Journal of Clinical and Experimental Transplantation
Open Access

Hypothermic; Heart Transplantation; Cellular immunity; Transplantation

Introduction

Indications

Heart transplantation is indicated in patients with end-stage heart failure who have exhausted all other medical and surgical options. The most common causes of heart failure leading to transplantation include ischemic cardiomyopathy (caused by coronary artery disease), dilated cardiomyopathy (enlarged and weakened heart muscle), and restrictive cardiomyopathy (stiff and non-compliant heart muscle) [1]. Other indications include congenital heart disease, valvular heart disease, and certain infections or toxicities that cause irreparable damage to the heart. Evaluation and Selection.

Before being listed for transplantation, patients undergo a comprehensive evaluation to assess their suitability for surgery and their ability to comply with postoperative care. This includes a complete medical history, physical examination, laboratory tests, imaging studies, and psychological evaluation [2]. Patients with significant comorbidities or contraindications to immunosuppressive therapy may be deemed ineligible for transplantation.

Once listed for transplantation, patients are prioritized based on their severity of illness as determined by their status on the United Network for Organ Sharing (UNOS) waitlist [3]. Candidates are assigned a status from 1A to 3 depending on their need for immediate transplantation, and may also be prioritized based on blood type, body size, and geographic location relative to the donor [4].

Donor procurement

Donor hearts are procured from brain-dead donors who have consented to organ donation. The donor heart is evaluated for its size, function, and absence of disease or infection. The heart is then preserved using cold storage or machine perfusion until it can be transplanted into the recipient [5]. Advances in organ preservation have led to longer transport times and improved graft function, expanding the pool of potential donors and improving outcomes.

Surgical Technique

Heart transplantation is typically performed via median sternotomy, in which the breastbone is divided to provide access to the heart. The diseased heart is removed; leaving behind the right and left atria, and the donor heart is implanted by connecting the aorta, pulmonary artery, superior and inferior vena cava, and four pulmonary veins to the recipient’s circulatory system. The new heart is then restarted, and the patient is weaned off cardiopulmonary bypass [6].

Immunosuppressive therapy

Following transplantation, patients require lifelong immunosuppressive therapy to prevent rejection of the donor heart. Immunosuppressive drugs target various components of the immune system, including T cells, B cells, and antibodies [7], and are usually given in combination to achieve maximal efficacy while minimizing toxicity. The most commonly used immunosuppressive drugs include calcineurin inhibitors (e.g. cyclosporine, tacrolimus), antiproliferative agents (e.g. mycophenolate, azathioprine), and corticosteroids [8].

Complications

Despite advancements in surgery and immunosuppression, heart transplantation is associated with several short-term and long-term complications. Acute complications include infection, bleeding, cardiac dysfunction, and rejection, which occur when the recipient’s immune system recognizes the donor heart as foreign and mounts an attack against it. Acute rejection episodes are typically treated with high-dose steroids and/or anti-T cell therapies, but repeated or severe episodes may lead to chronic rejection and irreversible graft damage [9].

Long-term complications of heart transplantation include infection, malignancy, cardiovascular disease, and drug toxicity. Cardiovascular disease remains the leading cause of death among heart transplant recipients, as the graft is subjected to chronic vascular injury due to a combination of immunologic and non-immunologic factors. This includes accelerated atherosclerosis, cardiac allograft vasculopathy (a diffuse narrowing of the coronary arteries), and myocardial fibrosis.

Future directions

To address the shortage of donor hearts, several strategies are being explored to increase the availability of viable organs. These include expanded criteria donors (i.e. donors who do not meet the strict criteria for donation but may still provide suitable organs), donation after cardiac death (i.e. donation from patients who have died from irreversible cessation of circulatory and respiratory function), and xenotransplantation (i.e. transplantation of organs from non-human sources).

Conclusion

In addition, advances in tissue engineering and regenerative medicine may offer alternative approaches to treating heart failure. This includes the use of stem cells to regenerate damaged myocardium, the development of bioengineered hearts and scoff

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