Valvular heart disease: classification, microscopic and gross pathomorphology
The valvular disorders we shall consider:
- Mitral stenosis
- Mitral regurgitation
- Aortic stenosis
- Aortic regurgitation
First, rheumatic fever, because it is a topic that keeps appearing. Rheumatic fever is the result of an untreated infection of Streptococcus pyogenes in the throat. 3% of untreated patients produce antibodies against the microbe that damage the CT around arterioles. It is in effect a type II hypersensitivity reaction. The CT most commonly affected is the joints (hence Rheumatic) and the heart, specifically, the heart muscle protein myosin.
RF can then go on to cause changes of valves in the heart, including valve thickening, fusion and changes to the tendinous cords. Fibrosis and scarring of the valve leaflets is visible. On autopsy, the classic triad of findings of RH in the heart are:
- Mitral valve thickening
- Thickened chordae tendineae
- Left ventricular hypertrophy (compensation for mitral dysfunction)
Remember: chronic rheumatic heart disease almost always involves the mitral valve: thickened leaflets, fused commissures and short, thick, fused chordae give a narrow "fish-mouth" (buttonhole) orifice. Pure mitral stenosis dilates the left atrium (thrombi in the atrial appendage) and spares the left ventricle.
Microscopically, we can also observe Aschoff bodies in acute rheumatic carditis. These are myocardial inflammatory lesions, collections of lymphocytes, scattered plasma cells and activated macrophages known as anitschkow cells. These bodies can be found in any of the layers of the heart, hence why rheumatic fever can be thought to cause pancarditis.
H&E, rheumatic myocarditis: Aschoff body in the interstitium (centre), fibrinoid change with plump Anitschkow cells and lymphocytes between the muscle fibres.
Image: “Aschoff Body in Rheumatic Myocarditis” by Ed Uthman, MD, CC BY-SA 2.0, via Wikimedia Commons.
We can diagnose RF with evidence of two of the following, in combination with Elevated antistreptolysin O titre:
- Polyarthritis
- Carditis
- Subcutaneous nodules (collagen fiber collections over bones or tendons)
- Erythema marginatum (rash on trunk or arms as macules)
- Sydenham’s chorea (a series of involuntary rapid movements of face and arms)
Mnemonic: the major Jones criteria spell J♥NES: Joints (migratory polyarthritis), ♥ carditis, Nodules (subcutaneous), Erythema marginatum, Sydenham chorea. Diagnosis: evidence of a recent group A streptococcal infection plus two major, or one major and two minor criteria (fever, arthralgia, raised ESR/CRP, prolonged PR interval).
Prevention, with early treatment of strep throat, is most important step, but treatment can be with anti-inflammatories (e.g. aspirin/corticosteroids) and ABs if strep still present.
OK, now some valvular disorders.