智慧人生

Echocardiographic Identification of Congenital Cardiac Anomalies

2D and Doppler echocardiography has had a major impact on the diagnosis and management of patients with congenital heart disease (Chaps. 63 and 64). From isolated congenital lesions to complex, extensive cardiac malformations, echocardiographic imaging (often with intravenous contrast injection) is usually sufficient to delineate cardiac anatomy. TEE is an important adjunctive technique as well; in many cases, a thorough echocardiographic evaluation may obviate the need for cardiac catheterization and angiography.²⁶⁸

The ultrasound diagnosis of a simple intracardiac shunt is usually straightforward, but the task of defining complex congenital cardiac abnormalities can be daunting. In these cases, it is useful to remember a few basic anatomic rules. The venae cavae and pulmonary veins generally empty into the morphologic right atrium and LA, respectively. The atrioventricular valves uniformly follow their ventricles through embryologic development: a TV accompanies the morphologic RV and a MV accompanies the left. Similarly, the semilunar valves follow the great vessels. The aorta and PA can be distinguished, regardless of their position, by the bifurcation of the PA.

Several features aid identification of the morphologic right and left ventricles. The RV has a tricuspid atrioventricular valve; in comparison with the mitral annulus, the tricuspid annulus is positioned slightly closer to the cardiac apex. The RV also has a moderator band, coarser trabeculations than those in the left ventricle, and an infundibulum that separates the inlet area from the RVOT.

Cardiovascular Shunts

Atrial Septal Defect

Most secundum and primum atrial septal defects (ASDs) are easily visualized by echocardiography, although sinus venous defects are often difficult to detect without TEE. Apical echocardiographic views often show artifactual "dropout" in the region of the fossa ovalis, since the interatrial septum is thin in this area and runs parallel to the ultrasound beam. Therefore the subcostal view provides the optimal imaging plane to detect lesions of the atrial septum.²⁶⁹ Ostium secundum defects are the most common form of ASD, and 2D imaging shows a localized absence of septal tissue in the midportion of the interatrial septum (Fig. 15–110A). Lack of any interatrial septal tissue between the defect and the base of the interventricular septum characterizes an ostium primum defect (Fig. 15–110B). Although ostium secundum defects are usually isolated, ostium primum (or partial AV canal) defects are often accompanied by other lesions, such as cleft anterior MV leaflet, MR, and atrioventricular canal ventricular septal defect.²⁷⁰ Sinus venosus defects are strongly associated with partial anomalous pulmonary venous return (for example, drainage of the right upper pulmonary vein into the right atrium or superior vena cava) (Fig. 15–111A). Rarely, the atrial septum may be completely absent (Fig. 15–112). With all but small ASDs, the right atrium is enlarged and RV volume overload is present, with a dilated RV and paradoxical septal motion.

Figure 15–110. A. Apical four-chamber view of an ostium secundum atrial septal defect (ASD). On the left, a defect in the mid atrial septum is apparent (arrow). On the right, there is color flow through the shunt. RV = right ventricle; RA = right atrium; LA = left atrium; LV = left ventricle. B. Apical four-chamber view of a large ostium primum atrial septal defect (as well as an inlet VSD) in a patient with Down's syndrome. RA = right atrium; LA = left atrium; LV = left ventricle; RV = right ventricle.

Figure 15–111. A. Transesophageal image of a sinus venosus atrial septal defect (ASD) (longitudinal plane). The defect is present in the superior portion of the interatrial septum. RA = right atrium; LA = left atrium; ASD = atrial septal defect; PA = pulmonary artery. B. Transesophageal image of an ostium secundum ASD. Color-flow Doppler confirms a left to right shunt, and the size of the defect can be measured accurately.

Figure 15–112. Transverse transesophageal image of single atrium. RV = right ventricle; LV = left ventricle. (From Blanchard DG, Scott ED. Single atrium. Circulation 1997;95:273. With permission.)

