Congenital H D Flashcards
What are congenital HD?
Congenital Heart Defects (CHD)
Congenital heart defects (CHD) are structural abnormalities of the heart or major blood vessels within the chest (intrathoracic vessels) that are present from birth. These defects can significantly impact heart function or have the potential to do so, depending on their severity and the specific structures involved.
Overview of CHD
- Prevalence: Congenital heart defects are the most common type of birth defect, affecting approximately 1% of all newborns.
- Severity Variation: Among these cases, about 25% are categorized as “critical congenital heart defects.”
- Critical CHD: This group of defects requires prompt medical intervention, either through surgical procedures or catheter-based treatments, typically within the first year of life. The need for early treatment is due to the severity of the defect and its impact on heart function and overall circulation.
What are the Types of Congenital Heart Defects
CHDs can vary in type and severity, affecting different parts of the heart or blood vessels. The defects can lead to issues such as abnormal blood flow, heart muscle strain, or mixing of oxygen-rich and oxygen-poor blood, potentially leading to life-threatening conditions without treatment.
How do you manage a patient with Congenital Heart disease.
History taking: what would you take note of?
In younger and older children
Approach to the Child with Heart Disease
The evaluation of a child suspected of having heart disease involves a thorough history and physical examination, both of which are essential in guiding the initial diagnostic approach. The process should be adapted to the child’s age and developmental stage, with information gathered from the child (if appropriate) and their parents.
History Taking in Children with Suspected Heart Disease
-
Age-Specific Considerations: The history should consider the child’s age, as symptoms and daily activities vary across different developmental stages. For example:
-
Newborns and Infants: The primary activity is feeding. Monitoring feeding habits provides important insights into potential cardiac issues. Healthy infants typically feed every 2-3 hours, completing feeds within 30 minutes. If heart function is compromised, as seen in congestive heart failure, signs may include:
- Frequent, Small Feeds: Infants may take smaller quantities more often because of fatigue.
- Excessive Sweating and Breathlessness: Sweating during feeding and difficulty breathing (dyspnea) can indicate heart failure.
- Older Children: Symptoms might manifest during activities or play. It is important to compare the child’s activity level, growth, and development with peers.
-
Newborns and Infants: The primary activity is feeding. Monitoring feeding habits provides important insights into potential cardiac issues. Healthy infants typically feed every 2-3 hours, completing feeds within 30 minutes. If heart function is compromised, as seen in congestive heart failure, signs may include:
-
Key Symptoms to Note:
- Central Cyanosis: This is a bluish discoloration of the skin and mucous membranes due to low oxygen levels in the blood. If the cause is cardiac, it usually does not improve significantly with oxygen inhalation, unlike respiratory causes.
- Tachypnea without Dyspnea: Rapid breathing that occurs without using accessory muscles for respiration may suggest cyanotic heart disease (a type of heart defect causing low oxygen levels). In contrast, grunting and labored breathing are more common in left-sided heart obstruction or respiratory conditions that reduce lung compliance.
-
Signs in Older Children:
- Fatigue and Exercise Intolerance: Children who tire easily or struggle to keep up with their peers during physical activities may have underlying heart disease.
- Cyanosis during Activity: This warrants further evaluation for heart conditions.
- Squatting: This posture, often seen in children with tetralogy of Fallot, can temporarily improve blood flow during episodes of cyanosis.
- Hypercyanotic Spells: These are episodes of severe cyanosis and breathlessness associated with tetralogy of Fallot.
- Syncope (Fainting): If fainting occurs during exercise, it may indicate an arrhythmia, an abnormality in the coronary arteries, aortic stenosis, or obstruction in the aortic arch.
Explain the pathogenesis of congenital heart defects
Pathophysiology of Congenital Heart Disease (CHD)
Congenital heart disease involves three main pathophysiological mechanisms that affect the structure and function of the heart. These are:
- Volume Overload
- Pressure Overload
- Cyanosis
Let’s break down each mechanism in detail:
- Volume Overload
- Definition: Volume overload occurs when the heart’s ventricles are required to pump more blood than normal. This often happens due to abnormal blood flow patterns within the heart.
