What is Intracardiac Shunts?
Intracardiac shunts are unusual routes in the heart where blood flow can take a detour, either alongside or replacing the regular routes for blood flow. They are heart defects that occur before birth due to irregular fetal development. As a result of this, blood flow changes and tends to affect how the body usually performs. Intracardiac shunts can cause different symptoms, ranging from no noticeable issues to life-threatening problems.
These shunts fall into two broad categories: cyanotic and acyanotic. Cyanotic shunts interfere with the lungs’ job of oxygenating blood, resulting in a condition called cyanosis, where the skin, lips, and nails can appear blue due to lack of oxygen. Acyanotic shunts, on the other hand, don’t disrupt the flow of blood to the lungs, meaning that oxygenation remains normal.
There are various types of both acyanotic and cyanotic shunts. For acyanotic shunts, these can include an atrial septal defect, ventricular septal defect, and patent ductal arteriosus. Cyanotic shunts can include multiple conditions such as Tetralogy of Fallot, truncus arteriosus, total anomalous pulmonary venous return (TAPVR), pulmonary atresia with ventricular septal defect, tricuspid atresia, hypoplastic left heart syndrome, transposition of great arteries, and double-outlet right ventricle.
The distribution of different types of these shunts can be seen in a pie chart (referred to as the Graph. Birth Prevalence of CHDs).
What Causes Intracardiac Shunts?
The causes of Intracardiac shunt formation – a condition where there’s abnormal blood flow between the heart’s chambers – can be many and varied, often involving a mix of genetic and outside factors. Genetic factors can include missing chromosomes, additional chromosomes (trisomies), and changes to single genes. For example, 40 to 50% of people born with Down Syndrome, which is also known as trisomy 21, have an atrial septal defect (ASD), a ventricular septal defect (VSD), tetralogy of Fallot (TOF), or transposition of the great arteries (TGA).
Pregnancy-related factors can also increase the risk for intracardiac shunt formation. Some of these factors include diabetes before becoming pregnant, using marijuana, catching rubella, taking ibuprofen, catching influenza, having a fever-related illness, and exposure to vitamin A.
Risk Factors and Frequency for Intracardiac Shunts
Intracardiac shunts, a type of congenital heart defect, are common among newborn babies around the world. Some regions have a higher number of cases than others. Asia reports the highest number, with 9.3 cases for every 1,000 babies born. Africa has the lowest number, with 1.3 cases per 1,000 live births, while North America reports 6.9 cases per 1,000 live births. The difference in numbers may be due to the availability of diagnostic tools in certain regions. In the USA, more cases are observed in white and Hispanic populations than in the black population.
- Intracardiac shunts are common forms of congenital heart defects.
- One in eight newborn babies worldwide have some sort of congenital heart anomaly.
- Asia has the largest number reported, with 9.3 cases per 1,000 live births.
- Africa has the lowest number, with 1.3 cases per 1,000 live births.
- North America sees 6.9 cases per 1,000 live births.
- The difference in numbers could be due to how widely available diagnostic tools are in each region.
- In the US, congenital heart defects are slightly more common in white and Hispanic populations than in the black population.
- In the US, slightly more females are affected than males, with 8.03 females and 7.67 males affected per 1,000 live births.
Thanks to improvements in medical and surgical treatments, more people born with these heart defects are living into adulthood.
Signs and Symptoms of Intracardiac Shunts
Congenital disorders are health conditions that a person is born with. Symptoms might not be immediately apparent, especially in children who can’t yet communicate what they’re feeling. However, as the child grows, they may start reporting symptoms like shortness of breath, lower than normal exercise capability, repeated infections, changes in skin color, coughing up blood, fainting, or swelling in the feet. Doctors will often rely on a physical examination to identify these conditions, since this is usually the first sign that something’s wrong.
During the physical examination, the doctor will look at the patient, touch certain areas to feel for abnormalities, and listen to their heart and breathing. They’ll be checking for things like:
- Bluish skin color (cyanosis)
- Abnormal fingernail shape
- Stunted growth
- Swollen neck veins
- Difficulty breathing
- Swelling in the feet
- A fluttering sensation when the heart is touched (thrill)
- A forceful or displaced heartbeat (heave)
Distinctive heart sounds can help the doctor diagnose certain conditions. Some of the typical heart sounds heard include a ‘split’ second heart sound with a ‘whooshing’ noise in the lungs area for atrial septal defects (ASD), a constant ‘whooshing’ sound on the left side of the chest for ventricular septal defects (VSD), and a continuous ‘machine-like’ sound for patent ductus arteriosus (PDA). If the child has Tetralogy of Fallot (TOF), the heart sound would be caused by a narrow pulmonary artery, not the accompanying VSD, and an ‘ejection’ sound will be heard on the upper left side of the chest. Sometimes these heart sounds can be tricky to identify precisely, so doctors will usually order an echocardiogram (a special ultrasound of the heart) to evaluate an abnormal heart sound.
Testing for Intracardiac Shunts
Once a doctor has examined a patient and heard about their symptoms, they may decide to do additional tests if needed. Whether or not further evaluation is done to look for heart abnormalities, known as ‘intracardiac shunts’, is decided on a case-by-case basis. These evaluations might include things like blood tests, heart monitor tests (EKG), ultrasound of the heart (echocardiogram), a chest x-ray, a CT scan, and a test where a thin tube is inserted into the blood vessels to the heart (cardiac catheterization). For example, an EKG could show signs of high blood pressure in the lungs, which is also known as pulmonary hypertension.
A chest X-ray can also reveal specific markers in different heart defects. For instance, a defect known as TOF could make the heart look boot-shaped on an x-ray, TAPVR could make the heart appear like a snowman, while TGA could make the heart look like an “egg-on-string”. Blood tests can indicate the severity of low oxygen levels, a condition known as hypoxemia, by identifying too many red blood cells.
