Inflammation and infection in nine surgically explanted Medtronic Freestyle® stentless aortic valves

Embedding and Backscattered Scanning Electron Microscopy (EM-BSEM) Is Preferential over Immunophenotyping in Relation to Bioprosthetic Heart Valves

Hitherto, calcified aortic valves (AVs) and failing bioprosthetic heart valves (BHVs) have been investigated by similar approaches, mostly limited to various immunostaining techniques. Having employed multiple immunostaining combinations, we demonstrated that AVs retain a well-defined cellular hierarchy even at severe stenosis, whilst BHVs were notable for the stochastic degradation of the extracellular matrix (ECM) and aggressive infiltration by ECM-digesting macrophages. Leukocytes (CD45+) comprised ≤10% cells in the AVs but were the predominant cell lineage in BHVs (≥80% cells). Albeit cells with uncertain immunophenotype were rarely encountered in the AVs (≤5% cells), they were commonly found in BHVs (≥80% cells). Whilst cell conversions in the AVs were limited to the endothelial-to-mesenchymal transition (represented by CD31+α-SMA+ cells) and the formation of endothelial-like (CD31+CD68+) cells at the AV surface, BHVs harboured numerous macrophages with a transitional phenotype, mostly CD45+CD31+, CD45+α-SMA+, and CD68+α-SMA+. In contrast to immunostaining, which was unable to predict cell function in the BHVs, our whole-specimen, nondestructive electron microscopy approach (EM-BSEM) was able to distinguish between quiescent and matrix-degrading macrophages, foam cells, and multinucleated giant cells to conduct the ultrastructural analysis of organelles and the ECM, and to preserve tissue integrity. Hence, we suggest EM-BSEM as a technique of choice for studying the cellular landscape of BHVs.

Structural abnormalities after aortic root replacement with stentless xenograft

OBJECTIVE

In complex and high-risk aortic root disease, the porcine Freestyle stentless bioprosthesis (Medtronic Inc, Minneapolis, Minn) is an important surgical treatment option. We aimed to determine prevalence and clinical effect of structural and functional abnormalities after full-root Freestyle implantation.

METHODS

Our cross-sectional 2-center study combined with clinical follow-up included 253 patients with full-root Freestyle bioprostheses implanted from 1999 to 2017. Patients underwent transthoracic echocardiography (TTE) and contrast-enhanced, electrocardiogram-gated 4-dimensional cardiac computed tomography (4DCT) at median age 70 (interquartile range, 62-75) years. After 4DCT, clinical follow-up continued throughout 2018. Median follow-up was 3.3 years before 4DCT and 1.4 years after.

RESULTS

We identified abnormalities in 46% of patients, including pseudoaneurysms (n = 32; 13%), moderate or severe coronary ostial stenosis (n = 54; 21%), and moderate-severe leaflet thickening or reduced leaflet motion (n = 51; 20%). TTE only identified 1 patient with pseudoaneurysm. After 4DCT, the unadjusted hazard ratio for surgical reintervention among patients with abnormal 4DCT was 4.2 (95% confidence interval, 1.2-15.3), in all, 10% required a reintervention. 4DCT abnormalities were associated with a statistically nonsignificant increased risk of death, stroke, or myocardial infarction (hazard ratio obtained using Cox proportional hazards regression analysis, 2.4; 95% confidence interval, 0.7-7.6). In all, 4.0% died, 3.6% had a myocardial infarction, and 2.0% had a stroke.

CONCLUSIONS

Structural and functional abnormalities of the aortic root are frequent after Freestyle implantation and TTE appears to be insufficient for follow-up. Abnormalities might be associated with increased risk of reintervention and potentially adverse clinical outcomes. Longer follow-up and larger study populations are needed to further clarify the clinical implications of abnormalities identified with 4DCT.

