2 Special Tools in Cardiac Evaluation

A number of special tools are available to the cardiologist in the evaluation of cardiac patients. Noncardiologists have access to some noninvasive tools, such as echocardiography, exercise stress test, and ambulatory ECG (e.g., Holter monitor). Magnetic resonance imaging (MRI) and computed tomography (CT) are other noninvasive tools that have become popular in recent years. Cardiac catheterization and angiocardiography are invasive tests. Although catheter intervention procedures are not diagnostic, they are included here because they are usually performed with cardiac catheterization.

I. ECHOCARDIOGRAPHY

Echocardiography (echo) is an extremely useful, safe, and noninvasive test used in the diagnosis and management of heart disease. Echo studies, which use ultrasound, provide anatomic diagnosis as well as functional information, especially with the incorporation of Doppler echo and color flow mapping.

A. 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 two-dimensional echo studies.

Figure 2-1 shows three important structures of the left side of the heart that are imaged using the M-mode echo. The following are some applications of the M-mode echo.

FIG. 2-1 Cross-sectional view of the left side of the heart along the long axis (top) through which ice-pick views of the M-mode echo recordings are made (bottom). (a), RV dimension. (b), LV diastolic dimension (Dd). (c), Thickness of ventricular septum. (d), Thickness of posterior free wall. (e), LA dimension. (f), Aortic dimension. (g), LV systolic dimension (Ds). AMV, Anterior mitral valve; PMV, posterior mitral valve; LVET, LV ejection time; PEP, preejection period.

(From Park MK: Pediatric cardiology for practitioners, ed 5, Philadelphia, 2008, Mosby.)

• Measurement of the dimensions of cardiac chambers and vessels, thickness of the ventricular septum and free walls

• LV systolic function (e.g., fractional shortening, ejection fraction)

• Study of the motion of the cardiac valves (e.g., MVP, MS) and the interventricular septum

• Detection of pericardial fluid

1. Normal M-mode echo values. The dimensions of the cardiac chambers and the aorta are measured during diastole, coincident with the onset of the QRS complex; the LA dimension and LV systolic dimension are exceptions (see Fig. 2-1). Table 2-1 shows normal M-mode values of cardiac chamber size, wall thickness, and aortic size, according to the patient’s weight. More detailed normal values of chamber dimensions and LV wall thickness by stand-alone M-mode echo are shown according to body surface area in Appendix D (Table D-1). M-mode echo measurement of the aortic annulus, LA, and LV dimensions as part of a two-dimensional study are shown by age in Table D-2. Table D-3 shows M-mode echo measurements of the LA and LV dimensions by height.

2. Left ventricular systolic function

a. Fractional shortening

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

TABLE 2-1 NORMAL M-MODE ECHO VALUES (MM) BY WEIGHT (LB): MEAN (RANGES)

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 systolic function, provided there is no regional wall-motion abnormality or abnormal motion of the interventricular septum.

(2) Normal FS is 36% (range 28% to 44%). Fractional shortening is decreased in a poorly compensated LV regardless of cause (e.g., pressure overload, volume overload, primary myocardial disorders, doxorubicin cardiotoxicity, and so on). It is increased in volume-overloaded ventricle (e.g., VSD, PDA, AR, MR) and pressure overload lesions (e.g., moderately severe AS, HOCM).

b. Ejection fraction. 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 ejection fraction and Dd and Ds are end-diastolic and end-systolic dimensions, respectively, of the LV. In the preceding formula the minor axis is assumed to be half of the major axis of the LV; this assumption is incorrect in children. Normal mean ejection fraction is 66% (range 56% to 78%).

c. Systolic time intervals

(1) The method of measuring left preejection period (LPEP) and left ventricular ejection time (LVET) is shown in the lower right panel of Figure 2-1. The preejection period usually reflects the rate of pressure rise in the ventricle during isovolumic systole (i.e., dp/dt). The ratio of preejection period to ventricular ejection time for both right and left sides is little affected by changes in the heart rate.

