Echocardiography in Congenital Heart Disease Richard A. Meyer,

E

CHOCARDIOGRAPHYhasbeen usedsuccessfully to study the individual cardiac valves s~14~15~18 to detect pericardial effusionp to measure left ventricular dimension,13and to assessleft ventricular function.’ rY1g,2112g733P34 Much of this work has been confined to adults, but recently pediatric patients have also been studied successfully by echocardiography.4,6,16,20,22-25,31,37 the purpose of this presentation to illustrate echocardiograms obtained in neonates, infants, and children with congenital heart diseaseand the methodsusedto obtain them.

Itis

THE

NORMAL

ECHOCARDIOGRAM

Before discussing specific cardiac lesions, it is worthwhile to emphasizethe echographicrelationships of the structures found in a normal heart (Fig 1). Sincethe echocardiographicwave forms of various structures are identical, proper interpretation of the echogramdependsupon knowledge of the transducer beam position. Normally the ultrasonic examination beginsat the left sternal border; however, if structures cannot be recorded from that position, then the transducer must be moved over the precordium in an effort to locate the desiredstructures. The mitral valve, which is found to the left of the tricuspid valve, is in fibrous continuity with the posterior margin of the aortic root; hence the mitral valve echo is continuous with and at the same depth from the chest wall as the posterior margin of the aorta. The tricuspid valve, although not in fibrous continuity with the aortic root, is related to the anterior margin of the aorta. These important anatomic relationships enable us to identify the ventricles, since the mitral valve, which is in continuity with the posterior margin of the semilunar valve, always denotes the left ventricle, while the tricuspid valve, which is not in continuity with a semilunar valve, identifies the right ventricle. Normally the aorta lies to the right of and posterior to the pulmonary artery (Fig 2). The aortic Richard A. Meyer, M.D.: Associate Professor of Pediatrics, Division of Cardiology, Children’s Hospital Medical Center, Cincinnati, Ohio 45229. 0 19 75 by Grune & Stratton, Inc. Seminen in Roentgenology,

Vol. X, No. 4 (October),

1975

M.D.

root echo is found by scanning the mitral valve medially and superiorly along the major axis of the left ventricle. In order to record the pulmonary artery in infants and children, it is seldom necessaryto move the transducer from the aortic position, but merely to direct its beam leftward and slightly superiorly (Fig 3). Echoes from the interventricular septum (Fig 4) aswell asfrom the right and left ventricle are recorded with the transducer in the mitral position. The relationship of the septum to the anterior margin of the aorta can be demonstratedby scanningthe mitral valve all the way to the aorta. Probably the greatest contribution of pediatric echocardiography is in the newborn period. Since in the neonate the signsand symptoms of respiratory disease,sepsis, metabolic derangement,and abnormalities of hemoglobin may mimic those of congenital heart disease,difficulty frequently is encounteredin arriving at a correct diagnosis. HYPOPLASTIC

LEFT

HEART

SYNDROME

The common presenting symptoms of critically ill newborns are a shock-like picture and cyanosis. Neonates with the clinical picture of shock may also have the hypoplastic left heart syndrome, resulting from aortic atresia, critical aortic stenosis, or mitral atresiawith ventricular septal defect. Aortic Atresia Newbornswith aortic atresiahave a characteristic echocardiogram that is diagnostic of this syndrome (Fig 5).23 The findings include a minute to absent aortic root echo, a small posterior ventricle in the presenceof a large anterior ventricle, and a mitral valve echo that is grossly distorted. The pathognomonic sign of this diseaseis a very tiny aortic root that in our experiencehas alwaysbeen less than 5 mm in diameter. Identification of the aortic root is accomplishedby directing the transducer beam carefully along the tricuspid valve until its anterior margin is identified (Fig 5B). The pulmonary artery is large and encroachesupon the aorta. The left ventricle is usually a third of normal size or less; on occasion, however, it may be large if a ventricular septal defect (VSD) is present. In that circumstance,the mitral valve echo appears 277

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NORMAL

PA c

Ao

normal and the left ventricle is large. In our experience with 29 patients, the aboveechographicfindings have enabled the diagnosisof aortic atresiato be made without resorting to cardiac catheterization or angiography.

