Congenital Heart Disease OverviewCHAPTER 1

Structural congenital heart diseases (CHD) are a night mare to the obstetrician who is challenged in multiple ways. For nine months he/she is the patient's friend, philosopher and guide and is a guardian of her and her infant's medical care. Moreover, he is intimately connected to her emotional and social wellbeing as well and wants to see all go well. Many primary obstetricians prefer to perform anatomical ultrasound in the office. It then becomes a crucial responsibility for the obstetricians individually as well for the specialty which is called upon to train residents and others to be skilled in performing fetal cardiac ultrasound. A basic knowledge of fetal cardiology is required for the primary obstetrician so that congenital heart disease can be suspected, even diagnosed and channeled to specialized team. Patient then can be offered all available options including pregnancy termination in a complex CHD or a successful conduct of pregnancy to achieve the best outcome possible. Most pregnant patients trust their obstetrician more than a specialist. Hence the obstetrician is charged with organizing a work-up plan, and a multispecialty team for further management. A multispecialty team must include, pediatric cardiologist and cardiac surgeon, geneticist, social service, neonatologist, etc. However, the obstetrician or the maternal-fetal medicine specialist remains the conductor of this team.

The obstetrician is then responsible for delivery of a potentially compromised baby in the safest manner, and must plan delivery at a suitable medical facility with all the specialty help available to address the needs of a sick neonate with hypoxia, acidosis and even hydrops/congestive heart failure. This must be done at a tertiary center with pediatric cardiology and cardiac surgery available and expert personnel are available for immediate newborn resuscitation, administration of cardiac medications, e.g. prostaglandins during fetal to adult type transition of circulation for ductal dependent lesions.

We have included relevant chapters in this book to answer these and other related questions.

High risk maternal-fetal diseases, e.g. diabetes, twin to twin transfusion syndrome (TTTs), intrauterine growth restriction (IUGR) and others are examples of situations in which fetal hemodynamic patterns can be altered and may indicate fetal cardiovascular instability, often an indicator of end-stage fetal disease preceding death. More importantly, abnormal blood flow patterns in peripheral blood vessels and cardiac dysfunction are indicators of extreme degree of fetal compromise dictating obstetrical management, timing of delivery and preparation for immediate treatment of the newborn. Appreciation of fetal functional cardiology is therefore so crucial to surveillance and management of the high risk fetus and certainly is a subject relevant to obstetricians.

Approaximately 70 to 80 percent of fetuses are sonographically examined in second trimester in the United States yearly. With the incidence of CHD being 8 to 9/1000, 17000 fetuses examined ultrasonically will have CHD. However, NIH sponsored RADIUS study reported accuracy in detection of CHD to be only (5/22) 23 percent at tertiary centers and none at nontertiary locations.² Extrapolation of these numbers concludes that only 3900 fetuses with CHD seen at tertiary centers are presently detected prenatally in second trimester. Todros³ summarised world literature showing that 23 percent of 631 cases of CHD were prenatally diagnosed among 108,182 patients screened, a prevalence of CHD 5.8/1000. Current trends appear to indicate a change toward better diagnostic abilities by screening for CHD in most fetuses.

Screening fetal heart for abnormality in normal mothers is the single most effective way to detect most cases of CHD. Fetal heart can be screened easily at the time of a mid trimester anatomy ultrasound in most patients. Occasionally obese patients, and twins may have to be seen at a later date for optimal scanning. The study can be repeated prior to calcifications of ribs at 24 to 28 wk in very high risk patients. Late third trimester examinations may be difficult and less reliable.

