lACC VoL 8, No.2August 1986:451-8

EDITORIAL REVIEWS

Uses and Abuses of Fetal Echocardiography: A PediatricCardiologist's View*

JAMES C. HUHTA, MD, FACC

Houston, Texas

451

The most valuable and widely applied technique for eval­uation of the human fetus is transabdominal ultrasonogra­phy, which may be useful from the first few weeks of ges­tation until the time immediately before birth. Proliferationof high quality equipment (1), including imaging systemsthat utilize dynamic focusing, plus the availability of a largebody of data on the subject (2) have led to sophisticationand accuracy in the recognition of cardiac abnormalities onthe part of noncardiologist providers of prenatal imagingservices.

There are three ultrasound techniques commonly used toevaluate the cardiovascular system: M-mode, two-dimen­sional and Doppler echocardiography. Most equipment foruse by obstetricians is not designed for performing M-modeor Doppler portions of the examination, but there is everyindication that Doppler techniques will become common­place in evaluating the high risk fetus in the next few years.Fetal echocardiography combines many such new devel­opments in technology for assessing the cardiovascular anat­omy and function of the fetus. Applications of these include1) the diagnosis of fetal cardiac and extracardiac anatomy.2) fetal arrhythmia diagnosis and monitoring during trans­placental therapy, and 3) cardiovascular function assessmentincluding measurement of ventricular ejection and the stateof the fetal myocardium and placenta using new Dopplertools for the measurement of blood flow velocities.

Interventions for the treatment of congenital defects ofthe kidneys and brain have already been performed and itappears that the practice of cardiac surgery will be extendedto the fetus in the near future (3), thereby focusing moreattention on the accuracy of complete cardiac diagnosis byultrasonography.

Indications and SafetyRoutine screening of fetuses has not been shown to sig­

nificantly alter outcome and, in the absence of specific in-

*Editorials published in Journal ofthe American College ofCardiologyreflect the views of the authors and do not necessarily represent the viewsof lACC or the American College of Cardiology.

From The Lillie Frank Abercrombie Section of Cardiology. Departmentof Pediatrics, Texas Children's Hospital, Houston, Texas.

Address for reprints: James C. Huhta, MD, The Lillie Frank Aber­crombie Section of Cardiology, Department of Pediatrics, Texas Children'sHospital, 6621 Fannin, Houston, Texas 77030.

dications in the prenatal period, it should not be standardpractice to order an ultrasound examination. When nonin­vasive evaluation of the fetus is indicated, brief examinationof the heart is important and, if an abnormality is suspected,the pediatric cardiologist enters the picture to provide ex­pertise in the noninvasive evaluation of cardiac anatomy andfunction. Other indications for referral include evidence offetal hydrops or polyhydramnios, the presence of a non­cardiac congenital defect, an abnormality of fetal rhythmand a positive family history of congenital heart disease.

The extremely rapid proliferation of the use of ultrasoundin the early assessment of the fetus has led to concern onthe part of many physicians and consumers and the gov­ernment that prolonged, high intensity exposure to ultra­sound energy may be harmful to the developing fetus in thefirst trimester (4). Evaluation of the fetal heart by Dopplerechocardiography requires higher intensity exposure than isrequired by standard B-mode or real-time two-dimensionalscanning and may exceed the 100 mW/cm2 spatial peaktemporal average federal guidelines, especially with con­tinuous wave Doppler technology. It is suspected that theintensities of a brief diagnostic ultrasound examination areunlikely to be dangerous in later gestation fetuses, but thefetus in need of frequent examinations may experience sig­nificant exposure. Therefore, because the risk-benefit ratioof repetitive diagnostic examinations lasting up to 30 min­utes each is unclear, we have adopted the policy that re­peated pulsed and continuous wave Doppler examinationsshould be performed only when a potentially life-threateningabnormality is present in the fetus (5,6).

Anatomic Diagnosis of CongenitalHeart Disease

Two-dimensional echocardiography can be used to per­form a complete segmental anatomic assessment of the heartand great arteries in the newborn infant (7-9) and there isevidence that such assessment may be possible for much ofthe cardiac anatomy of the fetus after 18 to 20 weeks'gestation (l0-12). Experience in the diagnosis of abnor­malities of atrial situs, atrioventricular (AV) connection,ventriculoarterial connection and the atrial and ventricularsepta have been reported (13-25). However, early experi-

452 HUHTAEDITORIAL

lACC Vol. 8, No.2August 1986:451-8

ence indicates that the same areas that cause difficulty inthe child will cause difficulty in the fetus: namely, ventric­ular septal defect, semilunar valve stenosis and extracardiacanatomy. Only a limited number of workers in the field havereported results with state of the art equipment performinga detailed cardiac examination before 18 weeks' gestation.Although one can recognize that the fetal heart has fourchambers, an examination of the anatomy comparable withwhat can be obtained in a newborn infant is not yet routinelypossible. If prenatal diagnosis of congenital heart disease isto achieve a standing comparable with diagnosis after birthby echocardiography plus angiography, one should not havea double standard of accuracy in diagnosis of cardiac anat­omy: one for the newborn child and one for the fetus. Meth­odology for complete diagnosis of intracardiac and extra­cardiac congenital defects is the first step in both situations.