Fig 2. This composite picture demonstrates the normal relationship of the great vessels in transverse sections, with corresponding echocardiograms. The pulmonary artery is anterior and to the left of the aorta. Abbreviations are the sameas in Fig 1.

Fig 1. This composite picture demonstrates the transducer position used to record the tricuspid and mitral valves of a normal heart, as well as the relationship of the cardiac structures. A. Anterior; Ao. aorta; L, left; LV, left ventricle; MV, mitral valve; P, posterior; PA, pulmonary artery; RV, right ventricle; TV, tricuspid valve. Abbreviations are the same for subsequent figures. lfleproduced with permission of American Journal of Cardiology.24)

Critical Aortic Stenosis

It is imperative to distinguish critical aortic stenosis from aortic atresia or mitral atresia with VSD, since prompt surgical relief of the severeobstruction improves the circulation of these neo-

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DISEASE

Fig 3. This frontal-plane diagram and corresponding echographic sweep demonstrate the relationship of the great vessels and the transducer positions used to record them.

nates. Patients with critical aortic stenosis or mitral atresia with VSD have almost normal aortic root dimensions (Fig 6). However, in patients with critical aortic stenosis the left ventricular cavity is small (Fig 7) and the free wall and septum are quite thick. In addition the mitral valve echo is generally thickened and has a very poor diastolic closure rate. Patients with mitral atresia do not have a recordable mitral valve. In addition, the aortic root echo and the left atrial dimension will be almost normal (Fig 8). Again, the aortic root can be identified by scanning the tricuspid valve superiorly.

NEWBORN

CYANOTIC

HEART

DISEASE

The common cardiac causes of cyanosis in the critically ill newborn include transposition of the great vessels, tricuspid atresia, pulmonary atresia, and total anomalous pulmonary venous return. Transposition of Great Vessels One characteristic feature of transposition of the great vessels is that the anterior root echo, which in normal patients (Fig 2) is recorded to the left of the posterior root, is now found to the right (Fig 9). However, this arrangement of the great vesselsis present in only 60% of patients. The aorta

of the heart in sagittal view with a corresponding slow swap ecbocardiogram Fig 4. A composite damomdmting normal septal-aortic and mitral-aortic relationships. Numbers represent the respective transducer positions. Alec, ante&or mitral leaflet; APM, anterior papillary muscle; DEC. AORTA, descending aorta; LA, left atrium: PMC, posterior mitral leaflet; PPM, posterior papillary muscle. (Reproduced with permission of F. A. Davis CO.*~)

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TV

(

IMV

TV 1”LA

Fig 5. Aortic atresia. Echogram A depicts the structures recorded from transducer position A. Echogram 6 depicts the structures recorded as the transducer is rotated from position A to position B. WC, inferior vena cava; LA, left atrium; LVED, left ventricular end-diastolic dimension; ROOT, aortic root; RVED, right ventricular enddiastolic dimension. (Reproduced with permission of Progress in Cardiovascular Diseases.28)

Fig 6. A composite comparison of aortic root dimensions on echograms and aortograms in neonates with aortic at&a (AA), severe aortic stenosis (AS), and mitral atresia with VSD (MAVSD). The arrows point to the aortic root. LA, left atrium. (Reproduced with permission of F. A. Davis co.231

CONGENITAL

HEART

DISEASE

281

Fig 7. Left atrial injection during systale and diastole in a patient with severe aortic stenosis, demonstrating a poorly contractile, thickwalled, small left Corre ventricle. sponding echograrr= exhibit similar finding. CW, cheat wall; RV Endo, right venendocartricular dium; S, septum. (Reproduced with permission of F. A. Davis CO.~‘)

TV

Fig 8. Echograms in mitral atresia and VSD showing an almost normal aortic root (B) and normal relationship of tricuspid valve to aorta (A).

Fig 9. The great vessels shown in the transverse plane of a patient with tmnsposition of the great arteria. Note the transducer position usad to record the rightward and anterior aorta.

