showing the features expected in a normal EMB. The endocardium (arrow head) is normal, the myocytes and their nuclei are of uniform size and shape, and there is no interstitial fibrosis. Small mural vessels (arrows) show some peri-vascular fibrosis. b This surveillance biopsy from a 33-year-old man shows active rejection (Grade 3A). Muscle fibre damage is seen (thick arrows). [Haematoxylin and eosin stain; original magnification: (a) 100; (b) 100.]. Figure 5

DIAGNOSTIC HISTOPATHOLOGY 16:1

24

Ó 2009 Published by Elsevier Ltd.

MINI-SYMPOSIUM: CARDIOVASCULAR PATHOLOGY

aec show amyloidosis while def show myocarditis. aec A right ventricular EMB from a 73-year-old woman showing amyloidosis. a shows a very significant interstitial infiltrate of fibrillar material (arrows). The infiltrate has led to loss of muscle fibres and some of the residual muscle fibres, trapped in this infiltrate, are ‘‘skinny’’ and narrow. In some areas (not shown here), the aggregates of infiltrative material appeared nodular. b shows a magnified view of the boxed area in Figure 2a. c This transmission electron micrograph shows extensive interstitial fibrillar deposits (asterisks) with a fibril size of 2e12 nm (average 9e11 nm). As well, many of the myocardial fibres show degenerative changes (arrow). There is an accumulation of lipofuscin granules (arrow head). def A right ventricular EMB from a 45-year-old man with features of acute, active myocarditis. d Features include multiple foci of interstitial mononuclear infiltrates (predominantly lymphocytes) with evidence of muscle fibre damage (thin arrows). In addition there is endocardial (thick arrows) and interstitial (arrow heads) fibrosis as well as evidence of fibre hypertrophy. No evidence of any infiltrative process is seen. e Focal but abundant patches of polymorphonuclear leukocytes are seen with scattered eosinophils (white arrows) in this magnified view of Figure 3d. The eosinophils suggest the possibility of toxicity or hypersensitivity myocarditis. f shows patchy areas of interstitial fibrosis (arrow heads). [Haematoxylin and eosin stain; original magnification: (a) 100; (b) 200; (d) 100; (e) 200; (f) 200. Electron micrograph; original magnification: (c) 5000.]. Figure 6

EMB is also important in narrowing down the differential diagnosis of clinically suspected dilated cardiomyopathy. Idiopathic dilated cardiomyopathy is a diagnosis of exclusion, thus whether there is histological evidence of a treatable underlying condition such as Fabry’s disease or iron toxicity-associated cardiomyopathy should be established. EMB can be useful in monitoring the effects of cardiotoxic chemotherapeutic agents including anthracyclines. Routine EMBs can be used to alter dosage or discontinue use of a drug pre-symptomatically when signs of cardiotoxicity arise.

Lung Transplantation recommends a minimum of three EMB fragments with at least 50% of the tissues being myocardium, excluding a previous biopsy site, scar, thrombus or non-interpretable tissue (e.g. crush artifact or poorly processed fragments).48 In comparison, the AHA/ACCF/ESC guidelines suggest that 5e10 EMB samples 1e2 mm3 in size should be obtained from more than one region of the right ventricular septum, depending on the studies being performed.49 The sensitivity of detecting transplant rejection can approach 98% with five adequate biopsy fragments, although more fragments may be necessary for focal myocardial diseases such as myocarditis. The greatest potential limitation to EMB interpretation is sampling error as a result of the focal nature of some cardiac

Technical considerations The size and number of biopsy specimens directly influence the sensitivity of EMB.48 The International Society of Heart and

DIAGNOSTIC HISTOPATHOLOGY 16:1

25

Ó 2009 Published by Elsevier Ltd.

