Disclosure
Background: Aortic regurgitation affects one tenth of all patients with valvular heart disease. It is characterized by an abnormal backward leakage of blood from the aorta into the left ventricle (LV) during the diastolic phase of the cardiac cycle. The disease process may involve the aortic valve cusps, the aortic root, or both. Clinically, aortic regurgitation aortic regurgitation manifests in a wide variety of ways ranging from recognition of an asymptomatic heart murmur on physical examination to symptoms owing to substantial LV dysfunction and heart failure. The diagnosis can be established by means of multiple noninvasive techniques. Echocardiography has emerged as the most important imaging technique in the diagnosis of aortic regurgitation, as well as in the determination of its causes, severity, and management strategy. Treatment often depends on whether the regurgitation develops acutely or as a chronic disease. Patients with acute aortic regurgitation have a poor prognosis unless rapid surgical treatment is undertaken. Chronic aortic regurgitation may remain asymptomatic for years and generally results in a better prognosis until the emergence of evidence of symptoms that indicate development of LV dysfunction. Medical management is the initial choice. This strategy involves the use of pharmacologic agents for afterload reduction, treatment of symptoms, and subacute bacterial endocarditis prophylaxis, as well as periodic echocardiographic assessment to monitor progression of aortic regurgitation. Aortic valve replacement is indicated in later stages before LV dysfunction sets in; however, determination of the exact timing of the procedure requires careful analysis of echocardiographic indices and, occasionally, cardiopulmonary exercise testing. The surgical outcome is usually good with mortality rates of 3-8%. After valve replacement, the progression of heart failure stops in most patients, and some have positive remodeling and improved exertion capacity. Pathophysiology: Aortic regurgitation represents a reflux of blood that has been ejected into the aorta back into the LV during the diastolic phase of each cardiac cycle. The LV receives blood from the left atrium at the same time. This results in volume overload of the LV that, over time, leads to structural as well as physiologic changes in the LV. The gradual structural change causes sizable LV enlargement greater than that seen in any other form of heart disease. LV end-diastolic volume becomes large, but LV compliance often increases and LV end-diastolic pressure stays near normal. LV hypertrophy is minimal, and it is of an eccentric variety, also known as hypertrophy in length. It is caused by replication of myocardial sarcomeres in series. Such hypertrophy occurs to maintain systolic wall stress at normal levels and the ratio of LV thickness to cavity radius remains normal. This adaptive response allows the LV to function as an effective low-compliance pump. As aortic regurgitation becomes severe, the regurgitant flow may exceed 20 L/min with total LV output almost 30 L/min, a level seen only in trained endurance runners at maximal exercise. Ultimately, a persistent rise in the preload and afterload in aortic regurgitation leads to myocardial dysfunction. LV end-diastolic volume increases disproportionately to the regurgitant amount. This process of decompensation may be gradual and may precede the onset of symptoms. With progressive LV decompensation, an increase in the pressure occurs in the left atrium, pulmonary bed, right ventricle, and right atrium, with a decrease in cardiac output even at rest. It is crucial for the clinician to detect the onset of such LV dysfunction to avoid missing the optimal time for valve replacement. The extent and severity of aortic regurgitation depends on the size of the diastolic aortic valve opening, the diastolic gradient between the aortic and LV pressure, and the length of the diastolic period. During dynamic exercise, as the heart rate increases, the diastolic period tends to shorten, leading to a decrease in the amount of aortic regurgitation. The increased systolic output into the aorta, and the diastolic blood reflux into the LV cause an increased pulse pressure manifesting as Corrigan pulse, Hill sign, etc. Lower diastolic aortic pressure further leads to a lower-pressure head in the coronary circulation, which may manifest as ischemia. The regurgitant jet may hit the anterior mitral cusp, causing its reverse doming in diastole. Fast moving blood produces a drop in pressure (Bernoulli effect), which can pull the anterior mitral leaflet and/or submitral chordae towards the outflow tract (systolic anterior motion [SAM]). The ascending aorta may progressively dilate in turn, leading to poorer aortic cusp coaptation and increasing regurgitation. Acute aortic regurgitation In contrast to chronic aortic regurgitation in which the LV has the opportunity to adapt to the volume overload with enlargement and hypertrophy, in acute aortic regurgitation, the regurgitated blood volume fills a LV of normal dimension and compliance. In this instance, the stroke volume cannot increase adequately, and forward cardiac output declines. LV volumes remain small, and the pulse pressure narrows. In order to compensate for the low stroke volume, the heart rate increases sharply, and patients have tachycardia. Rising LV end-diastolic pressure leads to early closure of the mitral valve, which protects the pulmonary vascular bed from the backward transmission of high pressure. However, it also reduces LV preload. Systolic pressure in the LV and aorta remains normal. Frequency:
Mortality/Morbidity: Mortality and morbidity depends on whether the process is acute in onset or chronic. In the latter case, it depends on the presence and severity of symptoms and LV dysfunction.
