The Adult with Congenital Heart Disease

17


The Adult with Congenital Heart Disease




There are two basic categories of congenital heart disease in adults:



In adult patients with no previous diagnosis of heart disease, a congenital defect often is not considered as a potential cause of symptoms, and thus the initial diagnosis may be made at the echocardiographic examination. In these patients, the diagnostic challenge is to recognize and correctly evaluate the congenital abnormality. In contrast, in patients with known congenital disease and previous surgical procedures, the goal is to identify the postoperative anatomy and assess the physiologic consequences of residual defects in each patient. With “corrective” surgery, as with “palliative” procedures, many patients have significant residual or progressive abnormalities.


Both of these challenges can be met by a logical and methodical approach to the echocardiographic examination with the application of the basic principles of ultrasound imaging and Doppler data described throughout this text. In addition to careful integration of imaging and Doppler data, evaluation with other imaging modalities, such as cardiac magnetic resonance (CMR) imaging or computed tomography (CT), may be needed for complete assessment of congenital heart disease.


A comprehensive discussion of the echocardiographic findings in adult congenital heart disease is beyond the scope of this text. Instead, an overview of the echocardiographic approach to these patients and examples of the more common abnormalities is presented. The reader is referred to the specialized references listed at the end of the chapter for more detailed information. The goal of this chapter is to allow preliminary diagnosis of congenital heart disease; advanced training is recommended for definitive imaging and diagnosis of congenital heart disease.



Echocardiographic Approach


Congenital heart disease in adults can be grouped into several categories (Table 17-1):





Congenital Stenotic Lesions


Congenital stenotic lesions, including obstruction to right ventricular (RV) or left ventricular (LV) outflow (either subvalvular, valvular, or supravalvular), obstruction to LV inflow (congenital mitral stenosis, cor triatriatum), and narrowings in the great vessels (aortic coarctation, branch pulmonary artery [PA] stenosis) are common.


The anatomy of a congenital stenotic lesion differs from that seen in acquired valve disease, but the physiology and fluid dynamics are similar, with normal velocity flow upstream and a flow disturbance downstream from the narrowing. In the narrowed region itself, a high-velocity laminar jet of flow is present, with velocity (V, in m/s) related to the pressure difference (ΔP, in mm Hg) across the narrowing as stated in the simplified Bernoulli equation:


image (17-1)


When a parallel intercept angle can be obtained between the jet and the ultrasound beam, quantitative data on stenosis severity and intracardiac hemodynamics can be derived. For example, if the maximum velocity across a subpulmonic membrane is 4.5 m/s, then the maximum RV to PA systolic pressure difference is approximately 80 mm Hg. Quantitative evaluation of stenosis severity for a congenitally stenotic lesion includes the calculation of maximum and mean pressure gradients as for acquired valve stenosis. Similarly, when possible, valve area calculations are performed using either the continuity equation (aortic valve) or the pressure half-time method (mitral valve).


Several significant differences between congenital and acquired stenosis should be noted. First, congenital stenosis of ventricular outflow, for both the RV and the LV, may involve the subvalvular or the supravalvular region rather than (or in addition to) stenosis of the valve itself (Fig. 17-1). Careful evaluation with conventional pulsed Doppler or color flow imaging to identify the poststenotic flow disturbance is helpful in determining the exact site of obstruction. Second, when serial stenoses are present, quantitation of the contribution of each level of obstruction to the overall degree of stenosis can be difficult using Doppler echo methods. Third, the proximal flow pattern in congenital stenosis often is characterized by a greater increase in velocity because of anatomic tapering of the proximal flow region (e.g., in aortic coarctation or in the congenitally stenotic pulmonic valve). In these situations, accurate pressure gradient calculations should include the proximal velocity (Vprox) and the jet velocity (Vjet) in the Bernoulli equation:


image (17-2)


Otherwise, the evaluation of congenital stenosis is similar to the evaluation of acquired stenosis in adults, and the methods described in detail in Chapter 11 can be applied in this patient group.