- Causes:
- Left-to-Right Shunt: This is a situation where blood abnormally flows from the left side of the heart to the right. For instance, in conditions like a ventricular septal defect (VSD), where a hole exists in the wall separating the left and right ventricles, blood moves from the high-pressure left side to the lower-pressure right side, increasing the amount of blood the right ventricle and lungs must handle.
- Valvular Regurgitation: Conditions like atrioventricular septal defects (where valves between the heart’s chambers don’t close properly) can cause blood to leak backward, leading to increased volume in the ventricles. - Pressure Overload
- Definition: Pressure overload occurs when there is resistance to blood flow, increasing the workload on the ventricles.
- Causes:
- Obstruction to Outflow: This can occur due to conditions like aortic or pulmonary valve stenosis, where the valves are narrowed, or coarctation of the aorta (narrowing of the aorta itself). These conditions force the heart to pump against higher resistance. - Cyanosis
- Definition: Cyanosis is a bluish discoloration of the skin and mucous membranes due to low levels of oxygen in the blood.
- Causes in CHD:
- Reduced Pulmonary Blood Flow: Conditions like tetralogy of Fallot lead to reduced blood flow to the lungs, resulting in less oxygenated blood being available for the body.
- Inadequate Mixing of Blood: In some congenital heart defects, such as transposition of the great vessels, the circulation is abnormal with two parallel circuits rather than a single continuous flow. This results in oxygen-rich blood not reaching the body efficiently.
Understanding these pathophysiological mechanisms is crucial for diagnosing, managing, and treating congenital heart defects, as different defects will have varying combinations and severities of these underlying issues.
What are the consequences of volume overload in congenital heart defects?
-
Consequences:
- Increased Pulmonary Blood Flow: The excess blood flow to the lungs can damage the small blood vessels within the pulmonary circulation, leading to pulmonary vascular changes and, eventually, pulmonary hypertension (high blood pressure in the lungs).
- Congestive Heart Failure (CHF): With large shunts or significant valve regurgitation, the heart struggles to pump effectively, leading to symptoms of CHF. This includes difficulty breathing, swelling, and poor growth in infants (failure to thrive).
- Pulmonary Vascular Obstructive Disease: Over time, the increased pressure and flow within the lungs can cause the blood vessels to become thickened and less flexible, leading to permanent damage and increased resistance to blood flow.
- arrhythmia
- heart failure
- pulmonary congestion
What are the consequences of pressure overload in congenital heart defects?
- Consequences:
- Ventricular Hypertrophy: To compensate for the increased workload, the heart muscle thickens (hypertrophy). While this initially helps the heart maintain its function, over time, it can reduce the heart’s compliance (ability to stretch and fill), leading to diastolic dysfunction (difficulty filling the heart with blood).
- Reduced Ventricular Compliance: The thickened ventricular walls become stiff, making it harder for the heart to fill with blood during diastole (the relaxation phase). This contributes to symptoms of heart failure over time.
- arrhythmia
- heart failure
What are the consequences & complications of chronic cyanosis in congenital heart defects?
-
Consequences of Chronic Cyanosis:
- Erythrocytosis: The body compensates for low oxygen levels by producing more red blood cells to improve oxygen transport. However, this can make the blood thicker (increased viscosity), leading to hyperviscosity syndrome, which may cause headaches, dizziness, and other symptoms.
- Bleeding Diathesis: Chronic cyanosis can also impair blood clotting, increasing the risk of bleeding.
-
Complications:
- Cerebral Venous Thrombosis: Thickened blood due to erythrocytosis increases the risk of blood clots in the brain.
- Cerebral Abscesses: Children with cyanotic heart disease are at a higher risk of brain infections due to the abnormal blood flow.
- Seizures and Paradoxical Emboli: In cases where blood can bypass the lungs (right-to-left shunt), clots or debris in the bloodstream can travel directly to the brain, causing strokes or seizures.
