Types of rejection and assessing graft dysfunction

CardioNerds (Dr. Shazli Khan, Dr. Jenna Skowronski, and Dr. Shiva Patlolla) discuss the management of patients post‑heart transplantation with Dr. Shelley Hall from Baylor University Medical Center and Dr. MaryJane Farr from UTSW. In this comprehensive review, we cover the physiology of the transplanted heart, immunosuppression strategies, rejection surveillance, and long-term complications including cardiac allograft vasculopathy (CAV) and malignancy. Audio editing for this episode was performed by CardioNerds intern Dr. Bhavya Shah.

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Pearls

1. The Denervated Heart: The donor heart is surgically severed from the autonomic nervous system, leading to a higher resting heart rate (90-110 bpm) due to loss of vagal tone. Because the heart relies on circulating catecholamines rather than neural input to increase heart rate, patients experience a delayed chronotropic response to exercise and stress. Importantly, because afferent pain fibers are severed, ischemia is often painless.
2. Rejection Surveillance: Rejection is classified into Acute Cellular Rejection (ACR), which is T-cell mediated, and Antibody-Mediated Rejection (AMR), which is B-cell mediated. While endomyocardial biopsy remains the gold standard for diagnosis, non-invasive surveillance using gene-expression profiling (e.g., AlloMap) and donor-derived cell-free DNA (dd-cfDNA) is increasingly utilized to reduce the burden of invasive procedures.
3. The Infection Timeline: The risk of infection follows a predictable timeline based on the intensity of immunosuppression. The first month is dominated by nosocomial infections. Months one through six are the peak for opportunistic infections (Cytomegalovirus, Pneumocystis, Toxoplasmosis) requiring prophylaxis. After six months, patients are primarily at risk for community-acquired pathogens, though late viral reactivation can occur.
4. Cardiac Allograft Vasculopathy (CAV): Unlike native coronary artery disease, CAV presents as diffuse, concentric intimal thickening that affects the entire length of the vessel, including the microvasculature. Due to denervation, patients rarely present with angina; instead, CAV manifests as unexplained heart failure, fatigue, or sudden cardiac death.
5. Malignancy Risk: Long-term immunosuppression significantly increases the risk of malignancy. Skin cancers (squamous and basal cell) are the most common, followed by Post-Transplant Lymphoproliferative Disorder (PTLD), which is often driven by Epstein-Barr Virus (EBV) reactivation.

Notes

Notes: Notes drafted by Dr. Patlolla

1. What are the unique physiological features of the transplanted heart?

The hallmark of the transplanted heart is denervation. Because the autonomic nerve fibers are severed during harvest, the heart loses parasympathetic or vagal tone, resulting in a resting tachycardia (typically 90-110 bpm). The heart also loses the ability to mount a reflex tachycardia; thus, the heart rate response to exercise or hypovolemia relies on circulating catecholamines, which results in a slower “warm-up” and “cool-down” period during exertion.

2. What are the pillars of maintenance immunosuppression regimen?

The triple drug maintenance regimen typically consists of:

1. Calcineurin Inhibitor (CNI): Tacrolimus is preferred over cyclosporine. Key side effects include nephrotoxicity, hypertension, tremor, hyperkalemia, and hypomagnesemia.
2. Antimetabolite: Mycophenolate mofetil (MMF) inhibits lymphocyte proliferation. Key side effects include leukopenia and GI distress.
3. Corticosteroids: Prednisone is used for maintenance but is often weaned to low doses or discontinued after the first year to mitigate metabolic side effects (diabetes, osteoporosis, weight gain).

3. How is rejection classified and diagnosed?

Rejection is the immune system’s response to the foreign graft and is categorized by the arm of the immune system involved:

• Acute Cellular Rejection (ACR): Mediated by T-lymphocytes infiltrating the myocardium. It is graded from 1R (mild) to 3R (severe) based on the extent of infiltration and myocyte damage.
• Antibody-Mediated Rejection (AMR): Mediated by B-cells producing donor-specific antibodies (DSAs) that attack the graft endothelium. It is diagnosed via histology (capillary swelling) and immunofluorescence (C4d staining).

Diagnosis has historically relied on endomyocardial biopsy. However, non-invasive tools are gaining traction. Gene Expression Profiling (GEP) assesses the expression of genes associated with immune activation to rule out rejection in low-risk patients. Donor-Derived Cell-Free DNA (dd-cfDNA) measures the fraction of donor DNA in the recipient’s blood. Elevated levels suggest graft injury which can occur in both ACR and AMR.

4. What is the timeline of infectious risk and how does it guide prophylaxis?

Infectious risk correlates with the net state of immunosuppression.

• < 1 Month (Nosocomial): Risks include surgical site infections, catheter-associated infections, and aspiration pneumonia.
• 1 – 6 Months (Opportunistic): This is the period of peak immunosuppression. Patients are at risk for PJP, CMV, Toxoplasma, and fungal infections. Prophylaxis typically includes Trimethoprim-Sulfamethoxazole (for PJP/Toxo) and Valganciclovir (for CMV, dependent on donor/recipient serostatus).
• > 6 Months (Community-Acquired): As immunosuppression is weaned, the risk profile shifts toward community-acquired respiratory viruses (Influenza, RSV) and pneumonias. However, patients with recurrent rejection requiring boosted immunosuppression remain at risk for opportunistic pathogens.

5. How does Cardiac Allograft Vasculopathy (CAV) differ from native CAD?

CAV is the leading cause of late graft failure. Unlike the focal, eccentric plaques seen in native atherosclerosis, CAV is an immunologically driven process causing diffuse, concentric intimal hyperplasia. It affects both epicardial vessels and the microvasculature. Because of this diffuse nature, percutaneous coronary intervention (PCI) is often technically difficult and provides only temporary palliation. The only definitive treatment for severe CAV is re-transplantation. Surveillance is critical and is typically performed via annual coronary angiography, often using intravascular ultrasound (IVUS) to detect early intimal thickening before it is visible on the angiogram.

References

1. Costanzo MR, Dipchand A, Starling R, et al. The International Society of Heart and Lung Transplantation Guidelines for the care of heart transplant recipients. J Heart Lung Transplant. 2010;29(8):914-956. doi:10.1016/j.healun.2010.05.034. https://www.jhltonline.org/article/S1053-2498(10)00358-X/fulltext
2. Kittleson MM, Kobashigawa JA. Cardiac Allograft Vasculopathy: Current Understanding and Treatment. JACC Heart Fail. 2017;5(12):857-868. doi:10.1016/j.jchf.2017.07.003. https://www.jacc.org/doi/10.1016/j.jchf.2017.07.003
3. Velleca A, Shullo MA, Dhital K, et al. The International Society for Heart and Lung Transplantation (ISHLT) guidelines for the care of heart transplant recipients. J Heart Lung Transplant. 2023;42(5):e1-e141. doi:10.1016/j.healun.2022.10.015. https://www.jhltonline.org/article/S1053-2498(22)02187-5/fulltext