MINI-SYMPOSIUM: CARDIOVASCULAR PATHOLOGY

Catecholamine cardiomyopathy B Occult pheochromocytoma B Cocaine abuse C Idiopathic cardiomyopathy C Rheumatic heart disease C Radiation Monitoring drug toxicity C Chloroquine toxicity C Anthracycline toxicity B Doxyrubicin (Adriamycin) toxicity C Herceptin toxicity B Cytoxan toxicity C

Applications of EMB tissue analysis Allograft surveillance C Graft rejection C Recurrence of previous condition (e.g. giant cell myocarditis, amyloidosis, hypersensitive/eosinophilic myocarditis) Diagnostic Ischaemic heart disease C Cocaine abuse mimicking an acute myocardial infarction C Vasospastic ischaemia C Thrombotic thrombocytic purpura Non-ischaemic heart disease C Familial cardiomyopathy C Congestive heart failure B Acute onset B Chronic or progressive C Restrictive cardiomyopathy (diastolic dysfunction) vs. constrictive pericarditis C Arrhythmias B Arrhythmogenic cardiomyopathy B Myocarditis C Cardiac tamponade C Superior vena cava syndrome C Iron overload C Storage diseases B Fabry’s disease B Glycogen storage diseases B Mucopolysaccharidosis B Haemochromatosis C Neoplasms B Carcinoid heart syndrome C Amyloidosis B Senile cardiac amyloidosis transthyretin amyloid fibrils B Immunoglobulin light-chain amyloidosis B Apolipoprotein-AI amyloidosis C Sarcoidosis C Endocardial fibrosis C Scleroderma C Myocarditis B Active B Infectious (bacterial, fungal, viral, parasitic) B Autoimmune C Post-viral autoimmune myocarditis C Fulminant C Subacute C Chronic active C Chronic persistent B Giant cell B Lymphocytic B Eosinophilic/hypersensitive B Idiopathic granulomatous C Endocardial fibrosis C Dilated cardiomyopathy B Alcoholic B Hormone imbalance C Growth hormone deficiency

DIAGNOSTIC HISTOPATHOLOGY 16:1

Table 2

conditions. While a positive EMB is diagnostic, a negative EMB does not exclude any condition, and further investigation is warranted. Artifacts Pathologists must be aware that a number of artifacts can arise during the biopsy procedure and preparation of EMB slides. Contraction band changes are frequently present in EMB specimens and may be over-interpreted by the inexperienced pathologist. Normal appearing nuclei in surrounding myocytes typically suggest artificially induced contraction bands. Adipose tissue may be seen in the sub-endocardium of the right ventricle and does not necessarily imply perforation, epicardial localization or ARVC. However, the presence of mesothelial cells does indicate a perforated ventricle. Chordae tendinae and fragments of valve tissue may be included in the biopsy material. They should be described in the pathology report, as they may help explain the onset of the new symptoms. Crush artifact refers to bioptome-induced tissue distortion which may be observed in biopsy samples. This can appear as a central waist-like constriction of the tissue fragment caused by the bioptome forceps mechanism. Artifacts are also introduced through rough handling of biopsy specimens. A resultant disruption of the myocardium may lead to a false diagnosis of interstitial oedema. Samples require prompt fixation because mitochondrial degeneration appears in specimens which have remained unfixed for long periods of time. Fresh or snap-frozen tissue is not ideal for the standard preparation of tissue fragments because of the potential for ice crystal artifacts. Clinical complications Reported incidences of EMB complications are low. Deaths related to EMB procedures are very rare, but can occur. An overall complication rate ranges from 0.12 to 5.6%50 in biopsies performed in transplantation and cardiomyopathy patients using the femoral or the internal jugular vein. Holzmann et al.50 reported a major complication rate of <0.12% and a minor complication rate of 0.2e5.5% with no deaths in 3048 procedures. Cardiac biopsy is associated with two types of complications: those related to central venous access (about half) and those related to performance of the biopsy itself. Complications related to cannulation include incidental arterial puncture, bleeding, haematoma, vaso-vagal reaction, nerve paresis, pneumothorax during the internal jugular vein approach and deep vein

26

Ó 2009 Published by Elsevier Ltd.