What are the Complications of Congenital Heart Defects (CHD)
Congenital heart defects can lead to several serious complications, including:
-
Congestive Heart Failure (CHF):
- This occurs when the heart cannot pump blood efficiently, leading to symptoms such as difficulty breathing, fatigue, and fluid retention.
-
Pulmonary Arterial Hypertension (PAH):
- PAH is high blood pressure in the arteries that supply the lungs, resulting from increased blood flow or resistance within the lungs.
-
Pulmonary Vascular Occlusive Disease:
- Over time, high pressure in the lungs can damage the pulmonary blood vessels, causing them to thicken and narrow, which worsens pulmonary hypertension.
-
Retardation of Growth and Development:
- Children with significant heart defects may have poor growth and delayed developmental milestones due to decreased oxygen delivery to tissues.
-
Hypercyanotic Attacks (Tet Spells):
- These are sudden episodes of increased cyanosis (bluish discoloration), often seen in children with conditions like tetralogy of Fallot. The spells are triggered by a drop in oxygen levels and can cause fainting or seizures.
-
Cerebrovascular Accidents (Strokes):
- CHD can increase the risk of blood clots, which can travel to the brain and cause strokes.
-
Subacute Bacterial Endocarditis (SBE):
- Children with certain types of CHD are at a higher risk for infections in the heart lining and valves, especially if there are defects that cause turbulent blood flow.
-
Cerebral Abscess:
- This is a collection of pus in the brain, more common in children with cyanotic heart disease due to the abnormal blood flow that bypasses the lungs.
What are the Classification of Congenital Heart Disease with examples
Congenital heart defects are classified into two main categories:
-
Cyanotic Heart Disease:
- Characterized by the presence of a right-to-left shunt or mixing of oxygen-poor and oxygen-rich blood, resulting in lower oxygen levels in the body. It includes three sub-groups:
- These defects reduce the blood flow to the lungs, causing significant cyanosis.
- Examples:
- Tetralogy of Fallot (TOF): A combination of four defects that decrease pulmonary blood flow.
- Tricuspid Atresia: The absence or closure of the tricuspid valve, obstructing blood flow to the lungs.
- Pulmonary Atresia: Complete blockage of the pulmonary valve.b) Cyanotic Heart Disease with Increased Pulmonary Blood Flow:
- In these conditions, there is increased blood flow to the lungs, but mixing of oxygenated and deoxygenated blood occurs.
- Examples:
- Transposition of the Great Arteries (TGA): The positions of the pulmonary artery and the aorta are switched, resulting in parallel rather than sequential circulation.
- Truncus Arteriosus: A single large vessel comes out of the heart instead of two separate vessels, leading to mixed blood flow.
- Cor Triatriatum: A rare defect where the left atrium is divided into two chambers, causing obstruction.c) Complex Cyanotic Defects (“Mixing Defects”):
- These conditions involve complex anatomical abnormalities that lead to mixing of blood.
- Examples:
- Double Outlet Right Ventricle (DORV): Both the aorta and pulmonary artery arise from the right ventricle, resulting in mixed blood flow.
- Truncus Arteriosus (as mentioned earlier): Also considered a mixing defect.
- Hypoplastic Left Heart Syndrome (HLHS): The left side of the heart is underdeveloped, causing blood to mix before reaching systemic circulation. -
Acyanotic Heart Disease:
- In these defects, oxygen levels in the blood are normal. They are categorized based on the effect on pulmonary blood flow:
- Blood flow to the lungs is normal, but there may be problems with blood flow out of the heart.
- Examples:
- Stenosis of the Left Ventricular Outflow Tract (LVOT): Narrowing that obstructs blood flow from the left ventricle.
- Congenital Aortic Stenosis: Narrowing of the aortic valve.
- Aortic Arch Anomalies: Abnormalities in the structure of the aortic arch.
- Coarctation of the Aorta: Narrowing of the aorta, usually after the branches to the head and arms.b) Acyanotic Heart Disease with Increased Pulmonary Blood Flow:
- There is excessive blood flow to the lungs due to defects that cause left-to-right shunting.