A case of freestyle valve reoperation 23 years after the first operation

We present a case of redo stentless valve operation in a 73-year-old man who underwent aortic valve replacement via the subcoronary approach with a freestyle aortic bioprosthesis 23 years ago at our institution. He was referred for surgery because an echocardiogram showed severe aortic regurgitation due to structural valve deterioration, and aortic valve replacement was planned. Severe circumferential calcification and adhesion were noted during the surgery between the freestyle and native roots. Redo-aortic valve replacement was successful despite the technical difficulty. In stentless valve reoperations following aortic valve replacement via the subcoronary method, the planning of valve-in-valve transcatheter aortic valve implantation and sutureless valve implantation may be a practical and safe strategy.

Investigation of failure modes of explanted porcine valves in the mitral position

Background

Porcine valves are used for mitral valve replacement, but the limited long-term durability has restricted the application in younger patients. Degenerated porcine mitral valves were explanted to analyze the failure modes and damage characteristics.

Methods

Twelve porcine valves were explanted via secondary mitral valve replacement surgery. Microcomputed tomography scanning, morphological and pathological examinations were performed to classify the cusp tears, calcification, and pannus formation. The causes of valve deterioration were subsequently analyzed.

Results

The mean age at first implantation was 45.42±19.58 years (range, 11–64 years). The mean duration of implantation was 9.39±4.14 years (range, 4.25–18.75 years). The indications for first surgery were rheumatic heart disease in 8 patients (66.67%), infective endocarditis in 2 patients (16.67%), degenerative valvular disease in one patient (8.33%), and congenital heart disease in one patient (8.33%). Type I cusp tears and commissural dehiscence that occurred near the stent post position were found in 6 (50%) and 5 (41.67%) valves, respectively. Calcification was detected in 6 (50%) cases, and pannus was found in most valves (91.67%).

Conclusions

Leaflet damage occurred near the stent posts area was the main failure mode of porcine mitral valves in this study. Patients who undergo the first surgery at younger age, the higher prevalence rate of rheumatic heart disease, the structure of bioprosthetic porcine valve, and left ventricular stresses could be considered as the main factors causing valve deterioration.

Right ventricular outflow tract reconstruction with Medtronic Freestyle valve in the Ross procedure: A systematic review with meta-analysis

Cryopreserved pulmonary homografts (PH) are the current gold standard for right ventricular outflow tract (RVOT) reconstruction in the Ross procedure. Unfortunately, their use is limited by a relatively scarce availability and high cost. Porcine stentless xenografts (SX) such as the Medtronic Freestyle SX are increasingly being used, although it is unclear whether the hemodynamic performance and the long-term durability are satisfactory. The present systematic review followed the Preferred Reporting Items for Systematic reviews and Meta-Analysis statement. The pooled treatment effects were calculated using a weighted DerSimonian-Laird random-effects model. We also evaluated the effect of time after RVOT reconstruction on valve gradients using meta-regression. Six studies with a total of 156 patients met the inclusion criteria. The pooled estimates for the pooled follow-up of 37 months were: 1.3% operative mortality, 94.8% overall survival, 7.5% structural valve deterioration, 5.2% reintervention, 73.3% asymptomatic, and 1.5% moderate or severe pulmonary insufficiency. Peak valve gradients were significantly correlated with time after RVOT, increasing during follow-up. Three studies compared PH with SX, one concluded that the SX is an acceptable alternative for RVOT reconstruction, whereas two concluded that this valvular substitute had inferior performance. The Freestyle SX can be considered as an alternative to PH, although it might be associated with more reinterventions, higher peak valve pressure gradients, and pulmonary valve dysfunction.

Structural valve deterioration and mode of failure of stentless bioprosthetic valves

BACKGROUND

Aortic stentless bioprosthetic valve (SLBPV), either porcine or pericardial, minimizes transvalvular gradient and favors regression of left ventricular hypertrophy. The drawback consists of longer time for suturing. While structural valve deterioration (SVD) in stented porcine and pericardial BPVs has been extensively investigated, less information is available on SLBPVs.

MATERIAL AND METHODS

We studied 82 SLBPVs explants, either porcine (Toronto SPV, [St. Jude Medical, MN, USA], CryolifeO'Brien Model 300 and CryoLife-O'Brien [Cryolife International, GA, USA], BioCor PVS [St. Jude Medical, MN, USA] Prima and Prima Plus [Edwards Lifesciences Corp. One Edwards Way, CA, formerly Baxter Inc, CA, USA]) or pericardial ([Pericarbon Freedom and Freedom Solo [Sorin-Biomedica, S.p.A., Saluggia, Italy]).