MINI-SYMPOSIUM: CARDIOVASCULAR PATHOLOGY

Appropriate steps for making common EMB-based diagnoses Diagnosis

Light Microscopy H&E Special stain

Cardiomyopathy Dilated

Yes

Movat, Elastic Trichrome

Hypertrophic

Yes

Fabry’s disease

Yes

Movat, Elastic Trichrome Movat

Infiltrative Amyloidosis

Yes

Congo Red

Haemochromatosis

Yes

Prussian Blue Stain

Inflammatory Myocarditis

Yes

Movat, Elastic Trichrome

Sarcoidosis

Yes

Movat

Immunohistochemistry

Mononuclear cells: e CD45 (lymphocytes) e CD68 (macrophages) e e Pre-albumin a light chain k light chain e Mononuclear cells: e CD45 (lymphocytes) e CD68 (macrophages) Mononuclear cells: e CD45 (lymphocytes and giant cells) e CD68 (macrophages)

Electron microscopy

Yes

Yes Yes Yes

e

e

e

Table 3

thrombosis following the femoral venous approach. Complications related to the procedure include supraventricular and ventricular tachycardia, right bundle branch and complete heart block, right ventricular pseudoaneurysm and fistula development. The most serious potential complication remains to be ventricular free wall perforation leading to cardiac tamponade and death.

A direct correlation has been established between the number of EMBs performed and the severity of tricuspid regurgitation in patients receiving EMBs to monitor allograft rejection. An upper limit of 31 EMBs has been proposed to reduce the risk of severe tricuspid regurgitation.51 The most important variable in determining the risk of EMB is the experience and technical skill of the bioptome operator.51

Examples of ventricular assist devices. a Pulsatile-flow NovacorÒ LVAS with tissues (*) adherent to the VAD. b Continuous-flow HeartMateÒ II LVAS with the inflow cannula still attached to the heart. The pump (P), inflow (IF) and outflow (OF) cannulae, and percutaneous lead (L) are labelled. Other components are not shown. Figure 7

DIAGNOSTIC HISTOPATHOLOGY 16:1

27

Ó 2009 Published by Elsevier Ltd.

MINI-SYMPOSIUM: CARDIOVASCULAR PATHOLOGY

Evidence for reverse remodelling during VAD support Prior to VAD support

After VAD support

Progressive ventricular dilatation/right-shift of the end-diastolic pressureevolume relationship C Pathological myocyte hypertrophy C Increased collagen content C Myocyte apoptosis 2þ C Decreased expression of Ca transporters (sarcoplasm reticulum 2þ Ca subtype 2a, ryanodine receptor, Naþ/Ca2þ exchanger) C Downregulation of the b-adrenergic receptor as a consequence of chronic sympathetic activation during heart failure C Elevated levels of inflammatory cytokines TNF-a, IL-6, and IL-8 C Elevated serum brain natriuretic peptide (BNP) levels C

C

C C C C

C

C C

Decrease in left ventricular size and improvement in ejection fraction Decrease in myocyte diameter Increase or decrease in collagen content Lower rates of myocyte apoptosis Increased expression of Ca2þ transporters (sarcoplasm reticulum Ca2þ subtype 2a, ryanodine receptor, Naþ/Ca2þ exchanger) Recovery of the b-adrenergic response Normalization of levels of TNF-a, IL-6, and IL-8 Decreased serum BNP levels

Table 4

Ventricular assist devices

a result, patients are often given anticoagulants and antiplatelet drugs. The initial LVADs were short-term pumps (<2 weeks) developed to assist patients after cardiac surgery as well as patients waiting for heart transplantation. Several studies showed that the survival to transplantation of patients with mechanical circulatory support is approximately 70%. In a study conducted by Frazier et al., it was noted that only 29% of patients supported by a HeartMate Vented Electric Left Ventricular Assist System died while waiting for a transplant, as compared to 67% of patients who did not have mechanical circulatory support. One major caveat to using VADs as a bridge to transplantation is that these patients are at a higher risk of developing antibodies to human leukocyte antigens (HLA) triggered by the neointima, which forms after VAD implantation. The Randomized Evaluation of Mechanical Assistance for the Treatment of Congestive Heart Failure (REMATCH) trial was

