Morphological findings in explanted Toronto stentless porcine valves

Recent Advances in the Modification and Improvement of Bioprosthetic Heart Valves

Valvular heart disease (VHD) has become a burden and a growing public health problem in humans, causing significant morbidity and mortality worldwide. An increasing number of patients with severe VHD need to undergo heart valve replacement surgery, and artificial heart valves are in high demand. However, allogeneic valves from donors are lacking and cannot meet clinical practice needs. A mechanical heart valve can activate the coagulation pathway after contact with blood after implantation in the cardiovascular system, leading to thrombosis. Therefore, bioprosthetic heart valves (BHVs) are still a promising way to solve this problem. However, there are still challenges in the use of BHVs. For example, their longevity is still unsatisfactory due to the defects, such as thrombosis, structural valve degeneration, calcification, insufficient re-endothelialization, and the inflammatory response. Therefore, strategies and methods are needed to effectively improve the biocompatibility and longevity of BHVs. This review describes the recent research advances in BHVs and strategies to improve their biocompatibility and longevity.

Guidelines for the Evaluation of Prosthetic Valve Function With Cardiovascular Imaging: A Report From the American Society of Echocardiography Developed in Collaboration With the Society for Cardiovascular Magnetic Resonance and the Society of Cardiovascular Computed Tomography

In patients with significant cardiac valvular disease, intervention with either valve repair or valve replacement may be inevitable. Although valve repair is frequently performed, especially for mitral and tricuspid regurgitation, valve replacement remains common, particularly in adults. Diagnostic methods are often needed to assess the function of the prosthesis. Echocardiography is the first-line method for noninvasive evaluation of prosthetic valve function. The transthoracic approach is complemented with two-dimensional and three-dimensional transesophageal echocardiography for further refinement of valve morphology and function when needed. More recently, advances in computed tomography and cardiac magnetic resonance have enhanced their roles in evaluating valvular heart disease. This document offers a review of the echocardiographic techniques used and provides recommendations and general guidelines for evaluation of prosthetic valve function on the basis of the scientific literature and consensus of a panel of experts. This guideline discusses the role of advanced imaging with transesophageal echocardiography, cardiac computed tomography, and cardiac magnetic resonance in evaluating prosthetic valve structure, function, and regurgitation. It replaces the 2009 American Society of Echocardiography guideline on prosthetic valves and complements the 2019 guideline on the evaluation of valvular regurgitation after percutaneous valve repair or replacement.

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.

Antigen removal process preserves function of small diameter venous valved conduits, whereas SDS-decellularization results in significant valvular insufficiency

Chronic venous disease (CVD) is the most common reported chronic condition in the United States, affecting more than 25 million Americans. Regardless of its high occurrence, current therapeutic options are far from ideal due to their palliative nature. For best treatment outcomes, challenging cases of chronic venous insufficiency (CVI) are treated by repair or replacement of venous valves. Regrettably, the success of venous valve transplant is dependent on the availability of autologous venous valves and hindered by the possibility of donor site complications and increased patient morbidity. Therefore, the use of alternative tissue sources to provide off-the-shelf venous valve replacements has potential to be extremely beneficial to the field of CVI. This manuscript demonstrates the capability of producing off-the-shelf fully functional venous valved extracellular matrix (ECM) scaffold conduits from bovine saphenous vein (SV), using an antigen removal (AR) method. AR ECM scaffolds maintained native SV structure-function relationships and associated venous valves function. Conversely, SDS decellularization caused significant changes to the collagen and elastin macromolecular structures, resulting in collagen fibril merging, elimination of fibril crimp, amalgaming collagen fibers and fragmentation of the inner elastic lamina. ECM changes induced by SDS decellularization resulted in significant venous valve dysfunction. Venous valved conduits generated using the AR approach have potential to serve as off-the-shelf venous valve replacements for CVI. STATEMENT OF SIGNIFICANCE: Retention of the structure and composition of extracellular matrix (ECM) proteins within xenogeneic scaffolds for tissue engineering is of crucial importance, due to the undeniable effect ECM proteins can impose on repopulating cells and function of the resultant biomaterial. This manuscript demonstrates that alteration or elimination of ECM proteins via commonly utilized decellularization approach results in complete disruption of venous valve function. Conversely, retention of the delicate ECM structure and composition of native venous tissue, using an antigen removal tissue processing method, results in preservation of native venous valve function.

