21. Aortic insufficiency

Definition:

• Incomplete closing of the aortic valve during diastole leads to regurgitation of blood from the aorta back into the left ventricle.

Etiology:

• Aortic root dilation – idiopathic in ~80% of cases Also caused by:
• Aging (degenerative changes)
• Syphilitic aortitis (from tertiary syphilis)
• Osteogenesis imperfecta
• Aortic dissection
• Systemic hypertension

• Congenital abnormalities – e.g., bicuspid aortic valve
• Connective tissue diseases:
• Marfan syndrome
• Ehlers-Danlos syndrome
• Inflammatory/Autoimmune:
• Ankylosing spondylitis
• Systemic lupus erythematosus (SLE)
• Acute cases:
• Infective endocarditis
• Aortic dissection
• Chest trauma

Pathophysiology:

• Diastolic regurgitation: Due to valve incompetence, blood flows back from the aorta into the left ventricle (LV) during diastole.
• The LV receives blood both from the regurgitant aorta and normal inflow from the LA → leads to LV volume overload.
• To compensate, the LV dilates and undergoes eccentric hypertrophy (sarcomeres added in series) to maintain forward stroke volume.
• Increased LV stroke volume → ↑ systolic blood pressure

• But during diastole, some of that volume leaks back → ↓ diastolic pressure
• This creates a wide pulse pressure (↑ systolic – ↓ diastolic) → leads to hyperdynamic circulation, producing the characteristic "water hammer pulse" (blood slams like a hammer against walls of a. in each heart beat).
• Regurgitation of blood flow causes LV end-diastolic pressure ↑ → transmitted backward to LA and pulmonary circulation → pulmonary congestion and oedema
• ↓ Cardiac output (CO) triggers sympathetic stimulation → increases heart rate and vascular resistance, which further aggravates regurgitation
• Stages:
• Stage I: LV dilatation, peripheral hypoperfusion
• Stage II: Relative mitral regurgitation (from dilated LV distorting mitral valve geometry)