Noninvasive Imaging Tools

A. Two-Dimensional Echocardiography

Routine 2D echo is obtained from four transducer locations: parasternal, apical, subcostal, and suprasternal notch positions. Abdominal and subclavicular views are also useful. Figs. 4.1 through 4.9 illustrate selected standard 2D echo images of the heart and great vessels. A brief description of the standard 2D echo views follows.

• 1.

  Parasternal long-axis views ( Fig. 4.1 )

  • a.

    The standard long-axis view ( Fig.4.1A ).

    • (1)

      This is a very important view in evaluating abnormalities in or near the mitral valve, LA, LV, LVOT, aortic valve, aortic root, ascending aorta, and ventricular septum.

    • (2)

      In the normal heart there is aortic-mitral continuity (i.e., the anterior mitral leaflet is contiguous with the posterior wall of the aorta).

    • (3)

      The right and noncoronary cusps of the aortic valve are imaged but the left coronary sinus (CS) cusp is out of this plane.

    • (4)

      VSDs of TOF and persistent truncus arteriosus are readily seen adjacent to the aortic valve.

    • (5)

      The anterior and posterior leaflets of the mitral valve and their chordal and papillary muscle attachments are imaged. MVP is best evaluated in this view.

    • (6)

      The CS is seen frequently as a small circle in the atrioventricular groove. An enlarged CS may suggest left SVC, TAPVR to CS, coronary AV fistula, and rarely elevated RA pressure.

    • (7)

      Pericardial effusion is readily seen in this view.

  • b.

    The RV inflow view ( Fig. 4.1B ).

    • (1)

      This view shows abnormalities of the RA cavity, RV inflow, and the tricuspid valve.

    • (2)

      Abnormalities in the tricuspid valve (regurgitation, prolapse) are evaluated. It is a good view to record the velocity of the TR jet (to estimate RV systolic pressure).

    • (3)

      The ventricular septum near the tricuspid valve (TV) is the inlet muscular septum; the remainder is the trabecular septum.

    • (4)

      The right atrial appendage (RAA) can also be imaged in this view.

  • c.

    The RV outflow view ( Fig. 4.1C ).

    • (1)

      Abnormalities in the RVOT, pulmonary valve, and main PA are readily imaged and their severity easily estimated.

    • (2)

      The supracristal infundibular (outlet) septum is seen near the pulmonary valve.

• 2.

  Parasternal short-axis views: These views evaluate the aortic valve, coronary arteries, mitral valve, and papillary muscles.

  • a.

    The aortic valve level ( Fig. 4.2A ).

    • (1)

      The normal aortic valve has a circle with a tri-leaflet aortic valve that has the appearance of the letter Y during diastole. Abnormalities of the aortic valve (bicuspid, unicuspid, or dysplastic) are evaluated in this view.

    • (2)

      Stenoses of the pulmonary valve and PA branches can be evaluated by Doppler and color flow mapping.

    • (3)

      PDA is interrogated with color flow imaging and Doppler study.

    • (4)

      The membranous VSD is seen just distal to the tricuspid valve (at the 10-o’clock position).

    • (5)

      Both the infracristal and supracristal outlet VSDs are imaged anterior to the aortic valve near the pulmonary valve (at the 12- to 2-o’clock position).

  • b.

    Coronary arteries ( Fig. 4.2B ).

    • (1)

      The right coronary artery (CA) arises from the anterior coronary cusp.

    • (2)

      The left main CA arises in the left coronary cusp near the main PA. Its bifurcation into the left anterior descending and circumflex coronary artery is usually imaged.

    • (3)

      The dimension of the coronary arteries is measured in this view (see Table D.6 in Appendix D).

  • c.

    The mitral valve. The mitral valve is seen as a “fish mouth” during diastole ( Fig. 4.2C ).

  • d.

    Papillary muscles (Fig. 42D).

    • (1)

      Two papillary muscles are normally seen at the 4-o’clock (anterolateral) and 8-o’clock (posteromedial) positions. Occasionally, accessory papillary muscles or left ventricular strands are imaged in the normal heart.

    • (2)

      The ventricular septum seen at this level is the trabecular septum.

• 3.

  Apical four-chamber views ( Fig. 4.3 ).

  • a.

    The CS ( Fig. 4.3A ) is seen in the most posterior plane. The ventricular septum seen in this view is the posterior trabecular septum.

  • b.

    The middle plane of the apical four-chamber view ( Fig. 4.3B ).

    • (1)

      This view is good to evaluate the atrial and ventricular chambers, such as relative size and contractility of atrial and ventricular chambers, AV valve abnormalities, and images of some pulmonary veins.

    • (2)

      Anatomic right and left ventricles can be identified in this view.

      • (a)

        Normally the TV insertion to the septum is more apicalward than the mitral valve (5–10 mm in older children and adults). The ventricle attached to the TV is the RV. (The TV insertion is displaced more apically in Ebstein anomaly.)