Intravenous contrast injection generally demonstrates shunting across the ASD, frequently with bidirectional flow.²⁷¹ Therefore "negative jets" of unopacified flow from the LA into the contrast-filled right atrium may alternate with the appearance of contrast bubbles flowing through the defect into the LA. When an ASD is present, contrast should appear quickly (within three to five heartbeats) in the LA after entering the right atrium. Delayed appearance of contrast in the LA may indicate an intrapulmonary shunt rather than an ASD.

Color Doppler imaging is also useful for detecting flow through ASDs (Fig. 15–110A), although the pressure drop between atria often does not produce turbulence. Inflow from the inferior vena cava and right-sided pulmonary veins may be prominent in normals and can be misinterpreted as a shunt.²⁷² Pulsed-wave Doppler recordings usually reveal continuous flow, which peaks in late systole. Pulmonary-to-systemic flow ratios can be estimated in ASD (and ventricular septal defects) by comparing volumetric flow measurements through the LVOT and RVOT. Such calculations are only moderately accurate in adults.²⁷³ With the advent of umbrella or "clamshell" devices that permit percutaneous closure of ASDs, TEE has assumed an important role in defining the cross-sectional dimensions and exact position of the ASD (Fig. 15–111B). TEE is also useful in confirming accurate placement of closure devices and subsequent correction of the interatrial shunt.

Ventricular Septal Defect

Ventricular septal defects (VSDs) may be classified as perimembranous, inlet, outlet, or trabecular. Echocardiography is quite useful for the detection and classification of VSDs.²⁷⁴ The defect itself is sometimes visible with 2D imaging alone (Fig. 15–113A), but smaller VSDs are easily missed. Complete absence of the interventricular septum (single ventricle) is quite rare (Fig. 15–113B). Pulsed- or continuous-wave Doppler interrogation often reveals discrete areas of high-velocity flow across the interventricular septum. Measurement of the peak CW velocity through the shunt allows calculation of the interventricular pressure gradient (via the modified Bernoulli equation); subtraction of this gradient from the systolic blood pressure (in the absence of AoV disease) approximates the RV systolic pressure.

Figure 15–113. A. Apical four-chamber image of an inlet ventricular septal defect (VSD). The defect (arrows) is situated more inferiorly than the typical position of a perimembranous VSD. RV = right ventricle; RA = right atrium; LA = left atrium; LV = left ventricle. B. Apical image of single ventricle. RA = right atrium; LA = left atrium.

Overall, color-flow imaging is the most useful Doppler technique for the diagnosis of VSDs.²⁷⁴ Typically, a high-velocity systolic color jet is seen traversing the interventricular septum, although the velocity is lower with large defects and in the presence of PH (Fig. 15–114). The appearance of the color jet in the standard imaging planes can be used to determine the type of VSD. Intravenous contrast injection may reveal a negative contrast jet in the RV, and contrast may cross the defect and partially opacify the left ventricle. In the absence of MR, contrast will not enter the LA, distinguishing an isolated VSD from an ASD. Doppler echocardiography can also be used to detect abnormalities associated with VSDs, such as ventricular septal aneurysm, MR and TR, ASD (especially with inlet VSDs), aortic insufficiency—with outlet (supracristal) VSDs—and "straddling" of the defect by the mitral or TV.²⁷⁵ Accurate detection of such lesions is especially critical before surgical intervention.

Figure 15–114. Parasternal short-axis images of a large perimembranous ventricular septal defect (VSD) (arrow) without (left) and with (right) superimposed color flow Doppler. A large, turbulent color jet crosses the VSD during systole (right). RVOT = right ventricular outflow tract; RA = right atrium; LA = left atrium; LVOT = left ventricular outflow tract.

