Cardiac Anomalies in the Fetus

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Cardiac Anomaliesin the Fetus

Christopher G. B.Turner, MDa, Wayne Tworetzky, MD

b,c,

Louise E. Wilkins-Haug, MD, PhDd, Russell W. Jennings, MD

e,f,*

As the most frequent congenital anomaly and the leading cause of death among

infants in the United States, congenital heart disease (CHD) is an attractive target

for fetal therapy. With the development of successful neonatal repair for many types

of CHD over the last 20 years, earlier postnatal therapy to restore physiologic anatomy

has been encouraged, and fetal therapy has become the next frontier. Concurrent

advances in interventional catheterization and fetal imaging provided a foundation

for the novel field of fetal cardiac intervention. This article focuses on the current status

of in utero catheter interventions for CHD with particular interest in therapy for defects

characterized by progressive stenosis or atresia of the semilunar valves, the aortic andpulmonary, with development of subsequent ventricular hypoplasia.

FETAL CIRCULATION

In the normal fetal circulation, oxygenated blood from the umbilical vein is able to

stream efficiently through the foramen ovale (FO) to the left heart and up to the brain.

The desaturated blood from the superior vena cava is directed through the ductus

arteriosus (DA) back to the placenta for reoxygenation ( Fig. 1 ). Because pulmonary

a Department of Surgery, Children’s Hospital Boston, 300 Longwood Avenue, Fegan 3, Boston,MA 02115, USAb Department of Pediatrics, Harvard Medical School, 300 Longwood Avenue, Pavillion 2,Boston, MA 02115, USAc Fetal Cardiology Program, Children’s Hospital Boston, 300 Longwood Avenue, Fegan 3,Boston, MA 02115, USAd Department of Maternal Fetal Medicine, Brigham and Women’s Hospital, 75 Francis St.,Boston, MA 02115, USAe Department of Surgery, Harvard Medical School, 300 Longwood Avenue, Pavillion 2, Boston,MA 02115, USAf

Advanced Fetal Care Center, Department of Surgery, Children’s Hospital Boston, 300Longwood Avenue, Fegan 3, Boston, MA 02115, USA* Corresponding author. Advanced Fetal Care Center, Department of Surgery, Children’sHospital Boston, 300 Longwood Avenue, Fegan 3, Boston, MA 02115.E-mail address: [email protected] (R.W. Jennings).

KEYWORDS

Congenital heart disease Fetal intervention Hypoplastic left heart syndrome Pulmonary atresia Balloon dilatation Valvuloplasty

Clin Perinatol 36 (2009) 439–449doi:10.1016/j.clp.2009.03.015 perinatology.theclinics.com

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vascular resistance is higher than systemic vascular resistance, blood shunts through

the DA from the right side to the left, diverting around the lungs. At the moment of birth,

however, pulmonary vascular resistance suddenly drops, the shunt reverses, andblood flows through the lungs. As the FO and DA close in the postnatal period, two

distinct circuits are formed, the pulmonary and systemic vasculatures.

With severe semilunar valve pathology, however, there is only a single functional

ventricular pump, the left ventricle in the case of pulmonary atresia (PA), and the right

ventricle in the case of aortic stenosis (AS). In these situations, the DA is essential to

continue perfusion to the systemic or pulmonary vasculature, and the FO is essential

to allow the mixture of oxygenated and deoxygenated blood in the single ventricle

system. As blood flows preferentially through the patent FO rather than the high-pres-

sure ventricle, however, the reduction in flow through the ventricle retards growth, and

in part, contributes to eventual hypoplasia.In addition to semilunar pathology, if the atrial septum is intact (IAS) or severely

stenosed, the circuit on the side of the atretic semilunar valve will become obstructed.

In the extremely rare case of PA with a stenotic atrial septum, the fetal circulation is

impaired and often not compatible with fetal life. In the case of established hypoplastic

left heart syndrome (HLHS) with an intact atrial septum, the postnatal circulation is

impaired and not compatible with neonatal life.

Fig. 1. Normal intracardiac fetal circulation. Physiologic shunting through the patentforamen ovale (FO) and the patent ductus arteriosus (DA). Oxygenated blood from theplacenta (red arrows ) reaches the right atrium (RA) by means of the inferior vena cava(IVC). This well-oxygenated blood is shunted preferentially from the RA across to the left

atrium (LA) through the FO and then is ejected out the left ventricle (LV) to the ascendingaorta (AO). Deoxygenated blood (blue arrows ) returning from the superior vena cava (SVC)preferentially travels from RA into the RV, then out through the main pulmonary artery(PA). Because of the high pulmonary vascular resistance in the fetal lungs, this deoxygen-ated blood bypasses lungs and enters the descending aorta by means of the DA. (From

Insaba AF. Cardiac disorders. In: Marx JA, editor. Rosen’s emergency medicine: conceptsand clinical practice. 6th edition. Philadelphia: Elsevier; 2006. p. 2568; with permission.)