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Fig 10. Idealized diagrams showing the relationship of the normal aorta to the left ventricle and the relationship of the pulmonary artery to the left ventricle in transposition of the great arteries. The arrows stress the difference in transducer beam positions necessary to record the semilunar valves. TGA, transposition of the great arteries.

may also reside directly anterior to the pulmonary artery (lo-15%) or even arise to the left of the pulmonary artery (lo-15%). Under these circumstancesdifficulty in identifying the anterior root structure may occur when using the position of the anterior root alone. Another helpful diagnostic echographic finding is that normally the aortic root echo is obtained by scanning the mitral valve in the long axis of the left ventricle and directing the transducer beam across the midline of the chest (Fig 10) over the right shoulder. In patients with transposition of the great vessels,the pulmonary artery is recorded to the left of the sternum with the transducer beam parallel to the sternum. This finding is rarely present in normal patients. Recently we have usedthe systolic time intervals to identify the great vessels.23The systolic time intervals of the right aswell as of the left ventricle may be determined by ultrasound as follows: The pre-ejection period is defined as the interval between the Q wave of the electrocardiogram and the opening of either the aortic or pulmonic valve; the ejection time representsthe interval from cusp openingto cusp closureof thesevalves.The systolic time intervals of the two ventricles are altered by

Fig 11. The echocardiogram of a patient with transposition of the great vessels, demonstrating the systolic time intervals derived from the posterior pulmonic valve and anterior aortic valve. LPEP, left pre-ejection period; LVET, left ventricular ejection time; PA. pulmonary artery: RPEP, right pre-ejection period; WET, right ventricular ejection time. (Reproduced with permission of the American Heart Association.“)

changesin the vascular resistanceof the vesselto which each ventricle is exposed. Therefore, if the vascular resistanceis high, as in the normal aorta, the systolic time-interval ratio will be high. If the vascularresistanceis low, as in the normal pulmonary artery, the ratio will be low. The systolic time intervals in patients with transposition of the great vessels were measured and compared to those of normal patients (Fig 11). They were found to be the reverseof normal. This information has enabled us to more accurately determine from which ventricle the aorta and pulmonary artery arise in patients with transposition of the great vessels. Tricuspid Atresia, Pulmonary Atresia

Uncomplicated tricuspid atresia can readily be diagnosedby ultrasound in the neonate.*“** The characteristic echographic criteria are (1) absent tricuspid valve, (2) a small anterior ventricular chamber with a large posterior ventricular chamber, and (3) a large aortic root that generally does not override the septum (Fig 12). Absenceof the tricuspid valve assumesgreat significance,sincethe

CONGENITAL

Fig 12. Sagittal mitral leaflet.

HEART

DISEASE

view

in tricuspid

283

atresia.

AML,

anterior

normal valve is easily demonstrable in every normal newborn.== Pulmonary valve atresia with intact ventricular septum and hypoplastic right ventricle may be difficult to distinguish from tricuspid atresia with hypoplastic right ventricle and no recordable pulmonary valve. In pulmonary atresia with large right ventricle, the tricuspid valve is identified; but when the right ventricle is small the tricuspid valve is very difficult to record. Knowledge of the size of the right ventricle in pulmonary atresia is very helpful in planning therapy. If the echocardiogram shows a small right ventricle, a systemic-pulmonary artery anastomosis can be undertaken; in the presence of a large right ventricle, a pulmonary valvotomy is the procedure of choice.

Total Anomalous Pulmonary VenousReturn Patients with total anomalous pulmonary venous return (TAPVR), particularly below the diaphragm, are usually symptomatic in the neonatal period. This condition produces signs of right ventricular volume overload and is associated with a smaller than normal left ventricle. For this reason it may be confused with hypoplastic left ventricle syndrome.3 Its echographic criteria are (1) a large right ventricle and small left ventricle, (2) a small aortic root or valve, and (3) usually a small left atrium (Fig 13). The left ventricle is about twothirds the normal size. The mitral valve echo is usually easily recordable and exhibits normal waveform. These two findings alone are frequently sufficient to exclude hypoplastic left ventricle syndrome. An important relationship between the pulmo-

mitral

leaflet;

