Cardiovascular ImagingAortic regurgitation
retrograde flow across the closed aortic valve during
diastole. It is caused by abnormalities of one or more of the following structures: aortic cusp, aortic annulus, aortic sinuses. It is invariably associated with dilatation or
aneurysm of the ascending
aorta. There are many causes of aortic
regurgitation including
rheumatic heart disease, infective
endocarditis,
bicuspid aortic valve,
aortoannular ectasia,
aortic dissection and
aneurysm, and several systemic diseases. The systemic diseases in which aortic
regurgitation may be a manifestation are:
ankylosing spondylitis,
rheumatoid arthritis,
Reiters syndrome, giant cell
aortitis,
psoriatic arthritis,
relapsing polychondritis cardiovascular manifestation,
Behcets disease,
syphilis cardiovascular,
Marfans syndrome,
Ehlers Danlos syndrome and
osteogenesis imperfecta. Mild or moderate aortic
regurgitation is frequent in patients with long-standing systemic
hypertension. It may also be caused by
trauma and radiation therapy. Aortic
regurgitation is a frequent complication of valvuloplasty of aortic
stenosis. Degeneration or infection of prosthetic valves causes aortic
regurgitation. Most aetiologies produce chronic aortic
regurgitation. Acute severe
regurgitation may be caused by infective
endocarditis,
trauma and
aortic dissection.
Imaging
Radiography shows cardiomegaly due predominantly to left ventricular enlargement (Fig.1). Typically, enlargement of the ascending, arch and descending thoracic aorta is evident. For most of the course of chronic aortic regurgitation there is no pulmonary venous hypertension or pulmonary oedema. On the other hand, acute aortic regurgitation not uncommonly causes severe pulmonary oedema and little or no cardiomegaly.
Angiography demonstrates the presence and severity of aortic regurgitation consisting of retrograde diastolic flow of opacified blood into the left ventricle. The density of opacification of the left ventricle relative to opacification of the aorta is used as a semiquantitative method for grading the severity of aortic regurgitation. The volume of aortic regurgitation can be quantified as the difference between the total left ventricular output (stroke volume x heart rate) calculated from ventriculography compared with the effective left ventricular output as measured by the Fick technique. Thoracic aortography also demonstrates the dimensions of the ascending aorta and aortic sinuses (sinuses of Valsalva).
Echocardiography, either transthoracic or transoesophageal, is the most frequently employed technique for the diagnosis and assessment of the severity of aortic regurgitation. Doppler colour flow mapping is highly sensitive for identifying aortic regurgitation but provides only a semiquantitative assessment of severity. Echocardiography is very effective for demonstrating vegetations on the aortic valve indicative of infective endocarditis. Transoesophageal echocardiography is the preferred noninvasive technique for the evaluation of regurgitation of prosthetic aortic valves including suspected infective endocarditis. Echocardiography is used to monitor increases in left ventricular dimensions, volumes and ejection fraction in order to define the severity of regurgitation and as a guide to timing of valve replacement.
Magnetic resonance imaging is highly accurate for demonstrating the presence of aortic regurgitation. On cine gradient echo (GRE) images the regurgitant jet is displayed as a signal void emanating from the closed aortic valves into the left ventricle during diastole (Fig. 2). The size of this signal void serves as a semiquantitative estimate of the volume of aortic regurgitation. Precise quantitation of the volume of aortic regurgitation can be accomplished using velocity-encoded (phase contrast) cine GRE of the ascending aorta. Cine GRE can be used to quantify left ventricular dimensions and volumes.
Magnetic resonance imaging is the optimal technique for detecting abnormalities of the aortic sinuses, annulus, and ascending aorta associated with aortic regurgitation. It is also the preferred method for monitoring the dimension of the sinus and ascending aorta in patients with aortoannular ectasia as the cause of aortic regurgitation.
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