Small Diameter Xenogeneic Extracellular Matrix Scaffolds for Vascular Applications

Currently, despite the success of percutaneous coronary intervention (PCI), coronary artery bypass graft (CABG) remains among the most commonly performed cardiac surgical procedures in the United States. Unfortunately, the use of autologous grafts in CABG presents a major clinical challenge as complications due to autologous vessel harvest and limited vessel availability pose a significant setback in the success rate of CABG surgeries. Acellular extracellular matrix (ECM) scaffolds derived from xenogeneic vascular tissues have the potential to overcome these challenges, as they offer unlimited availability and sufficient length to serve as "off-the-shelf" CABGs. Unfortunately, regardless of numerous efforts to produce a fully functional small diameter xenogeneic ECM scaffold, the combination of factors required to overcome all failure mechanisms in a single graft remains elusive. This article covers the major failure mechanisms of current xenogeneic small diameter vessel ECM scaffolds, and reviews the recent advances in the field to overcome these failure mechanisms and ultimately develop a small diameter ECM xenogeneic scaffold for CABG. Impact Statement Currently, the use of autologous vessel in coronary artery bypass graft (CABG) is common practice. However, the use of autologous tissue poses significant complications due to tissue harvest and limited availability. Developing an alternative vessel for use in CABG can potentially increase the success rate of CABG surgery by eliminating complications related to the use of autologous vessel. However, this development has been hindered by an array of failure mechanisms that currently have not been overcome. This article describes the currently identified failure mechanisms of small diameter vascular xenogeneic extracellular matrix scaffolds and reviews current research targeted to overcoming these failure mechanisms toward ensuring long-term graft patency.

Multimodality Imaging of Complications of Cardiac Valve Surgeries

Replacement with a prosthetic heart valve (PHV) remains the definitive surgical procedure for management of severe cardiac valve disease. PHV dysfunction is uncommon but can be a life-threatening condition. The broad hemodynamic and pathophysiologic manifestations of PHV dysfunction are stenosis, regurgitation, and a stuck leaflet. Specific structural abnormalities that cause PHV dysfunction include prosthetic valve-patient mismatch, structural failure, valve calcification, dehiscence, paravalvular leak, infective endocarditis, abscess, pseudoaneurysm, abnormal connections, thrombus, hypoattenuating leaflet thickening, and pannus. Multiple imaging modalities are available for evaluating a PHV and its dysfunction. Transthoracic echocardiography is often the first-line imaging modality, with additional modalities such as transesophageal echocardiography, CT, MRI, cine fluoroscopy, and nuclear medicine used for further characterization and establishing a specific cause. The authors review PHVs and the role of imaging modalities in evaluation of PHV dysfunction and illustrate the imaging appearances of different complications. Online supplemental material is available for this article. ^©RSNA, 2019.

Complementary role of cardiac CT in the assessment of aortic valve replacement dysfunction

Aortic valve replacement is the second most common cardiothoracic procedure in the UK. With an ageing population, there are an increasing number of patients with prosthetic valves that require follow-up. Imaging of prosthetic valves is challenging with conventional echocardiographic techniques making early detection of valve dysfunction or complications difficult. CT has recently emerged as a complementary approach offering excellent spatial resolution and the ability to identify a range of aortic valve replacement complications including structural valve dysfunction, thrombus development, pannus formation and prosthetic valve infective endocarditis. This review discusses each and how CT might be incorporated into a multimodal cardiovascular imaging pathway for the assessment of aortic valve replacements and in guiding clinical management.