      • (b)

        The anatomic RV is also heavily trabeculated and has the moderator band, while the LV is smooth walled without prominent muscle bundles.

    • (3)

      The inlet ventricular septum (where an ECD occurs) is imaged just under the AV valves; the remainder of the septum is the trabecular septum. (The membranous septum is not imaged in this view.)

    • (4)

      The presence and severity of regurgitation of both AV valves are evaluated in this view.

    • (5)

      The inflow velocities of both the mitral and tricuspid valves are measured here.

    • (6)

      The TR jet velocity is measured (to estimate RV systolic pressure).

    • (7)

      Abnormal chordal attachment of the atrioventricular valve (straddling) and overriding of the septum are also noted in this view.

  • c.

    The apical “five-chamber” view ( Fig. 4.3C ) is obtained by further anterior angulation of the transducer.

    • (1)

      The LVOT, aortic valve, subaortic area, and proximal ascending aorta are shown in this view.

    • (2)

      Stenosis and regurgitation of the aortic valve and the anatomy of the LV outflow tract (including subaortic membrane) are best evaluated in this view.

    • (3)

      The membranous VSD is visualized just under the aortic valve.

• 4.

  Apical long-axis views ( Fig. 4.4A )

  • a.

    The apical long-axis view (or apical three-chamber view) shows structures similar to those seen in the parasternal long-axis view.

  • b.

    The apical two-chamber view ( Fig. 4.4B ).

    • (1)

      The LA, mitral valve, and LV are imaged. The left atrial appendage (LAA) can also be imaged.

    • (2)

      The view of the LV apex provides diagnostic clues for cardiomyopathy, apical thrombus, and aneurysm.

• 5.

  Subcostal Long-Axis (Coronal) Views ( Fig. 4.5 ): These views are shown from posterior to anterior direction.

  • a.

    The CS is seen posteriorly ( Fig. 4.5A ). This plane shows structures similar to those shown in Fig. 4.3A .

  • b.

    The standard subcostal four-chamber view ( Fig. 4.5B ) is obtained by anterior angulation. This view emphasizes the atrial septum and its morphologic features, including the atrial septal defect and atrial septal aneurysm.

  • c.

    Further anterior angulation ( Fig. 4.5C ) shows the LV outflow tract, aortic valve, and ascending aorta.

  • d.

    Further anterior angulation ( Fig. 4.5D ) shows the entire RV (including the inlet, trabecular, and infundibular portions), the pulmonary valve, and the main pulmonary artery. Stenosis of the pulmonary valve and the anatomy of the RV outflow tract can be evaluated in this view.

  • e.

    Four parts of the ventricular septum can be imaged from this transducer position: trabecular (in A), inlet (in B), membranous (in C, under the aortic valve), and subarterial infundibular septum (in D) (see Fig. 7.7 for location of different types of VSD).

• 6.

  Subcostal short-axis (or sagittal) views ( Fig. 4.6 )

  • a.

    Fig. 4.6A :

    • (1)

      Both the SVC and IVC are seen to connect to the RA.

    • (2)

      A small azygos vein and the right PA can also be seen in this view.

    • (3)

      In patients with ASD, the size of the posterosuperior (PS) and postero-inferior (PI) rims of atrial septal defect is measured in this view.

  • b.

    A leftward angulation ( Fig. 4.6B ) shows the RV outflow tract, pulmonary valve, and pulmonary artery. The tricuspid valve is seen on end.

  • c.

    Further leftward angulation ( Fig. 4.6C ) shows views similar to the parasternal short-axis view ( Fig. 4.2D ).

• 7.

  Subcostal views of the abdomen

  • a.

    Abdominal short-axis view (left panel of Fig. 4.7A ).

    • (1)

      This view shows the descending aorta on the left and the IVC on the right of the spine. The aorta should pulsate.

    • (2)

      Both hemidiaphragms are seen, which move symmetrically with respiration. (Asymmetric or paradoxical movement of the diaphragm is seen with paralysis of the hemidiaphragm).

  • b.

    Abdominal long-axis views (right panel of Fig. 4.7B ).

    • (1)

      Left panel of Fig. 4.7B

      • (a)

        The IVC is imaged longitudinally to the right of the spine.

      • (b)

        The IVC collects the hepatic vein (HV) before draining into the RA. The failure of the IVC to join the RA indicates interruption of the IVC (with azygous continuation), which is seen in polysplenia syndrome.

      • (c)

        The eustachian valve may be seen at the junction of the IVC and the RA.

    • (2)

      Right panel of Fig. 4.7B

      • (a)

        The descending aorta is imaged longitudinally to the left of the spine.

      • (b)

        The celiac artery (CA) and the superior mesenteric artery (SMA) are easily imaged.

      • (c)

        A pulsed wave Doppler examination of the abdominal aorta in this view is helpful in identifying the coarctation by demonstrating delayed rate of systolic upstroke and persistent diastolic flow.

• 8.

  Suprasternal long-axis view (upper panel of Fig. 4.8 )

  • a.

