Cardiac Transplantation Pathology

Indications & Biopsy - Heartfelt Handoff

• Indications for Transplant:
  • End-stage heart failure (HF) refractory to maximal medical/device therapy.
    • NYHA Class III (ambulatory) or IV.
  • Common causes:
    • Dilated Cardiomyopathy (DCM) - leading cause.
    • Ischemic Cardiomyopathy (ICM).
    • Severe, inoperable valvular or congenital heart disease.
  • Refractory life-threatening arrhythmias.
  • Predicted < 1-year survival without transplant.
• Endomyocardial Biopsy (EMB):
  • Primary tool for monitoring allograft rejection.
    • Acute Cellular Rejection (ACR).
    • Antibody-Mediated Rejection (AMR).
  • Procedure: Right ventricular samples via jugular/femoral vein.
  • Grading: ISHLT classification for ACR severity.
  • Protocol: Routine surveillance, frequency ↓ over time.

> ⭐ Endomyocardial biopsy (EMB) is the gold standard for monitoring cardiac allograft rejection.

Rejection Types - Immune System Scuffles

• Immune responses against donor heart. Classified by timing & mechanism.

![Cardiac Allograft Biopsy Evaluation Methods](https://ylbwdadhbcjolwylidja.supabase.co/storage/v1/object/public/notes/L1/Pathology_Cardiac_Pathology_Cardiac_Transplantation_Pathology/43f2c66f-ced8-4acc-8c5b-a4100263ed24.jpg)

• Hyperacute Rejection:

  • Immediate (minutes-hours).
  • Mediator: Pre-formed Donor-Specific Antibodies (DSAs) vs ABO/HLA.
  • Patho: Thrombosis, necrosis.

  ⭐ Hyperacute rejection, occurring minutes to hours post-transplant, is mediated by pre-formed donor-specific antibodies (DSAs) against ABO or HLA antigens.

• Acute Cellular Rejection (ACR):

  • Weeks-months (common).
  • Mediator: T-lymphocytes.
  • EMB: Lymphocytic infiltrate, myocyte damage (ISHLT Grade 0R-3R).

• Acute Antibody-Mediated Rejection (AMR):

  • Days-months.
  • Mediator: DSAs (often anti-HLA), complement.
  • EMB: Microvascular inflammation, C4d deposition (ISHLT pAMR Grade 0-3).

• Chronic Rejection (Cardiac Allograft Vasculopathy - CAV):

  • Months-years (leading late cause).
  • Patho: Diffuse concentric intimal thickening of coronaries ("onion skinning").
  • Result: Ischemia, MI, graft failure.

Grading Rejection - Scorecard Showdown

• Standardized assessment of rejection severity.
• Acute Cellular Rejection (ACR) - ISHLT 2004 Grades:
  • Grade 0R: No rejection.
  • Grade 1R (Mild): Interstitial/perivascular infiltrate; ≤1 focus myocyte injury.
  • Grade 2R (Moderate): ≥2 foci infiltrate, myocyte injury.
  • Grade 3R (Severe): Diffuse infiltrate, multifocal injury ± edema, hemorrhage, vasculitis.
• Antibody-Mediated Rejection (AMR) - ISHLT Pathologic (pAMR) Grades:
  • pAMR 0: Negative.
  • pAMR 1(H+): Histology + Immunopathology (C4d/C3d/CD68).
  • pAMR 1(I+): Immunopathology only.
  • pAMR 2: Severe/diffuse Histology + Immunopathology.
  • pAMR 3: Severe changes (capillary injury, hemorrhage, necrosis) + Immunopathology.
  • Correlate with DSA & clinical status.

⭐ The International Society for Heart and Lung Transplantation (ISHLT) provides standardized grading criteria for acute cellular rejection (ACR) and antibody-mediated rejection (AMR).

Chronic Rejection & Complications - Long-Haul Headaches

• Cardiac Allograft Vasculopathy (CAV): Primary chronic rejection form; major cause of late graft loss.
  • Patho: Diffuse, concentric intimal thickening of coronary arteries (epicardial & intramyocardial), leading to luminal stenosis.
  • Mechanism: Endothelial injury, smooth muscle cell proliferation, inflammation, ECM deposition. Immune (alloantibodies, T-cells) & non-immune factors (e.g., CMV, dyslipidemia).
  • Clinical: Often silent ischemia/MI (denervated graft), arrhythmias, progressive heart failure.
  • Dx: Intravascular ultrasound (IVUS) is gold standard; angiography less sensitive for early disease.

⭐ Cardiac Allograft Vasculopathy (CAV) is a form of chronic rejection characterized by diffuse, concentric intimal thickening of coronary arteries, leading to late graft failure.

• Other Major Long-Term Complications:
  • Malignancy: Increased risk. Post-Transplant Lymphoproliferative Disorder (PTLD) - often EBV-driven; skin cancers (SCC > BCC).
  • Infections: Opportunistic due to chronic immunosuppression (e.g., CMV, Aspergillus, Pneumocystis jirovecii).
  • Drug Toxicity: Calcineurin inhibitor (CNI) nephrotoxicity; steroid-induced diabetes, hypertension, dyslipidemia.

High‑Yield Points - ⚡ Biggest Takeaways

• Hyperacute rejection: Minutes to hours, pre-formed anti-donor Abs (ABO/HLA); widespread thrombosis, ischemic necrosis.
• Acute Cellular Rejection (ACR): T-cell mediated, peaks 1-3 months; Endomyocardial Biopsy (EMB) shows lymphocytic infiltrate, myocyte damage.
• Antibody-Mediated Rejection (AMR): Donor-specific Abs (DSA), C4d deposition in capillaries, microvascular inflammation, poor prognosis.
• Chronic Rejection (Cardiac Allograft Vasculopathy - CAV): Major long-term limit; diffuse concentric intimal thickening of coronaries, leading to ischemia, graft failure.
• Infections: Major mortality risk with immunosuppression; CMV, fungal, bacterial pathogens common.
• Post-Transplant Lymphoproliferative Disorder (PTLD): EBV-driven B-cell proliferation; risk ↑ with intensity of immunosuppression.