Turner et al44 0



The most common indication for a fetal cardiac intervention is to attempt to prevent

the development of right or left ventricular (LV) hypoplasia. In the approach to fetal

cardiac interventions for semilunar valve stenosis, therefore, there are two funda-

mental conditions:

One must understand the in utero characteristics of the heart defect that wouldpredict progression to ventricular hypoplasia.

One must understand the characteristics of the heart defect that indicate that an in

utero intervention might lead to improvement in cardiac growth and function.

Moreover, one needs to understand the features that indicate the heart defect is too

far advanced and that fetal intervention would be futile and provide unnecessary risk

to the mother and fetus.

DIAGNOSTIC STUDIES

Echocardiography is the preferred modality for screening and determining the severity

of semilunar valve stenosis. Color Doppler imaging can identify reduced flow through

the aortic valve and retrograde flow in the transverse aortic arch, the hallmark of

evolving HLHS in this defect. The pressure gradient across the valve is affected by

the degree of stenosis and the competitive retrograde arch flow, as well as the func-

tion of the left ventricle. A low gradient therefore may indicate a stenotic valve with

poor LV function. Other indicators of LV dysfunction and evolving HLHS include retro-

grade flow in the aortic arch supplied via the ductus arteriosus, diminished mitral valve

diastolic excursion with reduced inflow, left-to-right flow across the FO, or left-to-right

bulge of an intact atrial septum.1–4

Also, although rare, a thrombus can form in thedilated left ventricle.

Thousands of prenatal screening ultrasounds are needed to detect a small number

of cardiac defects. Despite increased screening and improved detection rates, most

cardiac defects remain undiagnosed prenatally. If CHD is suspected, the mother

should be referred to a pediatric cardiologist as soon as possible. This early referral

allows for confirmation of the diagnosis, appropriate counseling, and arrangement

for delivery and treatment at a center capable of treating complex congenital heart

defects.5,6 Early prenatal diagnosis also allows for the option of palliative or thera-

peutic in utero interventions for amenable cardiac defects.7–9 Because these therapies

are available at only a few centers, early prenatal detection is critical. Increased overallscreening rates, improved detection, and earlier referral will allow for more patients to

potentially benefit from in utero interventions.

CONGENITAL HEART DEFECTS APPROPRIATE FOR FETAL INTERVENTION

Fetal intervention offers the tantalizing possibility to reverse the pathologic process

before significant cardiac structural and functional deterioration has occurred. Early

relief of semilunar valve stenosis in utero may reverse the progression toward ventric-

ular hypoplasia.10–12 This section discusses the specific defect on the left and right

side.

Defects on the Left Side

Aortic valve defects in the fetus range from mild stenosis with an adequately sized

ventricle to severe stenosis with evolving HLHS, a term that implies that the left ventricle

is unable to sustain systemic circulation. With a patent FO, blood in the left atrium flows

Cardiac Anomalies in the Fetus 441



preferentially to the low-pressure right atrium rather than the high-pressure left

ventricle. The resultant diminished flow through the left heart causes arrest of LV growth

and HLHS. Occasionally the left ventricle can be of normal size, but the myocardium

becomes damaged and fibrotic with significantly reduced filling and poor systolic func-

tion. In fetuses with aortic stenosis and an intact or restrictive atrial septum, there is no

low-pressure outlet for blood entering the left heart, so the left atrium and ventricle may

become severely dilated. This may lead to severe mitral regurgitation from mitral

annular dilation, with the resultant elevated pressure and compression of the right heart

causing right heart failure and hydrops fetalis. Patients with HLHS, one of the most

serious CHDs, require palliative surgery at birth to make the right ventricle the system-

ically functioning ventricle, or occasionally primary neonatal heart transplantation.

Therefore severe aortic valve stenosis with evolving HLHS is the defect for which fetal

intervention is most likely to be considered.1–3,7–9,13–15

Several centers have offered in utero aortic valvuloplasty as an alternative treatment

for midgestation fetal AS, with a high probability of progression of HLHS.7,9,14,16 The

objective of fetal aortic valvuloplasty is to relieve the obstruction to LV ejection,

thereby reducing LV work and damage, increasing flow through the left heart, and

slowing or preventing the progression to HLHS. Recent studies from the authors’

center demonstrate that fetal aortic valvuloplasty may increase blood flow through

the left heart and improve left heart growth.14,16 An oversized balloon was associated

with moderate or severe aortic regurgitation that was tolerated by the fetus and

improved through the gestation.16

To achieve maximal benefit from the procedure, it must be performed before the

occurrence of irreversible pathology. Much remains unknown with respect to the evolu-

tion of this CHD.17,18

Early attempts at fetal aortic valvuloplasties performed in the thirdtrimester were too late in gestation to reverse the disease, demonstrating that the

window for intervention must occur as early as possible during the second trimester.