Typically, cardiac catheterization is not needed to identify the heart defect but it might be recommended when planning for surgery. This procedure provides accurate measurements of the pressures inside the heart chambers. Furthermore, oxygen or a particular gas known as ‘nitric oxide’ can be administered into the patient’s lungs to check how the blood vessels there react. This information can be used to decide if the patient is suitable for surgical treatment or therapy to widen the blood vessels in the lungs.
Treatment Options for Intracardiac Shunts
Managing a medical condition that affects the “shunt”, or passage, between different parts of the heart depends on the specifics of each case. Treatment options vary and can include watching and waiting, medication, changes to daily habits, or even surgery. Some shunts, when they’re small and don’t decrease oxygen levels in the blood, can often just be monitored. Larger shunts that redirect the flow of blood from the left side of the heart to the right need to be closed to prevent additional health problems.
Some shunts cause low oxygen levels in the blood and are linked with more health risks. These often require surgery to fix. One example is a condition known as Tetralogy of Fallot (TOF), which is usually repaired with multiple surgeries. Initially, a connection is created between an artery in the upper body, called the subclavian artery, and the pulmonary artery, which transports blood to the lungs. This procedure is known as the Blalock-Tussing shunt.
Some doctors, however, don’t perform this initial procedure and instead move directly to the next steps. In the second step, a connection is made between the superior vena cava – a large vein that carries blood from the upper body to the heart – and the right pulmonary artery. This connection is known as a Glenn shunt. Finally, in the third step, the lower body’s main vein, the inferior vena cava, is connected to the pulmonary artery. This surgery is known as a Fontan procedure.
In cases where there’s not enough oxygen in the blood, the body may create too many red blood cells, a condition called reactive polycythemia, which could result in blood clotting. In such instances, doctors will carefully remove some blood to balance the patient’s hematocrit, the proportion of red cells in the blood.
For women affected by these conditions who are planning to get pregnant, it’s important to discuss this with a specialist in pregnancy care (an obstetrician) before conceiving. Some disorders can increase the risk of serious complications during pregnancy, and in some cases, pregnancy might not be advised.
What else can Intracardiac Shunts be?
When a doctor is examining unusual connections within the heart (known as intracardiac shunts), the symptoms can sometimes be confusing as they often resemble symptoms of diseases outside of the heart. These could include conditions related to the lungs, the nervous system, and even infectious diseases.
When dealing with intracardiac shunts that cause a blueness of the skin due to lack of oxygen (cyanotic intracardiac shunts), the doctor needs to consider other possible health conditions that might be causing the symptoms. These could include:
- Transient tachypnea of the newborn (rapid breathing immediately after birth)
- Bronchopulmonary dysplasia (lung disorder in neonates)
- Pulmonary hypoplasia (underdeveloped lungs)
- Laryngotracheomalacia (softened tissues of the windpipe)
- Vocal cord paralysis (loss of control of the vocal cords)
- Neonatal myasthenia gravis (a neuromuscular disease in infants)
- Spinal muscular atrophy (a rare genetic disorder that affects control of muscle movement)
- Infantile botulism (a serious infection that can lead to muscle weakness)
- Pneumonia (infection in the lungs)
Considering and screening for these conditions can help doctors more accurately pinpoint the cause of the symptoms and ensure they are providing the most effective treatment.
What to expect with Intracardiac Shunts
The outcome of a medical condition often depends on the specific subtype. This applies to shunts, which are abnormal pathways between blood vessels or organs. There are two types: noncyanotic and cyanotic. Noncyanotic shunts tend to have a better outlook and a higher recovery rate compared to cyanotic shunts.
Small abnormalities can sometimes close on their own, or they might not cause any symptoms throughout a person’s life. However, larger abnormalities often need to be surgically closed to prevent severe complications.
If the condition advances to the point where it causes severe high blood pressure in the lungs, the patient’s condition could worsen. In such scenarios, they may need to undergo a heart-lung transplant, a treatment option which isn’t widely available.
Severe cyanotic abnormalities, on the other hand, typically show symptoms soon after birth. In many cases, the chance of survival is slim without immediate surgical intervention.
Possible Complications When Diagnosed with Intracardiac Shunts
Common complications linked with intracardiac shunts involve issues such as lack of growth, repeated infections, high blood pressure in the lungs, failure of the right side of the heart, Eisenmenger syndrome (a type of heart defect), infections on the inner lining of your heart, irregular heart rhythms, and even death. Despite these potential issues, it’s important to note that not all intracardiac shunts lead to complications and most of them are harmless.
Possible Complications:
- Difficulty in growing properly
- Recurrent infections
- High blood pressure in the lungs
- Failure of the right side of the heart
- Eisenmenger syndrome (a type of heart defect)
- Infections on the inner lining of your heart
- Irregular heart rhythms
- Death
Preventing Intracardiac Shunts
Conditions like intracardiac shunts, which are basically abnormal connections between the heart’s chambers, can be caused by a mix of different factors, some of which we can control, and others that we cannot. Before a woman becomes pregnant, doctors like family physicians and obstetricians would advise her on safe habits to follow during pregnancy to reduce the chances of the baby having a heart condition. Such advice might include better managing diabetes if she has it, avoiding certain harmful substances like retinoids (a type of Vitamin A that can be harmful to an unborn baby) and ibuprofen (a common painkiller), and staying away from recreational drugs.
As these children grow into teenagers and start understanding more about the world, it’s important to explain their medical conditions to them in a way that’s kind and realistic, so they can better understand their bodies and take active roles in managing their health.
