Congenital Heart Defects: Everything Parents Need to Know About Diagnosis and Imaging

Ventricular Septal Defect (VSD): A hole in the interventricular septum—the wall that separates the two ventricles (lower chambers). It is the most common congenital heart defect (30% of cases). Blood flows abnormally from the left ventricle (more powerful) to the right ventricle (less powerful). Some small VSDs close spontaneously in the first few years. Larger ones require surgery.

Atrial Septal Defect (ASD): A hole in the interatrial septum—the wall between the two atria (upper chambers). It is the second most common heart defect (25% of cases). ASDs are generally more benign than ventricular septal defects (VSDs). Many cause no symptoms. Some are discovered late, sometimes in adulthood when a doctor hears a heart murmur.

Transposition of the Great Vessels (TVE): The aorta (which should originate from the left ventricle) originates from the right ventricle. The pulmonary artery (which should originate from the right ventricle) originates from the left ventricle. This is an absolute emergency. The fetus survives in utero because the lungs are not functioning (the placenta oxygenates the blood). But after birth, when the newborn needs to breathe, there is not enough oxygen. Immediate surgery is necessary.

Anomalous Pulmonary Venous Return (APVR): The veins carrying oxygenated blood from the lungs do not reach the left atrium (their correct destination). Instead, they return to the right atrium or elsewhere. Oxygenated blood mixes with deoxygenated blood. This is serious and requires surgical intervention.

Patent Ductus Arteriosus (PDA): Before birth, the ductus arteriosus—a vessel that connects the aorta to the pulmonary artery—is open. This is normal and necessary in utero. After birth, when the lungs begin to function, this duct should close. In some children, it remains open. A small PDA may not cause any symptoms. A large PDA causes cardiac overload and can lead to heart failure.

Aortic stenosis: The aortic valve is too narrow. The left ventricle has to work harder to pump blood through. Over time, this extra work can damage the ventricle.

Pulmonary stenosis: Similar, but in this case, the pulmonary valve is too narrow. It is generally less severe than aortic stenosis.

Tetralogy of Fallot: Four anomalies coexist—a ventricular septal defect (VSD), pulmonary stenosis, an enlarged right ventricle, and an aorta that straddles the VSD. It was once the most common cause of cyanosis ("blue baby"). Today, childhood surgery saves almost all of these children.

Totally Abnormal Pulmonary Venous Drainage: All pulmonary veins connect abnormally. This is serious and requires emergency surgery.

Thirty years ago, congenital heart defects were only diagnosed after birth — when the newborn turned blue, or when a pediatrician heard a hissing sound.

Today, many heart conditions are diagnosed before birth thanks to obstetric ultrasound.

In Switzerland, two obstetric ultrasounds are offered: at 12 weeks and at 20-22 weeks.

The 20-22 week ultrasound includes cardiac screening. At this stage, the fetal heart measures approximately 1-2 cm—tiny. But an experienced sonographer can see:

• The four rooms of the heart
• The four valves
• The connections of the heart with the aorta and the pulmonary artery
• Blood flow (using Doppler ultrasound)
• The orientation of the septa (the dividing walls)

When congenital heart disease is diagnosed prenatally, parents face existential questions:

Will my child survive birth? Will he or she have a normal life? Will he or she need one or more surgeries? How will this affect their development?

Accurate imaging and a consultation with a pediatric cardiologist are essential to answer these questions.

• No radiation — unlike X-rays, CT scans, or PET scans
• Quick — usually 20-30 minutes
• Non-invasive — no needle, no contrast injected
• Can be repeated — without limit, without risk
• Bedside examination — can be done in the neonatal intensive care unit
• Live information — the cardiologist sees the heart beating in real time

Anatomy: The exact position of the four chambers, the four valves, and the major vessels. Where exactly is the blood flowing abnormally?

Blood flow: Thanks to color Doppler, blood flow is seen in red and blue. An abnormal connection creates an aberrant pattern.

Function: How does the heart contract? Is there heart failure?

Pressures: Trichromatic Doppler estimates the pressures in the heart chambers and vessels.