Based on the current understanding of the risk–benefit ratio of fetal intervention,

fetal aortic valvuloplasty should not be performed in fetuses with AS that will not other-

wise progress to HLHS. Anatomic dimensions of left heart structures at the time of

diagnosis alone do not predict progression to HLHS. Instead, physiologic aberrations

such as reversed blood flow in the transverse aortic arch, left-to-right flow across the

FO, monophasic mitral valve inflow, and moderate-to-severe LV dysfunction in midg-

estation are important signs of evolving HLHS.19 These findings may be useful for

identifying appropriate candidates for fetal aortic valvuloplasty.The presence of an intact or highly restrictive atrial septum (I/HRAS) is a predictor

of poor outcome among patients with HLHS.20–23 Maintenance of a postnatal circu-

lation depends on an atrial septal defect (ASD) to allow the left atrium to decom-

press into the right heart. Without an adequate ASD, left atrial hypertension

prevents adequate pulmonary flow, and these infants die shortly after birth without

immediate intervention. Anatomic studies have described an intact atrial septum in

approximately 6% of patients with HLHS, and clinically deleterious restriction to

flow at the level of the atrial septum occurring in as many as 22%.24,25 In a recent

series at a major referral center with aggressive management involving prenatal

diagnosis and planned delivery, survival was only 28%.26 At the authors’ institution,a series of 24 fetuses that underwent attempted ASD creation in utero revealed that

the procedure can be performed with a high rate of technical success. Of 21 at-

tempted procedures, 19 were technically successful. Creation of a defect greater

than or equal to 3 mm was associated with better postnatal oxygenation and

less frequent need for emergent postnatal intervention, but it was not shown to

improve survival.27

Turner et al442



Defects on the Right Side

In a similar fashion to aortic valve disease, pulmonary valve disease occupies a spec-

trum from mild stenosis to severe atresia. Pulmonary atresia with an intact ventricular

septum (PA/IVS) produces hypoplastic right heart syndrome (HRHS). Some fetuses

with severe tricuspid regurgitations may develop high central venous pressures andresultant fetal hydrops. The size and rate of growth of the fetal tricuspid valve accu-

rately predicts postnatal outcomes and may be used for selecting patients for fetal

therapy.28 In addition, a right ventricular (RV)-dependant coronary artery supply

results in increased mortality after birth and is considered the most severe form. These

infants will require a palliative circulation or transplantation. If the fetus is likely to

require single ventricle palliation after birth, some fetuses with PA/IVS are appropriate

candidates for fetal intervention.

Unlike the left ventricle, the right ventricle has some capacity to grow postnatally,

and RV decompression in infancy allows the potential for RV growth. RV decompres-

sion in utero presumably also should lead to RV growth. Several attempts have beenmade at treating this defect in utero, but there have been no reports in which the infant

did not require postnatal surgery also.29–31 Further evolution in the technique for right-

sided heart interventions is needed, which may also benefit additional defects such as

tetralogy of Fallot with pulmonary atresia and hypoplastic pulmonary arteries.

PROCEDURE

Technique

Several techniques have been attempted for fetal balloon valvuloplasty. The least

invasive involves maternal sedation with percutaneous access to the fetus, as origi-nally described by Allan.7–9 A more invasive technique involves a laparotomy to

Fig. 2. Ideal fetal position and cannula course for aortic valvuloplasty. Course of cannulacorresponds to unobstructed pathway from maternal abdomen to left ventricle apex toaortic valve. (From Tworetzky W, Wilkins-Haug L, Jennings RW, et al. Balloon dilation ofsevere aortic stenosis in the fetus: potential for prevention of hypoplastic left heartsyndrome: candidate selection, technique, and results of successful intervention. Circulation2004;110(15):2127; with permission.)




expose the uterus, which allows for easier manipulation of the fetus, improved ultra-

sound image quality, and shorter distance to the fetal heart. The most invasive tech-

nique involves a uterine incision and fetal exposure, which allows for femoral and

carotid artery access.32 The more invasive techniques offer direct contact and the

Fig. 3. Ultrasound images of percutaneous in utero aortic valvuloplasty for aortic stenosis.( A) Aortic valve flow before intervention. (B) Alignment of needle. (C ) Guide wire acrossaortic valve in ascending aorta. (D) Inflated balloon across the aortic valve. (E ) Aortic valveflow after intervention.

Turner et al44 4



possibility of improved technical success, but these benefits occur at the cost of

increased maternal morbidity and premature delivery. Therefore, less-invasive percu-

taneous techniques when possible are preferable.