One difficulty that arises is the definition of the primarydiagnosis. Congenital heart disease often consists of a com­bination of defects rather than an isolated defect and onedefect may be palliated by another. For example, a 23 weekgestation fetus with trisomy 21 was found to have an AVcanal defect (Fig. 1). At the second examination, whichincluded Doppler echocardiography, infundibular and val­vular pulmonary stenosis (tetralogy of Fallot) were alsopresent. There was dilation of the aorta compared with theright pulmonary artery from right to left shunting in uteroas well as a left superior vena cava to the coronary sinus.The outlook for that child after birth was one of graduallyincreasing cyanosis rather than the more usual congestiveheart failure in the first few months. Therefore, the prognosisfor any given fetus with cardiac disease must be indivi­dualized while keeping the limitations of the test in mind.

An unintentional abuse offetal echocardiography resultsfrom poor communication between the perinatologist, thepediatric cardiologist and the parents. The identification ofa cardiac abnormality in a third trimester fetus sometimesleads to hasty decisions about early delivery or caesareansection, which can result in the additional problem of res­piratory distress syndrome in the newborn child. Often thereis little evidence that the cardiac problem has any effect onthe viability of the fetus by this late date or on its abilityto tolerate a normal vaginal delivery. A team approach com­bining the skills of many subspecialties is useful in suchsituations. Conversely, when the fetus appears moribundwith nonimmune hydrops fetalis, referral to such a specialtyteam is indicated to establish the cause or to provide assis­tance in the delivery.

Diagnosis of Fetal ArrhythmiasThe diagnosis of arrhythmias in the fetus is one area in

which prenatal cardiac evaluation has clearly shown prac­tical benefit. Arrhythmias in the fetus may be benign, symp­tomatic only late in gestation or life-threatening from the

moment of appearance. Because direct recording of the fetalelectrocardiogram is difficult and unpredictable, M-modeechocardiography has been used with success to evaluatefetal rhythm and has found widespread application (26-33).In addition, fetal Doppler techniques (34), which evaluatethe blood flow velocities instead of cardiac chamber wallmotion, are equally useful in diagnosis and may be superiorto the M-mode technique in the uncommon situation wheresevere dilation of the atria has reduced their movement.

Premature atrial contractions (Fig. 2) occur frequentlyand have little importance except as an occasional precursorof supraventricular tachycardia or when they may be mis­taken for bradycardia.

Supraventricular tachycardia is now a well recognizedcause of fetal hydrops and cardiac failure in utero. Becausetransplacental therapy is available to treat supraventriculartachycardia, a method to diagnose the cardiac rhythm andto evaluate the effects of treatment is very important. Inanimal experiments, atrial pacing of the fetus at rates greaterthan 300 beats/min causes hydrops and premature laborwithin I to 2 days (Gest A, Hansen T, personal commu­nication, January 1986). Failure to convert with drug ther­apy aimed at supraventricular tachycardia should suggestanother diagnosis.

Ventricular tachycardia in the fetus is rare and there isnot yet sufficient experience with diagnosis of this entity tocomment.

Bradycardia is due either to some form of AV block orto slowing of the sinus node. In a fetus near term, episodesof bradycardia at a rate less than 80 beats/min indicate fetaldistress that could be secondary to a cardiac defect.

Complete heart block in the fetus may be due to collagenvascular disease in the mother or to congenital heart disease,such as corrected transposition of the great arteries or leftatrial isomerism and AV canal defect. The diagnosis is basedon detection of independent atrial and ventricular contrac­tions with a faster atrial rate. Robert Carpenter at BaylorCollege of Medicine recently performed in utero transab­dominal transthoracic pacing of a moribund severely hy­dropic 27 week gestation fetus with congenital completeheart block and a normal heart. Such a capability and thewell established efficacy of transplacental therapy are justtwo examples of the feasibility of treating arrhythmias thatmay otherwise lead to a stillbirth. The key to success isaccurate diagnosis and a knowledge of the natural history.

