17
The Adult with Congenital Heart Disease
CONGENITAL DEFECTS SEEN IN ADULTS WITH OR WITHOUT PREVIOUS CARDIAC SURGERY
Obstruction to Left Ventricular Outflow
Congenital Obstructions to Right Ventricular Outflow
Congenital Abnormalities of the Aorta
Congenital Regurgitant Lesions
Corrected Transposition of the Great Arteries (CC-TGA)
“Incidental” Congenital Anomalies
ADULT CONGENITAL HEART DISEASE WITH PRIOR SURGICAL PROCEDURES
LIMITATIONS OF ECHOCARDIOGRAPHY AND ALTERNATE APPROACHES
There are two basic categories of congenital heart disease in adults:
The initial clinical presentation of previously undiagnosed and untreated congenital defects
Survival into adulthood of patients with known congenital heart disease and previous surgical procedures
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
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:
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:
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.
Figure 17–1 Subaortic stenosis.
Parasternal long-axis 2D view (top left) in a patient with a systolic murmur showing a subtle ridge (arrows) in the LV outflow tract. Color Doppler (bottom left) shows an increased flow velocity in this region, suggesting the possibility of a subaortic membrane (arrows). High-pulse repetition frequency Doppler (top right) shows an increase in velocity to at least 3.3 m/s at this location, and CW Doppler (bottom right) shows a maximum outflow velocity of 3.5 m/s.
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.
Figure 17–2 Cleft anterior mitral valve leaflet.
In the parasternal short-axis view (A), discontinuity of the anterior leaflet is seen (arrow). On color flow imaging in a long-axis view (B), an eccentric regurgitant jet with proximal acceleration is present.
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)
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.
Figure 17–3 Small, membranous VSD.
In the parasternal long-axis view, color flow Doppler shows acceleration of flow in the orifice with a systolic flow disturbance in the RV outflow tract. CW Doppler from the parasternal window demonstrates a high-velocity (5.2 m/s) signal toward the transducer (with some channel cross-talk) corresponding to the high pressure difference between the LV and the RV in systole. Because LV diastolic pressure is slightly higher than RV diastolic pressure, low-velocity flow from left to right also is seen in diastole.
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:
so that:
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).
Figure 17–4 Doppler shunt ratio calculation.
Pulmonary flow (Qp) is calculated from transpulmonic stroke volume calculation using PA diameter measured at the site of the Doppler sample position and the velocity-time integral (VTI) of PA flow. A circular cross-sectional area (CSA) is assumed. Similarly, systemic flow (Qs) is calculated from LV outflow tract (LVOT) diameter and the velocity-time integral of LV outflow tract.
Abnormal Chamber and Great Vessel Connections
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.
The anatomic RV and LV can be distinguished from each other by several features (Fig. 17-5). The anatomic RV has:
Figure 17–5 Transposition of the great arteries.
CMR images demonstrate the anatomic relationships of the great arteries and ventricles. A, The longitudinal view shows the side-by-side orientation of the great arteries and the systemic ventricle (SV) and pulmonary ventricle (PV). The aorta (Ao) is anterior to the pulmonary artery (PA). B, In a four-chamber view, the systemic ventricle is an anatomic RV as demonstrated by the presence of a moderator band, prominent trabeculation, and the slightly more apical insertion of the tricuspid valve (TV) compared to the mitral valve (MV). The SV is appropriately hypertrophied. The pulmonary ventricle is an anatomic LV.
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.
Knowledge of the patient’s clinical history, including previous surgical procedures and diagnostic tests
Formulation of specific clinical questions to be answered by the echocardiographic examination
During the examination, the physician and the sonographer work together to identify:
Cardiac chambers, great vessels, and their connections
Physiologic consequences of each lesion
Clinical questions that remain unanswered at the end of examination
Congenital Defects Seen in Adults with or Without Previous Cardiac Surgery
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:
Figure 17–6 Subpulmonic stenosis. In an anteriorly angulated 4-chamber view (top), color Doppler shows an increase in velocity proximal to the pulmonic valve in this patient with complete transposition. CW Doppler (bottom) demonstrates a velocity of 3.35 m/s and a diastolic signal consistent with moderate to severe pulmonic regurgitation. PA, pulmonary artery; PS, pulmonic stenosis; PV, pulmonic ventricle.
(1) RV systolic pressure (RVSP) based on the tricuspid regurgitant jet velocity (VTR) and RA pressure (RAP) estimated from the inferior vena cava size and respiratory variation:
(3) PA systolic pressure (PAP) by subtracting the transpulmonic gradient from the estimated RV systolic pressure:
Congenital Abnormalities of the Aorta
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
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.