Analysis of prosthetic cardiac devices: a guide for the practising pathologist

A parametric study on pulse duplicator design and valve hemodynamics

BACKGROUND

In vitro assessment is mandatory for artificial heart valve development. This study aims to investigate the effects of pulse duplicator features on valve responsiveness, conduct a sensitivity analysis across valve prosthesis types, and contribute on the development of versatile pulse duplicator systems able to perform reliable prosthetic aortic valve assessment under physiologic hemodynamic conditions.

METHODS

A reference pulse duplicator was established based on literature. Further optimization process led to new designs that underwent a parametric study, also involving different aortic valve prostheses. These designs were evaluated on criteria such as mean pressure differential and pulse pressure (assessed from high-fidelity pressure measurements), valve opening and closing behavior, flow, and regurgitation. Finally, the resulting optimized setup was tested under five different hemodynamic settings simulating a range of physiologic and pathologic conditions.

RESULTS

The results show that both, pulse duplicator design and valve type significantly influence aortic and ventricular pressure, flow, and valve kinematic response. The optimal design comprised key features such as a compliance chamber and restrictor for diastolic pressure maintenance and narrow pulse pressure. Additionally, an atrial reservoir was included to prevent atrial-aortic interference, and a bioprosthetic valve was used in mitral position to avoid delayed valve closing effects.

CONCLUSION

This study showed that individual pulse duplicator features can have a significant effect on valve's responsiveness. The optimized versatile pulse duplicator replicated physiologic and pathologic aortic valve hemodynamic conditions, serving as a reliable characterization tool for assessing and optimizing aortic valve performance.

Degeneration of biological heart valve grafts in a rat model of superoxide dismutase-3 deficiency

While oxidative stress is known as key element in the pathogenesis of atherosclerosis and calcific aortic valve disease, its role in the degeneration of biological cardiovascular grafts has not been clarified yet. Therefore, the present study aimed to examine the impact of oxidative stress on the degeneration of biological cardiovascular allografts in a standardized chronic implantation model realized in rats exhibiting superoxide dismutase 3 deficiency (SOD3^(-) ). Rats with SOD3 loss-of-function mutation (n = 24) underwent infrarenal implantation of cryopreserved valved aortic conduits, while SOD3-competent recipients served as controls (n = 28). After a follow-up period of 4 or 12 weeks, comparative analyses addressed degenerative processes, hemodynamics, and evaluation of the oxidative stress model. SOD3^(-) rats presented decreased circulating SOD activity (p = .0079). After 12 weeks, 58% of the implant valves in SOD3^(-) rats showed regurgitation (vs. 31% in controls, p = .2377). Intima hyperplasia and chondro-osteogenic transformation contributed to progressive graft calcification (p = .0024). At 12 weeks, hydroxyapatite deposition (p = .0198) and the gene expression of runt-related transcription factor-2 (Runx2) (p = .0093) were significantly enhanced in group SOD3^(-) . This study provides the first in vivo evidence that impaired systemic antioxidant activity contributes to biological cardiovascular graft degeneration.

Polymeric Tissue Adhesives

Polymeric tissue adhesives provide versatile materials for wound management and are widely used in a variety of medical settings ranging from minor to life-threatening tissue injuries. Compared to the traditional methods of wound closure (i.e., suturing and stapling), they are relatively easy to use, enable rapid application, and introduce minimal tissue damage. Furthermore, they can act as hemostats to control bleeding and provide a tissue-healing environment at the wound site. Despite their numerous current applications, tissue adhesives still face several limitations and unresolved challenges (e.g., weak adhesion strength and poor mechanical properties) that limit their use, leaving ample room for future improvements. Successful development of next-generation adhesives will likely require a holistic understanding of the chemical and physical properties of the tissue-adhesive interface, fundamental mechanisms of tissue adhesion, and requirements for specific clinical applications. In this review, we discuss a set of rational guidelines for design of adhesives, recent progress in the field along with examples of commercially available adhesives and those under development, tissue-specific considerations, and finally potential functions for future adhesives. Advances in tissue adhesives will open new avenues for wound care and potentially provide potent therapeutics for various medical applications.

Pathology of the Aortic Valve: Aortic Valve Stenosis/Aortic Regurgitation

PURPOSE OF REVIEW

This discussion is intended to review the anatomy and pathology of the aortic valve and aortic root region, and to provide a basis for the understanding of and treatment of the important life-threatening diseases that affect the aortic valve.

RECENT FINDINGS

The most exciting recent finding is that less invasive methods are being developed to treat diseases of the aortic valve. There are no medical cures for aortic valve diseases. Until recently, open-heart surgery was the only effective method of treatment. Now percutaneous approaches to implant bioprosthetic valves into failed native or previously implanted bioprosthetic valves are being developed and utilized. A genetic basis for many of the diseases that affect the aortic valve is being discovered that also should lead to innovative approaches to perhaps prevent these disease. Sequencing of ribosomal RNA is assisting in identifying organisms causing endocarditis, leading to more effective antimicrobial therapy. There is exciting, expanding, therapeutic innovation in the treatment of aortic valve disease.

Practical Approach to the Evaluation of Prosthetic Mechanical and Tissue Replacement Heart Valves

Mechanical and bioprosthetic substitute heart valves have dramatically improved life expectancy and quality of life in patients with valvular heart disease. Complications of substitute heart valves are a relatively infrequent occurrence, often due to thrombosis, infection, or structural/mechanical failure. It is important to accurately identify and systematically evaluate prosthetic heart valves when encountered as surgical pathology specimens or in the autopsy setting.

Biocompatibility and biofilm inhibition of N,N-hexyl,methyl-polyethylenimine bonded to Boston Keratoprosthesis materials

The biocompatibility and antibacterial properties of N,N-hexyl,methyl-polyethylenimine (HMPEI) covalently attached to the Boston Keratoprosthesis (B-KPro) materials was evaluated. By means of confocal and electron microscopies, we observed that HMPEI-derivatized materials exert an inhibitory effect on biofilm formation by Staphylococcus aureus clinical isolates, as compared to the parent poly(methyl methacrylate) (PMMA) and titanium. There was no additional corneal epithelial cell cytotoxicity of HMPEI-coated PMMA compared to that of control PMMA in tissue cultures in vitro. Likewise, no toxicity or adverse reactivity was detected with HMPEI-derivatized PMMA or titanium compared to those of the control materials after intrastromal or anterior chamber implantation in rabbits in vivo.

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.