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Aortic insufficiency (AI), also known as aortic regurgitation (AR), is the leaking of the aortic valve of the heart that causes blood to flow in the reverse direction during ventricular diastole, from the aorta into the left ventricle.
Aortic insufficiency can be due to abnormalities of either the aortic valve or the aortic root (the beginning of the aorta).
Additional recommended knowledge
EtiologyAbout half of the cases of aortic insufficiency are due to the aortic root dilatation (annuloaortic ectasia), which is idiopathic in over 80% of cases, but otherwise occurs with aging and hypertension, Marfan syndrome, aortic dissection, and syphilis. In about 15% the cause is innate bicuspidal aortic valve, while another 15% cases are due to retraction of the cusps as part of postinflammatory processes of endocarditis in rheumatic fever and various collagen vascular diseases. Additionally, aortic insufficiency has been linked to the use of some medications belonging to the class of serotonin reuptake inhibitors, specifically medications containing fenfluramine or dexfenfluramine isotopes.
In individuals with a normally functioning aortic valve, the valve is only open when the pressure in the left ventricle is higher than the pressure in the aorta. This allows the blood to be ejected from the left ventricle into the aorta during ventricular systole. After ventricular systole, the pressure in the ventricle decreases, as the ventricle relaxes and gets ready to fill up with blood from the left atrium. This relaxation of the left ventricle (early ventricular diastole) causes a fall in the pressure in the left ventricle. When the pressure in the left ventricle falls below the pressure in the aorta, the aortic valve will close, preventing blood from going from the aorta back into the left ventricle. The amount of blood that is ejected by the heart is known as the stroke volume or stroke work. Under normal conditions, the entire stroke volume delivers oxygenated blood to the body.
In aortic insufficiency, when the pressure in the left ventricle falls below the pressure in the aorta, the aortic valve is not able to completely close. This causes a leaking of blood from the aorta into the left ventricle. This means that some of the blood that was already ejected from the heart is regurgitating back into the heart. The percentage of blood that regurgitates back through the aortic valve due to AI is known as the regurgitant fraction. For instance, if an individual with AI has a stroke volume of 100 ml and during ventricular diastole 25 ml regurgitates back through the aortic valve, the regurgitant fraction is 25%. This regurgitant flow causes a decrease in the diastolic blood pressure in the aorta, and therefore an increase in the pulse pressure (systolic pressure - diastolic pressure) not to be confounded with hypertension.
Since some of the blood that is ejected during systole regurgitates back into the left ventricle during diastole, there is decreased effective forward flow in AI.
AI causes both volume overload (elevated preload) and pressure overload (elevated afterload) of the heart.
The pressure overload (due to elevated pulse pressure and hypertension) causes left ventricular hypertrophy (LVH). There is both concentric hypertrophy and eccentric hypertrophy in AI. The concentric hypertrophy is due to the hypertension associated with AI, while the eccentric hypertrophy is due to volume overload caused by the regurgitant fraction.
The hemodynamic sequelae of AI are dependent on the rate of onset of AI. Acute AI and chronic AI will have different hemodynamics and individuals will have different signs and symptoms.
Acute aortic insufficiency
In acute AI, as may be seen with acute perforation of the aortic valve due to endocarditis, there will be a sudden increase in the volume of blood in the left ventricle. The ventricle, unable to deal with the sudden change in volume, decompensates. The filling pressure of the left ventricle will increase. This causes pressure in the left atrium to rise, and the individual will develop congestive heart failure.
Severe acute aortic insufficiency is considered a medical emergency. There is a high mortality rate if the individual does not undergo immediate surgery for aortic valve replacement. If the acute AI is due to aortic valve endocarditis, there is a risk that the new valve may become seeded with bacteria. However, this risk is small.
Acute AI may be difficult to diagnose clinically, since the left ventricle had not yet developed the eccentric hypertrophy and dilatation that allow an increased stroke volume and bounding peripheral pulses that are common in chronic AI. On auscultation, there may be a short diastolic murmur and a soft S1. S1 is soft because the elevated filling pressures close the mitral valve in diastole (rather than the mitral valve being closed at the beginning of systole).