Patent Ductus Arteriosus

The ductus arteriosus originates just to the left of the PA bifurcation and inserts into the aorta slightly distal to and opposite from the ostium of the left subclavian artery. Given this posterior location, it is difficult to image a patent ductus arteriosus (PDA) itself with 2D TTE alone, and TEE is usually superior for direct visualization of the lesion⁵⁷⁴ (Fig. 15–115A and B). In most cases, 2D imaging of the communication is not essential, as CFD reliably detects high-velocity diastolic flow within the PA in nearly all non-Eisenmenger patients.²⁷⁶ The flow jet characteristically enters the distal left region of the main PA and streams anterior along the medial wall of the vessel (Fig. 15–115B). With large shunts, volume overload and subsequent dilation of the left ventricle occurs. Aortopulmonary window is a much rarer shunt involving the great vessels which presents as a communication anteriorly between the ascending aorta and proximal PA.²⁷⁷ It is embryologically distinct from a PDA and more closely related to a truncus arteriosus defect.

Figure 15–115. A. Transesophageal image of a patent ductus arteriosus (PDA). The upper panel shows a small communication (arrow) between the aorta (AO) and pulmonary artery (PA), which is confirmed with color-flow Doppler imaging (lower panel). B. Parasternal short-axis images at the aortic valve level. On the left, the pulmonary artery (PA) is somewhat enlarged. On the right, color imaging reveals diastolic flow within the PA, consistent with a patent ductus arteriosus. RV = right ventricle; RA = right atrium; LA = left atrium; AO = aorta.

Venous Inflow Abnormalities

Anomalous pulmonary venous return (APVR) may be partial or total. Partial APVR is present in 80 percent of sinus venosus ASD cases and is a feature of the scimitar syndrome.²⁷⁸ The usual finding on TTE is RV volume overload. TEE is quite useful in detecting these abnormal venous connections. In total APVR, the pulmonary veins may empty directly into the right atrium or into a common posterior chamber or vein. This structure and its connection with the right atrium may be visualized echocardiographically, along with the obligatory ASD.²⁷⁹ In some cases, the collecting chamber posterior to the LA may mimic the appearance of cor triatriatum, an entity characterized by a membrane in the posterior LA which may obstruct pulmonary venous inflow, causing symptoms similar to those of MS²⁸⁰ (Fig. 15–116).

Figure 15–116. Transverse transesophageal image of cor triatriatum. A membrane (arrow) is present in the left atrium. RA = right atrium; LA = left atrium; LV = left ventricle.

Persistent left superior vena cava occurs in 0.5 percent of the normal population. In most cases, the anomalous vein empties into the coronary sinus, which then drains into the right atrium (Fig. 15–117). Unless the coronary sinus is unroofed and drains into the LA, no shunting occurs. The typical echocardiographic finding is a large coronary sinus, which is especially well seen on transesophageal or parasternal trans-thoracic views. The diagnosis may be confirmed by intravenous contrast injection from the left arm, as this will opacify the coronary sinus shortly before filling the right atrium.

Figure 15–117. A. Transesophageal image (transverse plane) from a patient with persistent left superior vena cava. The coronary sinus (CS) is dilated. B. After injection of agitated saline into the left antecubital vein, contrast is seen entering the right atrium (RA) via the CS. TV = tricuspid valve; RV = right ventricle; LV = left ventricle. (From Blanchard DG, DeMaria AN. Cardiac and extracardiac masses: Echocardiographic evaluation. In: Skorton DJ, Schelbert HR, Wolf GL, Brundage BH, eds. Marcus' Cardiac Imaging, 2d ed. Philadelphia: Saunders; 1996:452–480. With permission.) C. Transthoracic parasternal long-axis image of persistent left superior vena cava. The coronary sinus is dilated.