- Examples:
- Patent Ductus Arteriosus (PDA): Persistence of a fetal connection between the aorta and pulmonary artery, allowing extra blood flow to the lungs.
- Atrial Septal Defect (ASD): A hole in the wall between the atria, causing left-to-right shunting of blood.
- Ventricular Septal Defect (VSD): A hole in the wall between the ventricles, leading to increased blood flow to the lungs.
What are the Factors Contributing to Cyanosis in Congenital Heart Defects (CHD)
Cyanosis in congenital heart disease occurs due to a lack of adequate oxygenation of the blood, leading to a bluish discoloration of the skin and mucous membranes. The primary mechanisms leading to cyanosis in CHD are:
-
Right-to-Left Shunting and Reduced Pulmonary Blood Flow:
- When blood is shunted from the right side to the left side of the heart without passing through the lungs, it remains deoxygenated. This results in cyanosis because oxygen-poor blood is delivered to the systemic circulation.
- Conditions such as Tricuspid Atresia (where the tricuspid valve is absent, obstructing blood flow to the lungs) and Tetralogy of Fallot (which involves four heart defects that reduce pulmonary blood flow) exemplify this mechanism.
-
Intracardiac Mixing of Oxygenated and Deoxygenated Blood:
- In some heart defects, both oxygen-rich and oxygen-poor blood mix within a heart chamber before being ejected into the systemic circulation, leading to systemic hypoxemia (low blood oxygen levels).
- Examples include defects like a single atrium or ventricle, double outlet right ventricle (DORV) (where both major arteries arise from the right ventricle), and truncus arteriosus (where a single large vessel serves both systemic and pulmonary circulations).
-
Failure of Pulmonary Venous Blood to Reach the Systemic Circulation:
- This can occur when oxygenated blood from the lungs is not effectively delivered to the body due to abnormal anatomy.
- Transposition of the Great Arteries (TGA) is a classic example where the pulmonary artery and aorta are switched, causing oxygenated blood to recirculate in the lungs while deoxygenated blood circulates through the body. Another example is total anomalous pulmonary venous connection, where the pulmonary veins drain into the right side of the heart instead of the left.
-
Severe Low Cardiac Output States Due to Obstructions:
- When there are significant obstructions in the heart’s outflow tracts, either on the right or left side, it limits the amount of blood that can be pumped forward.
- Conditions like critical pulmonary stenosis/atresia (narrowing or closure of the pulmonary valve) or hypoplastic left heart syndrome (HLHS) (where the left side of the heart is underdeveloped) lead to decreased cardiac output and cyanosis.
What are the Importance of Intracardiac Mixing for Survival
- In many cyanotic heart defects, the presence of an Atrial Septal Defect (ASD) or Ventricular Septal Defect (VSD) is crucial for survival. These defects allow blood mixing between the heart’s chambers, which provides some degree of oxygenation. This becomes particularly important when the ductus arteriosus (a fetal blood vessel connecting the pulmonary artery to the aorta) closes after birth.
- The ductus arteriosus plays a vital role in maintaining blood flow to the lungs or systemic circulation in cyanotic newborns. Once it closes, the lack of alternative pathways for blood flow can result in severe hypoxia.
How do you Manage Duct-Dependent Cyanotic Lesions
- In neonates with severe cyanosis due to ductus-dependent lesions (where the ductus arteriosus is essential for adequate blood flow), maintaining ductal patency is crucial.
- Prostaglandin E1 (PGE1) is used to keep the ductus arteriosus open. The dosage typically ranges from 0.01-0.02 micrograms per kilogram per minute. PGE1 acts as a vasodilator, which can prevent the ductus from closing.
Precautions When Using Prostaglandin E1
- Hypotension Risk: PGE1 can cause significant vasodilation, leading to low blood pressure. Therefore, volume infusion (administration of fluids) may be necessary to prevent severe hypotension.
-
Need for Additional Support:
- Intubation and Mechanical Ventilation: Many cyanotic neonates will require airway support due to compromised breathing.