Chronic aortic insufficiency
If the individual survives the initial hemodynamic derailment that acute AI presents as, the left ventricle adapts by eccentric hypertrophy and dilatation of the left ventricle, and the volume overload is compensated for. The left ventricular filling pressures will revert to normal and the individual will no longer have overt heart failure.
In this compensated phase, the individual may be totally asymptomatic and may have normal exercise tolerance.
Eventually (typically after a latency period) the left ventricle will become decompensated, and filling pressures will increase. While most individuals would complain of symptoms of congestive heart failure to their physicians, some enter this decompensated phase asymptomatically. Proper treatment for AI involves aortic valve replacement prior to this decompensation phase.
The physical examination of an individual with aortic insufficiency involves auscultation of the heart to listen for the murmur of aortic insufficiency and the S4 heart sound (which would indicate left ventricular filling against a hypertrophied LV wall). The murmur of chronic aortic insufficiency is typically described as early diastolic and decresendo, which is best heard at aortic area when the patient is seated and leans forward with breath held in expiration. The murmur is usually soft and seldom causes thrill. If there is radiation to the right parasternal region, ascending aortic aneurysm has to be excluded.
If there is increased stroke volume of the left ventricle due to volume overload, an ejection systolic 'flow' murmur may also be present when auscultating the same aortic area. Unless there is concomittant aortic valve stenosis, the murmur should not start with an ejection click.
There may also be an Austin Flint murmur, a soft mid-diastolic rumble heard at the apical area. It appears when regurgitant jet from the severe aortic insufficiency renders partial closure of the anterior mitral leaflet.
Peripheral physical signs of aortic insufficiency are related to the high pulse pressure and the rapid decrease in blood pressure during diastole due to the AI:
Rarer signs include:
Unfortunately, none of the above putative signs of aortic insufficiency is of utility in making the diagnosis. What is of value is hearing a diastolic murmur itself, whether or not the above signs are present.
The most common test used for the evaluation of the severity of aortic insufficiency is the echocardiogram, which can provide two-dimensional views of the regurgitant jet, and allow measurement of the velocity and volume of the jet.
The echocardiographic findings in severe aortic regurgitation include:
The risk of death in individuals with aortic insufficiency, dilated ventricle, normal ejection fraction who are asymptomatic is about 0.2 percent per year. Risk increases if the ejection fraction decreases or if the individual develops symptoms.
Aortic insufficiency can be treated either medically or surgically, depending on the acuteness of presentation, the symptoms and signs associated with the disease process, and the degree of left ventricular dysfunction.
Surgical treatment is typically warranted prior to the ejection fraction falling below 55% or the left ventricular end-systolic dimension increasing to more than 55mm, regardless of symptoms. If either of these thresholds is passed, the prognosis worsens.
Medical therapy of chronic aortic insufficiency involves the use of vasodilators. Small trials have shown a short term benefit in the use of ACE inhibitors, nifedipine, and hydralazine in improving left ventricular wall stress, ejection fraction, and mass. The use of these vasodilators is only indicated in individuals who suffer from hypertension in addition to AI. The goal in using the use of these pharmacologic agents is to decrease the afterload so that the left ventricle is spared somewhat. The regurgitant fraction may not change significantly, since the gradient between the aortic and left ventricular pressures is usually fairly low at the initiation of treatment.
In the case of severe acute aortic insufficiency, all individuals should undergo surgery if there are no absolute contraindications for surgery. Individuals with bacteremia with aortic valve endocarditis should not wait for treatment with antibiotics to take effect, given the high mortality associated with the acute AI. In stead, replacement with an aortic valve homograft should be performed if feasible.
In the future, it is believed that a percutaneous approach to aortic valve replacement will be feasible.
Roth, B Drugs and Valvular Heart Disease. N Engl J Med 2007;356:6 PMID 17202450
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Aortic_insufficiency". A list of authors is available in Wikipedia.|