Techniques at Children’s Hospital Boston and Brigham and Women’s Hospital have

evolved with the collaboration of many departments. Percutaneous transthoracic cardiac

puncture has been most effective, with minimal maternal risk.The access point to thefetal

heart depends on the type of procedure. All procedures are performed under two-dimen-

sional ultrasound guidance. The needle used to access the fetal heart is preferably as

small as possible, such as a 19G cannula. A minilaparotomy is performed to expose

the uterus only if certain factors require it, such as fetal position, anterior placenta, and

maternal body habitus.

For aortic balloon valvuloplasty, the large dilated left ventricle is the most easily ac-

cessed structure with proximity to the aortic valve. The cannula and stylet needle are

advanced through the maternal abdomen, uterine wall, and fetal chest wall ( Fig. 2 ).

The cannula, guide wires, and balloon shafts are premeasured and marked, allowing

positioning within the fetal heart by both external measurements and ultrasound

imaging. Correct fetal positioning is critical; the left ventricle is entered only when:

The left chest is anterior.

There are no limbs between the uterine wall and apex.

The apex is within 9 cm of the abdominal wall.

The outflow track is parallel to the cannula course.

Fig. 4. Ultrasound images of percutaneous in utero pulmonary valvuloplasty for pulmonaryatresia with intact ventricular septum. ( A) Needle aimed at pulmonary valve. (B) Guide wireacross pulmonary valve in pulmonary artery. (C ) Inflated balloon across the pulmonary valve.(D) Pulmonary valve flow after intervention.




The balloon valvuloplasty itself is performed with a small coronary artery balloon

over a thin, floppy-tipped guide wire. The balloon is inflated with pressure gauges to

precise inflation diameters. Flow across the dilated aortic valve is confirmed with

echocardiography ( Fig. 3 ).

For pulmonary balloon valvuloplasty, the right ventricle is accessed, although it

makes a more difficult target than the left because of small size, complex geometry,

and valvular atresia. The same principles of measurement and position are used.

Flow across the dilated pulmonary valve is confirmed with echocardiography

( Fig. 4 ).

For atrial septoplasty, the right atrium is accessed through the right chest wall. An

unobstructed line is identified from the fetal right atrium, through the left atrium, and

into a left pulmonary vein. An 18G or 19G introducer cannula on a sharp metal obtu-

rator is advanced into the right atrium and against the atrial septum. The septum is

punctured by the tip of the introducer or, more commonly, with a 22G Chiba needle

(Cook Incorporated, Bloomington, IN). A wire then is introduced into the left atrium

or a pulmonary vein, and the Chiba needle is exchanged for a balloon angioplasty

catheter. The balloon is inflated fully several times before the cannula is removed.

Flow across the new atrial septal defect is confirmed with echocardiography ( Fig. 5 ).

Anesthesia

Anesthesia is a necessary element of any of these procedures. Although maternal

sedation is possible, inhaled anesthetic allows for maximal uterine relaxation and

easy conversion to an open procedure if necessary. Additional fetal anesthesia is

Fig. 5. Ultrasound images of percutaneous in utero atrial septoplasty for hypoplastic leftheart syndrome. ( A) Needle penetrating left atrium from right atrium. (B) Balloon acrossatrial septum. (C ) Atrial septum flow after intervention.

Turner et al44 6



administered through an intramuscular injection, which allows for fetal manipulation

and optimal positioning. At Children’s Hospital Boston, a combination of fentanyl,

pancuronium, and atropine are used. Atropine counteracts the bradycardia that can

occur with fetal and uterine manipulation.

COMPLICATIONS

Fetal complications are usually treatable. Bradycardia is common with needle access

to the ventricle, occurring in about 50% of cases, and uncommon with needle access

to the atrium. The arrhythmia resolves by stopping manipulations or with intracardiac

administration of epinephrine, either into the muscle or by direct injection. Pericardial

effusions are also common and, if moderate to large, they can be drained successfully.

Low maternal complication rates also have been possible with in utero catheter

interventions. Despite well-executed procedures and extensive preprocedure evalua-

tion to exclude maternal contraindications, complications from the anesthesia, lapa-rotomy, and uterine manipulation do occur. A sick fetus can cause premature labor

or the maternal mirror syndrome, which resembles preeclampsia and requires delivery

of the fetus.

SUMMARY

On the frontier of pediatric cardiology, fetal cardiac interventions for CHD offer a prom-

ising therapeutic option for those conditions with significant morbidity and mortality

from current palliative operations. Early detection and referral of all fetuses with sus-

pected CHD would increase the number of patients that may benefit. Concurrent

multidisciplinary collaboration between perinatologists, cardiologists, fetal surgeons,

and anesthesiologists will improve patient selection criteria, techniques for safe

access to the fetus, the performance of the procedure, and perioperative care.

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Cardiac Anomalies in the Fetus