Race: Aortic regurgitation has been described in all races. Sex: No clear-cut sex predilection appears to exist. Age:
Anatomy: Rheumatic heart disease still remains the most common cause of severe AR. Over the past several decades, however, diseases involving the aortic root are becoming more frequent. Causes of aortic regurgitation include the following:
Aortic cusp disease Aortic cusp disease leads to aortic regurgitation by causing inadequate leaflet coaptation due to the shrinkage or retraction of the cusps because of inflammation. For example, in rheumatic fever, the cusps infiltrated by fibrous tissue gradually shrink, leading to regurgitation into the LV through a central opening. When the inflammatory process leads to fusion of the commissures, combined aortic stenosis and aortic regurgitation may occur. Other primarily valvular causes of aortic regurgitation Other primarily valvular causes of aortic regurgitation include the following:
Causes of aortic root disease Causes of aortic root disease include dilatation of the ascending aorta and other specific causes. Aortic regurgitation is secondary to severe dilatation of the ascending aorta is becoming more frequent than the presence of primary aortic cusp disease in patients operated on for isolated aortic regurgitation. Regarding specific causes, diseases that involve aortic root include degenerative aortic dilatation in the elderly, cystic medial necrosis of the aorta in patients with Marfan syndrome, syphilitic aortitis, and dissection of the ascending aorta. Clinical Details: Clinical findings in chronic aortic regurgitationMost patients with aortic regurgitation are asymptomatic, and the diagnosis is made with the detection of a heart murmur during physical examination. Symptoms Although a heart murmur and heart failure may develop rapidly in acute aortic regurgitation, patients with chronic regurgitation develop symptoms late in the time course of the disease. Chronic regurgitation may be present for a decade before exertional dyspnea develops as its presenting symptom. Patients whose functional capacity is reduced to NYHA class III generally have underlying LV dysfunction. Heart pounding is another frequent symptom, whereas chest pain occurs in 20% of the patients with aortic regurgitation. Concomitant coronary stenosis may also be present in 20% of the patients. Chest pain occurs less often in aortic regurgitation than in aortic stenosis; however, nocturnal angina often accompanied by diaphoresis may occur when the heart rate slows and arterial diastolic pressure falls to extremely low levels. Some patients with aortic regurgitation also report abdominal pain, presumably secondary to splanchnic ischemia. Signs In severe chronic aortic regurgitation, a marked decrease in diastolic pressure along with some increase in systolic blood pressure occurs. As a result, the pulse pressure may become high, often greater than 80 mm Hg. In patients with this finding, determination of the exact diastolic blood pressure becomes difficult because the Korotkoff sounds remain audible all the way down to zero. The diastolic pressure is established at the point of muffling. On inspection, visible pulsations of the carotid artery are noticeable. Such pulsations are due to a wide pulse pressure and rapid decreased and can be transmitted to the adjacent tissues in the neck, causing pulsatile movements of the head (Musset sign), larynx (Oliver-Cardarelli sign), and uvula (Muller sign). Capillary pulsations over the lips and the ball of the fingertips can be visualized as well, by lightly compressing with a glass slide. The pulsations in the abdominal aorta may be visible in the suprarenal region. On palpation, the rapid arterial filling followed by an abrupt fall in the intraluminal pressure due to aortic regurgitation causes a water-hammer pulse (Corrigan pulse). Auscultation over the femoral arteries in patients with at least moderate aortic regurgitation exhibits a loud, early systolic sound called a pistol-shot sound. On gentle compression of the femoral artery, one can hear a systodiastolic murmur (Duroziez sign). Precordial auscultation usually reveals a soft first heart sound (S1) and a loud S2. The latter becomes muffled as the aortic regurgitation becomes worse. An S3 gallop is audible once LV dysfunction sets in. The characteristic murmur of chronic aortic regurgitation is a diastolic decrescendo murmur, which is heard best in the right second intercostal space. If the patient sits up and leans forward, the same murmur can be heard in the left third and