Since their introduction in 1963, VADs have evolved significantly. Originally developed as a bridge to transplantation, the newer VADs can be potentially used as a destination therapy for patients ineligible for heart transplantations. They are also used as a bridge to recovery, that is, for temporary mechanical support of the circulatory system of patients with expected recovery of myocardial function. While the design of individual devices may vary, all VADs function by draining blood from the non-effective ventricle and pumping it into the systemic (or pulmonic) circulation at a desired rate and volume. VADs are designed to support either the left ventricle (LVAD) or the right ventricle (RVAD), and two devices may be used for biventricular support (BiVAD). LVADs are most commonly used, but for patients in need of biventricular support, it is more likely that a short-term device is used to support right-side function while a longer-term device is used for the left. All VADs have three basic components: a pump that receives and then pumps blood through inflow and outflow cannulae, a controller and a power supply. VADs can be classified by the position of device (extracorporeal, intracorporeal or paracorporeal), duration of support (short-term or long-term), type of blood flow (continuous or pulsatile flow), or by driving power (pneumatic or electric). Most devices today are either pulsatile or continuous-flow types (Figure 7). Pulsatile-flow devices are generally volume displacement pumps that fill with and eject blood in a similar fashion to systole and diastole of a native heart. Although these devices physiologically resemble the human heart more closely, they are often larger and bulkier with more moving parts and require prosthetic heart valves (PHVs). Consequently, they are more prone to mechanical dysfunction and failure. Continuousflow pumps, on the other hand, which are broadly characterized into axial flow and centrifugal flow pumps, are significantly smaller in size, have no PHVs and are less susceptible to deterioration and failure. Their major disadvantage, however, is that the greater shear stress on blood flowing through the pumps may lead to destruction of blood cells and platelets. As

DIAGNOSTIC HISTOPATHOLOGY 16:1

Complications of VAD Acute Complications C Thromboembolism C Haemorrhage C Altered immune response C Right ventricle failure C Multiorgan failure Chronic Complications C Infection C Abdominal complications C Device malfunction C Native aortic valve changes C Prosthetic valve dysfunction C Malnutrition C Psychosocial issues Table 5

28

Ó 2009 Published by Elsevier Ltd.

MINI-SYMPOSIUM: CARDIOVASCULAR PATHOLOGY

4 Davi G, Patrono C. Platelet activation and atherothrombosis. N Engl J Med 2007; 357: 2482e94. 5 Blair P, Flaumenhaft R. Platelet alpha granules: basic biology and clinical correlates. Blood Rev 2009; 23: 177e89. 6 Singh NN, Ramji DP. The role of TGF-b in atherosclerosis. Cytokine Growth Factor Rev 2006; 17: 487e99. 7 Adiguzel E, Ahmad PJ, Franco C, Bendeck MP. Collagen in the progression and complications of atherosclerosis. Vasc Med 2009; 14: 73e89. 8 Stary HC, Chandler AB, Dinsmore RE, et al. A definition of advanced types of atherosclerotic lesions and histological classification of atherosclerosis. A report from the Committee on Vascular Lesions of the Council on Arteriosclerosis, American Heart Association. Arterioscler Thromb Vasc Biol 1995; 15: 1512e31. 9 Virmani R, Burke AP, Farb A, Kolodgie FD. Pathology of the vulnerable plaque. Am J Coll Cardiol 2006; 47: C13e8. 10 Gruntzig AR, Senning A, Seigenthaler WE. Nonoperative dilatation of coronary-artery stenosis: precutaneous transluminal coronary angioplasty. N Engl J Med 1979; 301: 61e8. 11 Metha SR, Cannon CP, Fox KA, et al. Routine vs selective invasive strategies in patients with acute coronary syndromes: a collaborative meta-analysis of randomized trials. JAMA 2005; 293: 2908e17. 12 Trikalinos TA, Alsheikh-Ali AA, Tatsioni A, Nallamothu BK, Kent DM. Percutaneous coronary interventions for non-acute coronary artery disease: a quantitative 20-year synopsis and a network meta analysis. Lancet 2009; 373: 911e8. 13 Boam AB. Regulatory issues facing the development of drug eluting stents: a US FDA perspective. Expert Rev Med Devices 2006; 3: 297e300. 14 Soran O, Manchanda A, Schueler S. Precutaneous coronary intervention vs coronary artery bypass surgery in multivessel disease: a current perspective. Interact Cardiovasc Thorac Surg 2009; 8: 666e71. 15 Park D-W, Yun S-C, Lee S-W, et al. Long-term mortality after precutaneous coronary intervention with drug-eluting stent implantation versus coronary artery bypass surgery for the treatment of multivessel coronary artery disease. Circulation 2008; 117: 2079e86. 16 Colombo A. Bifurcation lesions. Ital Heart J 2005; 6: 475e88. 17 Rippstein P, Black MK, Boivin M, et al. Comparison of processing and sectioning methodologies for arteries containing metallic stents. J Histochem Cytochem 2006; 54: 673e81. 18 Bradshaw SH, Kennedy L, Dexter DF, Veinot JP. A practical method to rapidly dissolve metallic stents. Cardiovasc Pathol 2009; 18: 127e33. 19 Carter AJ, Farb A, Gould KE, Taylor AJ, Virmani R. The degree of neointimal formation after stent placement in atherosclerotic rabbit iliac arteries is dependent on the underlying plaque. Cardiovasc Pathol 1999; 8: 73e80. 20 Finn AV, Nakazawa G, Joner M, et al. Vascular responses to drug eluting stents. Importance of delayed healing. Arterioscler Thromb Vasc Biol 2007; 27: 1500e10. 21 Steffel J, Latini RA, Akhemdova, et al. Rapamycin, but not FK-506, increases endothelial tissue factor expressio´n: implications for drugeluting stent design. Circulation 2005; 112: 2002e11. 22 Nakazawa G, Finn AV, Kolodgie FD, Virmani R. A review of current devices and a look at new technology: durg-eluting stents. Expert Rev Med Devices 2009; 6: 33e42.

