Mechanical heart valves: 50 years of evolution

Revisiting echocardiographic features of prosthetic heart valves: the necessity of correct differentiation of mono-leaflet vs. bileaflet mechanical heart valves in a case report

BACKGROUND

Mechanical heart valve replacement is a standard treatment for severe valvular disorders. The use of mono-leaflet valves has decreased recently. Recognizing the echocardiographic features of mono-leaflet and bileaflet valves is crucial for accurate complication diagnosis and proper management.

CASE PRESENTATION

A 65-year-old female with mono-leaflet mitral and bileaflet tricuspid valves underwent an echocardiographic assessment. This simple educational case provides a unique opportunity to compare the echocardiographic features of these valves within a single patient.

CONCLUSION

There is a crucial need for clinicians, particularly those in training, to differentiate between mono-leaflet and bileaflet mechanical heart valves adeptly. With mono-leaflet valves decreasing in prevalence, proficiency in recognizing the echocardiographic nuances of each type is imperative. Failure to do so may result in misdiagnoses and inappropriate management. This underscores the significance of continuous education and vigilance in echocardiographic assessments to ensure optimal patient care.

Structural valve failure of TTK Chitra heart valve prosthesis

Mechanical prosthetic valve dysfunction can be structural or non-structural. Structural valve dysfunction includes disc dislodgement, disc fracture, and strut fracture. These events in an implanted valve are rare but could pose a risk to life. TTK Chitra heart valve prosthesis (CHVP), an Indian-made single tilting disc valve, has been implanted since 1990 as reported by Vayalappil and Bhuvaneswar (2005). There is limited literature on the structural valve dysfunction of CHVP. We hereby submit images of the dysfunctional valve from our patient, a case of acute severe mitral paravalvular regurgitation 16 years after implantation of CHVP.

Emerging transcatheter heart valve technologies for severe aortic stenosis

INTRODUCTION

Transcatheter aortic valve implantation (TAVI) is the standard of care for selected patients with severe aortic stenosis, irrespective of the surgical risk. Over the last two decades of TAVI practice, multiple limitations were identified. In addition, the extension of TAVI into a wider patient spectrum created new challenges.

AREAS COVERED

This review provides an overview of emerging transcatheter heart valves (THVs) beyond the approved contemporary THVs for the treatment of aortic stenosis.

EXPERT OPINION

The incidence of degenerative aortic stenosis is expected to increase with more aging of the population. Therefore, TAVI needs to meet this increase in the number of patients indicated for aortic valve replacement alongside a wide and complex anatomical variability. An increasing number of Aortic THVs are available in the market. This includes upgraded iterations of contemporary devices and innovative devices developed by emerging manufacturers. The new devices aim for the reduction or elimination of undesirable outcomes like paravalvular leakage and conduction disturbances requiring permanent pacemaker implantation. Alternatively, emerging THVs should provide feasibility regarding yet unproven TAVI indications like Bicuspid aortic valve, aortic regurgitation, or very large anatomy. Furthermore, some of the emerging THVs are designed to tackle the long-term durability issue of biological valves.

Scientific Evolution of Artificial Heart Valves: A Narrative Review

Cardiovascular disorders have always been the top contributors to the number of mortality occurring worldwide. But the last few decades have seen a drop in those numbers as the lives of millions of people have been saved due to ground-breaking advances in both therapeutic and surgical treatment modalities. Achieving this level of scientific glory in cardiology was a challenging feat. The credit goes to the scientists and physicians of the previous century who, despite their time's technological limitations, made discoveries and laid a solid foundation for modern medicine. Valvular complications are a major part of the global burden of cardiac diseases. The ongoing development of heart valve replacements remains a fascinating subject, as it continues to progress. Valve replacements comprise either mechanical heart valves or bioprosthetic heart valves. Both types of valves have their merits and demerits; their usage depends mostly on individual patient requirements. This article aims to review the evolution of the implantation of heart valves, and it is the objective of this article to give credit to scientists and physicians for their contributions. The article highlights the research gaps in finding more durable materials and the scope of further research in creating a heart valve that can be universally used for better patient outcomes.

Pediatric pulmonary valve replacements: Clinical challenges and emerging technologies

Congenital heart diseases (CHDs) frequently impact the right ventricular outflow tract, resulting in a significant incidence of pulmonary valve replacement in the pediatric population. While contemporary pediatric pulmonary valve replacements (PPVRs) allow satisfactory patient survival, their biocompatibility and durability remain suboptimal and repeat operations are commonplace, especially for very young patients. This places enormous physical, financial, and psychological burdens on patients and their parents, highlighting an urgent clinical need for better PPVRs. An important reason for the clinical failure of PPVRs is biofouling, which instigates various adverse biological responses such as thrombosis and infection, promoting research into various antifouling chemistries that may find utility in PPVR materials. Another significant contributor is the inevitability of somatic growth in pediatric patients, causing structural discrepancies between the patient and PPVR, stimulating the development of various growth-accommodating heart valve prototypes. This review offers an interdisciplinary perspective on these challenges by exploring clinical experiences, physiological understandings, and bioengineering technologies that may contribute to device development. It thus aims to provide an insight into the design requirements of next-generation PPVRs to advance clinical outcomes and promote patient quality of life.