CW, chest wall;

LS, left septum;

PML,

posterior

nary artery and the aorta has been consistently recorded in our patients with TAPVR3 and was further substantiated in 36 autopsied hearts: the aortic ring was always at the lower limits of normal or smaller (7-g mm) and the pulmonary artery was about 1.5 times as large as the root of the aorta. If the confluence of the anomalous pulmonary veins resides posterior to the left atrium, it may be possible to record this common venous chamber on the echogram. 31 However, caution must be exercised, since a similar echo may be seen in the left atrial cavity, originating from the mitral ring. OVERRIDING

AORTA

Tetralogy of Fallot, double-outlet right ventricle, truncus arteriosus, pulmonary valve atresia with a VSD, and anteriorly positioned VSD all have a common echocardiographic finding-an overriding aorta. Normally the ventricular septum lies at the same depth from the anterior chest wall as the anterior margin of the aortic root (Fig 4) and is in fibrous continuity with it. Aortic overriding is demonstrated by rotating the transducer from the body of the left ventricle to the aorta (Fig 14). However, false negative aortic override may occur because of improper transducer placement.12’23 As the transducer is rotated from the left ventricle to the aorta, an arc is inscribed. The transducer may not demonstrate that the aorta is actually located anterior to the ventricular septum, and thus fails to demonstrate the overriding. The transducer should be moved superiorly to the next interspace, and another scan or sweep of the left ventricle and aorta should be made in an ef-

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Fig 13. Sagittal view in total anomalous pulmonary venous return. Echogram at bottom shows ventricular dimensions and thick septum: echogram at top shows the semilunar valve and left atrial dimensions. Ao, aorta; LA, left atrium; LV, left ventricle; MV, mitral valve; PA, pulmonary artery; RV, right ventricle; TV, tricuspid valve.

fort to demonstrate aortic override. Generally, this maneuver will accentuate the override, if it is present. Patients with tetralogy of Fallot or anteriorly positioned VSD have mitral valve-aortic valve continuity (Fig 15). On occasion it is difficult to establish this continuity because the sweep from the mitral valve to the aorta is performed too quickly.

Ao Override

%E CUSP’

Sep Fig 14. Angiogram and echocardiogram tive tetralogy of Fallot showing marked overriding of the aorta.

in postoperaseptal (Sep)

Fig 15. Echogram in tetralogy of Fallot, showing mitralaortic valve continuity. In addition, aortic overriding of the septum is shown (arrows). (Reproduced with permission of Progress in Cardiovascular Diseases.28)

CONGENITAL

HEART

DISEASE

NORMAL SEPTUM

L.V.

Fig 16. Idealized diagram of the wave form of normal and abnormal septal motion in right ventricular volume overload. INTERMED, intermediate septal motion; LS, left septal surface; LV, left ventricle; R, right septal surface. (Reproduced with permission of Progress in Cardiovascular Diseases.28 1

increased right ventricular dimension.7926 Normally the septum moves posteriorly toward the left ventricular (LV) endocardium during systole and toward the transducer or away from the LV wall during diastole. This motion creates a pincer-like effect as the blood is ejected from the ventricle. Paradoxical septal motion exists if the septum moves anteriorly during systole, ie, synchronously with the LV wall. No septal motion at all may occur during systole or the motion may be intermediate between normal and paradoxical (Fig 16). Abnormal septal motion is not specific for right ventricular volume overload, since it may occur in left bundle branch block, coronary artery disease, aberrant origin of the left coronary artery, and prosthetic mitral or aortic valve.’ Enlargement of the right ventricle and right ven-

A slower sweep of the mitral valve that initially includes both the anterior and posterior leaflets and then the anterior leaflet alone as it merges with the posterior margin of the aorta should prevent misinterpretation of mitral-aortic continuity. Patients with double-outlet right ventricle have a subaortic conus that produces discontinuity of the mitral-aortic valve echo.S,23 There is a sudden, abrupt anterior displacement of the posterior margin of the aorta which prevents the mitral valve from becoming contiguous with it. This situation may also occur in truncus arteriosus and other conditions in which bilateral conuses exist. The feature that distinguishes tetralogy of Fallot from anteriorly placed VSD is the large left atrium. In tetralogy of Fallot, the left atrium is usually normal or small. ANOMALIES