Heart valve health, disease, replacement, and repair: a 25-year cardiovascular pathology perspective

The past several decades have witnessed major advances in the understanding of the structure, function, and biology of native valves and the pathobiology and clinical management of valvular heart disease. These improvements have enabled earlier and more precise diagnosis, assessment of the proper timing of surgical and interventional procedures, improved prosthetic and biologic valve replacements and repairs, recognition of postoperative complications and their management, and the introduction of minimally invasive approaches that have enabled definitive and durable treatment for patients who were previously considered inoperable. This review summarizes the current state of our understanding of the mechanisms of heart valve health and disease arrived at through innovative research on the cell and molecular biology of valves, clinical and pathological features of the most frequent intrinsic structural diseases that affect the valves, and the status and pathological considerations in the technological advances in valvular surgery and interventions. The contributions of many cardiovascular pathologists and other scientists, engineers, and clinicians are emphasized, and potentially fruitful areas for research are highlighted.

Tissue engineering of autologous heart valves: a focused update

The prevalence of valvular heart disease is expected to increase in the coming decades, with an associated rise in valve-related surgeries. Current options for valve prostheses remain limited, essentially confined to mechanical or biological valves. Neither selection provides an optimal balance between structural integrity and associated morbidity. Mechanical valves offer exceptional durability coupled with a considerable risk of thrombogenesis. Conversely, a biological prosthesis affords freedom from anticoagulation, but with a truncated valve lifespan. Tissue-engineered heart valves have been touted as a solution to this dilemma, by offering an immunopriviledged prosthesis combined with resistance from degeneration and the potential to grow. Although the reality of commercially available tissue-engineered heart valves remains distant, this article will highlight the cellular and clinical advancements in recent years.

Failing stentless aortic valves: redo aortic root replacement or valve in a valve?

OBJECTIVES

Reoperation for failing stentless aortic valve replacement is a technically demanding procedure that has traditionally been tackled in one of two ways: either root replacement or the more conservative option of implanting a stented valve within the valve. We sought to determine the relative operative risks, follow-up status and medium to long-term survival of these two methods.

METHODS

We conducted a retrospective review of a single surgeon's experience of the two techniques over a 10-year period from 2000 to 2010. Excluding cases of active endocarditis, 110 patients were identified, of which 65 underwent 'valve-in-valve' procedures ('Group A') and 45 had redo root replacement ('Group B'). The most common bioprostheses reoperated were homografts (roots or subcoronary implants) and Toronto Stentless Porcine Valves. Aortic valve replacement alone was performed in 68% in Group A and 64% in Group B, with males comprising 75% of Group A and 82% of Group B. Average ages were 61.5 ± 14.2 years and 61.9 ± 12.1 years, respectively.

RESULTS

Operative and cardiopulmonary bypass durations were significantly greater for redo root procedures and correspondingly, postoperative complications were more common. Thirty-day mortality after valve-in-valve replacement was 3%, and after redo root replacement it was 11%. Despite significantly higher transvalvular gradients in Group B, the symptomatic status was equally good at 2 months, 1 year and last follow-up. At an average interval of 5.1 ± 2.7 years for Group A, survival was 83% vs 76% at 7.3 ± 2.9 years for Group B. There have been two reinterventions in Group A and 3 in Group B. Only one valve-in-valve patient has developed a paraprosthetic leak.

CONCLUSIONS

This retrospective review has confirmed our hypothesis that where both root diameter permits and satisfactory debridement can be performed, valve-in-valve replacement is the more conservative surgical strategy for stentless aortic valve replacement revision. Although transvalvular gradients on echocardiography are significantly higher with the introduction of a stented prosthesis, medium-term outcomes in terms of symptomatic status, late complications and reintervention rate were non-inferior. We await the medium-term results of transcatheter aortic valve implantation for the same indication with interest.

