Dr. Sumitra V, Dr.S.S.Prabhu, Dr.N.J. Burkule
Division of Cardiology, Department of Pediatrics, B.J.Wadia Children's Hospital.

Over the past decade, specialized echocardiographic techniques have evolved as a major component of the noninvasive diagnosis of Pediatric and fetal heart diseases. Fetal echocardiography provides an opportunity to correlate anatomic and electrophysiologic information and cardiac haemodynamics and thus helps to determine the need and type of therapeutic intervention (1). New high-resolution transvaginal probes have been used to evaluate fetal heart in the early first and second trimester of pregnancy, between 10-15 weeks of gestation (2). With ongoing research in fetal cardiac surgery and fetal intervention, the need for consistent and accurate prenatal diagnosis of congenital heart diseases will become even more important. This article provides a brief overview of the indications and applications of fetal echocardiography and highlights the protocol of treatment in antenatally detected congenital heart diseases.

Congenital heart disease (CHD) is the most common severe congenital abnormality with an incidence of 8.8 in 1000 live births (3). Approximately half of these are major requiring intervention in the neonatal period or infancy which are associated with a high degree of mortality and morbidity even when corrected. The other half are comprising of minor lesions such as ventricular septal defects (VSD), atrial septal defects(ASD) and patent ductus arteriosus (PDA) etc.
In the Indian setting, the above figure translates into approximately 50-75,000 children being born with a major CHD every year. Lack of availability and affordability of specialized care except in certain pockets and relative high yield of prenatal diagnosis of CHD in setting of abnormal obstetric scan, stresses the need for fetal heart screening in routine obstetric scan.
A number of risk factors (Table -I) have been identified as possible contributory factors in the development of congenital heart defects, though it is paradoxically true that majority of fetuses with CHD have no identifiable risk factors (2).

Fetal:	Chromosomal abnormalities Extracardiac anatomic abnormalities Nonimmune hydrops Fetalis Fetal cardiac arrhythmias Suspected cardiac anomaly on routine ultrasound
Maternal:	Family history of CHD Maternal metabolic disorders Maternal teratogen exposure.

The decisions for most simple lesions if detected antenatally, which include small ventricular septal defect, atrial septal defect in the region of fossa ovalis, mild valvular stenosis, mild coarctation of aorta are routine antenatal care with normal delivery and a follow up of the child in neonatal or early infancy period. These defects usually escape detection and are the major limitations of fetal echocardiography. However , It is imperative here to stress that the potential parents should be reassured about the relative benign nature of these congenital heart lesions and thus allay their anxiety. Some of these lesions may be progressive during the childhood period, which would require routine follow-up, but most of them are easily amenable to interventional and surgical correction.

All complex congenital lesions detected antenatally need further evaluation to detect associated chromosomal anomalies and severe non-cardiac lesions as the management strategies and prognosis risk greatly varies if they are compounded. In most cases with multiple cardiac lesions and above mentioned associated factors, the choice of therapeutic termination of pregnancy is offered to the parents (if surgical correction for that cardiac lesion is not easily available, affordable and where there is a poor prognosis for long term survival (3).

• Atrioventricular Septal defect: This is the commonest of the serious structural abnormality seen on fetal echocardiography. Down's syndrome is commonly associated and other complex cardiac lesions include left atrial Isomerism, complete heart block and nonimmune hydrops. There is no left to right shunt in utero because of similar pressure in both atria and both ventricles. There is a potential risk of diminution of blood flow to ascending aorta and progressive coarctation of aorta as the gestation advances. Thus the management strategies in most patients with these defects is to advice a normal delivery as surgical repair is easier in larger patients. The prognosis is poor if compounded by chromosomal anomalies and other cardiac and noncardiac anomalies where therapeutic termination of pregnancy may be offered.
  
  
• Hypoplastic Left and right heart syndrome:The second most frequent lesion detected in most series is hypoplastic heart syndrome. Progressive ventricular hypertrophy, endocardial fibroelastosis of the obstructed ventricle leading to cardiac failure and fetal loss usually occur consequently. Certain centers in developed countries offer intervention by means of catheter dilation in an attempt to arrest the progressive obstruction to ventricular outflow but with limited success(4). In our setting the best option given to the potential parents would be to offer medical termination of pregnancy to the group with hypoplastic left heart syndrome. In the hypoplastic right heart the pregnancy is continued, with advise to deliver these fetuses in an institution offering specialized and intensive perinatal care and starting prostaglandin infusion immediately after birth to keep the ductus patent. Early surgical intervention and staged palliative repair is offered postnatally.
  