a breakthrough trial that reported the significant benefit of LVAD use as a destination therapy for patients with end-stage HF ineligible for heart transplantation. The study was conducted on 129 patients with end-stage HF who were ineligible for cardiac transplantation. 68 patients received a HeartMateÒ VE (Thoratec, CA, USA) LVAD, while the other 61 patients received optimal medical management. The one-year survival rates were 52% for those who received the device, and 25% for those treated medically. At two years, the rates were 23% and 8% respectively. The results of the REMATCH trial led to the Food and Drug Administration’s approval of the device for use as a destination therapy in 2002.52 The long-term use of LVADs has led to cardiac recovery in a few patients to the point where they no longer needed mechanical circulatory support and the devices could be removed without need of a graft heart.53e55 Heart failure leads to ventricular remodelling: a combination of the progressive functional, structural and molecular adaptations of the heart in response to damage. Clinical manifestations include left ventricular hypertrophy, dilatation, and dysfunction. By allowing haemodynamic unloading of the native heart, LVADs allow for reverse remodelling and functional improvement (Table 4). Significant cardiac recovery is however only observed in a small subset of patients, and those who have their LVADs explanted have often relapsed back into heart failure. The Harefield protocol combines LVAD use with administration of a pharmacologic agent, clenbuterol.54,55 Clenbuterol is a b2 adrenergic agonist that can induce physiological hypertrophy of cardiac muscle without adversely affecting cardiac function. This is of particular importance for patients supported with LVADs, because the reduced left ventricular pressure that results from chronic mechanical unloading leads to myocyte atrophy, explaining the poor outcome of patients after device explantation. Specifically, the Harefield protocol consists of two stages.54 The first stage promotes the process of reverse remodelling by coupling LVAD implantation with a drug regimen consisting of beta-blockers and drugs modulating the renineangiotensinealdosterone system. After maximal reverse remodelling is achieved, the second stage of pharmacologic treatment is initiated. With the LVAD still in place, clenbuterol is administered in order to induce physiologic hypertrophy, thus promoting normal functioning of the heart. Birks et al.54 were able to successfully explant the devices in 11 out of 15 patients treated with the Harefield protocol, and show that the quality of life for the patients after 3 years was nearly normal. As with any implanted device, there are many complications associated with VAD use56e58 (Table 5). While some complications are specific to the device being used, others are general to all devices. A

REFERENCES 1 Gotlieb AI. In: Rubin R, Strayer D, eds. Blood vessels in Rubin’s pathology. 5th edn. Lippincott, Williams and Wilkins, 2007: 397e426. 2 Cunningham K, Gotlieb AI. The role of shear stress in atherogenesis. Lab Invest 2005; 85: 9e23. 3 Hyduk SJ, Cybulsky MI. Role of alpha4beta1 integrins in chemokineinduced monocyte arrest under conditions of shear stress. Microcirculation 2009; 16: 17e30.