fourth intercostal spaces. As the disease worsens, the length of the murmur increases and finally occupies the entire diastolic period in the most severe cases. Occasionally, the diastolic murmur of aortic regurgitation sounds musical, like a seagull cry or "dove coo" murmur. A concomitant systolic ejection murmur is almost always present and due to increased turbulent flow through the aortic valve. Patients with severe aortic regurgitation sometimes exhibit a diastolic murmur at the apex (Austin Flint murmur) due to functional mitral stenosis. The anterior mitral leaflet closes early because of the aortic regurgitation jet hits it in diastole. Clinical findings in acute aortic regurgitationBecause of the limited ability of the LV to handle acute severe aortic regurgitation, patients with acute disease generally have a sudden onset of symptoms, including heart failure with weakness, severe dyspnea, and hypertension. Angina is uncommon. The pulse pressure is generally not wide; therefore, the signs related to increased pulsation are lacking. The murmur of aortic regurgitation is shorter as well, and it ends in the middle of the diastolic interval. Also, because the mitral valve closes in diastole, no S1 is audible. Preferred Examination: In patients with chronic aortic regurgitation, electrocardiography usually shows a normal sinus rhythm and evidence of LV hypertrophy as the disease progresses. Some patients may have a first-degree heart block. The presence of ST-segment depression and T-wave inversion is associated with an adverse prognosis. A bundle-branch block may develop in advanced aortic regurgitation. Holter monitoring In patients with aortic regurgitation, 24-hour Holter monitoring may show complex ventricular arrhythmias. The severity of arrhythmias is proportional to the deterioration of LV function. Systolic time intervals Carotid pulse tracing in chronic aortic regurgitation may exhibit rapid upstroke, and the absence of a clear-cut incisura on the down stroke. Systolic time intervals are rarely used at present. Chest radiography An enlarged cardiac silhouette is often the hallmark of a patient with significant AR. As aortic regurgitation becomes more severe, LV enlargement ensues, mainly in the transverse and caudal directions, leading to an increased cardiothoracic ratio. When the cardiothoracic ratio exceeds 0.60, survival is diminished. Dilatation of the aorta and aortic valvular calcification is occasionally seen. Echocardiography Two-dimensional, color, and Doppler echocardiography has become the preferred imaging techniques in the diagnosis and assessment of aortic regurgitation. The disease can be identified, and the severity and (in many instances) the etiology of can be determined with high sensitivity and specificity. In additional, analysis of the LV function and end-diastolic dimension can be used to determine the optimal timing of valve surgery. Radioisotope study Radioisotope studies can occasionally be used to quantify the severity of AR. The LV function can likewise be assessed. Determination of preexercise and postexercise LV ejection fraction (LVEF) can often show failure of the ejection fraction to increased with exercise; this is an indicator of early LV dysfunction. Echocardiography has replaced these tests in most patients, with reasonable reliability. Cardiopulmonary exercise testing Exercise capacity and maximal oxygen consumption can be measured for determining the onset of functional deterioration and subsequent surveillance to aid in deciding the optimal time for surgical intervention. Cardiac catheterization and angiography Cardiac catheterization is used mainly for evaluating the presence of concomitant coronary artery disease prior to surgery. Noninvasive techniques have supplanted angiocardiography for evaluation of aortic regurgitation. Limitations of Techniques: Electrocardiographic findings are generally nonspecific. Systolic time intervals are no longer used in clinical practice. Chest radiographic findings of increased cardiothoracic ratio can aid in the diagnosis, but they cannot be used by itself to make a diagnosis. Echocardiography is pivotal to making the diagnosis of aortic regurgitation, and determining its severity and timing for surgery. Limitations are minimal, and may include poor acoustic windows. Findings may be equivocal for determining the onset of the LV dysfunction, in which case a radioisotope technique may be helpful. Certain patients may need to undergo cardiopulmonary exercise testing to determine the optimal timing for valve replacement.