Transcatheter Aortic Valve Implantation in the Descending Aorta: History Revisited!

An elderly patient with significant aortic regurgitation presented with heart failure. Dilation of the aortic root precluded a transcatheter anatomic site valve implantation, and prohibitive operative risk ruled against surgical implantation. A bail-out transcatheter implantation of the aortic valve in the descending aorta was successfully carried out with satisfactory outcomes.

Treatment of valvular heart disease in young patients-"early evidence" versus "latest fashion"

Is the performance of locally manufactured mechanical valve prostheses relevant for modern cardiac surgery, in which mechanical valve replacement has become a rarity? This question comes to mind reading the article in this issue of the Journal demonstrating equal outcomes of the TTK Chitra tilting disk mechanical heart valve prostheses in comparison to the SJM bi-leaflet blockbuster. The evidence documenting efficacy of mechanical valve replacement stems from the early ages of cardiac surgery, but often demonstrates superior outcomes in terms of survival and hemodynamics. Yet, the latest fashion in the Western world consists biological choices in combination with new transcatheter techniques (valve in valve options) or the Ozaki or Ross procedures. As long-term results are often missing and documented advantages for mechanical valves stems from early evidence, the local emphasis of mechanical valve replacement may possibly result in superior individual prognoses compared to following the Western world's latest fashions. Individual patient information and decision making moves into focus.

Natural Polymers in Heart Valve Tissue Engineering: Strategies, Advances and Challenges

In the history of biomedicine and biomedical devices, heart valve manufacturing techniques have undergone a spectacular evolution. However, important limitations in the development and use of these devices are known and heart valve tissue engineering has proven to be the solution to the problems faced by mechanical and prosthetic valves. The new generation of heart valves developed by tissue engineering has the ability to repair, reshape and regenerate cardiac tissue. Achieving a sustainable and functional tissue-engineered heart valve (TEHV) requires deep understanding of the complex interactions that occur among valve cells, the extracellular matrix (ECM) and the mechanical environment. Starting from this idea, the review presents a comprehensive overview related not only to the structural components of the heart valve, such as cells sources, potential materials and scaffolds fabrication, but also to the advances in the development of heart valve replacements. The focus of the review is on the recent achievements concerning the utilization of natural polymers (polysaccharides and proteins) in TEHV; thus, their extensive presentation is provided. In addition, the technological progresses in heart valve tissue engineering (HVTE) are shown, with several inherent challenges and limitations. The available strategies to design, validate and remodel heart valves are discussed in depth by a comparative analysis of in vitro, in vivo (pre-clinical models) and in situ (clinical translation) tissue engineering studies.

Simulation of Mechanical Heart Valve Dysfunction and the Non-Newtonian Blood Model Approach

The mechanical heart valve (MHV) is commonly used for the treatment of cardiovascular diseases. Nonphysiological hemodynamic in the MHV may cause hemolysis, platelet activation, and an increased risk of thromboembolism. Thromboembolism may cause severe complications and valve dysfunction. This paper thoroughly reviewed the simulation of physical quantities (velocity distribution, vortex formation, and shear stress) in healthy and dysfunctional MHV and reviewed the non-Newtonian blood flow characteristics in MHV. In the MHV numerical study, the dysfunction will affect the simulation results, increase the pressure gradient and shear stress, and change the blood flow patterns, increasing the risks of hemolysis and platelet activation. The blood flow passes downstream and has obvious recirculation and stagnation region with the increased dysfunction severity. Due to the complex structure of the MHV, the non-Newtonian shear-thinning viscosity blood characteristics become apparent in MHV simulations. The comparative study between Newtonian and non-Newtonian always shows the difference. The shear-thinning blood viscosity model is the basics to build the blood, also the blood exhibiting viscoelastic properties. More details are needed to establish a complete and more realistic simulation.

The Caged-Ball Prosthesis 60 Years Later: A Historical Review of a Cardiac Surgery Milestone

Sixty years ago, 2 cardiac operations dramatically influenced the survival of patients with valvular heart disease. The replacement of an aortic valve by Dwight Harken and of a mitral valve by Albert Starr with mechanical caged-ball valves, both in 1960, was a true milestone in the history of cardiac surgery and the beginning of a long journey toward prosthetic valve replacement full of expectations, hopes, and dreams fulfilled. Caged-ball prostheses underwent numerous modifications in design and materials to improve reliability and prevent specific mechanical and thrombogenic complications. Clinical and pathologic experience gained during the past 6 decades has enabled the development of safe, durable, and minimally thrombogenic mechanical prostheses.

Design Variation, Implantation, and Outcome of Transcatheter Mitral Valve Prosthesis: A Comprehensive Review

The transcatheter mitral valve prosthesis is ideally suited for patients with inoperable mitral etiology. The transcatheter mitral valve implantation (TMVI) procedure has closely followed the evolution of transcatheter aortic procedures. There are considerable design variations amongst the limited TMVI prostheses currently available, and the implantation profiles of the devices are notably different. This comprehensive review will provide an overview of the current clinically tried TMVI devices with a focused outcome analysis. In addition, we have discussed the various design characteristics of TMVI and its associated failure mode, implantation technology, delivery methods, first-in-man trials, and pivotal trial summary for the synthesis of recent evidence.

