+++
Chronic Aortic Regurgitation
++
Patients with chronic AR remain asymptomatic for a long time. Palpitations are common and may be due to either awareness of forceful left ventricular contractions or occurrence of premature atrial or ventricular beats. Angina may occur either from concomitant coronary disease or from a combination of low diastolic pressure and increased oxygen demand from ventricular hypertrophy. When left ventricular dysfunction supervenes, patients initially experience exertional dyspnea and fatigue. At a later stage, resting heart failure symptoms occur with orthopnea and paroxysmal nocturnal dyspnea.
++
On physical examination, visible cardiac pulsations are common. The area of the apical impulse is increased on palpation and is displaced caudally and laterally. The first heart sound is usually normal. The aortic component of the second heart sound may be decreased in conditions where cusp excursion is reduced, such as with valve calcification. An S4 is often present due to underlying hypertrophy, and an S3 is audible when ventricular failure occurs. On auscultation, the characteristic sound of AR is a soft, high-pitched diastolic decrescendo murmur best heard in the third intercostal space along the left sternal border at end expiration, with the patient sitting and leaning forward. In the presence of aortic root disease, the murmur may be best heard to the right of the sternum. A systolic ejection murmur may be present at the aortic area due to the high flow state. Occasionally, a diastolic rumble may be heard at the apex, referred to as the Austin Flint murmur. The mechanism underlying this murmur remains unclear. A number of different causes have been proposed, the most recent being the aortic jet encountering the mitral inflow resulting in turbulence.
++
The systolic arterial pressure is increased due to a large stroke volume, whereas the diastolic pressure is decreased due to runoff from the aorta into both the ventricle and peripheral arteries. This is the underlying reason for a wide pulse pressure and for a variety of associated peripheral signs in chronic significant AR (Table 18–2). However, it must be remembered that these signs are not specific for AR and may occur in any high flow state such as occurs in anemia, thyrotoxicosis, and arteriovenous malformations. With the development of heart failure, the pulse pressure narrows and the peripheral signs of AR are attenuated.
++
+++
Acute Aortic Regurgitation
++
In contrast to chronic AR, most patients with acute severe AR are symptomatic. Initial presentation may vary depending on the underlying cause, which most commonly is aortic dissection, infective endocarditis, or trauma. In the presence of associated acute AR, clinical manifestations of severe dyspnea, orthopnea, and weakness often develop. The onset of symptoms is sudden, with rapid progression to hemodynamic collapse if left untreated.
++
In acute AR, the left ventricle has had no time to adapt to the volume overload state. The peripheral signs associated with chronic AR are therefore absent. Pulse pressure is usually normal, and hypotension may be present in severe cases. Bilateral rales are usually present on examination of the lungs and reflect underlying pulmonary edema. On precordial palpation, the apical impulse is not shifted. The first heart sound may be soft or absent due to the premature closure of the mitral valve. An S3 is often present, but an S4 is usually absent because there is little or no atrial contribution to ventricular filling due to high left ventricular end-diastolic pressure. The typical diastolic murmur of AR is shortened in duration, often difficult to hear, and easily missed.
Hamirani YS, et al. Acute aortic regurgitation.
Circulation. 2012;126(9):1121–6.
[PubMed: 22927474]
++
Laboratory findings depend on the underlying cause of AR. Elevated white blood cell count and erythrocyte sedimentation rate are seen in inflammatory conditions, such as infection and aortitis. Abnormal antinuclear antigen and rheumatoid factor titers may be seen in patients with rheumatologic disorders. When syphilis is suspected, serologic tests may be indicated. Plasma brain natriuretic peptide (BNP) levels are associated with prognosis in patients with AR and may contribute to the decision for surgery.