    This view images the entire (left) aortic arch. Failure to visualize the aortic arch in the usual manner may suggest the presence of a right aortic arch.

  • b.

    Three arteries arising from the aortic arch are the innominate (or brachiocephalic), left carotid, and left subclavian arteries.

  • c.

    The innominate vein is seen in front of and the right PA is seen behind the ascending aorta.

  • d.

    Good images of the isthmus and upper descending aorta are very important to diagnose coarctation of the aorta.

  • e.

    Doppler studies with the cursor placed proximal and distal to the coarctation are important in estimating the severity of the narrowing.

• 9.

  Suprasternal short-axis view (lower panel of Fig. 4.8 )

  • a.

    The SVC is seen to the right of the circular transverse aorta. The innominate vein is seen superior to the circular aorta.

  • b.

    The right PA is seen in its length under the circular aorta.

  • c.

    The left innominate vein can be imaged, which arises from the SVC and traverses superior to the circular aorta.

  • d.

    Beneath the right PA is the LA. Four pulmonary veins are imaged with a slight posterior angulation.

• 10.

  The subclavicular views

  • a.

    The right subclavicular view ( Fig. 4.9A ). This view is useful in the assessment of the SVC and the RA junction as well as the ascending aorta.

  • b.

    The left subclavicular view ( Fig. 4.9B ). This view is useful for examination of the branch pulmonary arteries.

• 11.

  Quantitative dimension of cardiovascular structures from 2D echo studies: Selected normal dimensions of cardiac structures and the great arteries are presented in Appendix D. These tables are frequently used in practice of pediatric cardiology. They include M-mode measurements of the LV (Table D.1); stand-alone M-mode measurements of the RV, aorta, and LA (Table D.4); two-dimensional measurements of aortic root and aorta (Table D.5). Normal dimensions of coronary arteries are shown in Table D.6.

B. M-Mode Echocardiography

The M-mode echo provides an “ice pick” view of the heart. It has limited capability in demonstrating the spatial relationship of structures but remains an important tool in the evaluation of certain cardiac conditions and functions, particularly by measurements of dimensions and timing. It is usually performed as part of 2D echo studies.

• 1.

  M-mode echo recording ( Fig. 4.10 )

  • a.

    Line 1 passes through the aorta (AO) and LA, where the dimensions of these structures are measured.

  • b.

    Line 2 traverses the mitral valve. Anterior and posterior mitral valve motion is recorded for analysis.

  • c.

    Line 3 goes through the main body of the RV and LV. Along line 3, the dimensions of the RV and LV and the thickness of the interventricular septum and LV posterior wall are measured during systole and diastole. Pericardial effusion is best detected on line 3.

  

• 2.

  Cardiac Chamber Dimensions. Most dimensions are measured during diastole, coincident with the onset of the QRS complex; the LA dimension and LV systolic dimension are exceptions (see Fig. 4.10 ). Normal values are shown as a function of growth (see Appendix D).

• 3.

  Left Ventricular Systolic Function. LV systolic function is evaluated by the fractional shortening (or shortening fraction) or ejection fraction.

  • a.

    Fractional shortening (or shortening fraction) is derived by the following formula:

    FS (%)=Dd −Ds/Dd×100

    where FS is fractional shortening, Dd is end-diastolic dimension of the LV, and Ds is end-systolic dimension of the LV. This is a reliable and reproducible index of LV function, provided there is no regional wall-motion abnormality and there is concentric contractility of the LV.

    • (1)

      Mean normal value of FS is 36%, with 95% prediction limits of 28% to 44%.

    • (2)

      Fractional shortening is decreased in a poorly compensated LV regardless of cause (e.g., pressure overload, volume overload, primary myocardial disorders, and doxorubicin cardiotoxicity).

    • (3)

      FS is increased in some volume-overloaded ventricles (e.g., VSD, PDA, AR, and MR) and HCM.

    • (4)

      If the interventricular septal motion is flat or paradoxical, the shortening fraction will not accurately reflect ventricular ejection.

  • b.

    Ejection fraction relates to the change in volume of the LV with cardiac contraction. It is obtained by the following formula:

    EF (%)=(Dd) ³ − (Ds) ³ /(Dd) ³ × 100,

    where EF is the ejection fraction and Dd and Ds are end-diastolic and end-systolic dimensions, respectively, of the LV.

    • (1)

      Normal mean ejection fraction is 66% with ranges of 56% to 78%.

    • (2)

      The ejection fraction is a derivative of the fractional shortening and offers no advantages over the fractional shortening. In the previous formula, the minor axis is assumed to be half of the major axis of the LV; this assumption is incorrect in children.

C. Color Flow Mapping

A color-coded Doppler provides images of the direction and disturbances of blood flow superimposed on the echo structural image. In general, red is used to indicate flow toward the transducer and blue is used to indicate flow away from the transducer. A turbulent flow appears as light green. This is useful in the detection of shunt or valvular lesions. Color may not appear when the direction of flow is perpendicular to the ultrasound beam.