Stenotic lesions

 Regurgitant lesions

 Intracardiac shunts

 Abnormal connections

 Combinations or complex congenital disease

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:

(17-1)

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 (V_prox) and the jet velocity (V_jet) in the Bernoulli equation:

(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 (Q_p:Q_s)—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 (Q_p) is calculated from PA cross-sectional area (CSA) and velocity-time integral (VTI), while systemic volume flow (Q_s) is calculated from measurements of LV outflow tract (LVOT) cross-sectional area and velocity-time integral:

(17-3)

(17-4)

(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 Q_p:Q_s 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.

Obstruction to Left Ventricular Outflow

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:

(17-6)

(17-7)

(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

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