++
No specific electrocardiographic abnormalities are characteristic of AR. Signs of left atrial enlargement, left ventricular hypertrophy, and a “strain pattern” (ST depression with T-wave inversion in lateral leads) are often seen in chronic significant AR. Arrhythmias, including ventricular ectopy and ventricular tachycardia, may occur in advanced cases with left ventricular dysfunction. In acute AR, sinus tachycardia may be the only abnormality. In cases of infective endocarditis, inflammation or abscess formation may spread to the atrioventricular node, resulting in prolongation of the PR interval or development of atrioventricular block.
++
Chest radiographic findings are not specific for AR and reflect an estimate of cardiac size and pulmonary vascular changes. In chronic significant AR, an increase in the size of the left heart chambers and the aorta is seen. In acute AR, the cardiac size is normal; the lung fields show increased markings due to pulmonary edema. When AR is due to aortic dissection, the chest film may show an enlarged ascending aorta. If calcification of the aortic knob is present, a helpful sign of dissection is increased separation between the outer margin of the aorta and the calcific density.
+++
Echocardiography and Doppler Techniques
++
Echocardiography is the method of choice for evaluating patients with AR. Two-dimensional echocardiography in combination with various Doppler modalities and, in selected cases, transesophageal imaging has provided a noninvasive means for not only diagnosing AR with a high sensitivity and specificity but also for assessing its etiology and severity. Furthermore, important information can be obtained on the hemodynamic impact of the regurgitant lesion, prognosis, and effectiveness of therapy.
+++
Detection of Aortic Regurgitation
++
Doppler techniques are extremely sensitive and specific in the detection of AR, manifested as a diastolic flow abnormality arising from the aortic valve, directed toward the left ventricle. Even trivial regurgitation can be detected, which commonly is not audible on physical examination. Although most cases of moderate-to-severe chronic AR have typical findings on physical examination, moderate lesions may occasionally be missed on examination because of the subtlety of auscultatory findings. Doppler echocardiography is also extremely valuable in patients with acute AR when the typical clinical findings of chronic AR are absent and the brief murmur can often be missed. Color Doppler echocardiography has proven to be extremely helpful in the evaluation of AR (Figure 18–1). It provides a spatial orientation of the regurgitant jet arising from the aortic root. A completely negative color Doppler examination in multiple planes virtually excludes the presence of AR. Echocardiographic imaging with M-mode and two-dimensional examinations cannot detect the presence of AR but can provide indirect clues to its presence. These include diastolic fluttering of the anterior mitral leaflet or septum depending on the impingement of the regurgitant flow on these structures. These signs, although specific, are not sensitive for the detection of AR and do not relate to the severity of regurgitation.
++
++
Because two-dimensional echocardiography can image cardiac structures, it provides valuable information on the cause of the AR. Structural abnormalities of the aortic valve, including calcifications or thickening, congenital deformities, vegetations, rupture, or prolapse, can be identified. Dilatation of the aortic root, calcifications, or dissection can also be evaluated. Although most of these conditions can be assessed with transthoracic echocardiography, transesophageal echocardiography has provided high-resolution images that allow for improved detection of such abnormalities, especially in technically difficult cases or in conditions such as infective endocarditis. Transesophageal echocardiography is also routinely performed when an aortic abnormality, such as aneurysm or dissection, is suspected (Figure 18–2). In patients with AR due to aortic disease, precisely defining the morphology of the valve and involvement of the aortic root is important in determining the surgical approach and deciding whether the valve can be preserved or requires replacement.
++
+++
Assessment of Severity
++
In addition to the detection of AR, Doppler echocardiography combined with two-dimensional echocardiographic imaging has recently allowed an assessment of the severity of the lesion. Several methods have been proposed, including color Doppler assessment of regurgitant jet size, continuous wave Doppler using the pressure half-time method, measurements of regurgitant volume and effective regurgitant orifice area derived from two-dimensional echocardiography and pulsed Doppler techniques, and three-dimensional echocardiography to directly visualize the size of the regurgitant orifice.