RESULTS

By excluding cases with leak and endocarditis, we focused the investigation on 46 SLBPVs, which failed because of SVD. Gender was male in 29 (63%). Mean age of patients at time of implant was 59.8 years. Postoperative time of SVD was 115.0 months for porcine and 79.0 months for pericardial SLBPVs. Dysfunction requiring reoperation was mainly incompetence for porcine and stenosis for pericardial SLBPVs. Even pinpoint mineralization at the commissures resulted in sudden cusp tearing and incompetence. Cuspal atheromasia accounted for cusp tearing even in the absence of calcification. Mineralization showed progression with time in pericardial but not in porcine SLBPVs.

CONCLUSIONS

Tissue mineralization remains the nightmare also of SLBPVs, with the peculiar features of pinpoint calcific deposits at commissures, tearing and abrupt incompetence in porcine SLBPVs and of massive cuspal mineralization and stenosis in pericardial SLBPVs.

Postimplant biological aortic prosthesis degeneration: challenges in transcatheter valve implants

Surgical aortic valve replacement (SAVR) is highly effective and can be achieved with relatively low risk in patients with severe aortic stenosis. Bioprostheses have been used most frequently during the past 60 years. However, the function of biological valves usually declines after 10-15 years from implant when structural valve degeneration occurs often mandating a reoperation once valve dysfunction becomes haemodynamically significant. Known for many years by surgeons and cardiologists taking care of patients with SAVR, the issue of postimplant structural valve degeneration has been recently highlighted also in patients with transcatheter aortic valve implant (TAVI). There is growing concern that TAVI valves exhibit structural valve degeneration due to inherent challenges of the deployment mode. The impact on postimplant degeneration of TAVI valves compared to SAVR has still to be understood and defined. Based on the ongoing process of expanding TAVI indications, several potential shortcomings and caveats, learned during the last 60 years of SAVR experience, should be taken into consideration to refine this technique.

Pseudoaneurysm formation after medtronic freestyle porcine aortic bioprosthesis implantation: a word of caution

BACKGROUND

A growing literature describes aneurysmal deterioration after implantation of the stentless porcine aortic Medtronic Freestyle bioprosthesis (MFB; Medtronic Inc, Minneapolis, MN), with some suggesting inadequate tissue fixation with immune response as a cause. However, disjointed reports make the significance of these findings difficult to interpret. We address this concern by aggregating available data.

METHODS

We reviewed institutional data, the Food and Drug Administration's Manufacturer and User Facility Device Experience registry, and the medical literature for mention of aneurysm or pseudoaneurysm after MFB. Case details were aggregated, and the rate of aneurysmal deterioration was estimated. Immunohistopathologic examination of institutional explanted specimens was performed to elucidate a cause.

RESULTS

We found 42 cases of aneurysmal deterioration with adequate detail for analysis; all occurred with full root replacement and valve sizes ranging from 23 to 29 mm. The rate of aneurysmal deterioration considering all data sources was 1.1% (9 of 851; 95% confidence interval, 0.5% to 2.0%) vs 4.7% (4 of 86; 95% confidence interval, 1.3% to 11.5%) at our institution, where yearly surveillance imaging is performed. Rate of aneurysmal deterioration appeared constant until 5 years after the operation; however, events are reported out to 10 years. Consistent with previous reports, histopathology demonstrated an immune cell infiltrate in areas of MFB wall breakdown.

CONCLUSIONS

Aneurysmal deterioration is an increasingly described complication of MFB implantation as a full root, with an incidence as high as 4.7%. Given the observed immune reaction and lack of occurrence in smaller (19-mm and 21-mm) valve sizes, inadequate pressure fixation of larger valves is a potential etiology. Patients with MFB require annual surveillance imaging, and consideration of this complication should factor into preoperative decision making because treatment mandates redo root replacement, which may not be feasible in high-risk patients.