- Correction of Acidosis: If metabolic acidosis is present, bicarbonate therapy may be needed to correct the blood pH.
- Inotropic Support: Medications that increase the strength of heart contractions may be used if the cardiac output is critically low.
Further Evaluation and Management
- While waiting for an accurate diagnosis through echocardiography or cardiac catheterization, these supportive measures are essential to stabilize the patient.
- In severe cases, urgent surgical palliation may be required to allow the heart and pulmonary structures to grow to a size suitable for more definitive surgical correction later on.
Palliation of Congenital Heart Disease
Palliation refers to surgical procedures that aim to temporarily alleviate the severe pathophysiological issues associated with congenital heart disease (CHD) in neonates and infants, without necessarily providing a permanent cure. The goal is to stabilize the child, improve symptoms, and optimize conditions for potential future corrective surgeries. As pediatric cardiology and cardiac surgery have advanced, the decision between palliative procedures and complete corrective surgery has shifted from being limited by the patient’s small size to being based on the specific pathophysiological issues related to the congenital heart anomaly
Palliative procedures for CHD are grouped into three main categories which are?
-
Procedures to Increase Pulmonary Blood Flow (Systemic-to-Pulmonary Artery Shunts):
- These procedures are necessary when there is inadequate blood flow to the lungs, which leads to poor oxygenation. Increasing pulmonary blood flow helps enhance the oxygenation of blood, thus alleviating cyanosis (bluish discoloration due to lack of oxygen).
- The most common example is the Blalock-Taussig shunt, which connects a systemic artery (like the subclavian artery) to a pulmonary artery. This creates an alternative route for blood to reach the lungs for oxygenation.
-
Procedures to Limit Excessive Pulmonary Blood Flow (Pulmonary Artery Banding):
- These procedures are used when there is an excessive amount of blood flowing to the lungs, which can damage the pulmonary circulation and lead to heart failure.
- Pulmonary artery banding involves placing a band around the pulmonary artery to restrict the amount of blood flowing into the lungs, thus reducing the risk of pulmonary hypertension (high blood pressure in the lungs) and heart failure.
-
Procedures to Improve Intra-Cardiac Mixing of Blood (Atrial Septectomy, Balloon Septostomy):
- In certain congenital heart defects, the mixing of oxygenated and deoxygenated blood within the heart is inadequate, leading to severe cyanosis. Increasing intra-cardiac mixing can help improve overall oxygenation.
- Atrial septectomy is a surgical procedure that creates or enlarges an opening between the atria (upper chambers of the heart), allowing better mixing of blood.
- Balloon septostomy is a less invasive catheter-based procedure where a balloon-tipped catheter is used to enlarge an existing atrial septal defect (ASD), improving blood mixing.
These palliative measures serve to stabilize critically ill children, allowing time for growth and development, and setting the stage for future corrective surgeries when the child is more stable and older.
What are Cyanotic Congenital Heart Defects
Cyanotic congenital heart defects are characterized by the presence of cyanosis, a condition where there is a bluish discoloration of the skin and mucous membranes due to insufficient oxygenation of the blood. Cyanosis occurs when there is a significant amount of deoxygenated blood entering the systemic circulation, causing lower oxygen levels in the body’s tissues.
What are the Factors Contributing to the Development of Cyanosis
Several factors can lead to cyanosis in congenital heart defects:
-
Right-to-Left Shunting with Reduced Pulmonary Blood Flow:
- This occurs when blood bypasses the lungs and is shunted from the right side of the heart (deoxygenated blood) to the left side (systemic circulation) without adequate oxygenation. This shunting reduces the volume of blood going to the lungs for oxygenation.
- Conditions such as Tetralogy of Fallot and Tricuspid Atresia are examples where right-to-left shunting leads to cyanosis.
-
Intracardiac Mixing of Oxygenated and Deoxygenated Blood:
- When there is a mixture of oxygenated and deoxygenated blood within the heart or a large vessel proximal to the aorta, the resulting mixed blood is not fully oxygen-rich.
- Examples include defects like Truncus Arteriosus, where a single vessel overrides both ventricles, causing mixing of blood, or double outlet right ventricle, which also leads to mixed circulation.