An unusual cause of acute mitral regurgitation in TTK Chitra heart valve prosthesis

Structural failure of mechanical heart valve was a known feature when it was evolving in the 1960s and 1970s. With the advent of pyrolytic carbon and a better design, it is a rare entity with present valves. We report a case of disc fracture leading to acute mitral regurgitation in TTK Chitra heart valve prosthesis (CHVP) (TTK Healthcare Limited, India) heart valve, 6 years after its implantation in mitral position.

Minimally Invasive and Robotic Mitral Valve Surgery: Methods and Outcomes in a 20-Year Review

In the mid- to late-1990s the cardiac surgery community began to apply limited incisions in mitral valve surgery. Ministernotomies and right-sided minithoracotomies were placed instead of the classic midline sternotomy. Adjunct technology such as videoscopy, advanced peripheral cannulation techniques, procedure specific long shafted surgical instruments, as well as surgical robots became available, and the procedures were refined in a stepwise fashion. In 2021, minimally invasive mitral valve repair is routine at many centers around the globe. We reviewed a total of 50 consecutive patient series published on the topic between 1999 and 2019. Three main versions of minimally invasive mitral valve surgery were applied in 20,539 patients. The surgical methods, their specific results, and the cumulative outcome of less invasive mitral valve surgery published over more than 20 years are reported and an integrated view on what less invasive mitral valve surgery can offer is presented.

Use of Sutureless and Rapid Deployment Prostheses in Challenging Reoperations

Sutureless and rapid-deployment bioprostheses have been introduced as alternatives to traditional prosthetic valves to reduce cardiopulmonary and aortic cross-clamp times during aortic valve replacement. These devices have also been employed in extremely demanding surgical settings, as underlined in the present review. Searches on the PubMed and Medline databases aimed to identify, from the English-language literature, the reported cases where both sutureless and rapid-deployment prostheses were employed in challenging surgical situations, usually complex reoperations sometimes even performed as bailout procedures. We have identified 25 patients for whom a sutureless or rapid-deployment prosthesis was used in complex redo procedures: 17 patients with a failing stentless bioprosthesis, 6 patients with a failing homograft, and 2 patients with the failure of a valve-sparing procedure. All patients survived reoperation and were reported to be alive 3 months to 4 years postoperatively. Sutureless and rapid-deployment bioprostheses have proved effective in replacing degenerated stentless bioprostheses and homografts in challenging redo procedures. In these settings, they should be considered as a valid alternative not only to traditional prostheses but also in selected cases to transcatheter valve-in-valve solutions.

Current Therapeutic Options in Aortic Stenosis

Aortic stenosis is the most common valvular disease requiring valve replacement. Valve replacement therapies have undergone progressive evolution since the 1960s. Over the last 20 years, transcatheter aortic valve replacement has radically transformed the care of aortic stenosis, such that it is now the treatment of choice for many, particularly elderly, patients. This review provides an overview of the pathophysiology, presentation, diagnosis, indications for intervention, and current therapeutic options for aortic stenosis.

Narrative review of the contemporary surgical treatment of unicuspid aortic valve disease

Unicuspid aortic valve disease (UAVD) is a frequent and long-lasting challenge for adult congenital heart disease centers. UAVD patients become usually symptomatic in their twenties or thirties and require a surgical treatment plan which should respect their complete lifespan combined with an adequate quality of life. Unfortunately, all current surgical strategies of congenital aortic valve disease bear some important limitations: (I) Aortic valve replacement using bioprosthetic valves is associated with early structural degeneration and leads frequently to re-operations. (II) Mechanical valves are commonly associated with lifelong risk of severe bleeding due to oral anticoagulation. (III) Using a pulmonary autograft (i.e., Ross procedure) for aortic valve replacement is associated with excellent long-term results in non-elderly patients. However, failure of pulmonary autograft or pulmonary homograft may require re-operations. (IV) Aortic valve repair or Ozaki procedure is only performed in a few heart centers worldwide and is associated with a limited reproducibility and early patch degeneration, suture dehiscence or increased risk of endocarditis. In contrast to degenerative tricuspid aortic valve disease, UAVD remains relatively understudied and reports on UAVD treatment are rare and usually limited to retrospective single-center observations. For this review, we searched PubMed for papers in the English language by using the search words unicuspid aortic valve, congenital aortic valve, Ross procedure, Ozaki procedure, aortic valve repair, mechanical/bioprosthetic aortic replacement, homograft. We read the abstracts of relevant titles to confirm their relevance, and the full papers were then extracted. References from extracted papers were checked for additional relevant reports. This review summarizes current surgical treatment strategies for UAVD including aortic valve replacement using bioprosthetic or mechanical valves, homografts, pulmonary autografts (i.e., Ross procedure) and aortic valve repair techniques for UAV. Furthermore, Ozaki procedure will be discussed.

