Congenital Heart Defects Screening

Introduction

Congenital defects are one of the concerns parents have when expecting a child. The most common congenital defect is cardiac malformation which affects 1% of live births and is a big cause of pregnancy termination and foetal death.¹ So, what are congenital heart defects (CHDs)? CHDs refer to the structural abnormalities in the heart or the large blood vessels next to the heart that are present at birth.² These changes occur during foetal development, mostly in the first trimester of pregnancy, and can affect the heart’s chambers, valves, or the vessels that transport blood to and from the heart.³ CHDs can be mild, with little to no impact on the person’s health, but can also be severe, requiring immediate medical intervention.⁴

Hence, early detection of such cases is quite vital; this is because proper treatment and timely intervention can help save a life. In addition, improving the patient’s life and preventing complications takes place when conditions are diagnosed early. This is achieved by screening programs that will be discussed in this article.

Types of congenital heart defects

Many types of CHDs vary in severity. Some of the common types of congenital heart defects include:^{4,5,6,7,8,9,10,11,12,13,14}

1. Atrial septal defect (ASD): this defect is represented as a direct communication between the atrial chambers; an opening that allows oxygen-rich blood to mix with oxygen-poor blood
2. Ventricular septal defect (VSD): a hole between the ventricles; the heart's lower chambers. Similarly to ASD, this causes oxygen-rich and oxygen-poor blood to mix before being pumped into the body
3. Patent ductus arteriosus (PDA): this defect is due to the failure of the ductus arteriosus, which is a blood vessel that connects the pulmonary artery and the aorta during foetal development, where it is supposed to close before birth. This can lead to aberrant blood flow between the two vessels and can cause health issues such as respiratory deterioration and pulmonary oedema
4. Tetralogy of Fallot: this is a combination of four heart defects: VSD, pulmonary stenosis, right ventricular hypertrophy, and an overriding aorta (the aorta is shifted to the right and receives blood from both ventricles)
5. Transposition of the great arteries (TGA): in the case of TGA, the aorta and the pulmonary artery are switched which leads to two separate circulatory systems. The oxygen-poor blood starts to circulate continuously to the body, while oxygen-rich blood circulates continuously to the lungs
6. Coarctation of the aorta: constriction/narrowing of the aorta which then restricts blood flow to the lower part of the body
7. Congenital aortic valve stenosis: narrowing of the aortic valve, which obstructs the flow of blood from the left ventricle to the aorta
8. Congenital pulmonary stenosis: narrowing of the pulmonary valve or pulmonary artery, hindering the flow of blood from the right ventricle to the lungs.
9. Ebstein's anomaly: malformation of the tricuspid valve, with a wide variety of morphology. This affects the right ventricle and leads to abnormal blood flow.
10. Hypoplastic Left Heart Syndrome (HLHS): HLHS is characterised by severely underdeveloped left-sided structures, which include the left ventricle, mitral and aortic valves, and aorta
11. Double Outlet Right Ventricle (DORV): DORV is a complex malformation with a ventriculoarterial connection where both the pulmonary artery and aorta arise primarily from the right ventricle, typically associated with discontinuity between the aorta and mitral valve

These are some examples of the many CHDs out there, and the severity of each defect can vary from patient to patient. For this, critical and non-critical defects are described below:^8,9,13,15,16

1. Critical CHDs
   • Definition: critical CHDs are ones that significantly affect the structure and function of the heart, leading to severe cardiovascular impairment
   • Characteristics:
     • Most require immediate medical attention, typically within the first days or weeks of life
     • Without intervention, critical CHDs can lead to life-threatening complications, e.g. heart failure, and inadequate oxygenation of the body
     • Examples: hypoplastic left heart syndrome (HLHS), transposition of the great arteries, and severe forms of tetralogy of Fallot

2. Non-Critical CHDs
   • Definition: non-critical CHDs are those that, while still having abnormalities in the cardiac structure, may not immediately pose a severe threat to a person's health
   • Characteristics:
     • Some non-critical CHDs may not require prompt medical intervention and can be managed or corrected over time
     • Individuals with non-critical CHDs may lead relatively normal lives without significant health complications
     • Examples: small atrial or ventricular septal defects (ASD or VSD) that may close on their own or may not cause major health issues

Screening methods

Screening methods are important for the early diagnosis and treatment of CHDs. These include:^17,18,19,20