Ankylosing Spondylitis
Marfan syndrome
Findings: The size of the heart is represented by the size of the cardiac shadow or silhouette seen on the chest radiograph. In patients with chronic aortic regurgitation, the size of the heart depends on both the severity and the duration of the regurgitation. In patients with aortic regurgitation, chest radiographs show cardiac enlargement, as manifested by an increased cardiothoracic ratio (ie, the diameter of the cardiac shadow divided by the diameter of the thoracic cavity). The LV is enlarged laterally and inferiorly. Therefore, the vertical diameter increases more prominently than the horizontal diameter. The left atrium may also be enlarged. Dilatation of the aortic root can be seen as well. In some patients with combined aortic stenosis and regurgitation, aortic valvular calcification can also be present. Linear calcifications in the wall of the ascending aorta may be seen in syphilitic aortitis. Degree of Confidence: Radiographic findings are nonspecific. |
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Findings: MRI can be a valuable tool in the assessment of aortic regurgitation. MRI may be used if echo windows are poor. For instance, the lung can block echo views, and aortic root calcifications can produce echo image artifacts. Aortic regurgitation is easily detected with MRI by using gradient recalled echo (GRE; FIESTA) sequences, and they can be accurately quantified by using dynamic 2-dimensional (2D) phase contrast. This method creates a series of images at the level of the aortic root that show the direction and speed of blood movement throughout the cardiac cycle. The forward and regurgitant volumes can be calculated more accurately with MRI than with sonography to compute regurgitant volume and regurgitant fraction. In patients with aortic regurgitation, MRI can still be helpful in cases in which the Doppler echocardiographic results are insufficient or not consistent with the clinical data. Pulse sequences Recent technologic advances in MRI computer technologies have enabled the use of many pulse sequences for cardiac imaging. The 2 main pulse sequences can be classified into dark-blood and bright-blood techniques. In the dark-blood technique, such as in spin-echo (SE) and fast SE (FSE) imaging, the fast-flowing blood is black and of low intensity. This method is principally useful for delineating the structure of cardiac chambers and the lumens of blood vessels. In contrast, the bright-blood techniques, such as GRE sequences, depict flowing blood as white and of high intensity. This method can be used to determine gradients and flows. In some cases, the cause of the regurgitation can be inferred by examining SE images. Examples include aortoannular ectasia, aortic dissection, and endocarditis. Certain structural changes related to valvular regurgitation, such as LV enlargement, can also be demonstrated on SE images. Blood has high signal intensity on cine GE images. An abnormal flow pattern due to aortic regurgitation creates dephasing of the spins in a voxel, causing signal loss, or flow void. This is better demonstrated with longer echo time (TE). Cine GE images enable quantitative assessment of the aortic regurgitation based on the area and the length of the signal void. Aortic regurgitation is best seen on a coronal plane as a signal void extending from the aortic valve into the LV during diastole. Fast cine GE imaging can be used to measure ventricular and stroke volumes and calculate the regurgitant fraction (regurgitant volume divided by LV stroke volume). Imaging planes The imaging planes for MRI of the thorax are the 3 orthogonal planes: transverse, sagittal, and coronal. As the cardiac axes are not parallel to the body axes, planes parallel and orthogonal to cardiac axes (short axis and long axis of the heart) are used for cardiac imaging. Velocity-encoded MRI Velocity-encoded MRI is the best way to calculate LV and right ventricular stroke volumes and to quantify the aortic regurgitant fraction. This technique can be used to measure the blood flow in the ascending aorta and pulmonary artery or to display phase shift. Fixed areas appear gray, whereas blood flow in forward and backward direction along a flow-encoding axis appears bright and dark respectively. These findings permit the estimation of antegrade and retrograde flow, which can also be color coded. Curves of flow versus time during cardiac cycle are then plotted. The area of the curve beneath the baseline indicates the regurgitant volume, and that above the baseline represents the stroke volume. The regurgitant fraction can then be calculated. Degree of Confidence: Cine GE images with measurements such as the area and depth of signal void provide only a semiquantitative assessment of the