DIAGNOSTIC HISTOPATHOLOGY 16:1

29

Ó 2009 Published by Elsevier Ltd.

MINI-SYMPOSIUM: CARDIOVASCULAR PATHOLOGY

23 Farb A, Burke AP, Kolodgie FD, Virmani R. Pathological mechanisms of fatal late coronary stent thrombosis in humans. Circulation 2003; 108: 1701e6. 24 Joner M, Finn AV, Farb A, et al. Pathology of drug-eluting stents in humans: delayed healing and late thrombotic risk. J Am Coll Cardiol 2006; 48: 193e202. 25 Ge L, Airoldi F, Iakovou I, Virmani R. Clinical and angiographic outcome after implantation of drug-eluting stents in bifurcation lesions with the crush stent technique: importance of final kissing balloon post dilation. J Am Coll Cardiol 2005; 46: 613e20. 26 Nakazawa G, Ladich E, Finn AV, Virmani R. Pathophysiology of vascular healing and stent mediated arterial injury. EuroIntervention 2008; Suppl C: C7e10. 27 Virmani R, Ursell PC, Fenoglio JJ. Examination of the heart. Hum Pathol 1987; 18: 432e40. 28 Ribichini F, Pugno F, Ferrero V, et al. Long-term histological and immunohistochemical findings in human venous aorto-coronary bypass grafts. Clin Sci 2008; 114: 211e20. 29 Ricco JB, Marchand C, Neau JP, Marchand E, Cau J, Fe´brer G. Prosthetic carotid bypass grafts for atherosclerotic lesions: a prospective study of 198 consecutive cases. Eur J Vasc Endovasc Surg 2009; 37: 272e87. 30 Dobrin PB, Mirande R, Kang S, Sheng DQ, Mrkvicka R. Mechanics of end-toend artery-to-PTFE graft anastomoses. Ann Vasc Surg 1998; 12: 317e23. 31 Roll S, Muller-Nordhorn J, Keil T, et al. DacronÒ vs. PTFE as bypass materials in peripheral vascular surgery e systematic review and meat-analysis. BMC Surg 2008; 8: 22. 32 Aavik A, Lieberg J, Kals J, Pulges A, Kals M, Lepner U. Ten years experience of treating aorto-femoral bypass graft infection with venous allografts. Eur J Vasc Endovasc Surg 2008; 36: 432e7. 33 Olofsson P, Rabahie GN, Matsumoto K, et al. Histopathological characteristics of explanted human prosthetic arterial grafts: implications for the prevention and management of graft infection. Eur J Vasc Endovasc Surg 1995; 9: 143e51. 34 Ailawadi G, Eliason JL, Upchurch Jr GR. Current concepts in the pathogenesis of abdominal aortic aneurysm. J Vasc Surg 2003; 38: 584e8. 35 Davies MJ. Aortic aneurysm formation: lessons from human studies and experimental models. Circulation 1998; 98: 193e5. 36 Coady MA, et al. Familial patterns of thoracic aortic aneurysms. Arch Surg 1999; 134: 361e7. 37 Nesi G, Anichini C, Tozzini S, Boddi V, Calamai G, Gori F. Pathology of the thoracic aorta: a morphologic review of 338 surgical specimens over a 7-year period. Cardiovasc Pathol 2009; 18: 134e9. 38 Motro M, Fisman EZ, Tenenbaum A. Cardiovascular management of Marafan syndrome. IMAJ 2008; 10: 182e5. 39 Adam DJ, Mohan IV, Stuart WP, Bain M, Bradbury AW. Community and hospital outcome from ruptured abdominal aortic aneurysm within the catchment area of a regional vascular surgical service. J Vasc Surg 1999; 30: 922e8. 40 Brown LC, Epstein D, Manca A, Beard JD, Powell JT, Greenhalgh RM. The UK Endovascular Aneurysm Repair (EVAR) trials: design, methodology and progress. Eur J Vasc Endovasc Surg 2004; 27: 372e81. 41 Prinssen M, Buskens E, Blankensteijn JD. The Dutch Randomised Endovascular Aneurysm Management (DREAM) trial. Background, design and methods. J Cardiovasc Surg (Torino) 2002; 43: 379e84. 42 EVAR trial participants. Endovascular aneurysm repair versus open repair in patients with abdominal aortic aneurysm (EVAR trial 1): randomised controlled trial. Lancet 2005; 365: 2179e86. 43 Blankensteijn JD, et al. Two-year outcomes after conventional or endovascular repair of abdominal aortic aneurysms. N Engl J Med 2005; 352: 2398e405.