Prenatal screening

• Foetal echocardiography:
  • Description: a specialised ultrasound that captures detailed images of the foetal heart
  • Timing: typically performed during the 2^nd trimester of pregnancy
  • Purpose: detects structural abnormalities and assesses heart function in the developing foetus
• Maternal blood tests:
  • Description: blood tests that analyse specific markers, such as maternal serum alpha-fetoprotein or human chorionic gonadotropin (hCG)
  • Timing: usually, part of routine prenatal screening during the 1^st and 2^nd trimesters
  • Purpose: identifies potential risk factors for CHDs and other developmental abnormalities

Postnatal screening

• Pulse oximetry:
  • Description: the oxygen saturation levels in a newborn's blood are measured by attaching a sensor to the baby's skin
  • Timing: typically performed within the first 24 - 48 hours after birth
  • Purpose: detects low oxygen levels, which may indicate the presence of critical CHDs
• Physical examination:
  • Description: a thorough physical examination by healthcare personnel, including listening to the heart sounds and checking for signs of distress
  • Timing: conducted shortly after birth and during routine check-ups
  • Purpose: identifies any physical signs or symptoms that may suggest the presence of a heart defect
• Electrocardiogram (ECG):
  • Description: recording the electrical activity of the heart using electrodes placed on the skin
  • Timing: can be performed shortly after birth or during follow-up assessments
  • Purpose: checks the cardiac rhythm and detect any abnormal electrical patterns
• Chest X-rays:
  • Description: imaging the chest area for heart size and lung congestion
  • Timing: done if clinical signs/symptoms suggest a cardiac problem
  • Purpose: provide additional information about the cardiac structure and potential complications

Screening guidelines and recommendations

The American Academy of Paediatrics (AAP) provides guidelines for the screening of critical CHDs in newborns. These guidelines are intended to assist healthcare providers in identifying critical CHDs in infants early on, allowing for timely intervention and management. Some of the AAP guidelines for CHD screening include:²¹

1. Pulse oximetry screening: the AAP recommends performing pulse oximetry screening on all newborns before discharge from the birthing facility or at 24 hours of age
2. Interpretation of screening results:
   • If the oxygen saturation level is below the specified threshold or if there is a significant difference in pre-ductal (right hand) and post-ductal (foot) readings, further evaluation is recommended
   • Abnormal results should be followed up by additional diagnostic testing, such as echocardiography, to confirm or rule out the presence of critical congenital heart disease
3. Documentation and reporting:
   • Healthcare providers are encouraged to document and report screening results, including both normal and abnormal results
   • Communication with parents should include information about the purpose of screening, the results, and the need for further evaluation if required

Challenges and limitations

As with any other test, these screening processes are also faced with challenges and limitations such as:^3,21

1. False positives and false negatives:
   • Limitation: screening tests may give false-positive results, which can indicate the presence of CHDs even though none is present. It can also give false-negative readings which can leave some CHDs left undiagnosed  
2. Variability in sensitivity and specificity:
   • Challenge: the sensitivity and specificity of screening tests can vary which can affect the ability to correctly identify true positives and true negatives
   • Limitation: variability in test performance may impact the accuracy of identifying infants with CHDs, leading to missed or incorrect diagnoses
3. Maternal and foetal factors:
   • Challenge/limitation: maternal factors such as obesity, gestational diabetes, or certain medications can influence the accuracy of screening tests. This can then lead to over or misdiagnosing infants with CHDs.

Importance of early intervention

There are several reasons why early intervention in CHDs is important, this will be summarised in the points below:

1. Prevention of complications: such as heart failure, and pulmonary hypertension
2. Optimising heart function
3. Avoid critical situations: for example, surgical or medical interventions may be required shortly after birth to stabilise the infant's condition and provide adequate oxygenation
4. Improved growth and development
5. Enhanced quality of life
6. Minimising long-term complications

Summary

Congenital heart defect (CHD) screening plays a vital role in the early detection and management of structural abnormalities of the heart and its major blood vessels. The significance of these screening programs lies in their potential to positively impact the lives of patients and their families. Through prenatal and postnatal screening methods, healthcare providers can identify CHDs early on, which enables them to provide timely intervention and proper support. While CHD screening has proven to be a valuable tool, ongoing research, advancements in medical knowledge, and updates to screening protocols are essential to address challenges and enhance the effectiveness of these programs. As we continue to refine our understanding of congenital heart defects, early screening remains a cornerstone in providing timely and comprehensive care to infants with CHDs, fostering better health outcomes and improved quality of life.