Cardiovascular Function AssessmentVentricular dysfunction. The heart is one of the few

organ systems whose function in the fetus can be evaluatedby noninvasive means. Cardiac function in the fetus can beestimated using measurements of ventricular chamber sizesand shortening fraction by M-mode techniques (35-38),systolic time intervals (39) and acceleration time of the great

Figure 1 (right). Imaging of cardiac anatomy in a23 week gestation fetus. Upper panel, the atrio­ventricular canal defect with its anterior bridgingleaflet (AL) and normal pulmonary venous connec­tions (white arrow). Middle panel, The aortic arch(AAo) is dilated compared with the right pulmonaryartery (RPA). Lower panel, There is a left superiorvena cava connecting to the coronary sinus (C8)anterior to the spine (8). A = anterior; DAo =descending aorta; I = inferior; LeA = left carotidartery; LV = left ventricle; P = posterior; RA =right atrium; RV = right ventricle; 8 = superior.

Figure 2 (below). Fetal Doppler echocardiogramof the mitral valve (MV) in a 22 week gestationfetus with an irregular heart rate. During normalbeats the normal rapid filling velocities (E) are fol­lowed by the contribution of atrial systole (A) oc­curring immediately before the fetal ventricularejection (open arrows). Premature atrial contrac­tions cause an early or absent ventricular responsedepending on the degree of prematurity. Numbersindicate the A-A interval in milliseconds. LAleft atrium; LV = left ventricle.

E

500

E

500I

E i 420

E+A

J

I·

E

1 ·1

Figure 3 (left). Two-dimensional(upper panel) and M-mode (lowerpanel) echocardiograms from a 32week gestation fetus with cardio­myopathy showing a dilated andpoorlyfunctioning left ventricle(LV).The location of the measurement isshown in the upper panel (arrow).Somewhat preserved right ventricu­lar function suggests primary leftventricular myocardial disease.RV = right ventricle.

Figure 4 (below). Doppler echo­cardiogram showing mild triscuspidvalve insufficiency (II) in a normal20 week gestation fetus. The mildnature of the insufficiency is sug­gested by the relatively low peak ve­locity of the jet. This finding was notdetectable I year after birth. A =atrial systole; E = rapid filling phaseof diastole; RA = right atrium;RV = right ventricle.

LV 1.7cm

RV

t

IRA - 1s -

lACC Vol. 8, No.2August 1986:451-8

HUHTAEDITORIAL

455

Figure 5 (right). Doppler ultrasound sampling in the umbilicalartery (UmArt) show a significant difference between systolic anddiastolic velocities (systolic/diastolic ratio, 0.31/0.08 = 3.9).

Figure 6 (below). Dopplerechocardiogram of the fetal ductus andmainpulmonary artery (MPA). The increased velocityof bloodflowin the normal fetal ductus (0.8 mls) on pulsed Doppler echocardi­ography compared with the main pulmonary artery indicates mildphysiologic constriction at this level. Note the diastolic runoff inthe ductus due to a high pulmonary/systemic resistance ratio.

23 ks

Ductus

UmArt

15

MPA

artery Doppler flow velocity (40). Ventricular dysfunctionmay result from end-stage fetal distress , as in hydrops fe­talis , or may be due to primary cardiomyopathy. The short­ening fraction of the left ventricle is a useful measure ofventricular function in combination with the ventricular size(41). Growth in ventricular sizes studied longitudinally hasbeen shown to be useful in detecting intrauterine growthretardation. However, few data are available concerning thefeasibility of treating ventricular dysfunction in utero. Inone 32 week gestation fetus with primary cardiomyopathy(endocardial fibroelastosis), transplacental treatment withdigoxin was attempted. This baby presented with a dilated,

poorly functioning left ventricle (Fig. 3) and no evidenceof outflow tract obstruction as is seen in critical aortic ste­nosis. There was no improvement in the left ventricularshortening fraction with this treatment and the baby diedshortly after an uncomplicated delivery at term .