DIAGNOSTIC HISTOPATHOLOGY 16:1

44 Stewart S, Winters GL, Fishbein MC, et al. Revision of the 1990 working formulation for the standardization of nomenclature in the diagnosis of heart rejection. J Heart Lung Transplant 2005; 24: 1710e20. 45 Hamour IM, Burke MM, Bell AD, Panicker MG, Banerjee R, Banner NR. Limited utility of endomyocardial biopsy in the first year after heart transplantation. Transplantation 2008; 85: 969e74. 46 Luk A, Metawee M, Ahn E, Gustafsson F, Ross H, Butany J. Do clinical diagnoses correlate with pathological diagnoses in cardiac transplant patients? The importance of endomyocardial biopsy. Can J Cardiol 2009; 25: e48e54. 47 Cunningham KS, Veinot JP, Butany J. An approach to endomyocardial biopsy interpretation. J Clin Pathol 2006; 59: 121e9. 48 Karatolios K, Pankuweit S, Maisch B. Diagnosis and treatment of myocarditis: the role of endomyocardial biopsy. Curr Treat Options Cardiovasc Med 2007; 9: 473e81. 49 Cooper LT, Baughman KL, Feldman AM, et al. The role of endomyocardial biopsy in the management of cardiovascular disease: a scientific statement from the American Heart Association, the American College of Cardiology, and the European Society of Cardiology. Endorsed by the Heart Failure Society of America and the Heart Failure Association of the European Society of Cardiology. J Am Coll Cardiol 2007; 50: 1914e31. 50 Holzmann M, Nicko A, Kuhl U, et al. Complication rate of right ventricular endomyocardial biopsy via the femoral approach: a retrospective and prospective study analyzing 3048 diagnostic procedures over an 11-year period. Circulation 2008; 118: 1722e8. 51 Nguyen V, Cantarovich M, Cecere R, Giannetti N. Tricuspid regurgitation after cardiac transplantation: how many biopsies are too many? J Heart Lung Transplant 2005; 24: S227e31. 52 Drakos SG, Charitos EI, Nanas SN, Nanas JN. Ventricular-assist devices for the treatment of chronic heart failure. Expert Rev Cardiovasc Ther 2007; 5: 571e84. 53 Maybaum S, Kamalakannan G, Murthy S. Cardiac recovery during mechanical assist device support. Semin Thorac Cardiovasc Surg 2008; 20: 234e46. 54 Birks EJ, Tansley PD, Hardy J, et al. Left ventricular assist device and drug therapy for the reversal of heart failure. N Engl J Med 2006; 355: 1873e84. 55 Bruggink AH, van Oosterhout MF, de Jonge N, et al. Reverse remodeling of the myocardial extracellular matrix after prolonged left ventricular assist device support follows a biphasic pattern. J Heart Lung Transplant 2006; 25: 1091e8. 56 Barnes K. Complications in patients with ventricular assist devices. Dimens Crit Care Nurs 2008; 27: 233e41. quiz 242e3. 57 Rose AG, Park SJ. Pathology in patients with ventricular assist devices: a study of 21 autopsies, 24 ventricular apical core biopsies and 24 explanted hearts. Cardiovasc Pathol 2005; 14: 19e23. 58 Khan NA, Butany J, Zhou T, Ross HJ, Rao V. Pathological findings in explanted prosthetic heart valves from ventricular assist devices. Pathology 2008; 40: 377e84. FURTHER READING Liu AC, Gotlieb AI. Molecular basis of cardiovascular disease. In: Coleman WB, Tsongalis GJ, eds. Molecular pathology. Academic Press, 2009.

30

Ó 2009 Published by Elsevier Ltd.