Tetralogy of Fallot – Symptoms and Causes

Overview

Tetralogy of Fallot is a congenital heart defect present at birth. This rare condition involves four distinct heart problems that change the heart’s structure and affect blood flow.

Babies with this condition often have bluish or grayish skin due to low oxygen levels. Most diagnoses occur during pregnancy or shortly after birth. However, some cases may go undetected until adulthood if symptoms are mild.

Tetralogy of Fallot includes four heart defects that occur together:

1. Ventricular septal defect – a hole between the heart’s lower chambers.
2. Pulmonary stenosis – narrowing of the pulmonary valve and outflow tract.
3. Right ventricular hypertrophy – thickened right ventricle muscle.
4. Overriding aorta – the aorta is positioned over the ventricular septal defect.

These problems cause oxygen-poor blood to flow directly to the body instead of going to the lungs first, resulting in low oxygen levels.

Signs and Symptoms

People with tetralogy of Fallot show various symptoms based on how much blood flow to the lungs is blocked. The severity of symptoms can differ from person to person.

Common symptoms include:

• Blue or gray skin coloration (cyanosis)
• Difficulty breathing and fast breathing patterns
• Difficulty feeding
• Poor weight gain
• Easy fatigue during activity
• Unusual irritability
• Extended crying episodes
• Fainting spells

Blue or Tet Spells

Some babies with this heart condition experience sudden episodes where their skin, nails, and lips turn deep blue or gray. These events are known as “blue spells” or “tet spells.”

They typically happen when the baby is crying, eating, or upset.

Tet spells occur due to a rapid decrease in blood oxygen levels. These episodes most commonly affect young infants around 2 to 4 months old. In some cases, loss of consciousness can occur.

Older children may have less obvious spells and may instinctively squat when short of breath, which helps improve blood flow and oxygen levels.

When Medical Help Is Needed

If you notice any of these warning signs in your child, seek medical attention right away:

• Breathing difficulties
• Bluish skin coloration
• Decreased alertness
• Seizure activity
• Unusual weakness
• Increased irritability

Emergency Action: If your baby turns blue or gray, place them on their side and gently pull their knees toward their chest to help increase lung blood flow. Call 911 immediately.

Causes

Tetralogy of Fallot develops during fetal heart formation in pregnancy. In most cases, doctors cannot identify a specific cause for this heart defect.

This condition consists of four structural heart problems that occur together:

1. Pulmonary Valve Stenosis: This narrowing reduces blood flow from the heart to the lungs. The narrowing might affect just the valve or extend to multiple points along the pathway to the lungs. In severe cases called pulmonary atresia, a solid tissue layer completely blocks blood flow.

2. Ventricular Septal Defect: This hole between the lower heart chambers allows oxygen-poor and oxygen-rich blood to mix. This mixing forces the heart to work harder to pump blood throughout the body, potentially weakening the heart over time.

3. Misplaced Aorta: The aorta, which is the body’s main artery, shifts to the right instead of connecting normally to the left ventricle. This repositioning occurs directly above the ventricular septal defect, changing blood flow patterns.

4. Right Ventricular Hypertrophy: The right lower heart chamber develops thickened walls due to overwork. This thickening may eventually lead to heart weakness and failure if not treated.

Some patients with Tetralogy of Fallot have additional heart abnormalities. These may include problems with the aorta, coronary arteries, or an atrial septal defect (a hole between the upper heart chambers).

The combination of these four defects creates a complex heart condition that requires medical intervention. Blood flow to the lungs decreases while oxygen-poor blood flows to the body, resulting in lower oxygen levels throughout the circulatory system.

Heart development occurs early in pregnancy, with these structures forming during the first eight weeks of fetal growth. During this critical period, any disruption to normal heart development can lead to structural defects like those found in Tetralogy of Fallot.

Risk Factors

Several factors may raise the chance of a baby developing tetralogy of Fallot:

• Family history of congenital heart defects
• Maternal infections during pregnancy, especially rubella
• Lifestyle choices during pregnancy:
  • Alcohol consumption
  • Poor nutrition
  • Smoking

Other risk factors include:

• Mother’s age over 35 years
• Presence of genetic conditions in the baby, such as Down syndrome or DiGeorge syndrome

These factors don’t always cause the condition, but they might increase the likelihood of heart defects forming during pregnancy.

Health Problems

People with tetralogy of Fallot may face serious health problems if not treated. These issues can cause disability or even death by young adulthood.

One possible problem is infection of the heart’s inner lining or valves, called infective endocarditis. Some patients need antibiotics before dental work to prevent this infection. Ask your doctor if these preventive medicines are right for you or your child.

After surgery to fix tetralogy of Fallot, most people do well. However, some complications can happen:

• Blood flowing backward through a heart valve
• Irregular heartbeats
• Persistent hole in the heart after surgery
• Changes in heart chamber size
• Swelling of part of the aorta (aortic root dilation)
• Sudden cardiac death

Sometimes another procedure or surgery is needed to fix these problems.

For women born with complex heart defects, pregnancy can bring special challenges. The heart works harder during pregnancy, which may cause problems for those with heart conditions.

It’s important to talk with your healthcare team about possible risks before becoming pregnant. Your doctors can help create a plan for safe care during pregnancy and delivery.

Prevention

Taking steps to reduce the risk of congenital heart defects in babies involves several healthy practices before and during pregnancy. While many heart defects cannot be prevented because their causes remain unknown, certain measures may help lower the overall risk.

Before and During Pregnancy

Pregnant women should get regular prenatal checkups to monitor both their health and their baby’s development. Healthcare providers can identify potential issues early and recommend appropriate care.

• Essential Supplements: Taking a daily multivitamin with 400 micrograms of folic acid can help prevent birth defects. Research suggests folic acid may reduce the risk of heart defects along with brain and spinal cord abnormalities.
• Avoid harmful substances:
  • No alcohol consumption
  • No smoking
  • Stay away from secondhand smoke
  • Have someone else handle painting or cleaning with strong chemicals

Managing Health Conditions

Several health-related precautions can make a difference:

1. Get vaccinated for rubella (German measles) before pregnancy.
2. Control blood sugar levels if you have diabetes.
3. Work with healthcare providers to manage chronic conditions like phenylketonuria.

Medication Safety

Always check with your healthcare team before taking any medications during pregnancy. Some drugs can cause birth defects.

This includes:

• Prescription medications
• Over-the-counter drugs
• Herbal supplements

For those with a family history of heart defects, genetic testing and screening might be recommended during pregnancy to assess risk factors.

These tests cannot guarantee protection against all congenital heart defects, but they represent the best available approaches to reducing risk.