(2) Normal values (and ranges) for the RV and LV are as follows:

(a) RPEP/RVET, 0.24 (0.16 to 0.3)

(b) LPEP/LVET, 0.35 (0.3 to 0.39)

B. TWO-DIMENSIONAL ECHOCARDIOGRAPHY

The two-dimensional (2D) echo has an enhanced ability to demonstrate the spatial relationship of cardiovascular structures. The Doppler and color mapping study has added the ability to easily detect valve regurgitation and cardiac shunts during the echo examination. It also provides some quantitative information such as pressure gradients across cardiac valves and estimation of pressures in the great arteries and ventricles.

Routine 2D echo is obtained from four transducer locations: parasternal, apical, subcostal, and suprasternal notch positions. Sometimes, abdominal and subclavicular views are also obtained. Figures 2-2 through 2-10 illustrate selected standard images of the heart and great vessels. Selected normal dimensions of cardiac chambers and the great arteries are presented in Appendix D. Table D-4 shows the dimensions of the aorta and pulmonary arteries. Table D-5 shows the aortic root dimensions. Table D-6 shows the mitral and tricuspid valve annulus dimensions, and Table D-7 shows the valve annulus in the neonate.

FIG. 2-2 Diagram of 2D echo views obtained from the parasternal long-axis transducer position. Standard long-axis view (A), RV inflow view (B), and RV outflow view (C). AO, aorta; CS, coronary sinus; Desc. Ao, descending aorta; LA, left atrium; LV, left ventricle; PA, pulmonary artery; RA, right atrium; RAA, right atrial appendage; RV, right ventricle.

(From Park MK: Pediatric cardiology for practitioners, ed 5, Philadelphia, 2008, Mosby.)

FIG. 2-3 Diagram of a family of parasternal short-axis views. Semilunar valves and great artery level (A), coronary arteries (B), mitral valve level (C), and papillary muscle level (D). AO, aorta; LA, left atrium; LCA, left coronary artery; LPA, left pulmonary artery; LV, left ventricle; MPA, main pulmonary artery; MV, mitral valve; PM, papillary muscle; RA, right atrium; RCA, right coronary artery; RPA, right pulmonary artery; RV, right ventricle; RVOT, right ventricular outflow tract.

(From Park MK: Pediatric cardiology for practitioners, ed 5, Philadelphia, 2008, Mosby.)

FIG. 2-4 Diagram of 2D echo views obtained with the transducer at the apical position. A, A posterior plane view showing the coronary sinus. B, The standard apical four-chamber view. C, The apical “five-chamber” view is obtained with further anterior angulation of the transducer. AO, aorta; CS, coronary sinus; LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle.

(From Park MK: Pediatric cardiology for practitioners, ed 5, Philadelphia, 2008, Mosby.)

FIG. 2-5 Apical long-axis views. A, Apical “three-chamber” view. B, Apical “two-chamber” view. AO, aorta; LA, left atrium; LAA, left atrial appendage; LV, left ventricle; RV, right ventricle.

(From Park MK: Pediatric cardiology for practitioners, ed 5, Philadelphia, 2008, Mosby.)

FIG. 2-6 Diagram of subcostal long-axis views. A, Coronary sinus view posteriorly. B, Standard subcostal four-chamber view. C, View showing the left ventricular outflow tract and the proximal aorta. D, View showing the right ventricular outflow tract and the proximal main pulmonary artery. AO, aorta; CS, coronary sinus; LA, left atrium; LV, left ventricle; PA, pulmonary artery; RA, right atrium; RV, right ventricle; SVS, superior vena cava.

(From Park MK: Pediatric cardiology for practitioners, ed 5, Philadelphia, 2008, Mosby.)

FIG. 2-7 Subcostal short-axis (sagittal) views. A, Entry of venae cavae with drainage of the azygous vein. B, View showing the RV, RVOT, and pulmonary artery. C, Short-axis view of the ventricles. Azg. V, azygous vein; LA, left atrium; LV, left ventricle; MV, mitral valve; PA, pulmonary artery; RA, right atrium; RPA, right pulmonary vein; RV, right ventricle; SVC, superior vena cava; TV, tricuspid valve.