Multiscale Characterization of Isotropic Pyrolytic Carbon Used for Mechanical Heart Valve Production

Usage of pyrolytic carbon (PyC) to produce mechanical heart valves (MHVs) has led to heart valve replacement being a very successful procedure. Thus, the mechanical properties of employed materials for MHV production are fundamental to obtain the required characteristics of biocompatibility and wear resistance. In this study, two deposition methods of PyC were compared through a multiscale approach, performing three-point bending tests and nanoindentation tests. Adopted deposition processes produced materials that were slightly different. Significant differences were found at the characteristic scale lengths of the deposited layers. Setting changes of the deposition process permitted obtaining PyC characterized by a more uniform microstructure, conferring to the bulk material superior mechanical properties.

Nina Braunwald: The First Female Cardiothoracic Surgeon

Dr Nina Braunwald is celebrated for her work as the first female cardiothoracic surgeon and her key role in the design and implementation of the first prosthetic mitral valve. She began her residency at Bellevue Hospital in 1952, a time in the United States where the scope of women's work was limited. Once her training took her to the National Institutes of Health (NIH), her historic flexible leaflet valve was developed and Dr Braunwald paved an innovative step toward the advanced prostheses of today. Afterward, she was recognized by the American Board of Thoracic Surgery in 1963. Her extensive research and educational passion for cardiothoracic surgery led to numerous publications, a leadership role with the NIH, and associate professorship at University of California San Diego and Harvard; leaving behind a significant legacy to be memorialized in awards and fellowships to women in academic cardiac surgery. Her work inspired continued evolution of the prosthetic valve and countless women to pursue surgery as a career before passing away in 1992, leaving behind a new generation of women surgeons. Despite her successful career, she was never promoted to full professor by her academic institutions.

[Clinical results of cardiac valve repair with bicuspid full-flow mechanical prosthesis 'MedEng-ST']

Prosthetic repair of cardiac valves with artificial mechanical prostheses is ubiquitously performed using prostheses consisting of two cusps (bicuspidal). Several years ago, new bicuspid full-flow prostheses appeared on the market. From the first use they immediately proved reliable, with stable haemodynamic characteristics. At the Interregional Clinical and Diagnostic Centre, bicuspid full-flow mechanical prostheses 'MedEng-ST' have been used since 2017. We carried out a retrospective follow up of 84 patients subjected to prosthetic repair of cardiac valves with full-flow prostheses 'MedEng-ST' in mitral and aortic positions. There were no prosthesis-associated or procedural complications during follow up. Neither were there major complications in the postoperative period. All complications were related to peculiarities of the approach to the heart. We assessed the functional parameters of the heart by standard echocardiography. The obtained findings demonstrated good haemodynamic parameters on the 'MedEng-ST' prostheses, improved intracardiac haemodynamics, which eventually had a beneficial effect on the patients' clinical picture. The transprosthetic gradients had stable parameters with a decrease in time when placing the 'MedEng-ST' prosthesis into the aortic position (p≤0.05). Proceeding from the obtained results, as well as taking into account the absence of thromboembolic events it may be stated that the proposed design of the device is universal for replacement of the aortic and mitral valves of the heart. Based on the obtained findings of the study we recommend to use the 'MedEng'ST' prostheses in clinical practice. Further studies are required for more convincing data and explicit recommendations.

Bioprosthetic or mechanical heart valves: prosthesis choice for borderline patients?-Results from 9,616 cases recorded in Polish national cardiac surgery registry

Background

In middle-aged patients undergoing aortic valve replacement (AVR), the selection of prosthesis type is a complex process. Current guidelines do not unequivocally indicate the type of prosthesis (bioprosthetic or mechanical) recommended for patients between 60–70 years of age. The aim of the study was to present the trends in AVR prosthesis selection in borderline patients over a 10-year period, based on real-life registry data.

Methods

The study population comprised of 9,616 consecutive patients aged between 60–70 years, who underwent isolated AVR between 2006 and 2016 in all cardiac surgery departments in Poland. Data were extracted from the Polish National Registry of Cardiac Surgery.

Results

Among 27,797 consecutive AVR procedures, patients aged 60–70 years represented 34.6% of the population operated on. From 2006 to 2016, bioprosthetic valves (BVs) were implanted in 53.9% cases, (and) mechanical valves (MVs) in 42.1%. The proportion of different valve types changed in time: from 77.5% of MVs vs. 22.5% of BVs in 2006 to 23.2% of MVs vs. 76.8% of BVs in 2016 (P<0.001). The most commonly implanted BV was the Hancock II (used in 36.4% of BV implantations), the most commonly used MV was the Saint Jude Mechanical prosthesis (implanted in 36.4% of MV implantation cases). A multivariable model identified smaller annulus [OR (95% CI) 0.89 (0.86–0.92), P<0.001], atrial fibrillation [OR (95% CI) 1.32 (1.05–1.67), P=0.017], male sex [OR (95% CI) 1.47 (1.24–1.74), P<0.001] and year of implantation [OR (95% CI) 0.75 (0.71–0.79), P<0.001] as predictors of MV implantation.

Conclusions

Patients aged 60–70 years represent more than one-third of all AVR patients. Between 2006 and 2016, the proportion of implanted prostheses has changed dramatically. In 2016 BVs were implanted in nearly 75% of AVR cases, three times more often than in 2006.

In-home Compared With In-Clinic Warfarin Therapy Monitoring in Mechanical Heart Valves: A Population-Based Study

Objective

To evaluate differences in time in therapeutic range (TTR), major bleeding, thromboembolism, and survival comparing in-home and in-clinic international normalized ratio monitoring for patients with mechanical heart valves receiving warfarin anticoagulation.