Bioprosthetic heart valves of the future

Glutaraldehyde-fixed bioprosthetic heart valves (GBHVs), derived from pigs or cows, undergo structural valve deterioration (SVD) over time, with calcification and eventual failure. It is generally accepted that SVD is due to chemical processes between glutaraldehyde and free calcium ions in the blood. Valve companies have made significant progress in decreasing SVD from calcification through various valve chemical treatments. However, there are still groups of patients (e.g., children and young adults) that have accelerated SVD of GBHV. Unfortunately, these patients are not ideal patients for valve replacement with mechanical heart valve prostheses as they are at high long-term risk from complications of the mandatory anticoagulation that is required. Thus, there is no "ideal" heart valve replacement for children and young adults. GBHVs represent a form of xenotransplantation, and there is increasing evidence that SVD seen in these valves is at least in part associated with xenograft rejection. We review the evidence that suggests that xenograft rejection of GBHVs is occurring, and that calcification of the valve may be related to this rejection. Furthermore, we review recent research into the transplantation of live porcine organs in non-human primates that may be applicable to GBHVs and consider the potential use of genetically modified pigs as sources of bioprosthetic heart valves.

Bioprosthetic Heart Valves: Impact of Implantation on Biomaterials

Prosthetic heart valves are commonly used in the treatment of valvular heart disease. Mechanical valves are more durable than the bioprosthetic valves; however, the need for long-term anticoagulant therapy renders them unsuitable for some patient groups. In this paper we discuss the different types and models of bioprosthesis, and in particular, pericardial bioprosthesis. We also discuss the preimplantation preparation processes, as well as their postimplantation changes and modes of failure.

Rupture of valsalva sinus after aortic root replacement with freestyle stentless bioprosthesis

We report a case of aortic wall rupture in a patient with a Medtronic Freestyle stentless bioprosthesis (Medtronic Inc, Minneapolis, MN) after full root implantation. A 68-year-old man who underwent aortic root replacement with a Freestyle bioprosthesis 12 years prior was found to have a large pseudoaneurysm originating from the ruptured noncoronary porcine aortic sinus. A reoperation for aortic root replacement was successfully performed. Despite excellent durability of porcine aortic root bioprostheses, several cases with a ruptured aortic wall have been reported. Degeneration of the elastic tissue and inflammatory reactions may be the main mechanism of this potentially catastrophic complication.

Porcine bioprosthetic heart valves: The next generation

There have been significant advances in organ xenotransplantation (cross-species transplantation), especially in the development of genetically engineered pigs, but clinical trials of solid organ transplants are still a time away. However, there is a form of pig-to-human xenotransplantation that has been taking place since the 1960s-bioprosthetic heart valve (BHV) replacement. Recently, there has been increasing evidence that, despite glutaraldehyde fixation of BHVs, there is a significant immune reaction to the valves, leading to calcification, rapid structural deterioration, and failure, particularly in young patients who have a more vigorous immune system and metabolism than the elderly. However, it is the young patients who would most benefit from such BHVs because these avoid the complications associated with the lifelong anticoagulation required with mechanical valves. In this review, we examine pathologic and immunohistochemical reports of failed BHVs that suggest that there is an immune response to these valves. Small animal studies that link the development of calcification and BHV failure to the immune response are reviewed. We draw parallels between the problems of glutaraldehyde-fixed tissue xenotransplantation and those currently being faced in live organ xenotransplantation. Finally, we discuss the advances being made in the production of genetically modified pigs and the evidence that these pigs may become a source of BHVs that can be used worldwide to treat valvular heart disease in children and young adults (for whom there is no ideal valve replacement in existence today). The design of a BHV that is resistant to the host's immune response would be a major step forward in cardiac surgery.