Since 1980s, increasing number of studies have shown efficiency in prenatal detection of complex CHD requiring postnatal intervention by screening for CHD. The mid trimester routine anatomy check allows only a few minutes to specifically screen the heart. A four chamber view of the fetal heart is the single most useful screening test in detection of CHD., with a 40 to 50 percent detection rate (Copel, Simpson).^5,5a,5b Overall 15 to 45 percent of infants with CHD are diagnosed prenatally in the United States (Bromely, Small).^9,10

DeVore⁶ found addition of outflow tracts to routine examination of the heart to improve detection to close to 80 percent. Recently, examination of outflow tracts have been included within a screening scan program as recommended by, the American College of Obstetrics⁷ and the American Institute of Ultrasound in Medicine⁸ increasing the detection rate to close to 60–80 percent.

Inclusion of ductal and aortic arches may improve upon the detection rate.

The purpose of fetal heart screening is to confirm a normal cardiac status, detect abnormalities of cardiac position, size, basic structural components, function and rhythm. The purpose of a comprehensive fetal echocardiography is to detect and define life threatening 3congenital heart disease, detect congestive heart failure and fetal arrhythmias. It offers an accuracy of detection of virtually 90 to 100 percent. Twenty-five percent of newborns with CHD will have such life threatening abnormalities. Currently, the screening examination is usually performed in an obstetrical ultrasound unit at major centers, or by individual obstetrician in the office, while a comprehensive echocardiography is performed by maternal fetal specialists or pediatric cardiology departments.

Hagemann and Zielinsky^10a reported on 3980 fetuses who underwent echocardiographic screening for cardiovascular malformations during a program of “population screening of fetal cardiac abnormalities” in PortoAlegre. Overall prevalence of CHD was 12.5/1000. Three false-negative and no false-positive results were encountered. Perinatal planning was then possible for these pregnancies and the researchers recommended routine screening for all fetuses with four chamber and outflow tracts views. Recently it has been suggested by many to perform full echocardiography in all fetuses. (Stumfplen, Yagel^11,12). In an editorial to this, Kleinert¹³ estimated need for 400additional cardiac specialists in Great Britain alone to provide this level of care to all pregnant patients. World wide this would be an impossible task.

Screening echocardiographic examination of all fetuses allowing sufficient time exclusively for examination of the heart alone may be a desirable proposition, whose time has not yet come.

Although not universal in clinical practice, early diagnosis of CHD is possible in major centers with increasing experience. Using a combination of high resolution transvaginal ultrasound and detection of nuchal translucency, up to 25 percent of the cardiac defects may be detected in early pregnancy. Hook¹⁹ has reported up to 92 percent detection rate of CHD with complete cardiac exam at 13 to 14 weeks.

Many structural abnormalities are difficult to diagnose prenatally. Defects such as atrial septal defect and patent 4ductus arteriosus may not be distinguishable from normally patent foramen ovale and ductal patency in fetal life. Ventricular septal defects, valvular abnormalities and abnormalities of pulmonary venous return may not be identified in most fetuses until blood flow patterns change during transition to extrauterine circulation. Obstruction of cardiac blood flow during course of pregnancy may result in fetal hydrops or ventricular hypoplasia and account for unexpected CHD in late pregnancy.

Hypothetically, prenatal diagnosis must result in distinct parental and perinatal benefits. Parental benefits include full information and counseling, organization of support system and participation in peripartum care, chromosomal investigation, referral to tertiary center with ability to address multidisciplinary needs of the neonate, including pediatric cardiology and surgery, genetics, social service, etc.

Possible benefits of prenatal diagnosis to the infant should include reduction of mortality and morbidity, Copel²⁰ compared outcome of 45 prenatally diagnosed and 54 postantally diagnosed newborns with structural CHD at Yale University between Jan 1991 and June 30,1996. Outcome parameters included short-term survival, cost of hospitalization and length of stay in newborn nursery. Newborn survival among prenatally diagnosed and postnatally diagnosed infants were 80 percent and 66 percent respectively, while length of hospitalization was 16 days among the former and 11 days among the latter group with the cost of hospitalization being proportionately greater in the prenatally diagnosed infants. Forty-five to fifty percent of the parents chose to terminate the pregnancy resulting in a reduced cost. The study did not find any benefits in survival, cost of hospitalization or length of stay. However, it was concluded that parental benefits are certain and that the fetal benefits may be emerging as management of anomalous fetuses improves with time.