Patients and Methods

An observational population-based study of 383 patients (mean ± SD age, 61.5±14.1 years; 38.6% female) with mechanical heart valves (aortic, 77.8%; mitral, 31.1%; tricuspid, 1%; pulmonic 0.2%; and multiple, 9.7%) was performed from January 1, 2012, through December 31, 2017. The target international normalized ratio was 2.5 for 199 patients (52.0%) and 3.0 for 184 (48.0). Of these patients, 37.9% (n=145) were managed by in-home monitoring (cases) and 62.1% (n=238) were monitored in the clinic (controls).

Results

During median follow-up of 3.1 years, mean ± SD TTR was similar between in-home (66.6%±19.2%) and in-clinic (67.2%±19.8%) monitoring (P=.76). There were no differences between the in-home and in-clinic groups regarding survival to major bleeding (5.7% per person-year vs 6.7% per person-year; P=.66) or thrombotic complications (2.3% vs 1.8%; P=.56). In-home monitoring was associated with reduced all-cause mortality (hazard ratio, 0.40; 95% CI, 0.19 to 0.83; P=.01) on univariate analysis; however, this was no longer apparent when controlling for age and baseline left ventricular ejection fraction.

Conclusion

In this real-world population-based study of patients with mechanical heart valves, in-home monitoring was equivalent to in-clinic monitoring regarding TTR and important clinical outcomes.

Porous Carbon Microparticles as Vehicles for the Intracellular Delivery of Molecules

In this study the application of porous carbon microparticles for the transport of a sparingly soluble material into cells is demonstrated. Carbon offers an intrinsically sustainable platform material that can meet the multiple and complex requirements imposed by applications in biology and medicine. Porous carbon microparticles are attractive as they are easy to handle and manipulate and combine the chemical versatility and biocompatibility of carbon with a high surface area due to their highly porous structure. The uptake of fluorescently labeled microparticles by cancer (HeLa) and normal human embryonic Kidney (HEK 293) cells was monitored by confocal fluorescence microscopy. In this way the influence of particle size, surface functionalization and the presence of transfection agent on cellular uptake were studied. In the presence of transfection agent both large (690 nm) and small microparticles (250 nm) were readily internalized by both cell lines. However, in absence of the transfection agent the uptake was influenced by particle size and surface PEGylation with the smaller nanoparticle size being delivered. The ability of microparticles to deliver a fluorescein dye model cargo was also demonstrated in normal (HEK 293) cell line. Taken together, these results indicate the potential use of these materials as candidates for biological applications.

Modern concepts from old ideas in manufacture of cardiac valve prostheses

In reviewing the history of mechanical prosthetic valves, it appears evident how many improvements and technical advances have been obtained in this field. Looking to the past, it must also be underlined how some old concepts, which can be considered quite revolutionary for those years, clearly indicate the great skill and ingenuity of those who conceived them. Old ideas have been revitalized by modern concepts, and this is exemplified when considering the developments of bileaflet and sutureless prostheses.

Evaluation of Supercritical CO2-Assisted Protocols in a Model of Ovine Aortic Root Decellularization

One of the leading trends in the modern tissue engineering is the development of new effective methods of decellularization aimed at the removal of cellular components from a donor tissue, reducing its immunogenicity and the risk of rejection. Supercritical CO₂ (scCO₂)-assisted processing has been proposed to improve the outcome of decellularization, reduce contamination and time costs. The resulting products can serve as personalized tools for tissue-engineering therapy of various somatic pathologies. However, the decellularization of heterogeneous 3D structures, such as the aortic root, requires optimization of the parameters, including preconditioning medium composition, the type of co-solvent, values of pressure and temperature inside the scCO₂ reactor, etc. In our work, using an ovine aortic root model, we performed a comparative analysis of the effectiveness of decellularization approaches based on various combinations of these parameters. The protocols were based on the combinations of treatments in alkaline, ethanol or detergent solutions with scCO₂-assisted processing at different modes. Histological analysis demonstrated favorable effects of the preconditioning in a detergent solution. Following processing in scCO₂ medium provided a high decellularization degree, reduced cytotoxicity, and increased ultimate tensile strength and Young’s modulus of the aortic valve leaflets, while the integrity of the extracellular matrix was preserved.

Tissue "valve-over-valve" implantation in previous mechanical Bentall

The authors present a case report about the elective replacement of a mechanical Bentall with a bioprosthetic valve. The authors describe a technique whereby the mechanical valve is "broken" off its mechanism and the new valve is sutured in the old cuff.

Body donation as a grateful gift for a long and active life with a Björk-Shiley valve

An 87-year-old patient donated his body to the Institute of Anatomy and Cell Biology in gratefulness for the longevity of a Björk-Shiley convexo-concave (BSCC) prosthetic aortic valve, implanted 34 years ago. The dissection of the enlarged heart showed no major signs of thrombosis, malignant fibrosis, or any other relevant issue that could potentially lead to valve failure as in other patients. Despite the reported high mortality rate of the earlier designs, especially of the BSCC valves, some patients survived for longer than expected. In more than 34 years after the BSCC valve implantation, the patient was a very active and lively man, working both as full-time and volunteer firefighter. The lifespan of this BSCC valve is among the longest reported.

