Historical Overview of Vascular Allograft Transplantation

Transplantation of cryopreserved cardiovascular homografts

Due to degeneration, homografts were since the 1950s only used strictly for replacement of complex arterial segments and lesions incl. the aortic valve, replacement of infected arterial prostheses, and vascular access for patients on haemodialysis. During the 1990s, rate-differentiated freezing methods and anti-crystallization agents proved to prevent crystallisation, and more widespread use with expanded indications incl. coronary and lower limb bypasses began justified by promising midterm results. In 2021, the first Scandinavian homograft biobank was founded in Odense in Denmark. This review summarises the history and the experiences from this biobank.

The mechanical characterization of blood vessels and their substitutes in the continuous quest for physiological-relevant performances. A critical review

During the last 50 years, novel biomaterials and tissue engineering techniques have been investigated to produce alternative vascular substitutes that recapitulate the unique elastic mechanical features of blood vessels. A large variation in mechanical characterization, including the test type, protocol, and data analysis, is present in literature which complicates the comparison among studies and prevents the blooming and the advancement of this field. In addition, a limited mechanical assessment of the substitute for the intended application is often provided. In this light, this review presents the mechanical environment of blood vessels, discusses their mechanical behavior responsible for the suited blood flow into the body (non-linearity, anisotropy, hysteresis, and compliance), and compares the mechanical properties reported in literature (obtained with compression, tensile, stress-relaxation, creep, dynamic mechanical analysis, burst pressure, and dynamic compliance tests). This perspective highlights that the mechanical properties extracted through conventional tests are not always suitable indicators of the mechanical performance during the working life of a vascular substitute. The available tests can be then strategically used at different stages of the substitute development, prioritizing the simplicity of the method at early stages, and the physiological pertinence at later stages, following as much as possible ISO standards in the field. A consistent mechanical characterization focused on the behavior to which they will be subdued during real life is one key and missing element in the quest for physiological-like mechanical performance of vascular substitutes.

Registry of Valvular and Vascular Allograft Transplants in the Autonomous Community of Catalonia, Spain (ReVAC): Design of the Registry

BACKGROUND

In recent years, there have been significant changes in the perception of valvular and vascular allograft transplants. Despite the constant evolution of the field of transplant and the involvement of multiple surgical specialties, there is not an official registry for administrative and clinical control. This study aims to design a registry of vascular and valvular allograft transplantation in Catalonia, Spain (ReVAC).

MATERIALS AND METHODS

Three consecutive focal groups were designed. Focal groups established administrative, technical, and clinical requirements of ReVAC. ReVAC included patients with a transplanted cryopreserved vascular segment or cardiac valves that were distributed by Catalan tissue banks to public and private hospitals in Catalonia. Ten hospitals were involved in this study. Data were collected on 380 patients between January 1995 and November 2015.

RESULTS

The project resulted in the completion of a growing platform available online. ReVAC was divided into the following 3 levels: patient-related, surgery-related, and transplant-related data. Online access is available through the website of applications of the "Generalitat de Catalunya."

CONCLUSION

ReVAC has been useful for administrative and clinical control of transplants in Catalonia. Currently, data related to outcomes of arterial allografts are available, reinforcing the current guideline-supported indications, as well as opening a window for further analysis and guideline creation.

Cryopreserved Allografts for Treatment of Chronic Limb-Threatening Ischemia in Patients Without Autologous Saphenous Veins

BACKGROUND

Revascularization is the best alternative to reduce symptoms and to improve the limb salvage rate in patients with chronic limb-threatening ischemia (CLI). Alternative grafts as synthetic prostheses and allografts must be considered for patients without a suitable autologous graft. Our aim was to evaluate outcomes of cryopreserved allografts used as a vascular conduit for bypass surgery in the infrainguinal territory.

METHODS

A retrospective analysis (January 1995 to January 2014) of the Registry of vascular and valvular allografts transplant in the autonomous community of Catalonia, Spain was performed for identifying patients with CLI who required infrainguinal bypass with cryopreserved arterial allografts. Statistical analysis was performed using SPSS, ver. 20, for Mac (Chicago).

RESULTS

A total of 149 patients with CLI (mean age of 70.1 years) were analyzed. One hundred two patients (68.5%) had a grade IV lesion (Fontaine classification). In the overall follow-up, 24.8% of patients required a reintervention. Overall graft occlusion, infection, and dilation rate were 52.3%, 6%, and 5.4% respectively. Overall 30-day mortality was 0.7%. Five-year primary patency rate and limb salvage rate were 38.6% and 50.2%, respectively. Survival rate at 5 years was 54.2%. Major adverse limb event (MALE)-free rate was 21.5% at 5 years. Revascularization to a distal target vessel was an independent positive predictive risk factor for a lower limb salvage rate and lower primary patency rate. Dyslipidemia was related to a lower limb salvage rate and represents a risk factor involved in MALEs.

CONCLUSIONS

Although arterial allografts seem to represent a suboptimal alternative, some selected patients could beneficiate from them. Five-year results are disappointing, and more studies are required to know other predictive factors for better selection of patients.