Long-term neurologic and developmental outcomes in children with CHD are adversely affected by hypoxia due to vascular and blood flow abnormalities particularly if optimal care is not available immediately at birth. Specific events including strokes, seizures, coma, and change in level of consciousness contribute to poor mortality and morbidity outcomes.

It is s obvious that CHD does pose a long-term neurologic risk to the newborn. Approaximately 5000 babies yearly require cardiac surgical repair in the newborn period. Ten percent (250) will have perinatal hypoxic injury from ductal closure (Wernosky).²¹ These and other like infants can theoretically benefit from prenatal diagnosis when they can be diverted to appropriate medical facilities during prenatal life, and delivered with necessary support. More severe the anomaly, less the benefits of prenatal diagnosis appears to be. Prenatal diagnosis with appropriate newborn management is the most crucial approach to CHD and can be even beneficial in cases requiring perinatal manipulations of ductal dependent anomalies with prostaglandins, for treatment of fetal heart arrhythmias and for immediate life saving surgical treatments such as atrial septostomy to restore circulation after birth for obstructive defects.

Certailnly a case can be made for prenatal screening for CHD (Table 1.3).

Nineteen seventys (1970s) marked beginnings of high resolution 2D ultrasound to detect structural cardiac abnormalities. Thereafter, 1980s were marked by detection of fetal heart arrhythmias by fetal M-mode echocardiography. Normal data for fetal heart size and rhythm were developed from M-mode images by Devore et al.²³

Echoanatomy depiction and cross sectional anatomy were described by Lange, Sahn, and Allen and others in Engalnd.^24–26 Along the same time, Kleinman et al²⁷ documented fetal arrhythmias to be major causes of fetal hydrops.

Fetal heart screening programs came into being in the UK and systematic fetal cardiac evaluations began to be practiced. Population studies at this time revealed a higher incidence of the disease than encountered in birth statistics. Mid 1980s marked the arrival of pulsed and continuous Doppler to assess quantification of blood flow velocities. Fetal and placental physiology, and fetal heart hemodynamics assessment became a reality in clinical setting. Diagnosis of placental insufficiency, stenotic and other obstructions to fetal cardiac blood flow became possible (Sahn).²⁸ At the world congress in late 1980s Japanese clinicians presented potential of color Doppler use for evaluation of fetal hemodynamics.

Recent decade will be known for advent of 3D–4D imaging and tissue harmonic technology. The latter is built into the system to minimise scattered echoes and display clean images so important in the examination of the fetal heart. Three D and 4D machines offer a unique vision of volume based organ examination particularly cardiac anatomy enabling one to evaluate ventricular function flow through great vessels. Ability to post process computer imaging is a god sent when the fetus is not so cooperative. A single acquisition of 3D anatomy of the heart could be processed to allow views of the entire heart and great vessels by Spatio-Temporal Image Correlation technology (STIC). This technology makes it possible to examine the entire heart from one sweep of the transducer, saving three dimensional images in a multiplanar storage system and manipulating images long after the patient is gone in an effort to perform detailed scrutiny of the cardiac system. Surface rendering of the cardiac structures may allow the imager real views of the structures as seen at surgery.

These and other technological advances allows one to obtain “any plane” image of the fetal heart in acquisition of its anatomy in a multi planar imaging, later to post process for examination in a very short time making it possible to routinely examine the heart in great detail similar to the MRI technique. When widely used, these and other computerized processing will allow consultation by experts in major centers by interpretation from imaging performed and acquired in small clinics when complex cases pose difficult diagnostic problems.

This overview of the status of fetal cardiology in the early third millennium is just the beginning. One imagines a screening cardiac echocardiography for each and every baby born in the world to address the needs of this most commonly occurring abnormality, and perhaps with more skilled and better management in future, survival and quality of life of infants with CHD will improve and efforts at diagnosing CHD will be all worth while.