Diamond Anniversary of Mechanical Cardiac Valve Prostheses: A Tale of Cages, Balls, and Discs

This year marks the 60th anniversary of the first aortic and mitral valve replacements using mechanical artificial prosthesis. The first caged-ball devices represented a milestone in cardiac surgery and in the treatment of valvular disease. The following decades witnessed a great evolution in mechanical valve technology providing, through frustrating complications and stimulating successes, more reliable models to be safely used in the clinical setting. This review pays tribute to pioneers of this field who made currently available the most advanced models of mechanical prostheses with extended records of durability and performance, to be used as reliable alternatives to biological devices.

Endocarditis risk with bioprosthetic and mechanical valves: systematic review and meta-analysis

OBJECTIVE

Bioprosthetic valves are being used with increased frequency for valve replacement, with controversy regarding risk:benefit ratio compared with mechanical valves in younger patients. However, prior studies have been too small to provide comparative estimates of less common but serious adverse events such as infective endocarditis. We aimed to compare the incidence of infective endocarditis between bioprosthetic valves and mechanical valves.

METHODS

We searched PubMed, Cochrane, EMBASE, Scopus and Web of Science from inception to April 2018 for studies comparing left-sided aortic and mitral bioprosthetic to mechanical valves for randomised trials or observational studies with propensity matching. We used random-effects model for our meta-analysis. Our primary outcome of interest was the rate of infective endocarditis at follow-up.

RESULTS

13 comparison groups with 43 941 patients were included. Mean age was 59±7 years with a mean follow-up of 10.4±5.0 years. Patients with bioprosthetic valves had a higher risk of infective endocarditis compared with patients receiving mechanical valves (OR 1.59, 95% CI 1.35 to 1.88, p<0.001) with an absolute risk reduction of 9 per 1000 (95% CI 6 to 14). Heterogeneity within the included studies was low (I²=0%). Exclusion of the study with maximum weight did not change the results of the analysis (OR 1.57, 95% CI 1.14 to 2.17, p=0.006). A meta-regression of follow-up time on incidence of infective endocarditis was not statistically significant (p=0.788) indicating difference in follow-up times did not alter the pooled risk of infective endocarditis.

CONCLUSIONS

Bioprosthetic valves may be associated with a higher risk of infective endocarditis. These data should help guide the discussion when deciding between bioprosthetic and mechanical valves in individual patients.

Spontaneous rupture of a mechanical valve in a mitral position (On-X) with migration-embolization to aortic bifurcation from the perspective of the vascular surgeon

We report on the case of spontaneous rupture of an On-X-pure pyrolytic carbon mechanical valve prosthesis implanted seven years earlier, in a mitral position, at our hospital. The patient was admitted with valvular dysfunction and acute pulmonary edema requiring emergency surgery (prosthesis replacement); the absence of a leaflet was confirmed intraoperatively. The patient presented severe respiratory failure, which prolonged the postoperative period. A CT scan showed that the migrated leaflet was located in the aortic bifurcation with no apparent arterial lesion. Four months later, once the patient had recovered, laparotomy and aortotomy were performed in order to retrieve the leaflet, which was found to have become included (neoendothelized) in the aortic wall without compromising the latter's integrity or obstructing the blood flow. A subsequent CT scan confirmed the persistence of the leaflet in its initial position. The literature review highlights two singular facts: 1) this is the second published case of the escape of a leaflet from an On-X prosthesis (the first patient died); 2) this is the first case in which a laparotomy was performed to retrieve the leaflet but finally a decision was made to leave it in situ. Seven months later, the patient remained asymptomatic.

Materials and manufacturing perspectives in engineering heart valves: a review

Valvular heart diseases (VHD) are a major health burden, affecting millions of people worldwide. The treatments for such diseases rely on medicine, valve repair, and artificial heart valves including mechanical and bioprosthetic valves. Yet, there are countless reports on possible alternatives noting long-term stability and biocompatibility issues and highlighting the need for fabrication of more durable and effective replacements. This review discusses the current and potential materials that can be used for developing such valves along with existing and developing fabrication methods. With this perspective, we quantitatively compare mechanical properties of various materials that are currently used or proposed for heart valves along with their fabrication processes to identify challenges we face in creating new materials and manufacturing techniques to better mimick ​the performance of native heart valves.

How Did We Get Here?: A Historical Review and Critical Analysis of Anticoagulation Therapy Following Mechanical Valve Replacement

Managing severe valvular heart disease with mechanical valve replacement necessitates lifelong anticoagulation with a vitamin K antagonist. Optimal anticoagulation intensity for patients with mechanical valves remains uncertain; current recommendations are inconsistent across guideline bodies and largely based on expert opinion. In this review, we outline the history of anticoagulation therapy in patients with mechanical heart valves and critically evaluate current antithrombotic guidelines for these patients. We conclude that randomized trials evaluating optimal anticoagulation intensity in patients with mechanical valves are needed, and that future guidelines must better justify antithrombotic treatment recommendations.