Valvular insufficiency. An associated finding with ven­tricular dysfunction is insufficiency of one or both AV valves(5,6,42) . Pulsed Doppler echocardiography can be used tosample at the valve or in the atrium to detect this abnor­mality. Although not a feature of the normal fetal Dopplerexamination, mild tricuspid valve insufficiency can occurin a normal fetus (Fig. 4), but is encountered most com-

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Figure 7. ColorDopplerflow mapfrom a 26weekgestation fetus.Upper panel, Normal systolic flow toward the transducer in theascending (AAo, red) and descending (DAo, blue) aortas. Middlepanel, The normal patternof flow in the right ventricular outflowtract appearsblueas flowawayfrom the transducer. Lower panel,The increased ductus systolicvelocity in Figure6 is confirmed bycolor Dopplerechocardiography which shows increasing velocity(change from blueto green) from the mainpulmonary artery (MPA)to the ductus (open arrow) in a normal fetus. Ao = aorta; LV =left ventricle; RV = right ventricle.

monly in distressed babies with hydrops fetalis, and in thosewith some types of arrhythmia. In association with con­genital heart disease and hydrops, AV valve insufficiencyis a poor prognostic sign (12). Pulsed Doppler echocardi­ography is limited in the quantitation of the severity of valveinsufficiency, but color Doppler techniques may be usefulin this regard in the future.

Systolic and diastolic flow velocities. Many workersare now using Doppler techniques for monitoring umbilicaland uterine blood flow velocities (43-47). The same limi­tations mentioned earlier apply to the quantitation of bloodflow but the patterns of systolic and diastolic flow velocitiesin the fetal aorta and the umbilical cord give clues to thehemodynamic situation of the fetus (Fig. 5). The placentalcirculation is a high flow, low resistance circuit and onewould expect significant diastolic flow when the placentalresistance is normal. One finds that the ratio of systolic todiastolic umbilical artery flow velocity is normally less than3 at term and less than 4 before 30 weeks' gestation (46).In situations where there is growth retardation related toplacental insufficiency, the resistance of the placental circuitincreases and the ratio of systolic to diastolic velocity in theumbilical artery markedly increases above normal values.

Future DirectionsIn the future, technical advances in transumbilical vas­

cular access to the fetus will allow cardiac catheterizationto be performed in utero in selected cases. With the currentexplosion of interventional techniques for the treatment ofcongenital heart defects without surgery there is a high prob­ability that these skills could be applied to the fetus. Butdecisions about such treatment require research into morereadily applicable methods of fetal assessment such as: 1)quantitation of ventricular stroke volume by pulsed Dopplerechocardiography; 2) noninvasive measurement of ventric­ular pressures by quantitation of the velocity of the AVvalve insufficiency jet; 3) evaluation of the pulmonary tosystemic resistance ratio by Doppler technique, perhaps bysampling the velocity pattern in the ductus arteriosus (Fig.6); 4) improved neurologic examination, perhaps by ultra­sound evaluation of fetal eye movements; and 5) color Dop­pler echocardiography, which may be very important in thefuture as a screening tool for the evaluation of fetal hemo­dynamics (Fig. 7).

Ethical ConsiderationsGiven what has been accomplished thus far in fetal di­

agnosis and what is just over the horizon, it is timely toask, "So what?" Without well established in utero methodsof treating the defective or malfunctioning heart, is it usefulor even advisable to work in this area, further refining ourdiagnostic acumen? Is this an area that will experience rapid

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and sustained growth and deserve substantial research fund­ing and trainee involvement, or is this field ahead of its timeor impractical in the face of limited resources and abortionon demand?

No more than 30 years ago, the postpartum diagnosis ofa "blue baby" meant an early death. The introduction ofcardiac surgery and high quality cineangiographic tech­niques dramatically altered the outcome for such infants. Itis possible that a similar evolution could occur in interven­tional fetal/perinatal medicine today . The widespread avail­ability of ultrasound equipment for fetal diagnosis shouldlead to interventions to affect fetal cardiovascular devel­opment that have yet to be imagined (48). Earlier interven­tion for defects, that appear hopeless later in gestation maysignificantly alter the natural history . The element that isuncertain for such achievements in fetal care is the convic­tion on the part of the medical community that progress intreating the fetus with congenital heart disease before de­livery will benefit mankind both now and in the future .Although the natural history of some defects results in spon­taneous abortion due to severe congestive heart failure be­fore birth, parents and physicians are faced with the choiceof treatment or termination long before this information isavailable. In such a situation, termination of a pregnancyafter the diagnosis of a defect represents a value judgmentabout fetal life and its future quality, and the practice oftermination fundamentally changes the approach of physi­cians to this group of patients . We are living in a genuinelyambivalent society that praises the possibility that physicianswill someday eliminate patients with congenital defects ratherthen treating them. Never before has our profession beenso challenged by the presupposition that there is some lifethat is not worthy to be lived. The acceptance of "wrongfullife" is only one example of this attitude (49). Surely theknowledge and skills accumulated in such a noble endeavoras improving the welfare of the fetus in trouble with con­genital heart disease are worthy of our best efforts. Knowl­edge gained in this way will have immediate application tomonitoring of the fetus in complicated pregnancies wherethe heart is anatomically normal.

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