Early stenosis of stentless aortic valve prosthesis: a word of caution

Early stenosis of stentless bioprosthetic valves is rarely reported. In this report, we discuss a 75-year-old woman who presented with signs of congestive heart failure 5 months after a stentless aortic valve replacement, complicated by postoperative heparin-induced thrombocytopenia. Intraoperative findings were highly unusual, consisting of a fibrous band in the subvalvular apparatus linking the interventricular septum to the free wall of the left ventricle, resulting in significant left ventricular outflow tract obstruction. The possible causes of the fibrous band are discussed.

Aortic valve translocation for treatment of a deteriorated stentless valve

A 54-year-old woman was admitted to our hospital with recurrent chest pain for 1 month. She had a history of aortic root replacement with a stentless valve following aortic valve replacements done twice 12 years ago, and coronary artery bypass grafting 6 years ago. The stentless valve was implanted with the full-root technique. After admission, she was diagnosed with a saphenous vein graft aneurysm in the proximal anastomotic site and severe aortic regurgitation due to stentless valve deterioration. These lesions were successfully treated using aortic valve translocation. The advantage of this procedure is that it avoids dissection and removal of the stentless valve implanted using the full-root technique. Aortic valve translocation can be one of useful alternatives for stentless valve reoperation.

Pathological healing response of explanted MitraClip devices

BACKGROUND

The safety and effectiveness of the MitraClip device (Abbott Vascular, Menlo Park, CA) is being evaluated in the Endovascular Valve Edge-to-Edge Repair Study (EVEREST) clinical studies. The healing response after device implantation has not previously been characterized in humans.

METHODS AND RESULTS

A total of 67 explanted devices (implantation duration, 1 to 1878 days) from 50 patients were submitted for histological evaluation. Explants were analyzed in 4 implantation intervals: acute (≤30 days; n=7), subacute (31 to 90 days; n=23), chronic (91 to 300 days; n=18), and long term (>300 days; n=19). The acute healing response consisted of platelet/fibrin deposition. The subacute response exhibited granulation tissue with early fibrous encapsulation (pannus). The chronic response was characterized by various degrees of tissue bridging between the device arms. The long-term healing response demonstrated collagen-rich matrix (by type I collagen), incorporating the device components with complete encapsulation by organized, fibrous growth. In long-term devices with minimal surgical disruption, a fibrous tissue bridge (mean area, 7.39±4.3 mm(2)) was observed over and between the device arms, resulting in atrial tissue continuity between the 2 valve leaflets. Devices demonstrated no evidence of endocarditis, mechanical wear, component fracture, or corrosion up to the time of explantation (median, 119 days; first and third quartiles, 42 and 365 days).

CONCLUSIONS

In all patients, device mechanical integrity was maintained up to the time of explantation. Four phases of physiological healing were observed: platelet and fibrin deposition, inflammation, granulation tissue, and finally, fibrous encapsulation. Long-term device fibrous encapsulation with extension over adjacent mitral leaflets and tissue bridge formation adds structural stability. Clinical Trial Registration- URL: http://clinicaltrials.gov/show/NCT00209274. Unique identifiers: NCT00209339 and NCT00209274.

Torn cusp in a freestyle stentless bioprosthesis 5 years after implantation: report of a case

The Freestyle stentless bioprosthesis (Freestyle valve) is widely used throughout the world because of its durability and benefits for hemodynamic function. However, we encountered a patient who required reoperation for a cuspal tear 5 years after the implantation of a Freestyle valve. The histological findings suggested that tissue degeneration with pannus formation might play a critical role in cuspal tears.

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

BACKGROUND

The Medtronic Freestyle valve is fixed in glutaraldehyde at zero pressure on the cusps and treated with alpha-amino oleic acid. This valve reportedly has excellent clinical and hemodynamic results, but little has been reported about its long-term pathology.