Congenital Regurgitant Lesions


Careful imaging of a congenitally regurgitant valve may reveal the specific mechanism of regurgitation in that patient. For the atrioventricular valves, particular attention is focused on the number and position of papillary muscles; the chordal attachments (especially aberrant ones); leaflet size, shape, thickness, redundancy, and motion; and annulus size and shape. Malformations can include myxomatous changes of the leaflets, abnormal leaflet position (Ebstein anomaly), and abnormal chordal attachments (atrioventricular canal defect) (Fig.17-2). The semilunar valves may be regurgitant because of great vessel dilation or a leaflet fenestration. Three-dimensional (3D) imaging may be helpful in the evaluation of leaflet anatomy and the mechanism of regurgitation.



The physiology of congenital regurgitation is no different from that of acquired regurgitation. There is a flow disturbance in the chamber receiving the regurgitant flow with progressive dilation (and eventual dysfunction) of the volume-overloaded cardiac chambers. The evaluation of congenital regurgitation is similar to the evaluation of acquired regurgitation, as detailed in Chapter 12.



Abnormal Intracardiac Communications (Shunts)


An abnormal intracardiac communication is characterized by blood flow across the defect, with the direction, timing, and volume of flow determined by the size of the orifice, the pressure gradient across the defect, and the relative resistance to flow of the vascular beds on each side of the defect. If left-sided heart pressures exceed right-sided pressures (pulmonary vascular resistance is low), left-to-right flow across the defect predominates. Small degrees of right-to-left shunting may be present briefly during the cardiac cycle, because right-sided pressures may transiently exceed left-sided pressures.


With conventional pulsed Doppler ultrasound or with color flow imaging, a flow disturbance is found downstream from the defect: on the right side of the interventricular septum for a ventricular septal defect (VSD), in the right atrium (RA) for an atrial septal defect (ASD), and in the PA for a patent ductus arteriosus.


Analogous to a stenotic or regurgitant orifice, the velocity of blood flow through the shunt orifice is related to the pressure gradient across the defect, as stated in the Bernoulli equation. Thus, a small VSD results in a high-velocity systolic flow signal (approximately 5 m/s), because LV systolic pressure greatly exceeds RV systolic pressure (by approximately 100 mm Hg) (Fig. 17-3). Conversely, flow across an ASD typically is low in velocity because only a modest left atrial (LA) to RA pressure difference is present.



A left-to-right intracardiac shunt imposes a chronic volume overload on the receiving chamber(s) with consequent dilation of the affected chamber(s). With an ASD, both RA and RV dilation, along with paradoxical septal motion, are seen. With a patent ductus arteriosus, the volume overload is imposed on the LA and LV. Although it might seem that a VSD would cause RV volume overload, in fact, RV size usually is normal because the LV effectively ejects the shunt flow across the defect and then directly into the PA in systole. Instead, LA and LV dilation are seen, because these chambers receive the increased pulmonary blood flow as it returns to the left side of the heart via the pulmonary veins.


The volume of blood flow (Q) across an intracardiac shunt—the ratio of pulmonary to systemic blood flow (Qp:Qs)—can be determined by Doppler echo measurements of stroke volume at two intracardiac sites (Fig. 17-4). In the case of an ASD, transpulmonic volume flow (Qp) is calculated from PA cross-sectional area (CSA) and velocity-time integral (VTI), while systemic volume flow (Qs) is calculated from measurements of LV outflow tract (LVOT) cross-sectional area and velocity-time integral:


image (17-3)


image (17-4)


so that:


image (17-5)


This approach is accurate when two-dimensional (2D) images are of adequate quality for precise diameter measurements (for calculation of a circular cross-sectional area) and when Doppler velocity data are recorded at a parallel intercept angle to flow. Potential errors in estimation of the Qp:Qs ratio may arise as for any Doppler echo stroke volume measurement (see Chapter 6).