Complications: Is there a pericardial effusion (fluid around the heart)? Are the atria dilated?

In newborns and young children, this is the ideal examination. But in older children, adolescents, and adults, the chest wall becomes thicker. Ultrasound waves don't penetrate as well.

This is where cardiac MRI and CT scans come into play.

In young children: Generally not necessary — echocardiography is sufficient.

For children aged 6-8 years and older: When:

• Echocardiography does not provide enough detail
• A complex malformation is suspected
• We want to precisely assess the vascular connections
• The child had surgery and we want to evaluate the outcome

In adolescents and adults: For regular monitoring and evaluation before a second intervention.

Detailed anatomy of the vessels: The connections of the coronary arteries (the arteries that supply the heart with blood). If a coronary artery branches abnormally, it is potentially dangerous.

3D blood flow: An MRI angiography shows blood flow in three dimensions, revealing complex malformations.

Myocardial scarring: After surgery or scarring due to prolonged heart failure, MRI reveals tissue scarring.

Precise function: Exact measurement of ejection fraction (percentage of blood pumped with each contraction) and chamber volume.

Unlike a cardiac CT scan, an MRI does not deliver radiation. This is critically important in a child, who will have a lifetime during which other imaging tests may be necessary.

A child with complex heart disease may need:

• A first MRI at 8 years old (post-surgical evaluation)
• A second MRI at age 15 (before intensive exercise)
• A third child at 25 (before pregnancy if female)
• A fourth at age 40 (monitoring of degeneration)

Repeating four cardiac CT scans would expose this child to a significant cumulative dose of radiation. MRI scans can be repeated indefinitely.

implants : MRI cannot be performed if the child has an implanted pacemaker or defibrillator (although "MRI-safe" pacemakers are emerging).

Sedation in young children: Children under 6-8 years old cannot remain still for 30-45 minutes. Mild sedation is often necessary.

Noise: The machine is extremely noisy. Earplugs or music help.

CT scans are less commonly used than MRIs in children due to radiation exposure. However, they remain useful for:

Coronary anomalies: Are the coronary arteries properly connected? A coronary anomaly can cause sudden death during exercise.

Complex vascular connections: Some malformations require exceptional precision.

When MRI is impossible: Implanted pacemaker, metallic implant incompatible with MRI.

Emergency: When an aortic dissection or other serious condition requiring a rapid response is suspected.

Modern scanners use "low-dose" protocols—minimal exposure while maintaining image quality. A single acquisition can generate an exquisite 3D reconstruction of the heart.

The dose from a cardiac CT scan in a child is approximately 3-5 mSv — equivalent to 1-2 years of natural background radiation. This is not negligible, but for a single scan, it is acceptable.

A thin tube (catheter) is inserted into an artery or vein (usually in the groin) and guided to the heart. This is the only technique that allows:

• Directly measure the pressures in the heart
• Determine the blood flow in each chamber
• Identify shunts (abnormal connections) accurately
• Calculate vascular resistance

Diagnosis: Simply measuring pressures and flows. This is rare now — non-invasive imaging (echocardiography, MRI) usually provides enough information.

Interventional: In addition to measuring, the pediatric cardiologist performs an intervention:

• Closing a hole (VSD, ASD) with an implanted device
• Dilate a stenotic valve with a balloon
• Creating a connection between the heart and lungs in a child whose physiology requires it

Catheterization is more invasive than an echocardiogram or an MRI. It carries minor risks (bleeding at the insertion site, allergic reaction to the contrast) and very rarely major risks.

But if an endovascular intervention can avoid open chest surgery, the benefits outweigh the risks.

Once the diagnosis is made, the question becomes: what do we do?

The options:

Follow-up without intervention: Some heart conditions are benign. A small atrial septal defect (ASD), a small ventricular septal defect (VSD) that closes spontaneously, or a slight stenosis only require monitoring.

Interventional catheterization: Less invasive than surgery. A child can go home the next day. It is often the first choice for closing holes (ASD, PFO) or dilating minor strictures.