Conotruncal and Aortic Abnormalities

Tetralogy of Fallot is one of the more common conotruncal abnormalities, and affected individuals may sometimes survive to adulthood without surgical intervention. The classic echocardiographic features include a large perimembranous VSD, an anteriorly displaced aorta which overrides the VSD, RV enlargement and dysfunction, and pulmonic stenosis (either infundibular, valvular, or supravalvular) (Fig. 15–118).²⁸¹ The VSD and aorta are well visualized in the parasternal long-axis view, while the RVOT and proximal PA are best seen in the parasternal short-axis view at the base of the heart. Doppler interrogation can provide evaluation of the severity of pulmonic stenosis, both before and after surgery. Echocardiography may aid detection of infants with tetralogy who will require early surgical intervention as well as patients who are at high risk for sudden death after surgical repair.²⁸²,²⁸³ Although double-outlet RV (DORV) shares several clinical characteristics with tetralogy of Fallot (VSD and anterior aortic displacement are invariably present, and pulmonic valvular stenosis and ASD are common in both), it is morphologically distinct (Fig. 15–119). Normal continuity of the posterior aortic wall with the anterior MV leaflet (always present in tetralogy of Fallot) is absent in DORV, and an interposed mass of fibrous tissue between the LA and the nearest great vessel is seen on 2D imaging. In addition, the great vessels may be transposed in DORV, resulting in a characteristic side-by-side appearance of the aorta and PA on parasternal short-axis images.²⁸⁴

Figure 15–118. Parasternal long-axis (A) and apical four-chamber (B) images of tetralogy of Fallot. The right ventricle (RV) is enlarged, and a large VSD is present. The aorta (AO) overrides the interventricular septum. LV = left ventricle. (Courtesy of Reinaldo W. Beyer, MD.)

Figure 15–119. Parasternal long-axis image of double-outlet right ventricle. A large VSD is present (small arrow) and the normal continuity between the posterior aortic wall and the anterior mitral leaflet is absent. Fibrous tissue is seen (large arrow) between the left atrium (LA) and the nearest great vessel [in this case, the pulmonary artery (PA)]. LV = left ventricle.

Echocardiography has become a valuable tool for the detection, management, and postoperative follow-up of patients with transposition of the great arteries. Attention to the anatomic rules mentioned earlier is essential for accurate diagnosis of both D (classic) and L ("congenitally corrected") transposition. In D-transposition, the aorta arises from the RV, the PA arises from the LV, and one or more obligatory shunts are present. With L-transposition, the morphologic right and left ventricles are switched, and associated anomalies such as VSD and pulmonic stenosis are common. In both types of transposition, the normal echocardiographic orientation of the great vessels on parasternal short-axis images (a sausage-shaped RVOT and PA draped over a circular aorta) is no longer present, and the two great vessels are typically side by side and parallel (Fig. 15–120).²⁸⁵ In general, the aorta is anterior and to the right of the PA in D-transposition and anterior and to the left in L-transposition. Both TTE and TEE are an important part of continuing care after surgical repair or palliation of transposition; they can detect valvular regurgitation, outflow tract narrowing, and stenosis of the atrial baffle systems used to palliate D-transposition surgically.²⁸⁶

Figure 15–120. Transverse transesophageal image through the semilunar valves in L-transposition. The aortic valve (A) is anterior and to the left of the pulmonic valve (P). LA = left atrium.

Truncus arteriosus is a rare anomaly characterized by a large VSD, a single semilunar valve, and a single great vessel that divides into the ascending aorta and PA.²⁸⁷ Ultrasound imaging can determine the anatomy of the great vessels and assist in defining the various subsets of truncus arteriosus.

