Aortic insufficiency
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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).
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Etiology
Diseases of the aortic valve leaflets that can cause AI include endocarditis, rheumatic heart disease (in individuals with rheumatic fever), and various collagen vascular diseases. Diseases of the aortic root that can cause AI include annuloaortic ectasia (dilatation of the proximal aortic root that occurs with aging and hypertension), Marfan syndrome, aortic dissection, and syphilis. Of all these causes of AI, the most common are endocarditis and annuloaortic ectasia.
Physiology
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 oxygentaed blood to the body.
Pathophysiology
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, and therefore an increase in the pulse pressure (systolic pressure - diastolic pressure) and hypertension.
Since some of the blood that is ejected during systole regurgitates back 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.
Hemodynamics
The hemodynamic sequelae of AI are dependant 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, and will decompensate. 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.1
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 dilitation 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. Whlie 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.
Physical examination
The physical examination of an individual with aortic insufficiency involves auscultation of the heart to listen for the murmur of aortic insufficiency and related heart sounds. The murmur of chronic aortic insufficiency is a holodiastolic (lasts all of diastole) decrescendo murmur (starts off loud and becomes soft). The murmur of chronic aortic insufficiency has the following characteristics:
- Systolic ejection click
- Ejection murmur
- S3 present
- Holodiastolic decrescendo murmur (If radiation to the right parasternal region, consider ascending aortic aneurysm
- Austin flint murmur (an apical diastolic rumble due to mitral regurgitation)
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:
- de Musset's sign (Head nodding in time with the heart beat)
- Quincke's sign (Pulsation of the capillary bed in the nail)
- Corrigan's pulse (rapid upstroke and collapse of the carotid artery pulse)
- Duroziez's sign / "Pistol shot femoral pulse"
- Hill's sign (A ≥ 20 mmHg difference in popliteal and brachial systolic cuff pressures, seen in chronic severe AI)
Diagnostic evaluation
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:
- An AI color jet dimension > 60 percent of the left ventricular outflow tract (LVOT) diameter (may not be true if the jet is eccentric)
- The pressure half-time of the regurgitant jet is < 250 msec
- Early termination of the mitral inflow (due to increase in LV pressure due to the AI.)
- Early diastolic flow reversal in the descending aorta.
- Regurgitant volume > 60 ml
- Regurgitant fraction > 55 percent
Prognosis
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.
Treatment
| Symptoms | Ejection fraction | Other information |
|---|---|---|
| NYHA class III - IV | ≥ 50 % | |
| NYHA class II | ≥ 50 % | Progression of symptoms or worsoning parameters on echocardiography |
| CHA class ≥ II angina | ≥ 50 % | |
| Regardless of symptoms | 25 - 49 % | |
| Cardiac surgery for other cause (ie: CAD, other valvular disease, ascending aortic aneurysm) | ||
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 falling below 55mm, regardless of symptoms. If either of these thresholds is passed, the prognosis worsens.
Medical treatment
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.
Surgical treatment
The surgical treatment of choice at this time is an aortic valve replacement. This is currently an open-heart procedure, requiring the individual to be placed on circulatory arrest.
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.
References
1. al Jubair K, al Fagih MR, Ashmeg A, Belhaj M, Sawyer W. Cardiac operations during active endocarditis. J Thorac Cardiovasc Surg. 1992 Aug;104(2):487-90. (Medline abstract (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=1495315))
2. Bonow et al., ACC/AHA Task Force Report. ACC/AHA Guidelines for the Management of Patients With Valvular Heart Disease. JACC Vol. 32, No. 5, November 1998:1486-1588 (Full article (http://www.acc.org/clinical/guidelines/valvular/dirIndex.htm))