severity of aortic regurgitation. The signal void is generally traced manually and can vary depending on the image display settings. Therefore, this method has limitations because the display of signal void can vary, as it is affected by the difference in TE, display parameters, and even physiologic factors such as variance in LV volume and pressure. Cine GE is not a determinant of MRI confidence. Also, 2D phase-contrast analysis does not rely on the assumptions commonly used with echo Doppler study, and it produces reliable model-independent measurements. However, arrhythmias, electrocardiographic gating problems, and obesity can reduce MRI quality. Good-quality MRI offers a high degree of confidence, but with gating or other problems, the confidence level may be low. False Positives/Negatives: There is essentially never a false-positive MRI. The display of the signal void on cine GE images depends on several technical parameters, such as display parameters including window level and window width, flip angle, and (most importantly) the TE. With a short TE, the signal void may even disappear, whereas with a long TE, it tends to show up well. This dependency must be taken into account, and the TE should be kept long. One way to decrease the acquisition time by a factor of 2 or 3 is to use segmentation of k space, depending on the heart rate. 2D phase-contrast imaging can produce a false-negative result if the parameters are set incorrectly (few temporal bins, low velocity sensitivity, or velocity aliasing) or if gating is poor. Simple GE imaging could produce a false-negative result if MRIs are acquired with only a short TE, but this is much less of an issue with GRE.
Findings: Echocardiography is generally the most important diagnostic imaging study for evaluating patients with aortic regurgitation. The presence or absence of regurgitation is reliably established by means of Doppler echocardiography. However, quantification of the severity is difficult, and it requires integration of several M-mode, 2D, and Doppler indices; no one index alone has proven reliable. M-mode echocardiography M-mode echocardiogram shows diastolic fluttering of the anterior mitral leaflet (AML), which is a finding of diagnostic significance. It results from the AR jet hitting the AML, and can be seen in even milder degrees of aortic regurgitation. In severe cases, the AML may fully close from the impact of the jet; this finding can serve as an indication for valve surgery. Diastolic flutter of the interventricular septum may also be seen in some patients. Aortic root and LV dimensions are increased. M-mode echocardiography may also show systolic anterior motion of the anterior mitral valve leaflet or chordae. 2D echocardiography Structural integrity of the aortic valve leaflet, LV outflow tract, and aortic root can be examined in detail in several planes by means of 2D echocardiography. Often, the cause of aortic regurgitation can be determined from these images. For example, presence of aortic valve vegetation, flail aortic leaflet, aortic cusp retraction and shortening, or aortic root abnormalities are discernible with reasonable ease. Determination of LV dimensions and systolic function is central to the decision regarding the timing of surgery. Some of the echocardiographic indices that represent indications for surgery include dilatation of the LV beyond 70 mm in diastole or beyond 55 mm in systole, a fractional shortening of less than 25%, and progressive dilation of the LV of 1.0 cm or more over a 12-month period. Color flow imaging Aortic regurgitation can also be quantified in terms of its severity by color and Doppler echocardiography. Color flow imaging can display the regurgitant jet in various planes. While the size and depth of the jet is only poorly correlated with the severity of aortic regurgitation, measurement of width or the cross-sectional area of the regurgitant jet as a ratio of the total width or cross-sectional area of the outflow tract is more reliable. Aortic regurgitation can be classified into mild, moderate, or severe forms on the basis of whether the width of the regurgitant jet occupies less than 20%, 20-40%, or more than 40% of the total width of the LV outflow tract, respectively. Another way of estimating the severity of regurgitation is by examining the regurgitant color Doppler jet involves measurement of the linear distance the jet travels into the LV cavity or by mapping the area of the color jet. Doppler echocardiography By using continuous-wave Doppler imaging from the apex, the actual velocity of the regurgitant flow can be recorded. A relatively flat slope of velocity and pressure decay indicates mild aortic regurgitation, whereas a steep slope of velocity decay over the diastolic pressure curve (rapid deceleration