With significant left-to-right shunting, pulmonary pressures become elevated, and irreversible pulmonary hypertension may develop over time. When pulmonary vascular resistance equals or exceeds systemic vascular resistance, the direction of shunt flow reverses, resulting in decreased systemic oxygen saturation and cyanosis. Irreversible pulmonary hypertension with equalization of pulmonary and systemic pressures due to an intracardiac shunt is known as Eisenmenger physiology. This phenomenon can occur in infancy, particularly with a large VSD, but also can occur later in life when the pulmonary-to-systemic shunt ratio chronically exceeds 2:1.



Abnormal Chamber and Great Vessel Connections


Echocardiographic diagnosis is more difficult when there are abnormal connections between the atrium and the ventricles, between the ventricles and great vessels, or both. In adults, poor acoustic access may further compromise the examination. However, with a systematic approach, a correct anatomic evaluation usually is possible.


Because the position of the heart in the chest may be abnormal, the echocardiographer cannot rely on the intrathoracic position of the chambers for correct identification of cardiac anatomy. Dextroposition is a rightward shift in the cardiac position with otherwise normal anatomy; for example, due to decreased right lung volume or severe scoliosis. Acoustic windows are shifted rightward, but image planes are similar to normal. With dextroversion, the cardiac apex points to the right, but the right and left heart chambers are otherwise normally related. Long-axis views are obtained with the image plane aligned from the left shoulder to the right hip, and the apical window is midline or right of the sternum. In contrast, with mirror image dextrocardia, cardiac anatomy is a mirror image of normal (the right-sided chambers are left of the left-sided chambers), and the heart is located in the right hemithorax with the apex in the right mid-clavicular line. Thus, acoustic windows are on the right chest with image planes mirror images of normal. The term situs inversus refers to right-to-left reversal of thoracic and abdominal viscera.


Atrial situs refers to the position of the RA and LA in the chest. The inferior vena cava nearly always drains into the RA, allowing correct identification of this chamber by imaging the inferior vena cava from a subcostal approach and following it into the RA. Thus, the subcostal window often is a useful starting point for the examination of a patient with complex congenital heart disease. The LA, then, is the “other” atrial chamber, because although the pulmonary veins normally drain into the LA, this is not always the case (e.g., partial or total anomalous pulmonary venous return).


The anatomic RV and LV can be distinguished from each other by several features (Fig. 17-5). The anatomic RV has:




Fibrous continuity of the anterior mitral valve leaflet and the aortic valve occurs only with a normally related LV and aortic root. When the anatomic RV connects to the aortic root, a band of myocardium is seen between the base of the atrioventricular valve leaflet and the great vessel. When there are abnormal connections of the anatomic ventricles, the ventricle pumping blood to the pulmonary bed is called the “pulmonary ventricle,” and the ventricle pumping blood into the aorta is called the “systemic ventricle.”


The atrioventricular valves develop with the appropriate anatomic ventricle, so identification of the mitral valve is another feature that differentiates the LV from the RV. Caution is needed if a cleft anterior mitral valve leaflet is present, because it may superficially resemble the tricuspid valve. In addition to the number of atrioventricular valve leaflets, the relative positions of the atrioventricular valve annuli are helpful, because the tricuspid valve annulus lies slightly closer to the apex than the mitral valve annulus. Note that ventricular size, shape, and/or wall thickness do not distinguish the two ventricles, because congenital lesions can result in dilation and hypertrophy of either chamber.


After identifying the atrium and ventricles, attention is directed toward the great vessels. The aortic root is best identified by following the vessel downstream to image the arch and head and neck vessels. Origins of the coronary arteries also may be seen, but anomalous origin of the coronary arteries from the PA must be considered. The PA is identified by its bifurcation into right and left branches.


The position of the great vessels within the thorax and relative to one another often is altered in congenital disease. Normally, the PA lies anterior and slightly medial to the aortic root at its origin and then courses posteriorly and laterally, with the right PA lying posterior to the ascending aorta. The aortic annulus normally lies posterior to the RV outflow tract, with the aortic root extending medially and anteriorly before turning posterolaterally to form the aortic arch. The normal relationship of the aortic and pulmonic valve planes is approximately perpendicular to each other, with the pulmonary valve slightly more superior within the chest than the aortic valve. With transpositions of the great vessels, these relationships are altered, so the semilunar valves lie in the same tomographic plane, and the aorta and the PA lie parallel to each other instead of in their normal “crisscross” positions. If the aorta is located anterior and to the left, L (for levo) transposition is present. An anterior and medial (rightward) aorta is termed D (for dextro) transposition.