WITH VOLUME

RIGHT VENTRICULAR OVERLOAD

The conditions most commonly associated with right ventricular volume overload include secundum atrial septal and ostium primum defects, atrioventricular canal, tricuspid and pulmonary insufficiency, and TAPVR. Less common causes include left ventricular-right atria1 shunt and systemic arteriovenous fistula, particularly those in the central nervous system. The two echographic features classically associated with right ventricular volume overload are abnormal septal motion and

Fig 17. Echograms show large right ventricular dimensions (RVD), and dilated right ventricular outflow tract (RVOT) in atrial septal defect. LVID, left ventricular internal dimension.

RICHARD

tricular out-flow tract is a more reliable sign of right ventricular volume overload than abnormal septal motion (Fig 17). Normal right ventricular dimensions for children and for adults are available.‘*lo ABNORMAL

MITRAL

VALVE

ECHO

The distinguishing feature of secundum atria1 defect and endocardial cushion defects is the mitral valve echo.32137 In endocardial cushion defect the wave form of the mitral valve echo is grossly abnormal. There are multiple systolic echoes,the amplitude of the echo is decreased,the atria1 wave of the mitral valve is absent, and the valve hits the interventricular septum without benefit of full excursion. Further, the mitral valve frequently narrows the left ventricular outflow tract (Fig 18). These abnormalities are less pronounced if the mitral regurgitation has produced left ventricular dilatation. The mitral valve echo in atrioventricular canal

A.

MEYER

traverses the interventricular septal echo during the sweep of the mitral valve to the aorta (Fig 19).32*37This occurs as a result of the conjoined septal leaflets of the tricuspid and mitral valves. The finding is specific for this lesion and has not been seen in patients with large VSD. Partial anomalous pulmonary venous drainage demonstrates findings similar to those of atria1 septal defect. LEFT VENTRICULAR

VOLUME

OVERLOAD

Left ventricular volume overload can be produced by aortic insufficiency, mitral insufficiency, patent ductus arteriosus,or VSD. Aortic Regurgitation

Aortic regurgitation results in dilatation of the left ventricle (Fig 20). However, the left atrium should be normal in size unlesscoexistent congestive heart failure or mitral diseaseis present.Mitral flutter is frequently present (Fig 21). It is not a specific finding, since the mitral valve will also flutter if there is a large VSD and obstruction to the right ventricular outflow tract.27 If the degree of regurgitation is severe and the end-diastolic pressureis elevated,premature closure and delayed opening of the mitral valvemay occur.23 In mitral regurgitation there is also a markedly dilated left atrium aswell asa large left ventricle. Mitral Insufficiency

Mitral valve prolapse in mitral regurgitation is a common form of mitral valve dysfunction in children.3s We were able to demonstrate either discrete (Fig 22) or pansystolic prolapseof the mitral valve in about 90% of patients. Prolapse of the anterior or posterior mitral leaflets during systole is diagnosedwhen the leaflets move posterior to an imaginary line drawn parallel to the chest wall at the onset of ventricular ejection as determinedby aortic cusp opening. The prolapse may occur any time during ventricular systole,but doesnot return to normal until ventricular diastole. Patent Ductus Arteriosus

Fig 18. Top: Normal mitral valve echo (MV) in atrial saptal defect. Bottom: Ostium primum defect showing abnormal mitral valve echo (MVL

Diagnostic ultrasound has been extremely useful in assessingthe effect of left-to-right shunting through a patent ductus arteriosus in the premature infant.2’36 The left ventricular and left atria1 dimensionswere measuredserially in 37 premature infants and found to be enlargedwhen there was

CONGENITAL

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DISEASE

287

Fig 19. Echogram in canal atrioventricular showing the common valve atrioventricular (CAV) traversing the septal echo.