A rapid structural degeneration of a porcine mitral valve

A 73-year-old woman underwent both mitral and aortic valve replacements with porcine heart valve prostheses because of severe mitral regurgitation and severe aortic regurgitation. Ten months after surgery, maximal flow velocity of the aortic valve reached 4.6 m/sec and moderate mitral regurgitation was detected. Repeated mitral and aortic valve replacements with mechanical heart valves were performed. The excised mitral valve showed thinning of the 3 cusps, and 2 of them were perforated. There was pannus overgrowth on the flow surface of the porcine aortic valve. Histologic examination of the excised mitral valve revealed marked inflammatory changes with macrophages.

Unusual presentation of cryolife O'Brien(R) stentless aortic valve bioprosthesis dysfunction mimicking infective endocarditis

OBJECTIVES

We previously reported a possible but unusual prosthetic-valve infective endocarditis (PV-IE) occurring on a Cryolife O'Brien Stentless Porcine Xenograft (CLOB) (anatomic damages suggestive of IE but negative inflammatory and microbiological markers). We reviewed all cases of aortic PV-IE admitted in our institution and compared the clinical presentation, bacteriological and echocardiographic features according to the type of prosthesis.

METHODS

Sixty consecutive cases with possible or definite aortic PV-IE (23 CLOB, 26 mechanical valve and 11 stented bioprosthesis) were admitted between 2002 and 2008.

RESULTS

Patients with CLOB had more prosthetic dehiscence (P = 0.006) and severe regurgitation (P = 0.01) than those with mechanical or stented prosthetic valves. In contrast, they had less fever (P = 0.003), lower C-reactive protein (CRP) levels (P = 0.02) and more frequently negative blood cultures (P = 0.08). Differences were due to seven patients who presented with no fever, low CRP, negative blood culture, negative valve culture and PCR when performed, despite echocardiographic features suggestive of IE (abscess or valve dehiscence). All were first operated on since 2004 when the manufacturing process changed and required a second surgery. The French Authority of Health was informed leading to the withdrawal of the CLOB from the market in 2010.

CONCLUSIONS

One-third of patients with CLOB admitted for possible or definite PV-IE presented with anatomic damages suggestive of IE but with negative inflammatory and microbiological markers. The exact aetiology remains unclear, but the present data have led to the worldwide withdrawal of prosthesis in 2010. A close follow-up of patients implanted with CLOB should be advised, especially if it has been manufactured since 2004.

Truly stentless autologous pericardial aortic valve replacement: an alternative to standard aortic valve replacement

OBJECTIVE

The aim of this study was to determine the feasibility and durability of truly stentless aortic valve replacement using autologous pericardium sutured directly onto the aortic wall.

METHODS

Eleven patients (mean age, 55.9 years) requiring aortic valve replacement were recruited. A circular piece of pericardium about 8 cm in diameter was harvested and treated in 0.6% glutaraldehyde for 10 minutes. The aortic valve was excised and, with the use of specially designed instruments (CardioMend LLC, Santa Barbara, Calif), the sinotubular junction was sized and the pericardium was tailored to the required size and shape and then sutured directly onto the aortic wall. The reconstructed valve was assessed directly and by echocardiography at the end of the operation; it was assessed by echocardiography and cardiac magnetic resonance imaging at 6 months and yearly. Computed tomographic scan of the aortic valve to assess for valve calcification was performed at last follow-up.

RESULTS

Hospital mortality was 0%. Mean follow-up was 6.5 years (range, 5.3-7.5 years). Freedom from structural valve deterioration, thromboembolism, endocarditis and reoperation was 100%, 100%, 72.7%, and 63.6%, respectively. There were 4 reoperations at 4, 13, 15, and 46 months, 3 of them owing to endocarditis and 1 owing to technical failure noted at the time of surgery. The remaining 7 patients are alive and well with a mean New York Heart Association class of 1.3 and normally functioning aortic valves with no calcification.

CONCLUSIONS

Truly stentless aortic valve replacement using autologous pericardium sutured directly onto the aortic wall is safe and feasible and has excellent durability up to 7.5 years with no calcification.

Early obstruction of decellularized xenogenic valves in pediatric patients: involvement of inflammatory and fibroproliferative processes

BACKGROUND

Decellularization of pulmonary valve substitutes is believed to eliminate immunogenicity and improve conduit durability. This study focused on a detailed histopathological and immunohistochemical analysis of explanted Matrix P plus valves, following their early obstruction in pediatric patients.