Cardiac surgery: For more serious malformations. An open chest procedure. More invasive, riskier, but often necessary for transpositions, tetralogy of Fallot, and complex malformations.

Absolute emergency: Transposition of the great arteries. The child must be operated on within hours of birth.

Relative emergency: A large VSD with signs of heart failure. Surgery must be performed within weeks.

Planned: A small ASD or mild stenosis. Can wait months or years.

The best decisions are made in a "multidisciplinary conference" bringing together:

• Pediatric cardiologist
• Cardiac surgeon
• Pediatric Anesthetist
• Nurses
• Sometimes a geneticist

Together, they discuss the specific case and propose the best plan for this child.

The First Year: Echocardiograms at 2 weeks, 6 weeks, 3 months, then every 3-6 months depending on the malformation.

Subsequent Years: Annual or biennial echocardiograms.

Adolescence and Adulthood: Formal imaging (MRI) every 5-10 years.

Arrhythmias: Heart rhythm disturbances can develop after surgery. Periodic ECGs and Holter monitoring (24-hour ECG) can detect them.

Progressive valvular insufficiency: A repaired or replaced valve can deteriorate over time.

Chamber dilation: If the heart pumps poorly, the chambers dilate. MRI detects this.

Ventricular dysfunction: The heart is no longer pumping properly. Requires medical treatment.

Diet: Generally normal, unless the child has severe heart failure (sodium restriction).

Physical activity: This depends on the malformation and its repair. Some children can participate in intensive sports. Others need moderate activity. A pediatric cardiologist will provide specific recommendations.

Endocarditis prevention: If the malformation or repair creates turbulent blood flow, there is a risk of infective endocarditis (heart infection). Some children require prophylactic antibiotics before dental procedures.

Pregnancy in women: If a woman with repaired heart disease is considering pregnancy, prior cardiac imaging and a cardiac consultation are essential. Certain heart conditions make pregnancy risky.

Pediatric cardiology is centralized in Switzerland. The major centers are:

University Hospital Zurich (USZ): The largest center. Specialized pediatric cardiologists, cardiac surgeons, interventional catheterization laboratory, pediatric cardiac MRI.

University Hospital of Basel (USB): Pediatric cardiology, cardiac surgery.

Geneva University Hospital (HUG): Pediatric cardiology, cardiac imaging.

Inselspital in Bern: Pediatric cardiac surgery.

University Hospital of Lausanne (CHUV): Pediatric cardiology, access to advanced imaging.

Echocardiography: Available in most hospitals and some private centers.

Pediatric cardiac MRI: Available in major pediatric centers (Zurich, Geneva, Basel). In Lausanne, accessible via CID Lausanne.

Cardiac scanner: Available everywhere, but generally reserved for specific situations.

In Switzerland, diagnostic tests for congenital heart disease are covered by basic health insurance if prescribed by a doctor. Children with serious chronic illnesses (including complex heart conditions) are often exempt from deductibles and co-payments.

AI algorithms are beginning to analyze cardiac images with superhuman precision:

• Automatic anomaly detection
• Automatic measurement of heart function
• Predicting the progression of the disease
• Surgical planning assistance

These are not tools to replace doctors. They are to augment their work.

Clinical trials are beginning to explore whether stem cells or gene therapy can repair damaged heart tissue. It's still a long way from the clinical market, but the outlook is promising.

And information allows us to decide: when to intervene, how to intervene, how to monitor, and above all, how to live.

Parents of a child diagnosed with congenital heart disease today face a radically different reality than in the 1990s. Most of their children will live to adulthood. A majority will live a life without significant limitations.

This is thanks to three things:

1. Prenatal imaging that detects problems before birth, allowing for preparation.
2. Diagnostic imaging (echocardiography, MRI, CT scan) gives doctors the precise information needed to make decisions.
3. Pediatric surgeons and cardiologists who dedicate themselves to these children.

We understand parental anxiety. We know that every picture must be exquisite, every diagnosis clear, every explanation kind.

That's why we invest in the best technology and expertise in pediatric cardiac imaging.

Because a child with congenital heart disease deserves the best possible chance.