Aortic Insufficiency
Definition
Failure of the valve to prevent backflow from the aorta into the left ventricle.
Pathoanatomy
Aortic insufficiency (AI) is frequently the result of the repair of aortic stenosis, (whther surgically or by balloon dilatation), and is due to fibrosis, thickening, and contracture of the valve leaflets. AI can also occur after rheumatic heart disease, and is primary complication seen in juvenile rheumatoid arthritis. Other less common etiologies of AI include bacterial endocarditis and Marfan's Syndrome.
Pathophysiology
AI occurs when the valve leaflets cannot close the aortic orifice during diastole. A regurgitant area as small as 20% of the valve can double the workload of the left ventricle (LV), this will result in gradual LV dilation. Initially, the LV volume does not increase the end-diastolic volume because of an increase in left ventricular compliance (see LaPlace's law). Reflex peripheral dilation is used to reduce the afterload and improve the forward flow. Another compensatory mechanism is left ventricular hypertrophy which normalizes left ventricular wall pressure. The insufficiency increases preload, which then increases LV stroke volume. As a consequence of the compensatory mechanism systolic pressure is increased but the diastolic pressure decreases widening the pulse pressure.
AI also increases myocardial oxygen consumption, since the myocardial blood flow occurs during diastole and the aortic valve is insufficient the blood flow through the coronaries is reduced. Myocardial oxygen supply is decreased but the demand is increased, leading to ischemia, and failure of compensatory mechanisms, eventually leading to LV failure. However, normal ejection fraction is usually present with this type of anomaly.
Aortic Stenosis (AS) may present as well if AI has been present for some time. This restriction of forward flow interfers with the ventricle's ability to deal with regurgitant flow and causes the compensatory mechanisms to fail more quickly.
Surgical Interventions
Valve replacement is the usual surgical approach to AI because valve repair usually does not eliminate the hemodynamic problems necessitating surgery. Prosthetic valves are commonly used, however, homografts may also be used. Bioprosthetic valves are sometimes preferred over mechanical valves because they have a lower incidence of thrombosis, and do not require the same degree of anticoagulation as the mechanical valves (see Mechanical valves vs. Bioprosthetic valves). Ross procedure may also be utilized.
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