Structural heart disease remains the most often missed diagnosis on antenatal ultrasound. Antenatal cardiac diagnosis has become possible in the last two decades with the advancement of echocardiography and sonography. The field of foetal cardiology has evolved since definitive diagnosis has become possible. The scope of this field has evolved from understanding the progression of foetal cardiac disease to possible foetal intervention to treat the conditions. The current article evaluates the role of antenatal diagnosis in the Indian scenario, the implications of such a diagnosis to the obstetric and neonatal management.
At what gestational age does one do foetal echo?
Foetal echo has been possible as early as at 20 weeks gestation for a long time. Current recommendations are for performing foetal echo at 18 weeks. Also, in special situations the foetal echo may be possible as early as 12 weeks via trans-vaginal route.
When is foetal echo to be performed?
Foetal echo need not be performed in every pregnancy. This is not because of any other reason but because it is a very labour intensive field and the margin of error is high. For this reason, screening with ultrasound is imperative.
The indications have been defined for performing foetal echo in pregnancies. These would only cover pregnancies with some indication that there may be a problem. Primigravida with no prior history may still contribute the largest number of patients with congenital heart disease if they are not suspected on ultrasound.
The indications can be divided as those which are due to foetal indications and those which are due to maternal indications and familial/miscellaneous indications.
Screening for heart abnormalities
During a routine antenatal scan the sonologist invariably assesses the heart. The most common view they come across is the four-chamber view. This is good enough to rule out only about 40 per cent of the heart abnormalities. Additionally, if one intently assesses the five-chamber view, more abnormalities are likely to be picked. In the four-chamber view the atria, ventricles and the interventricular septum (only inlet and muscular septum) can be evaluated. Structures like outflow tract, great arteries and outlet and perimembranous septum can only be evaluated in the five-chamber view. In addition, arch views will allow assessment of the arch and ductus arteriosus.
In a study conducted by us, 100 consecutive newborn babies with a confirmed heart abonormality were queried for ultrasound during pregnancy. All patients had had ultrasound performed during pregnancy. More than 90 per cent of the diagnoses were missed on ultrasound and were not even suspected.
Unlike other abnormalities, a cardiac diagnosis implies potential cardiac surgery or mortality. Therefore, an accurate diagnosis and a detailed assessment of the heart are imperative. Assessment of the heart can best be made by segmental analysis. In this method, the heart is assessed by individual ‘segments’ rather than by ‘impressions’ of a four-chamber or a five-chamber or a three-vessel view. This offers the most comprehensive assessment in completeness and also rules out any individual part being missed in the assessment. This method is followed most often by congenital heart disease specialists like paediatric cardiologists.
Counselling for foetal echo
Not all heart defects can be diagnosed by foetal echocardiogram. This is mainly for two reasons: a) the size of heart is such that detailed evaluation and small defects may not be picked up. Additionally, the heart will be growing from the 18th to the 37th week. Disproportionate growth may allow some diagnoses to show up later on. b) Physiologic changes related to birth and the lungs becoming functional add another dimension to the physiology after birth. Lastly, some structures, which are normal for a foetus, may not be normal in the newborn period e.g. patent ductus arteriosus.
We counsel the family prior to performing the foetal echocardiogram about these aspects of the foetal circulation. Also, parents are made aware that there is a significant distance between where the probe is (skin) and where the heart is (several centimetres below the skin). In addition, parental counselling begins from the time the patient is first initiated into the foetal echocardiography. The counselling has two aspects, one before performing the foetal study, and another following the study.
Impact of foetal diagnosis of heart disease
The early diagnosis of a major heart defect before 20 weeks opens the option of legal termination of pregnancy. Additionally, if the problem is not significant, parents get enough time to prepare themselves to accept the problem and assess its progression during foetal life. Occasionally, the problem may resolve during the foetal life itself. Many times, only neonatal and paediatric follow up is required. Rarely, the child may require surgery when born or in the first few months.
Surgical and interventional outcomes of congenital cardiac conditions
The current outcomes of congenital cardiac conditions in contemporary Indian practice have not been published. A survey of tertiary care centres dedicated to congenital heart disease management showed excellent outcomes of most congenital cardiac conditions.
Management of foetal arrhythmias
Foetal arrhythmias are identified in approximately one per cent of foetuses. Foetal arrhythmia that warrant an echocardiogram include tachycardia, bradycardia and irregular or ectopic rhythm. Extrasystoles account for up to 89 per cent of the arrhythmias. Extrasystoles are generally benign, with the foetus remaining hemodynamically stable and demonstrating spontaneous resolution of the ectopy either late in the pregnancy or in the early neonatal period. Assessment and management of foetal arrhythmias is a topic requiring independent discussion to do justice to it.
Foetal cardiology in contemporary practice
With 65 per cent of the Indian population under the age of 35 years, it is imperative that antenatal diagnosis will gain more importance in the contemporary practice. Younger and educated parents want to know more and are readily seeking antenatal diagnosis and counselling. In this scenario, there is a significant role of cardiac diagnosis antenatally. When cardiac diagnosis implies good survival, albeit a single procedure (surgical or interventional), the families have tended to accept it well.
Current survival rates of congenital cardiac surgery have had a major impact on the perception of congenital heart disease. Similarly, improving antenatal diagnoses will affect outcomes of pregnancy and foetuses with congenital heart disease. As the field advances, teams with obstetricians, neonatologists, congenital heart disease specialists (cardiologists and surgeons) and perinatologists will impact the survival of these foetuses in a significant way.