SCAD is a rare condition that is morphologically similar to what happens in aortic dissection; i.e. blood dissects into the wall of the artery through an intimal tear. It affects the coronary arteries, typically in younger women, often in association with pregnancy or the postpartum state. It has a high mortality, since it may result in sudden coronary artery blockage. See the Wall Street Journal, August 30, 2011 (I couldn’t find it in Robbins).
Dysfunction ranging from trivial to rapidly fatal depending on how bad the defect is and how rapidly it developed
May cause secondary changes in heart and blood vessels
The valve leaflets are simple, mostly avascular laminated structures. The strength of the leaflet comes from the middle layer, the lamina fibrosa. A lamina spongiosa is a cushioning layer on the inflow surface. Elastic fibers are also present. The outer surfaces are covered with endothelium. Valvular interstitial cells within the leaflets maintain the matrix.
The chordae tendineae are also avascular and blend with the lamina fibrosa.
The arterial valves work passively. The mitral and tricuspid valves require a functioning tensor apparatus (papillary muscles and chordae tendineae) to prevent gross incompetence.
The most important secondary changes from valve damage include myocardial hypertrophy, atrial dilatation and hypertensive changes in pulmonary vasculature.
Most lesions are acquired, chronic and affect the left-sided valves
Congenital causes include malformed (dysplastic) valves, which are stenotic, regurgitant, or both. Congenital valvular lesions are relatively rare. Bicuspid aortic valve is one of the most common congenital valvular abnormalities affecting 1 – 2% of the population.
Acquired causes include degenerative diseases, infection, autoimmune disorders, and papillary muscle dysfunction (e.g. as a complication of MI). Inheritable connective tissue disorders are technically congenital, but the manifestations are “acquired” later in life (e.g. Marfan’s, floppy mitral valve). It is now recognized that adult survivors of childhood cancers who have received high dose irradiation to the chest may develop secondary abnormalities of cardiac valves or coronary arteries starting in early middle age.
See Table 12-7, p. 561, Robbins 8th Ed. for a listing of the major causes of acquired valvular heart disease.
Most Frequent Chronic Valve Lesions of Major Functional Significance:
Mitral stenosis secondary to rheumatic heart disease
Mitral insufficiency secondary to myxomatous degeneration (floppy mitral valve)
Not exactly the same as atherosclerosis, but chronic injury due to hypertension and hyperlipidemia play a role
Typically presents in 70s & 80s (50s & 60s if bicuspid aortic valve)
Hallmark is heaped up masses of calcium on the downstream side of the leaflets preventing opening of valve
Calcification begins in the fibrosa layer at the attachment of the leaflet, which is the point of maximum flexion – usually does not involve free edges. The early lesion is “aortic valve sclerosis.” Rather than accumulating smooth muscle cells, the abnormal valves contain cells resembling osteoblasts.
The commissures are not fused (at least early on) as in rheumatic. Also the mitral valve is not involved (although calcium may extend through aortic annulus to involve anterior leaflet of the mitral valve).
Calcific Aortic Stenosis Clinical Features
Progresses at a variable (slow) rate and causes an increasing pressure gradient, 75 – 100 mm Hg LV hypertrophy
Angina or syncope may ensue
Ca++ may rarely extend into septum & cause AV conduction block (not mentioned in Robbins but true)
Eventually get cardiac decompensation & CHF end stage with 50% mortality in three years