Coarctation of the aorta is associated with a bicuspid aortic valve and is best visualized from the suprasternal position. 2D imaging may identify the site of coarctation, but the natural mild curving of the descending aorta can occasionally lead to a false-positive diagnosis. Clear visualization of narrowing in the proximal descending aorta with poststenotic dilatation, however, is pathognomonic of coarctation.²⁸⁸ Doppler interrogation from the suprasternal notch demonstrates increased systolic velocity in the descending aorta and may also reveal a persistent flow gradient throughout diastole in cases of severe coarctation (Fig. 15–121A).²⁸⁹ Color imaging may display flow acceleration proximal to the site of coarctation and aliasing distal to it (Fig. 15–121B,). The maximum velocity through the coarctation can be used to estimate the pressure gradient, and this measurement can be particularly valuable for the detection of restenosis after surgical repair or percutaneous balloon aortic dilatation.²⁹⁰ Supravalvular aortic stenosis, either isolated or associated with Williams syndrome (Chap. 12), is generally imaged best from the suprasternal and superior parasternal positions. Transesophageal imaging is also very helpful (Fig. 15–122E). Echocardiography reveals either an hourglass-shaped stenosis of the aorta above the sinuses of Valsalva, diffuse hypoplasia of the ascending aorta, or a focal fibrous ridge at the sinotubular junction (Fig. 15–122E). Doppler imaging can help estimate the gradient across the stenosis, and marked aliasing of color-flow imaging in the ascending aorta should raise suspicion of the diagnosis. Thickening of the aortic valve leaflets and stenoses of the coronary ostia are important associated findings that may be detectable by echocardiography.

Figure 15–121. A. Continuous-wave Doppler tracing of the descending aorta (from the suprasternal position) in aortic coarctation. Peak systolic velocity is 3.7 m/s, and there is persistent flow during diastole, suggesting severe coarctation. B. Suprasternal image of aortic coarctation. The descending aorta (DAo) is focally narrowed and tortuous, and turbulent (aliased) flow is present distal to the site of coarctation.

Figure 15–122. Subvalvular and supravalvular aortic stenosis. A. Apical three-chamber view of discrete subaortic stenosis. A fibromuscular ridge (arrow) is present in the left ventricular out-flow tract. LV = left ventricle; LA = left atrium; A = aortic root. B. Apical five-chamber view of discrete subaortic stenosis with color-flow Doppler, demonstrating aliasing and proximal flow convergence in the left ventricular outflow tract. LV = left ventricle; LA = left atrium. C. Transesophageal image of discrete subaortic stenosis. A fibrous ridge in the outflow tract of the left ventricle (LV) is present (arrow). LA = left atrium. D. Transesophageal image with color-flow Doppler, demonstrating mild aortic insufficiency associated with discrete subaortic stenosis. LV = left ventricle; LA = left atrium; Ao = aortic root. E. Transesophageal image of supravalvular aortic stenosis. A fibrous ridge extends into the aortic lumen just above the sinus of Valsalva.

Abnormalities of the Ventricular Outflow Tract and Semilunar Valve

Right Ventricle

Infundibular stenosis is rare outside the setting of tetralogy of Fallot and is much less common than valvular PS. On 2D imaging, muscular hypertrophy is often visualized proximal to the PA, while Doppler interrogation reveals increased flow velocities through the infundibulum.²⁹¹ PS is reasonably common and may be either isolated or associated with other congenital lesions (such as VSD, transposition, and tetralogy of Fallot). Typical echocardiographic features include thickening of the leaflets, restricted leaflet motion, systolic doming of the valve, and elevated systolic flow velocity on Doppler (Fig. 15–85). As with other stenotic lesions, the gradient can be estimated using the modified Bernoulli equation. The PV is best visualized in the parasternal short-axis view through the base (or a modified parasternal view of the RVOT). In children, the subcostal position frequently provides excellent visualization of the RVOT and PV. When TTE is suboptimal, TEE can provide detailed images of the PV. In pulmonic stenosis, the valve leaflets may calcify over time, and poststenotic dilatation of the PA is often present.

Left Ventricle

Subvalvular obstruction may be dynamic or fixed. Hypertrophic cardiomyopathy, which may present at any age, is discussed above. Discrete subaortic stenosis may be caused by a thin membrane in the LVOT, a fibromuscular ridge, or diffuse muscular narrowing of the outflow tract (Fig. 15–122A–D). 2D echocardiographic imaging can distinguish these various forms of discrete subvalvular stenosis, and Doppler analysis permits estimation of the systolic gradient.²⁹² Color-flow imaging demonstrates increased turbulence in the LVOT as well as aortic valvular regurgitation in about 50 percent of cases (Fig. 15–122D). Apical views are sometimes more useful for detecting thin subaortic membranes, as these structures are parallel to the ultrasound beam on parasternal images. Subaortic fibromuscular ridges are sometimes associated with anomalous MV chordae connecting the papillary muscles or the anterior MV leaflet to the septum.²⁹³ M-mode imaging may reveal midsystolic partial closure of the AoV, differentiating subvalvular from valvular AS.