(From Park MK: Pediatric cardiology for practitioners, ed 5, Philadelphia, 2008, Mosby.)

FIG. 2-8 Abdominal views. A, Abdominal short-axis view. B, Abdominal long-axis views. AO, aorta; CA, celiac axis; HV, hepatic vein; IVC, inferior vena cava; RA, right atrium; SMA, superior mesenteric artery.

(From Park MK: Pediatric cardiology for practitioners, ed 5, Philadelphia, 2008, Mosby.)

FIG. 2-9 Diagram of suprasternal notch views. Top panel, Long-axis view. Bottom panel, Short-axis view. AO, aorta; Asc. Ao, ascending aorta; Desc. Ao, descending aorta; Inn. A, innominate artery; Inn. V, innominate vein; LA, left atrium; LCA, left carotid artery; LSA, left subclavian artery; MPA, main pulmonary artery; PA, pulmonary artery; RPA, right pulmonary artery; SVC, superior vena cava.

(From Park MK: Pediatric cardiology for practitioners, ed 5, Philadelphia, 2008, Mosby.)

FIG. 2-10 Diagram of subclavicular views. A, Right subclavicular view. B, Left subclavicular view. AO, aorta; IVC, inferior vena cava; LPA, left pulmonary artery; MPA, main pulmonary artery; RA, right atrium; RPA, right pulmonary artery; RV, right ventricle; SVC, superior vena cava.

(From Park MK: Pediatric cardiology for practitioners, ed 5, Philadelphia, 2008, Mosby.)

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.

D. DOPPLER ECHOCARDIOGRAPHY

A Doppler echo combines the study of cardiac structure and blood flow profiles. Doppler ultrasound equipment detects frequency shifts and thus determines the direction and velocity of blood flow with respect to the ultrasound beam. By convention, velocities of red blood cells moving toward the transducer are displayed above a zero baseline; those moving away from the transducer are displayed below the baseline. The Doppler echo is usually used with color flow mapping (see following) to enhance the technique’s usefulness.

The two commonly used Doppler techniques are continuous wave and pulsed wave. The pulsed wave (PW) emits a short burst of ultrasound, and the Doppler echo receiver “listens” for returning information. The continuous wave (CW) emits a constant ultrasound beam with one crystal, and another crystal continuously receives returning information. The pulsed-wave Doppler can control the site at which the Doppler signals are sampled, but the maximal detectable velocity is limited, making it unusable for quantification of severe obstruction. In contrast, continuous-wave Doppler can measure extremely high velocities (e.g., for the estimation of severe stenosis), but it cannot localize the site of the sampling; rather, it picks up the signal anywhere along the Doppler beam. When these two techniques are used in combination, clinical application expands.

Normal Doppler velocities in children and adults are shown in Table 2-2. Normal Doppler velocity is less than 1 m/sec for the pulmonary valves, but it may be up to 1.8 m/sec for the ascending and descending aortas. With stenosis of the atrioventricular valves, the flow velocity of the E and A waves increases (Fig. 2-11). Normally, the E wave is taller than the A wave, except for the first 3 weeks of life, during which the A wave may be taller than the E wave. In normal subjects 11 to 40 years of age, mitral Doppler indexes are as follows (mean ± SD). The average peak E velocity is 0.73 ± 0.09 m/sec, the average peak A velocity is 0.38 ± 0.089 m/sec, and the average E:A velocity ratio is 2.0 ± 0.5.

TABLE 2-2 NORMAL DOPPLER VELOCITIES IN CHILDREN AND ADULTS: MEAN (RANGES) (IN M/SEC)

	CHILDREN	ADULTS
Mitral Flow	1.0 (0.8–1.3)	0.9 (0.6–1.3)
Tricuspid Flow	0.6 (0.5–0.8)	0.6 (0.3–0.7)
Pulmonary Artery	0.9 (0.7–1.1)	0.75 (0.6–0.9)
Left Ventricle	1.0 (0.7–1.2)	0.9 (0.7–1.1)
Aorta	1.5 (1.2–1.8)	1.35 (1.0–1.7)