or short pressure half-time) indicates severe disease. The pressure half-time value of the aortic regurgitation jet that is greater than 450 ms indicates mild regurgitation, and one less than 250 ms indicates severe regurgitation. Often, the continuity equation can be used to calculate the regurgitant volume. Retrograde flow should be assessed in the descending aorta. Small, retrograde, early diastolic signals are normal in the descending thoracic or abdominal aorta. However, any degree of holodiastolic retrograde flow indicates severe aortic regurgitation. Degree of Confidence: The degree of confidence is high. In the assessment of aortic regurgitation severity with color Doppler techniques, the measurements depend on imaging the jet in its minor axis. An eccentric jet crossing across the outflow tract results in a jet that is disproportionate to its true dimension. Transesophageal echocardiography often provides more accurate visualization of the true direction and size of the regurgitant jet. False Positives/Negatives: Doppler echo imaging can produce a false-positive result if continuous Doppler wave, a side lobe, or a distant multiple pulsed wave picks up a similar flow pattern (eg, from a resistive VSD). Doppler echo sonography can produce a false-negative result if the valve is not studied thoroughly at varied angles and if the regurgitant jet is angulated or off-center (eg, from a leaflet perforation).
Findings: Radioisotope techniques, especially first-pass multiple-gated acquisition (MUGA) scanning, can be used to determine the LVEF. Such techniques can also be used to assess the severity of aortic regurgitation. In patients who are minimally symptomatic or even asymptomatic, an evaluation of LVEF before and after dynamic exercise can provide valuable clues regarding the onset of the early stages of LV dysfunction. In patients in whom myocardial dysfunction begins to develop, the ejection fraction does not increase after exercise. Degree of Confidence: The degree of confidence is moderate. Often, patients have LV dysfunction, but the studies may not show the absence of an increased ejection fraction during exercise.
Findings: Invasive evaluation of moderate-to-severe degrees of AR may be indicated when clinical deterioration appears to have begun as indicated by progressive symptoms, increased cardiothoracic ratio on chest radiogram, ST-T changes on electrocardiography, and <25% fractional shortening on the echocardiogram along with end-diastolic LV diameter >7 cm. Angiography also helps in determining the presence of concomitant coronary artery disease, which may be found in 20% of the patients. Hemodynamic arterial tracings typically show greatly increased pulse pressure. In severe aortic regurgitation, the aortic and LV pressures tend to equalize at the end diastole. A regurgitant fraction can be calculated by using green dye. A regurgitant fraction of <0.3 represents mild regurgitation, whereas that above 0.5 represents severe regurgitation. An overall LVEF <50% has a prognostic value, and it has been found to predict greater postoperative mortality and inability to recover cardiac pump function. Degree of Confidence: The degree of confidence is high. In the current era of thorough echocardiographic evaluation, the need for cardiac catheterization has diminished tremendously. Often the only indication for performing catheterization in patients with chronic aortic regurgitation is the need to rule out the presence of significant coronary stenosis in those older than 40 years. False Positives/Negatives: False findings are infrequent. A false-positive finding can occur from ectopy or if the catheter interferes with the valve closure. A false-negative result can occur from ectopy and/or outflow tract obstruction.
Intervention: No percutaneous treatment modality is applicable to the treatment of aortic regurgitation. Prompt surgical treatment is recommended for symptomatic patients and patients with acute aortic regurgitation. The central aim in recommending valve replacement surgery is the preservation of LV function. In contrast, asymptomatic patients generally have an excellent prognosis for a number of years. Therefore, aortic valve replacement is deferred as long as the patient has good exercise tolerance, an ejection fraction of 50% or greater, and an LV end-diastolic diameter of under 7 cm. In asymptomatic patients with normal LVEF close follow-up at 6-month intervals is recommended. Aortic valve replacement surgery should be undertaken if the LV end-diastolic dimension increases to greater than 7 cm, if the end-systolic diameter becomes 5.5 cm or more, and if the fractional shortening decreases to less than 25%. Medical/Legal Pitfalls:
Special Concerns:
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