++
With color-flow Doppler, the AR jet can be spatially oriented in the two-dimensional plane arising from the aortic valve and directed toward the left ventricle. The ratio of the AR jet diameter just below the leaflets to that of the left ventricular outflow diameter has been shown to correlate well with the severity of regurgitation when compared with the angiographic standard (Table 18–3, see Figure 18–1). Similarly, a good estimation of AR severity has been found by relating the cross-sectional area of the jet at its origin to the left ventricular outflow area. Recently, measurement of the width of the AR jet at the level of the leaflets (vena contracta) has been used to quantitatively approximate AR severity. A vena contracta of > 0.6 cm is considered a sign of severe AR. On the other hand, it is important to note that the length of the AR jet does not correlate well with AR severity. This is in part because color Doppler flow mapping is also highly dependent on the velocity of regurgitation, or the driving pressure, in addition to the regurgitant volume.
++
++
Another index of AR severity that has been useful clinically is the pressure half-time derived from continuous wave Doppler recordings of the AR jet velocity. The velocity of the regurgitant jet is related to the instantaneous pressure difference between the aorta and left ventricle in diastole by the modified Bernoulli equation: ΔP = 4V2, where ΔP is the pressure gradient in millimeters of mercury and V is the blood velocity in meters per second. The pressure half-time index is the time it takes for the initial maximal pressure gradient in diastole to fall by 50%. In patients with mild regurgitation, there is a gradual small drop in the pressure difference in diastole, whereas with severe AR, a more precipitous drop occurs (Figure 18–3). A pressure half-time greater than 500 ms is seen in mild AR, but more significant regurgitation is usually associated with a shorter pressure half-time (see Table 18–3, Figure 18–3). The severity of AR using this index may be overestimated in patients who have elevated left ventricular end-diastolic pressure.
++
++
The severity of AR can also be assessed using regurgitant volume and regurgitant fraction derived from two-dimensional and pulsed Doppler echocardiography. This method is based on the continuity equation, which states that, in the absence of regurgitation, blood flow is equal across all valves. Stroke volume at the level of a valve annulus is calculated as the product of the cross-sectional area obtained by two-dimensional echocardiography and the time velocity integral of flow recorded by pulsed Doppler. In the presence of AR, stroke volume at the left ventricular outflow tract is higher than that across another valve without regurgitation. Therefore, AR volume can be calculated as the difference between stroke volume at the left ventricular outflow and that derived at another valve site. Dividing the regurgitant volume by stroke volume across the aortic valve gives an estimate of regurgitant fraction. A regurgitant fraction of less than 30% is usually mild, whereas regurgitant fraction greater than 50% denotes severe AR (see Table 18–3). A similar approach to estimating severity of AR can be achieved using pulsed Doppler echocardiography in the proximal descending aorta. In patients with significant AR, a large reversal of flow is observed in diastole toward the aortic arch and ascending aorta. This simple method should be used routinely to qualitatively grade the severity of regurgitation and can also be used quantitatively to derive a regurgitant fraction.
++
Proximal flow convergence is more difficult to identify in AR, but when it is present, the proximal isovelocity surface area method can be used to determine the effective regurgitant orifice area. This method is less accurate in eccentric jets and aortic root dilatation.
++
Although color-flow Doppler allows a good estimation of the severity of AR in most patients, its accuracy depends on optimization of the color Doppler examination, including gain settings, frame rate, and interrogation of multiple tomographic planes. The availability of other independent Doppler indices of AR severity further allows the corroboration of color Doppler findings. This is particularly helpful in patients with eccentric AR jets, for which severity may be difficult to assess by color-flow Doppler alone. A detailed transthoracic examination usually provides all the necessary information. When the transthoracic approach is inadequate or inconclusive, transesophageal echocardiography can be performed in this setting for the diagnosis and assessment of severity of the lesion.
++
Another important caveat in classifying the severity of AR is that it is in part dependent on hemodynamic status, including preload and, more importantly, afterload. Raising blood pressure may significantly increase AR severity.