Most patients with abnormal connections between the cardiac chambers and great vessels have associated abnormalities that require echocardiographic evaluation. These include intracardiac shunts, stenotic and regurgitant lesions, pulmonary hypertension, and ventricular dysfunction. The echocardiographic examination in these patients is facilitated by:



During the examination, the physician and the sonographer work together to identify:



In addition, the echocardiographer may suggest other appropriate imaging modalities to address any areas of uncertainty.



Congenital Defects Seen in Adults with or Without Previous Cardiac Surgery



Obstruction to Left Ventricular Outflow



Congenital Aortic Valve Stenosis


Although a congenital bicuspid aortic valve is the most common type of congenital heart disease (reported to occur in 1% to 2% of the general population), the bicuspid valve often is functionally normal until about age 50 to 60 years, when superimposed fibrocalcific changes lead to aortic valve stenosis. Significant regurgitation of a congenital bicuspid valve occurs somewhat less commonly but presents in young adulthood with a diastolic murmur and symptoms of exercise intolerance.


The presentation of significant LV outflow obstruction in a young adult should prompt consideration of abnormalities other than a bicuspid valve—specifically a unicuspid aortic valve, a subaortic membrane, or hypertrophic cardiomyopathy. A unicuspid aortic valve will appear as a thickened, deformed valve with systolic bowing of the valve on ultrasound imaging. A high parasternal short-axis view may show the eccentric unicuspid opening in systole, even allowing planimetry of the valve orifice. Three-dimensional transthoracic echocardiography (TTE) or transesophageal echocardiography (TEE) may further define valve anatomy. Doppler echocardiography can be used to determine the transvalvular gradient and valve area as for any type of aortic valve stenosis. Restenosis of the aortic valve in patients who previously underwent surgical valvotomy in childhood or adolescence is common. Restenosis occurs in up to 40% of patients a mean of 13 years after open surgical valvotomy.



Subaortic Stenosis


Congenital subaortic obstruction can range anatomically from a muscular ridge to a thin membrane. Although typically located 1 to 1.5 cm apically from the aortic valve plane, the membrane may be located immediately adjacent to the aortic valve. In either case, a subaortic membrane can be difficult to see in adults because of poor acoustic access. The possibility of a subaortic membrane should be considered when high-velocity flow is recorded in the LV outflow tract, but the aortic valve leaflets appear normal. TEE echocardiography may allow direct imaging of the subaortic membrane, especially if multiple image planes or 3D imaging are used to identify this thin structure. Conventional pulsed Doppler, high-pulse repetition frequency Doppler, and color flow imaging can be helpful from either TTE or TEE approaches in demonstrating that, in contrast to valvular aortic stenosis, the increase in antegrade velocity and poststenotic flow disturbance occur on the LV side of the aortic valve, indicating that subaortic obstruction is present. Coexisting aortic regurgitation may be present because of chronic exposure of the aortic valve leaflets to the high-velocity subaortic flow, resulting in a “jet lesion” on the aortic valve, or (rarely) because of fibrous attachments from the subaortic membrane to the aortic valve leaflets.



Congenital Obstructions to Right Ventricular Outflow


RV outflow obstruction may be subvalvular (in the muscular outflow tract), valvular, or supravalvular (either in the main PA or its major branches). Pulmonic stenosis can occur as an isolated anomaly but more often is part of a complex of defects (for example, tetralogy of Fallot) or is associated with other abnormalities (for example, corrected transposition). The level of outflow obstruction can be determined using pulsed Doppler and color flow to identify the anatomic site at which the flow velocity increases and the poststenotic flow disturbance appears. The obstruction itself may be depicted on 2D or 3D imaging as a muscular subpulmonic ridge; as deformed, doming pulmonic valve leaflets; or as a narrowing in the PA. If significant obstruction is present, compensatory RV hypertrophy typically is seen.