The early days of vascular and heart valve prostheses: a historical review

This surgical heritage article provides a historical overview of the most important early advances of vascular- and valvular surgery, that lead to the development of currently used vascular- and valvular prostheses and materials. The first writings describing techniques in vascular surgery mainly focussed on hemorrhage control and date from around 1600 B.C. The strategy of vessel ligation was first mentioned in Western literature around 200 B.C. In the 18^th century, techniques of ligation were expanded towards attempts of vessel restoration. The first artificial vascular prosthesis was made in 1894. From this time on, vascular prostheses were used in animal experiments and around 1900 for the first time in humans. More than 60 years later, in 1952, the first mechanical heart valve prosthesis was implanted. Four years later, the first successful biological heart valve implantation followed. In 2000, a transcatheter heart valve was successfully implanted in a human for the first time. Over time, procedures and techniques became more efficient and effective. This led to new developments, such as the manufacturing of a tissue engineered blood vessel in 1986. Nowadays, dozens of different valve prostheses have been devised, both mechanical and biological. Still, no ideal model of vascular and heart valve prosthesis exists.

High-Resolution Measurements of Leakage Flow Inside the Hinge of a Large-scale Bileaflet Mechanical Heart Valve Hinge Model

PURPOSE

It is believed that non-physiological leakage flow through hinge gaps during diastole contributes to thrombus formation in Bileaflet Mechanical Heart Valves (BMHVs). Because of the small scale and difficulty of experimental access, fluid dynamics inside the hinge cavity has not yet been characterised in detail. The objective is to investigate small-scale structure inside the hinge experimentally, and gain insight into its role in stimulating cellular responses.

METHODS

An optically accessible scaled-up model of a BMHV hinge was designed and built, preserving dynamic similarity to a clinical BMHV. Particle Image Velocimetry (PIV) was used to visualize and quantify the flow fields inside the hinge at physiological Reynolds number and dimensionless pressure drop. The flow was measured at in-plane and out-of-plane spatial resolution of 32 and 86 μm, respectively, and temporal resolution of [Formula: see text] RESULTS: Likely flow separation on the ventricular surface of the cavity has been observed for the first time, and is a source of unsteadiness and perhaps turbulence. The shear stress found in all planes exceeds the threshold of platelet activation, ranging up to 168 Pa.

CONCLUSIONS

The scale-up approach provided new insight into the nature of the hinge flow and enhanced understanding of its complexity. This study revealed flow features that may induce blood element damage.

Smeloff-Cutter Mechanical Prosthesis in the Aortic Position for 49 Years

We describe a 76-year-old male physician who at age 27 underwent replacement of his stenotic aortic valve with a Smeloff-Cutter mechanical prosthesis which functioned normally for 49 years. He died of a noncardiac condition. A normally functioning substitute cardiac valve for this length of time has not been previously reported (1).

Identification of mechanical prosthetic heart valves based on distinctive cinefluoroscopic and echocardiographic markers

The past 65 years have witnessed remarkable progress in the development of safe, hemodynamically favorable mechanical heart valves. Today, there are a large number and variety of prostheses in use and many prostheses have been used for a while and then discontinued. When patients lack reliable information about their heart valve prostheses, identification of valve model becomes difficult even for specialized physicians in this area. A combination of cinefluoroscopy and echocardiography makes it possible to provide accurate and detailed information regarding identification of prosthetic valve models. Fluoroscopic examination is a useful technique to evaluate patients following mechanical heart valve replacement. However, transthoracic echocardiography and transesophageal echocardiography have almost replaced cinefluoroscopy in the evaluation of prosthetic heart valves. Especially, real-time three-dimensional transesophageal echocardiography provides distinctive images of prosthetic heart valves, particularly for those in the mitral position. A large body of literature has been published to familiarize physicians with the radiological appearance of numerous mechanical prostheses. However, there is a lack of data regarding the identification of prosthetic valve models based on echocardiographic appearance. In this review, we aimed to describe distinctive echocardiographic and cinefluoroscopic markers for identifying the type and brand of several commonly used mechanical prosthetic heart valves.

Recent advances and challenges on application of tissue engineering for treatment of congenital heart disease

Congenital heart disease (CHD) affects a considerable number of children and adults worldwide. This implicates not only developmental disorders, high mortality, and reduced quality of life but also, high costs for the healthcare systems. CHD refers to a variety of heart and vascular malformations which could be very challenging to reconstruct the malformed region surgically, especially when the patient is an infant or a child. Advanced technology and research have offered a better mechanistic insight on the impact of CHD in the heart and vascular system of infants, children, and adults and identified potential therapeutic solutions. Many artificial materials and devices have been used for cardiovascular surgery. Surgeons and the medical industry created and evolved the ball valves to the carbon-based leaflet valves and introduced bioprosthesis as an alternative. However, with research further progressing, contracting tissue has been developed in laboratories and tissue engineering (TE) could represent a revolutionary answer for CHD surgery. Development of engineered tissue for cardiac and aortic reconstruction for developing bodies of infants and children can be very challenging. Nevertheless, using acellular scaffolds, allograft, xenografts, and autografts is already very common. Seeding of cells on surface and within scaffold is a key challenging factor for use of the above. The use of different types of stem cells has been investigated and proven to be suitable for tissue engineering. They are the most promising source of cells for heart reconstruction in a developing body, even for adults. Some stem cell types are more effective than others, with some disadvantages which may be eliminated in the future.