+++
Assessment of Hemodynamic Effects
++
The hemodynamic effects of AR are assessed with both echocardiographic imaging and Doppler echocardiography. Two-dimensional echocardiography provides quantitation of ventricular size and function, in addition to the degree of left ventricular hypertrophy and ventricular mass. End-diastolic and end-systolic left ventricular dimensions and volumes as well as left ventricular ejection fraction provide important measures of the hemodynamic effects of AR and help identify patients at higher risk. In patients with acute AR, premature closure of the mitral valve can be demonstrated by both two-dimensional and M-mode imaging. In these situations, diastolic mitral regurgitation can also be detected by Doppler echocardiography, reflecting the rapid rise of left ventricular pressure in diastole, exceeding that of left atrial pressure. These findings indicate severe AR. In patients with chronic AR, assessment of the ventricular and atrial filling dynamics at the mitral and pulmonary venous inflow, respectively, allows for noninvasive estimation of ventricular diastolic pressure, further adding to the overall evaluation of the hemodynamic effect of AR on ventricular function. Newer modalities such as Doppler tissue imaging further enhance the accuracy of noninvasive assessment of ventricular diastolic function. Thus, in patients with chronic AR, two-dimensional echocardiography with Doppler provides serial assessment of left ventricular volumes, hypertrophy, and function and helps assess the progression of the disease and optimum timing of surgical intervention.
+++
Cardiac Catheterization and Angiography
++
Prior to the introduction of Doppler echocardiography, the evaluation of the severity of AR invariably required invasive testing by cardiac catheterization. With the improvement in the accuracy of noninvasive tests, routine cardiac catheterization is no longer necessary in most patients. At catheterization, the detection of AR is achieved with the injection of radiopaque contrast into the aortic root and the appearance of dye in the left ventricle (Figure 18–4). In addition, aortography allows evaluation of the ascending aorta for dilatation or dissection. Some of the structural abnormalities of the aortic valve may also be identified. The severity of AR is quantitatively approximated using a grading system that takes into account the intensity of contrast dye in the left ventricle and its clearance (Table 18–4). This grading system has been helpful clinically in the assessment of AR severity. However, it is important to emphasize that, similar to other diagnostic techniques, a number of technical factors may also affect interpretation. Positioning the catheter too close to the valve may itself cause regurgitation. The volume and rapidity of contrast injection, ventricular function, and type of catheter used are important factors that may affect the interpretation of AR severity.
++
++
++
At catheterization, the severity of AR can also be assessed by the determination of regurgitant volume and regurgitant fraction. In the absence of regurgitation or shunts, the left ventricular stroke volume derived from contrast ventriculography is equal to right ventricular stroke volume obtained by the Fick method or thermodilution. When isolated AR is present, subtracting left ventricular from right ventricular stroke volume gives the regurgitation volume. Regurgitant fraction is derived as the regurgitant volume divided by left ventricular stroke volume. In the presence of concomitant mitral regurgitation, a total regurgitant volume or fraction can only be assessed using this method. Because of inherent variability in the determination of stroke volume, a 10–15% error in these measurements is not infrequent and is similar to those obtained with Doppler echocardiography.
++
Cardiac catheterization provides an accurate assessment of the hemodynamic effect of AR. Using contrast ventriculography, preferably in biplanar projections, accurate determination of left ventricular volumes and ejection fraction can be performed. Furthermore, direct measurements of pressures in the various cardiac chambers can be recorded. In compensated chronic AR, the only abnormality that may be observed is a widened pulse pressure on the aortic pressure tracing. As decompensation occurs, left ventricular end-diastolic pressure rises. In severe, particularly acute AR, aortic and left ventricular pressures may equalize at end-diastole.