The degree of obstruction can be measured by Doppler ultrasound using the Bernoulli equation (Fig. 17-6) with the proviso that only an estimate of the total obstruction may be possible if serial stenoses are present. Note that in the presence of pulmonic stenosis, the tricuspid regurgitant jet velocity remains an accurate reflection of the RV to RA systolic pressure difference but no longer indicates PA systolic pressure. Instead, PA systolic pressure (PAP) can be estimated by calculating the:




image (17-6)



image (17-7)



image (17-8)


The end-diastolic velocity in the pulmonic regurgitation jet also may give useful data on PA pressures, because it reflects the diastolic pressure difference between the PA and the RV (high in patients with pulmonary hypertension, low in patients with pulmonic stenosis, and normal PA diastolic pressures).



Congenital Abnormalities of the Aorta



Aortic Coarctation


A congenital narrowing in the proximal descending thoracic aorta most often is located just upstream from the entry site of the ductus arteriosus. Less often, postductal coarctation is seen. The coarctation may be relatively discreet, with involvement of only a short segment of the aorta, or may be a long, tubular narrowing. Imaging of the coarctation site is difficult from transthoracic or suprasternal notch windows in adults. From the suprasternal notch approach, the descending thoracic aorta has a tapering appearance, even in normal individuals, because of the oblique tomographic view of the descending aorta obtained as the descending aorta leaves the image plane. Restenosis may present in adults with previous surgical repair of a coarctation depending on the specific surgical procedure used and the patient’s age at the time of repair. For both operated and unoperated coarctations, TEE imaging with a long-axis view of the descending aorta may be helpful.


Doppler examination shows an increased velocity across the coarctation and, if the obstruction is severe, persistent antegrade flow into diastole (Fig. 17-7) sometimes called “diastolic run-off.” If the velocity proximal to the coarctation is elevated, proximal velocity should be included in the Bernoulli equation for pressure gradient estimation. The jet direction in an unoperated coarctation may be very eccentric, so it rarely is possible to achieve a parallel alignment between the ultrasound beam and the jet direction, which can lead to underestimation of the severity of the obstruction. In restenosis of a previously operated coarctation, the jet orientation tends to be more symmetrical, and a parallel intercept angle with correct estimation of the pressure gradient is more likely. In either case, other clinical methods for assessing the severity of the coarctation are available (e.g., upper versus lower extremity blood pressure).




Marfan Syndrome


Marfan syndrome is inherited in an autosomal dominant pattern with variable penetrance. It is characterized by a specific, but variable, gene defect coding for fibrillin resulting in musculoskeletal, ocular, and cardiovascular manifestations. Cardiovascular abnormalities of Marfan syndrome include dilation, aneurysm formation and rupture of peripheral arteries, an abnormally redundant anterior mitral valve leaflet, and most important, dilation and dissection of the aorta. Echocardiography may be helpful in confirming or excluding a diagnosis of Marfan syndrome in patients with a suspected diagnosis. Examination also is indicated to screen first-degree relatives of an affected individual.


Characteristic echocardiographic findings include dilation of the aortic annulus, aortic root, sinuses of Valsalva, and ascending aorta, with loss of a clearly defined sinotubular junction (see Chapter 16). Aortic annular dilation results in aortic regurgitation and consequent LV volume overload. Aortic dissection occurs frequently and can occur even when aortic dilation is not severe. With an aortic root diameter of more than 50 mm in adults, the risk of spontaneous rupture is high, so many clinicians recommend periodic echocardiographic examination and prophylactic aortic root replacement with a valved aortic conduit when ascending aortic diameter exceeds this limit, or at even smaller diameters depending on patient size, the specific genetic defect, and family history.

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Jul 10, 2018 | Posted by in CARDIOLOGY | Comments Off on The Adult with Congenital Heart Disease
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