Cardiac Amyloidosis I
From the morphologic standpoint, cardiac amyloidosis is characterized by infiltration of the myocardial interstitium (atrial and ventricular) by amyloid. The amyloid deposition is composed of amyloid fibrils (~10 nanometer thick extracellular thread like fibrils). The fibrils are in turn composed of proteins that have a beta-pleated-sheet conformation.
There are may proteins that can have this conformation and precipitate as amyloid deposits in the human body. In the human heart the more common proteins tha form amyloid deposits are as follows: 1. immunoglobulin light chains (kappa and lambda) and transthyretin. Other amyloid forming proteins that can affect the heart are immunoglobulin heavy chains, amyloid A fibrils and atrial natriuretic peptide. The more commonly seen seen clinically associated with cardiac dysfunction are the first three.
Amyloid deposits can present in different morphologic patterns: 1. Fine interstitial; 2. Coarse interstitial (perimyocytic); 3. Nodular; 4. Plaque like replacement; 5. Arteriolar; 6. Venular; 7 Endocardial; 8. Arterial; 9. Valvular; 10. Foreign body giant cell reaction to the amyloid.
Four chamber view of heart infiltrated by amyloid deposits. This image shows a formalin fixed heart in which the atria are "stiff" and do not collapse as the atria of a normal heart after fixation. The endocardium of the left atrium is as usual distinctly white because of the normal multiple elastic lamellae, but, with conspicuous yellow-ochre discolored plaques (highlighted in red in the drawing).
These yellow-ochre plaques represent subendocardial and endocardial amyloid deposits. In addition, the left ventricle shows faint plaques of paler brown material towards the subendocardium also representing amyloid deposits. Close up of the atrial deposits shows that the form discrete small nodules that can coalesce into forming plaques on gross exam in ai ton.