  
• Tricuspid regurgitation with or without associated Tricuspid dysplasia:It is not uncommon to find mild to moderate tricuspid regurgitation on fetal echocardiography, but most of them are benign and secondary to high pulmonary pressures. The follow up of these fetuses in neonatal period generally show regression of right ventricular hypertrophy and tricuspid regurgitation. It is important to distinguish these from the structurally abnormal and dysplastic tricuspid valve conditions like Ebstein's where the right ventricular cavity is small with associated severe tricuspid regurgitation. Most of these fetuses have additionally severe hydrops, heart failure or complete heart block with a high incidence of fetal loss or neonatal deaths.
  
  
• Conotruncal anomalies: Transposition of Great Vessels, Double Outlet Right Ventricles, Tetralogy of Fallot and its variants and persistent Truncus Arteriosus These group of lesions are compatible with normal fetal development and survival. In most lesions, early corrective surgery can be offered postnatally with fair prognosis and a decreased morbidity and mortality. Associated cardiac, noncardiac lesions and chromosomal anomalies have to be ruled out. Transposition of Great Vessels with intact ventricular septum need prostaglandin infusion in neonatal period to keep the ductus arteriosus patent.
  
  
• Univentricular Hearts: These complex forms of cardiac defects are usually associated with fetal losses due to nonimmune hydrops .In most cases normal delivery is advocated with staged univentricular repair in the postnatal period.
  
  

Fetal electrocardiographic tracings and a complete fetal echocardiography with M- mode analysis and a Color Doppler flow pattern at the mitral and aortic valve helps to distinguish atrial and ventricular components of the cardiac cycle and thus determine the nature and type of arrhythmia. Additionally, cardiac dimensions, presence of hydrops and ventricular functions should be assessed to determine the haemodynamic consequences of these arrhythmias on the fetus. Most cases of fetal arrhythmias are benign and are premature atrial or ventricular contractions. Routine antenatal follow-up for noting the fetal heart rate is advised at 2-4 weekly interval . If fetal tachycardia is noted repeat scan is advocated. The mother should also be advised to avoid caffeine and sympathomimetic drugs. Fetal tachycardia is defined as sustained heart rate of more than 200 beats per minute.

Fetal echocardiography assessment is done and if any three of the seven criteria are present : fetal HR (>200 bpm), hydrops, cardiomegaly (heart area / chest area - HA/CA>0.42), atrio-ventricular valve regurgitation, fractional shortening (FS)< 25% suggestive of ventricular dysfunction, ventricular dysfunction reversal of flow in the IVC and distended hepatic and umbilical veins >6 mm , then fetal therapy is warranted. If the fetus is near term with good lung maturity and in absence of hydrops, an early delivery with antiarrhythmic treatment of the neonate is advised. Fetus if premature with poor lung maturity and hydrops, fetal antiarrhythmic treatment is advised which is delivered either by maternal administration or intra-amniotic or direct instillation in umbilical vessels, though the former is preferred. The mother is admitted and a base line assessment of serum electrolytes, serum calcium, serum magnesium, renal profile , thyroid functions and electrocardiogram is done. The antiarryhthmic drugs are started in a stepwise manner as shown in table (IV), monitoring for side effects. If the fetus responds and tachycardia reverts these medications are continued till term.

Fetal bradycardia is defined as sustained heart rate of less than 100 beats per minute. A structurally normal heart by fetal echocardiography determines the prognosis, with complex heart lesions carrying a poor outcome. If the heart is structurally normal maternal Systemic Lupus has to be ruled out. Maternal therapy with steroids and immunoglobulins have been tried with success and arrest the destruction of fetal conduction pathways by the maternal antibodies. In fetus with ventricular rate less than 55 bpm in a structurally normal heart and 45 bpm in abnormal heart and an atrial rates less than 80 bpm with or without hydrops, maternal administration of sympathomimetics like isoproternol, terbutaline or salbutamol is advocated. An early delivery with neonatal management of the arrhythmias is generally advocated.

Fetal echocardiography has indeed revolutionized the present day management of fetus with structural and functional heart diseases. Early diagnosis, frequent monitoring of fetus for cardiac functions and haemodynamics have greatly improved the outcome and helped in better understanding of the Congenital Heart Disease

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6. Tworetzky W, Mc Elhinney DB, Reddy VM et al :Does prenatal diagnosis of hypoplastic left heart lead to improved surgical outcome J Am Coll Cardiol , 1998 ; 13(suppl A):71-75