Fig 20. Echogrems from a patient with isolated eortic regurgitation, demonrtrating the larg?s left ventri+e (left) and normal-size left atrium (right).

significant shunting through the ductus (Fig 23). Following ligation of the ductus these values returned to normal. Not infrequently an echo will appear in the left atrial cavity, which we think originates from the mitral ring, and may be mistaken for the left atrial wall. A scan from the left ventricle to the left atrium should be made to identify the left atrial wall, which generally residesposterior to the left ventricular wall and is in continuity with it. This should help prevent erroneousmeasurementof the left atrium. Ventricular Septal Defect

The echogram in VSD is very similar to that in ductus arteriosus. At this time, it is difficult to

Fig 21. Mitrel valve echo9mms. Lrft: paknt with koleted aortic regurgitation shows mitral flutter. Right: Normal patient shows no flutter.

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ular septal echo (Fig 24). In the majority of our patients two atrioventricular (AV) valves were demonstrated, usually at different depths, without an intervening ventricular septal echo. On occasion only a single AV valve is present. Another sign that helps distinguish the single ventricle from other lesions that have a common mixing chamber is that it is difficult to record simultaneously the anterior and posterior margins of the posterior root structure arising from the ventricle. The transducer must be moved in order to record the anterior margin of the root structure. This is in contrast to either aortic atresia or tricuspid atresia. Ebstein ‘sAnomaly

Fig 22. Echogam showing prolapse of posterior mitral leaflet. AML, anterior mitral leaflet; PML, posterior mitral leaf let.

separate the two diseases, since both show an enlarged left atrium and left ventricle. If the VSD is large and longstanding, right ventricular enlargement may be associated. OTHER

ANOMALIES

Single Ventricle In single ventricle, the most important echocardiographic finding is the absence of the ventric-

Ebstein’s anomaly of the tricuspid valve can also be diagnosed echographically.“130 This is accomplished by recording mitral valve closure (Fig 25) and tricuspid valve closure. The interval of these closures measured from the onset of the Q wave of the electrocardiogram is expressed as Q-MC (mitral closure) and Q-TC (tricuspid closure). The difference in the time interval between the two closures has been termed the delta value. An interval of greater than 65 msec is specific for Ebstein’s anomaly. Echocardiography has proved to be an important noninvasive method for accurately diagnosing many congenital cardiac defects. This method provides significant information, so that cardiac cath-

-I-

LVED

_L

Fig 23. Preoperative achocardiograms A and C show enlarged left atrium (LA) and left ventricle (LV) in premature infant with patent ductus arteriosus. Postop erative echograms B and D show reduction in left atrial (LAD) and left ventricular (LVED) dimensions. LAW, left atrial wall: LVE, left ventricular endocardium; LS, left septum; MR. mitral ring. (Reproduced with permission of Journal of Pediatrics.2 1

CONGENITAL

HEART

289

DISEASE

Fig 24. Echogram of a patient with single ventricle and transposition of the great arteries. The septum is not identified. Two atrioventricular valves. SV, single ventricle. (Reproduced with permission of Progress in Cardiovascular Diseases.28 1

eterization and angiocardiography, when necessary, can be planned with greater facility. This is particularly important in severely ill babies in whom these diagnostic methods are not without risk. The value of the sonar method rests not only in its ability to diagnose specific cardiac defects but also in its ability to exclude heart disease, especially in infants with shock or cyanosis from noncardiac

Fig 26. Echogram of patient with Ebstein’s anomaly, showing closure of mitral valve and tricuspid valve with resultant large delta value. Diastolic closing velocity (E-F slope) normal. MC, mitral valve closure; TC, tricuspid valve closure.

causes. Many investigations assessing the various parameters of ventricular function are currently in progress. With advances in technique, greater application of echocardiography should be forthcoming.