METHODS AND RESULTS

Nine Freestyle valves explanted between 2003 and 2005 were reviewed to assess the reasons for bioprosthesis failure (six implanted at our institution). All valves were examined in detail, using histochemistry and immunohistochemistry to identify the cellular response. One Freestyle valve, explanted for mitral valve endocarditis on the fifth postoperative day, was excluded from analysis. Average implant duration was 52.8+/-35.5 months. Four valves were explanted for infective endocarditis, three for aortic insufficiency, two for aortic stenosis with cusp calcification seen in five valves, pannus and thrombus in all valves and a chronic inflammatory reaction involving the xenograft arterial wall seen in eight of nine valves. This was associated with significant damage to the porcine aortic wall in seven cases, and cusp myocardial shelf damage in six cases.

CONCLUSIONS

In this series of valves, we found (1) infective endocarditis; (2) pannus, thrombus, and calcification; and (3) unusual and significant inflammatory reaction and aortic tissue damage, which could by itself lead to aortic incompetence.

Stentless Aortic Valve Reoperations: A Surgical Challenge

BACKGROUND

Stentless aortic valve reoperations may become more common as these bioprostheses reach the limits of their durability. Relatively few studies have examined stentless valve reoperation, and we therefore reviewed our results for these procedures.

METHODS

All patients with stentless valves undergoing redo aortic valve replacement (AVR) at our institution were examined (n = 57). Ten patients had a prior Freestyle valve (Medtronic, Minneapolis, MN), and 47 patients had a Toronto stentless porcine valve (SPV; St. Jude Medical St Paul, MN).

RESULTS

Redo AVR was performed 8.4 +/- 3.7 years (range, 0.1 to 16.5 years) after stentless valve implantation. Reoperations were elective in 27 patients (49%), and 30 (51%) underwent urgent or emergency procedures. The indication for redo AVR was structural valve dysfunction in 48 patients (84%), acute endocarditis in 7 (12%), and other in 2 (4%). Aortic insufficiency was present in 47 patients (82%). A total of 36 aortic root replacement operations (63% of patients) were required, of which 19 were secondary to severe adhesions between the stentless valve and the native aortic root. Operative mortality was 11% (n = 6) for the entire group. Mortality was higher in patients undergoing redo AVR less than 1 year after stentless valve implantation versus more than 1 year (67% versus 7%, p = 0.03). Long-term survival at 5 years postoperatively was 79% +/- 7% in all patients, and 81% of survivors were in New York Heart Association class I or II.

CONCLUSIONS

Reoperation after stentless AVR is a challenging procedure that frequently requires aortic root replacement. Stentless valve reoperation is associated with an increased risk of death, particularly in patients operated on within 1 year of implantation.

Early changes in bioprosthetic heart valves following ventricular assist device implantation

Heart valve bioprostheses can undergo early post-implantation changes, including pannus and thrombus, which may be hastened by the presence of a left ventricular assist device (LVAD). We report the case of a 21 year-old male who was diagnosed with dilated cardiomyopathy and severe aortic insufficiency, and had his aortic valve replaced with a #25 BioPhysio valve (currently in clinical trials--Edwards Life Sciences, Irvine, CA, USA). His symptoms of congestive heart failure continued to worsen, and he received a Novacor LVAD (WorldHeart, Oakland, CA, USA), and subsequently, an orthotopic heart transplantation. The relevant pathologies of the heart, BioPhysio valve (in place for 4.5 months), and Novacor device are presented.

Pathology of infectious and inflammatory diseases in prosthetic heart valves

Prosthetic heart valves, both mechanical and biological (xenograft valves, stented or unstented), show an inflammatory reaction (infective endocarditis), associated predominantly with bacterial/fungal infection. Somewhat surprisingly, no immune-mediated reaction has been reported thus far. This may, among other reasons, be related to the fact that the tissues are "fixed" with aldehydes and are virtually isolated from host circulation, separated by synthetic material (the valve stent and the fabric covering it). Stentless valves (especially these without fabric covering them), however, have no such "isolation" from the host circulation. While the Toronto-Stentless Porcine Valve has a covering of fabric, the Medtronic Freestyle valve has no such covering. It is perhaps not so surprising therefore that at the intermediate time point of 5 to 6 years, some valves are beginning to show such an immune reaction.