Adverse Hemodynamic Conditions Associated with Mechanical Heart Valve Leaflet Immobility

Artificial heart valves may dysfunction, leading to thrombus and/or pannus formations. Computational fluid dynamics is a promising tool for improved understanding of heart valve hemodynamics that quantify detailed flow velocities and turbulent stresses to complement Doppler measurements. This combined information can assist in choosing optimal prosthesis for individual patients, aiding in the development of improved valve designs, and illuminating subtle changes to help guide more timely early intervention of valve dysfunction. In this computational study, flow characteristics around a bileaflet mechanical heart valve were investigated. The study focused on the hemodynamic effects of leaflet immobility, specifically, where one leaflet does not fully open. Results showed that leaflet immobility increased the principal turbulent stresses (up to 400%), and increased forces and moments on both leaflets (up to 600% and 4000%, respectively). These unfavorable conditions elevate the risk of blood cell damage and platelet activation, which are known to cascade to more severe leaflet dysfunction. Leaflet immobility appeared to cause maximal velocity within the lateral orifices. This points to the possible importance of measuring maximal velocity at the lateral orifices by Doppler ultrasound (in addition to the central orifice, which is current practice) to determine accurate pressure gradients as markers of valve dysfunction.

Tunable Elastomers with an Antithrombotic Component for Cardiovascular Applications

This study reports the development of a novel family of biodegradable polyurethanes for use as tissue engineered cardiovascular scaffolds or blood-contacting medical devices. Covalent incorporation of the antiplatelet agent dipyridamole into biodegradable polycaprolactone-based polyurethanes yields biocompatible materials with improved thromboresistance and tunable mechanical strength and elasticity. Altering the ratio of the dipyridamole to the diisocyanate linking unit and the polycaprolactone macromer enables control over both the drug content and the polymer cross-link density. Covalent cross-linking in the materials achieves significant elasticity and a tunable range of elastic moduli similar to that of native cardiovascular tissues. Interestingly, the cross-link density of the polyurethanes is inversely related to the elastic modulus, an effect attributed to decreasing crystallinity in the more cross-linked polymers. In vitro characterization shows that the antiplatelet agent is homogeneously distributed in the materials and is released slowly throughout the polymer degradation process. The drug-containing polyurethanes support endothelial cell and vascular smooth muscle cell proliferation, while demonstrating reduced levels of platelet adhesion and activation, supporting their candidacy as promising substrates for cardiovascular tissue engineering.

Normal function of a 43-year-old Braunwald Cutter heart valve

We present the case of a 72-year-old woman diagnosed with rheumatic fever at the age of 6. In 1972, she was diagnosed with mitral valve insufficiency and mitral valve stenosis, then in 1974, a decision was made to perform mitral valve replacement surgery with a 32-mm Braunwald-Cutter ball cage prosthesis. An echocardiogram performed in 2014 revealed normal biventricular systolic function, mechanical prosthesis in mitral position with maximum speed of 1.9 m/s, maximum gradient of 15 mmHg, mean gradient of 6 mmHg, severe tricuspid valve insufficiency, inferior vena cava measuring 15 mm with more than 50% collapse and pulmonary artery systolic pressure of 40 mmHg. We report the use of the 32-mm Braunwald-Cutter ball cage prosthesis with the longest longevity that remains functional after more than 43 years of implantation.

Clinically advancing and promising polymer-based therapeutics

In this review article, we will examine the history of polymers and their evolution from provisional World War II materials to medical therapeutics. To provide a comprehensive look at the current state of polymer-based therapeutics, we will classify technologies according to targeted areas of interest, including central nervous system-based and intraocular-, gastrointestinal-, cardiovascular-, dermal-, reproductive-, skeletal-, and neoplastic-based systems. Within each of these areas, we will consider several examples of novel, clinically available polymer-based therapeutics; in addition, this review will also include a discussion of developing therapies, ranging from the in vivo to clinical trial stage, for each targeted area of treatment. Finally, we will emphasize areas of patient care in need of more effective, accessible, and targeted treatment approaches where polymer-based therapeutics may offer potential solutions.

Developing a Clinically Relevant Tissue Engineered Heart Valve-A Review of Current Approaches

Tissue engineered heart valves (TEHVs) have the potential to address the shortcomings of current implants through the combination of cells and bioactive biomaterials that promote growth and proper mechanical function in physiological conditions. The ideal TEHV should be anti-thrombogenic, biocompatible, durable, and resistant to calcification, and should exhibit a physiological hemodynamic profile. In addition, TEHVs may possess the capability to integrate and grow with somatic growth, eliminating the need for multiple surgeries children must undergo. Thus, this review assesses clinically available heart valve prostheses, outlines the design criteria for developing a heart valve, and evaluates three types of biomaterials (decellularized, natural, and synthetic) for tissue engineering heart valves. While significant progress has been made in biomaterials and fabrication techniques, a viable tissue engineered heart valve has yet to be translated into a clinical product. Thus, current strategies and future perspectives are also discussed to facilitate the development of new approaches and considerations for heart valve tissue engineering.