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10. Feigenbaum H: Echocardiography. Philadelphia, Lea and Febiger, 1972, p 218 11. Fortuin NJ, Hood WP, Sherman EM, et al: Determination of left ventricular volumes by ultrasound. Circulation44:575-584,197l 12. French JW, Popp R: Variability of echocardiographic discontinuity in double outlet right ventricle and truncus arteriosus. Circulation 5 1:848-854,1975 13. Gibson DG: Estimation of left ventricular size by echocardiography. Br Heart J 35:128-134,1973 14. Gramiak R, Shah PM: Echocardiography of the normal and diseased aortic valve. Radiology 96: l-8, 1970 15. Gramiak R, Nanda NC, Shah PM: Echo detection of the pulmonary valve. Radiology 102:153-157, 1972 16. Gramiak R, Chung KJ, Nanda NC, et al: Echocardiographic diagnosis of transposition of the great vessels. Radiology 106:187-189,1973 17. Hirschfeld S, Meyer RA, Schwartz DC, et al: Measurement of right and left ventricular systolic time intervals by echocardiography. Circulation 5 1: 304-309, 1975 18. Joyner CR, Hey EB, Johnson J, et al: Reflected ultrasound in the diagnosis of tricuspid stenosis. Am J Cardiol 19:66-73, 1967 19. Konecke LL, Feigenbaum H, Chang S, et al: Abnormal mitral valve motion in patients with elevated left ventricular diastolic pressures. Circulation 47:989-996, 1973

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20. Lundstrom NR: Applications of echocardiography in infants and children. Acta Pediatr Stand 63:23-41, 1974 21. Meyer RA, Stockert J, Kaplan S: Echographic determination of left ventricular volumes in pediatric patients. Circulation 51:297-303,197s 22. Meyer RA, Kaplan S: Echocardiography in the diagnosis of hypoplasla of the left or right ventricles in the neonate. Circulation 46:55-64, 1972 23. Meyer RA: Echocardiography in congenital heart disease, in Fowler N (ed): Diagnostic Methods in Cardiology, Cardiovascular Clinics, vol 6. Philadelphia, F.A. Davis, 1975, pp 219-423 24. Meyer RA, Schwartz DC, Covitz W, et al: Echocardiographic assessment of cardiac malposition. Am J Cardiol33:896-903, 1974 25. Meyer RA, Schwartz DC, Kaplan S: The diagnosis of aortic atresia by echocardiography. Am J Cardiol 29: 280,1972 26. Meyer RA, Schwartz DC, Benzing G III, et al: The ventricular septum in right ventricular volume overload. Am J Cardiol30:349-353, 1972 27. Meyer RA, Bloom KR, Schwartz DC, et al: Mitral flutter without aortic Incompetence. Circulation (Suppl IV) 48:81,1973 28. Meyer RA, Kaplan S: Non-invasive techniques in pediatric cardiovascular disease. Prog Cardiovasc Dis 15: 341-367,1973

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29. McDonald IG, Feigenbuam H, Chang S: Analysis of left ventricular wall motion by reflected ultrasound. Circulation 46:14-25,1972 30. Milner S, Meyer RA, Venables AW, et al: The tricuspid valve in children-an echocardiographic and phonocardiographic study. Am J Cardiol35:157, 1975 3 1. Paquet M, Gutgesell H: Echocardiographic features of total anomalous pulmonary venous connection. Circulation 51:599-605,1975 32. Pieroni DR, Homey E, Freedom RM: Echocardiography in atrioventricular canal defect. A clinical spectrum. Am J Cardiol35:54-58, 1975 33. Pompo JF, Troy BL, Russell RO Jr: Left ventricular volumes and ejection fraction by echocardiography. Circulation 43:480-490,1971 34. Popp RL, Harrison DC: Ultrasonic cardiac echography for determining stroke volume and valvular regurgitation. Circulation 41:493-502, 1970 35. Schwartz DC, Kaplan S, Meyer RA: Mitral valve prolapse in children: Clinical, echocardiographic and tine-angiographic findings in 81 cases. Am J Cardiol 35: 169,197s 36. Silverman NH, Lewis AB, Heymann MA, et al: Echocardiographic assessment of ductus arteriosus shunt in premature infants. Circulation 50:821-825,1974 37. Williams RG, Rudd M: Echocardiographic features of endocardlal cushion defects. Circulation 49:418422, 1974