Incorporates old grades 1A, 1B and 2 into a single category. (See examples- 1A, 1B, 2).

Inflammation usually mononuclear with some eosinophils. Neutrophils not present except in severe forms, plasma cells not typically present.

Myocyte damage may be manifest by clearing of cytoplasm and nucleus with nuclear enlargement, sometimes nucleolar prominence; also by irregular scalloped borders with associated inflammation

Histologic features include intravascular activated mononuclear cells, including macrophage accumulation in capillaries and venules, and/or endothelial cells with enlarged nuclei and expanded cytoplasmic projections that appear to narrow or occlude lumens.

Severe AMR (see below) can contain hemorrhage, interstitial edema, myocyte necrosis, capillary fragmentation, mixed inflammation including neutrophils, and endothelial pyknosis or karyorrhexis.

Intact myocardium should be assessed, avoiding areas of ischemic injury, prior biopsy sites, Quilty lesions and fibrous scars.

Paraffin C4d and CD68 or frozen section C4d, C3d, HLA-DR recommended as primary panels.

C4d interpretation: <10% capillary uptake: Negative; 10-50% uptake: focal; >50%: diffuse. Interpreted as positive if >50% uptake regardless of intensity (intensity 0= no stain; 1=faint stain, 2=strong stain) Assessment limited to capillaries. Ignore any staining of venules, arteries, arterioles, capillaries in Quilty lesions, vessels in scars, subendocardial connective tissue and necrotic myocytes.

CD68 interpretation: interpretation based on intravascular macrophages, which have chain-like, linear or beading stainingn profiles in capillaries and small venules, in contrast to interstitial macrophages. <10%: negative; 10-50% focal; >50% diffuse. Interpreted as positive if 10% or more.

Positive C4d or CD68 alone is considered sufficient to establish immunopathologic features of AMR.

See descriptions of pAMR (H+) and pAMR (I+) above.

See descriptions of pAMR (H+) and pAMR (I+) above.

Myocyte injury or necrosis (contraction band necrosis, coagulative necrosis) often with myocyte vacuolization, fat necrosis. Myocyte injury disproportionately high for small amount of inflammation, or no inflammation in early stages.

Related to perioperative ischemic injury, seen up to 6 weeks posttransplant.

Over time, inflammation develops, contains neutrophils in addition to other cells.

Acute rejection usually has more inflammation relative to myocyte injury; neutrophils uncommon in acute rejection unless severe. However, neutrophils may also occur in antibody mediated rejection.

Trichrome or C4d stains may be helpful in detecting myocyte damage in some cases.

See example: Ischemia

Incorporates older terminology encompassing both infiltrating (Type A) and non-infiltrating (Type B) Quilty lesions.

Tangential section may obscure relationship between infiltrating portion and endocardial portion. Additional sections may be helpful.

Presence of B cells, plasma cells, background fibrosis and prominent vascularity favor Quilty effect over acute rejection.