Bicuspid aortic valve is the most common congenital cardiac lesion in adults and is present in 1 to 2 percent of all individuals (men are affected more often than women). Initially, eccentric diastolic coaptation of the aortic cusps was reported on M-mode in patients with bicuspid valves. However, M-mode findings are less accurate than 2D imaging, and the parasternal short-axis view is generally best for defining the fish-mouthed systolic aortic valvular anatomy (Figs. 15–60 and 15–61). Bicuspid valves are sometimes easy to detect in diastole as well, but raphes and remnants of commissures may obscure the diagnosis and mimic a trileaflet valve. In general, asymmetry of the aortic leaflets suggests congenital deformation. In equivocal cases, TEE is usually diagnostic (Fig. 15–61).

Abnormalities of the Ventricular Inflow Tract

Ebstein's anomaly is a congenital deformity of the TV in which the leaflets are displaced into the RV. Associated findings include TR, right atrial enlargement, and ASD.²⁹⁴ 2D imaging typically shows abnormal apical displacement of the septal leaflet insertion, with variable deformity of the leaflet (Fig. 15–123). The anterior leaflet originates from the tricuspid annulus but is elongated and often tethered to the RV free wall by abnormal chordal attachments. The tricuspid deformity and regurgitation are best visualized in the apical four-chamber view, although the subcostal and modified parasternal views also may be helpful.

Figure 15–123. Ebstein's anomaly, apical four-chamber view. The tricuspid valve annulus (thin arrow) is apically displaced in comparison to the mitral annulus (thick arrow). The right ventricle (RV) and right atrium (RA) are enlarged.

Atrioventricular valvular atresia is usually accompanied by hypoplasia of the corresponding ventricle. Echocardiographic images of tricuspid atresia characteristically show a small, nonfunctional RV, an interatrial communication of variable size, and a normally developed left ventricle. Associated lesions include VSD, transposition, and RV outflow obstruction. Echocardiography is an important tool in the management of patients with tricuspid atresia after palliation with the Fontan procedure. Mitral atresia is associated with a hypoplastic LV. Additional rare congenital mitral anomalies imaged by echocardiography include parachute MV and congenital MS.

Fetal Echocardiography

The average risk for significant heart disease in the fetus is approximately 0.4 to 0.8 percent. Fetal echocardiography has evolved over the past 20 years into a sophisticated method for intrauterine detection of cardiac abnormalities²⁹⁵ (Fig. 15–124). The technique has been advocated for the preterm diagnosis of congenital heart disease, especially in higher-risk cases [for example, maternal congenital heart disease or diabetes mellitus, maternal teratogen exposure, or TORCH (toxoplasmosis, other intrauterine infections, rubella, cytomegalovirus, and herpesvirus) infection, and familial syndromes that may affect the heart]. Fetal echocardiography has successfully identified a variety of congenital lesions including atrial and ventricular septal defect, pulmonic stenosis, transposition, tetralogy of Fallot, hypoplastic left heart, Ebstein's anomaly, and tricuspid atresia.²⁹⁶ Prenatal detection of these lesions may improve prognosis and guide therapy. Although some have recommended routine limited fetal echocardiography during the second or third trimester, recent reports have suggested a low yield and limited diagnostic accuracy.²⁹⁷,²⁹⁸ Like many imaging techniques, fetal echocardiography is evolving, and further study is required to define its optimal clinical use.

Figure 15–124. Fetal echocardiogram (four-chamber view). LV = left ventricle; RV = right ventricle.