Valvular Diseases of the Heart

I.  The Basics

1.       There are four heart valves: the aortic and mitral on the left, and the pulmonary and tricuspid on the right. They have delicate valve leaflets (“like butterfly wings”).

2.       Valvular disease leads to structural abnormalities that cause dysfunction.
   a)  Stenosis: the valve can’t open completely, impeding forward flow
   b)  Regurgitation (or insufficiency): the valve can’t close completely, permitting
        reversal of flow.

3.       Dysfunction
   a)  “Pure” if it’s caused by only one problem (stenosis or regurgitation);
        “Mixed” if it’s due to a combination.
   b)  “Isolated” if it involves only one valve;
        “Combined” if more than one valve.
   c)  Murmurs result from abnormal valvular flow (sometimes audible without stethoscope)

4.       The left-sided valves are more predisposed to dysfunction. Why?
   a)  They have higher intracardiac pressure.
   b)  The undergo more forceful (and traumatic) valvular openings and closings.

5.       Valvular disease is more likely to be acquired than caused by genetics.

 II. Calcific (degenerative) aortic stenosis

·      This is the most common cause of isolated aortic stenosis in the U.S. Similar calcification can occur in the mitral valve as well.

A. Etiology and pathogenesis

·      The heart undergoes 40 million cycles a year, yielding a lifetime of repetitive mechanical stress on the leaflets.

·      Basically, the wear and tear leads to small leaflet injuries à inflammation à healing via fibrosis (collagen deposition).

·      Over time there are nodules due to scarring and dystrophic calcification, especially at the bases of the valves (arrow in picture). This causes stenosis.

B. Morphological features

 -     The valve cusps are rigid, distorted, and deformed due to fibrosis and calcifications. 

·      Again, the cause of stenosis is the calcified deposits that protrude into the sinuses of Valsalva, preventing complete opening of the valve cusps.

·      Note that the commissures and free edges of the valve cusps are not fused. Contrast this with chronic rheumatic valvulitis (where fusion results in aortic stenosis). (Commissure = where a leaflet and cusp meet, similar to wear two lips meet; circled in the photo.)

III. Mitral Valve Prolapse (“floppy valve syndrome” or “myxomatous degeneration”)

• This is the most common valve disorder and the most common cause of isolated mitral valve regurgitation in the U.S., where 1-2% of the adult population has this disorder.

·        Other valves may also be affected.

A. Etiology and pathogenesis

·        Essentially unknown. There’s increased incidence of MV prolapse in patients with Marfan syndrome (an autosomal dominant mutation in the gene encoding fibrillin, a component of elastic connective tissue).

·        This suggests that MV prolapse in non-Marfan patients may also be linked to some connective tissue disorder.

·       One would see clear mucopolysaccharide-filled areas between the mesenchymal cells. These stain with Alcian blue.

C. Morphological features

1. An accumulation of mucopolysaccharides (“ground substance”) in the valve leaflets causes them to be enlarged, redundant (thickened), and rubbery. The overgrown leaflets don’t close well à regurgitation.
2. The valve cusps are soft, enlarged, and “hooded,” meaning they prolapse into the left atrium (white arrow). This prolapse causes regurgitation.
3. There is a dilated annulus (ring of fibrous tissue around the base of the valve).
4. The prolapsed valves cause thinning and elongation of the chordae tendinae.
   The chordae may rupture, making the insufficiency worse.
5. Blood flow is disrupted by the weird growth. The excess stasis and turbulence causes fibrin-platelet thrombi to form on the valvular surface. These are prone to infection (thrombi are like magnets for bacteria), so they can break off and cause septic embolization.
6. Note that the commissures and leaflets are not fused.

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