++
With the improvement in noninvasive testing, routine cardiac catheterization is no longer necessary in most patients for the sole assessment of the lesion. Currently, cardiac catheterization is indicated in the assessment of AR severity when noninvasive testing is equivocal or discordant with the clinical presentation and, more commonly, in the assessment of coronary artery disease prior to aortic valve surgery. Preoperative coronary angiography should be performed prior to elective surgery for AR in men older than 35 years of age, premenopausal women over 35 who have risk factors for coronary artery disease, postmenopausal women, and any patients with clinical suspicion of coronary artery disease.
+++
Electrocardiographically Gated Multi-Slice Computed Tomography Angiography (CTA)
++
This test allows rapid diastolic frame rates from which the regurgitant orifice can be planimetered. Studies have shown excellent agreement with echo Doppler measures in the same patients. In addition, the size of the aorta and left ventricle can be determined as well as ejection fraction. CTA can also be used to detect significant coronary artery disease in patients with chest pain or who are being considered for surgery.
+++
Magnetic Resonance Imaging (MRI)
++
Advances in MRI have recently allowed for evaluation of patients with AR. At present, three basic approaches are available: spin echo imaging, gradient echo imaging (cine-MRI), and phase velocity mapping. Spin echo imaging provides an excellent approach for depicting cardiac morphology and detecting aortic root disease. However, aortic valve visualization is poor. Using cine-MRI, AR is detected as a decrease in the signal intensity in the left ventricular outflow during diastole. In preliminary studies, the ratio of area of low-intensity signal to the area of the left ventricular outflow has provided an accurate estimate of AR severity. Regurgitant fractions have been determined by comparing right and left ventricular volumes and stroke volumes. Furthermore, using phase velocity mapping, flow in a region of interest can be assessed. Regurgitant fraction with this method can be derived by comparing flows in the ascending aorta and pulmonary artery.
++
The use of MRI is promising in the assessment of AR. It is particularly helpful in defining the severity and extent of AR. Imaging can be performed in any plane, without attenuation from lung or bone. However, this modality cannot be used in patients carrying metallic objects such as defibrillators or pacemakers. Its current drawbacks are lack of availability of cardiac MRI and high cost. It is an alternative to echocardiography and for centers with expertise in cardiac MRI.
+++
Exercise Stress Testing
++
Exercise stress testing can be used to evaluate patients with equivocal symptoms or to guide patients who wish to participate in athletic activities. Early studies using exercise radionuclide angiography to assess ejection fraction suggested that a failure to rise or a fall in ejection fraction correlated with poor outcomes and was a criteria for considering surgery. However, when resting ejection fraction and end-diastolic left ventricular volume were considered, this exercise response in asymptomatic patients had no independent predictive value. Thus, radionuclide imaging with exercise in patients has been largely abandoned.
Alkadhi H, et al. Aortic regurgitation: assessment with 64-section CT.
Radiology. 2007;245(1):111–21.
[PubMed: 17717329]
Bekeredjian R, et al. Valvular heart disease: aortic regurgitation.
Circulation. 2005;112(1):125–34.
[PubMed: 15998697]
Debl K, et al. Assessment of the anatomic regurgitant orifice in aortic regurgitation: a clinical magnetic resonance imaging study.
Heart. 2008;94(3):e8.
[PubMed: 17686805]
Myerson SG, et al. Aortic regurgitation quantification using cardiovascular magnetic resonance: association with clinical outcome.
Circulation. 2012;126(12):1452–60.
[PubMed: 22879371]
Pizarro R, et al. Prospective validation of the prognostic usefulness of B-type natriuretic peptide in asymptomatic patients with chronic severe aortic regurgitation.
J Am Coll Cardiol. 2011;58:1705–14.
[PubMed: 21982316]
Scheffel H, et al. Accuracy of 64-slice computed tomography for the preoperative detection of coronary artery disease in patients with chronic aortic regurgitation.
Am J Cardiol. 2007;100(4):701–6.
[PubMed: 17697832]