METHODS

Occurrence of fibrosis, scar formation, neovascularization, and inflammatory infiltrates were determined in longitudinal sections of four valve specimens explanted after 12-15 months. Valves were immunohistochemically analyzed for presence of different subtypes of inflammatory cells. The expression of smooth muscle actin and connective tissue growth factor was determined.

RESULTS

We observed a foreign body-type reaction accompanied by severe fibrosis and massive neointima formation around decellularized porcine valve wall, whereas the equine pericardial patch remained separated from porcine layer and acellular. Re-cellularization of decellularized matrix was low, and neovascularization was observed only in the neointima and scar tissue. Inflammatory infiltrates, composed mainly of T cells, B cells, and plasma cells, as well as the presence of dendritic cells, macrophages, and mast cells were detected in the tissue surrounding the porcine matrix. In the fibrous tissue, overexpression of connective tissue growth factor was observed. The leaflets remained functional, with normal endothelialization and no degenerative changes. Control pre-implant samples of Matrix P plus valve revealed incomplete decellularization of porcine matrix, which may have contributed to increased immunogenicity of these conduits.

CONCLUSIONS

Early obstruction of decellularized Matrix P plus valve is associated with massive inflammatory reaction and exaggerated fibrotic scaring around porcine conduit wall. Detailed studies will be necessary to determine factors that contribute to remnant immunogenicity of decellularized grafts.

Postimplantation morphologic changes of glutaraldehyde-fixed porcine aortic roots and risk of aneurysm and rupture

OBJECTIVE

Rupture of glutaraldehyde-fixed porcine aortic roots has been reported, but the mechanism and incidence of this complication is unknown. This study evaluates the clinical outcomes and the risk of dilation and rupture of porcine aortic roots after implantation.

METHODS

Commercially available porcine aortic roots were used for aortic root replacement in 308 patients (Freestyle bioprosthesis [Medtronic, Minneapolis, Minn] in 251 patients and Toronto Root [St Jude Medical, St Paul, Minn] in 57 patients) whose mean age was 62 +/- 13 years. The main indication for aortic root replacement was dilation of the native aortic root. Clinical follow-up was complete at a mean of 5.3 +/- 2.5 years. Valve function and aortic root diameter were assessed by means of echocardiography.

RESULTS

There were 10 (3.2%) operative and 39 (12.6%) late deaths. At 8 years, patients' survival was 79.0% +/- 3.1%, freedom from reoperation was 95.3% +/- 1.7%, and freedom from severe aortic insufficiency was 93.8% +/- 2.7%. The diameter of the aortic sinuses increased from 31.9 +/- 4.3 to 34.1 +/- 4.8 mm (P < .0001), and it exceeded 40 mm in 10% of the patients. Linear regression analysis revealed that the duration of follow-up (P < .0001) and the size of the valve implanted (P < .0001) were associated with risk of sinus dilation. There was only 1 early rupture of the noncoronary aortic sinus and 2 late aneurysms that required repeat operations. Histologic examination of explanted aneurysmal porcine roots revealed marked changes in the xenograft arterial wall, with abundant mononuclear cells suggestive of immunologic reaction.

CONCLUSIONS

Mild dilation of porcine aortic roots after aortic root replacement is common, but aneurysm formation and rupture are rare during the first decade of follow-up. Annual surveillance with echocardiography is recommended.

Long-term morphological changes in a cryopreserved pulmonary valve homograft

Pulmonary homografts (PHs) are frequently used to replace the native pulmonary valve in the Ross procedure, and in the reconstruction of the right ventricular outflow tract. The case of a 25-year-old man whose PH was replaced 12 years after undergoing the Ross procedure is reported. The clinical cause of the PH failure was stenosis. Morphological studies showed cusp tissue degeneration with tears and calcification, as well as pannus growth on the flow and nonflow surfaces of the cusps and the pulmonary artery graft. The durability of this PH was likely due to a combination of low pressure on the right side of the heart and the patient's age at surgery.