-
Failure of Pulmonary Venous Blood Delivery to the Systemic Circulation:
- In conditions where pulmonary venous blood (oxygenated blood from the lungs) does not properly reach the systemic circulation, cyanosis results.
- This situation is seen in Transposition of the Great Arteries and Total Anomalous Pulmonary Venous Connection, where the connections of the heart and major vessels are abnormal, leading to inadequate oxygenation of the systemic blood flow.
-
Severe Low Cardiac Output States Due to Obstructions:
- Severe obstructions on the right or left side of the heart can cause reduced cardiac output and lead to cyanosis.
- Conditions such as critical pulmonary stenosis or atresia (severe narrowing or absence of the pulmonary valve) and hypoplastic left heart syndrome (underdeveloped left side of the heart) result in significant reductions in blood flow and oxygen delivery.
The Importance of Ductal Patency in Cyanotic Congenital Heart Defects
- For survival in most cyanotic congenital heart defects, especially in neonates, it is crucial to maintain a connection between the pulmonary and systemic circulation. Once the ductus arteriosus (a fetal blood vessel that connects the pulmonary artery to the descending aorta) closes, survival becomes difficult because it may be the only pathway allowing some degree of mixing between oxygenated and deoxygenated blood.
- Therefore, patency of the ductus arteriosus is critical for the survival of neonates with severe cyanotic congenital heart disease. When the ductus arteriosus remains open, it helps to maintain some level of blood flow to the lungs or systemic circulation, depending on the nature of the defect.
Medical Management for Maintaining Ductal Patency
-
Prostaglandin E1 (PGE1) is administered to keep the ductus arteriosus open. This drug is a potent vasodilator that helps maintain ductal patency, thereby allowing blood to bypass the blocked or narrowed areas of the heart and lungs.
- The usual dose ranges from 0.01 to 0.05 micrograms/kg/min, administered intravenously.
- However, because PGE1 causes blood vessels to dilate, it can lead to hypotension (low blood pressure), so careful monitoring is needed, and volume infusion may be necessary to maintain adequate blood pressure.
Additional Management Strategies for Severe Cyanosis
- Neonates with severe cyanosis often require endotracheal intubation and mechanical ventilation to support breathing and improve oxygenation.
- Correction of acidosis with bicarbonate is performed to address the buildup of acids in the blood due to poor oxygenation.
- Inotropic support may be needed to strengthen heart contractions and improve cardiac output.
- These interventions help stabilize the patient while awaiting further diagnostic evaluation, such as echocardiography or cardiac catheterization, which are crucial for identifying the exact nature of the congenital heart defect and planning urgent surgical interventions if needed.
The management of cyanotic congenital heart defects aims to ensure adequate oxygen delivery to tissues and stabilize the patient for potential definitive surgical correction.
What’s Tetralogy of Fallot (TOF) & it constitutes
Tetralogy of Fallot (TOF) is a congenital heart disease characterized by a combination of four cardiac abnormalities that contribute to the development of cyanosis. The condition was first described by the French physician Louis-Etienne Arthur Fallot in 1888. It is one of the most common types of cyanotic congenital heart disease and includes the following four defects:
-
Ventricular Septal Defect (VSD):
- A VSD is a hole in the septum that separates the right and left ventricles, allowing deoxygenated blood from the right ventricle to mix with oxygenated blood in the left ventricle. This mixing contributes to cyanosis because the oxygen content in the systemic circulation is reduced.
-
Right Ventricular Outflow Tract Obstruction:
- This refers to the narrowing or blockage that impedes blood flow from the right ventricle to the pulmonary artery. The obstruction can range from mild stenosis to complete atresia (absence of a normal opening). The degree of obstruction influences the severity of cyanosis, as it restricts blood flow to the lungs for oxygenation.
-
Right Ventricular Hypertrophy:
- The increased workload on the right ventricle due to the outflow tract obstruction leads to thickening of the right ventricular muscle. This hypertrophy is a compensatory response to pump blood through the narrowed pathway.
-
Overriding Aorta:
- The aorta is positioned directly over the VSD, rather than solely over the left ventricle. As a result, it receives blood from both the left and right ventricles, leading to the delivery of a mixture of oxygenated and deoxygenated blood to the systemic circulation.
These four defects work together to reduce the amount of oxygenated blood reaching the body, causing cyanosis.
Diagnostic Subgroups of TOF
There are four subtypes of Tetralogy of Fallot based on the variations in the anatomical abnormalities:
-
TOF with Pulmonary Stenosis:
- The most common form of TOF, characterized by varying degrees of narrowing in the pulmonary valve or right ventricular outflow tract.
-
TOF with Pulmonary Atresia:
- In this variant, the pulmonary valve is completely closed, and there is no direct connection from the right ventricle to the pulmonary artery. Blood flow to the lungs relies entirely on alternative pathways, such as a patent ductus arteriosus or collateral vessels.
-
TOF with Absent Pulmonary Valve Syndrome:
- This rare form involves the absence of a functional pulmonary valve, leading to severe pulmonary regurgitation and significant enlargement of the pulmonary arteries.
-
TOF with Common Atrioventricular Canal (Atrioventricular Septal Defect):
- In this type, there is a large defect in the center of the heart that involves both the atrial and ventricular septa, along with abnormalities in the atrioventricular valves, resulting in a common atrioventricular connection.
What’s the Pathophysiological Implications of TOF
The severity of symptoms and the degree of cyanosis in TOF depend on the extent of the right ventricular outflow obstruction and the size of the VSD. The more severe the obstruction, the less blood reaches the lungs for oxygenation, increasing cyanosis. Management may involve medical stabilization, palliative procedures to improve blood flow to the lungs, and definitive surgical repair, often performed in infancy.
This is the most common form of Tetralogy of Fallot (TOF), it’s Pathophysiology and clinical implications
TOF with Pulmonary Stenosis
This is the most common form of Tetralogy of Fallot (TOF) and is characterized by the presence of right ventricular outflow tract obstruction (RVOTO) along with the other three classical features of TOF: ventricular septal defect (VSD), right ventricular hypertrophy, and an overriding aorta.
Features and Pathophysiology
-
Right Ventricular Outflow Tract Obstruction (RVOTO):
- In TOF with pulmonary stenosis, the obstruction can occur at three levels:
- Subvalvular (infundibular): Below the pulmonary valve, caused by thickened muscle tissue in the right ventricular outflow tract.
- Valvular: At the level of the pulmonary valve itself, which may be narrowed or malformed.
- Supravalvular: Above the valve, involving the pulmonary artery.
- The obstruction can also be a combination of these levels. RVOTO can be either:
- Fixed: Due to structural abnormalities such as valve leaflet stenosis or a small (hypoplastic) pulmonary valve annulus.
- Dynamic: Caused by hypertrophied muscle in the infundibular region (below the valve), which can change in severity with varying conditions.
- In TOF with pulmonary stenosis, the obstruction can occur at three levels:
-
Ventricular Septal Defect (VSD):
- The VSD in TOF is typically large, unrestrictive, and located just below the aortic valve (subaortic). Because the defect is unrestrictive, blood pressures in the right and left ventricles are nearly equal. This allows deoxygenated blood from the right ventricle to flow into the left ventricle and out to the systemic circulation, contributing to cyanosis.
-
Right Ventricular Hypertrophy:
- Due to the obstruction in the right ventricular outflow tract, the right ventricle must work harder to pump blood to the lungs, leading to the thickening of the right ventricular muscle (hypertrophy). This adaptation helps maintain blood flow despite the increased resistance.
-
Overriding Aorta:
- In TOF, the aorta is positioned above the ventricular septal defect, rather than solely arising from the left ventricle. This means the aorta receives blood from both the left and right ventricles, leading to the mixing of oxygenated and deoxygenated blood.
- Usually, less than 50% of the aortic root sits over the right ventricle, but this still contributes to systemic desaturation and cyanosis.
Clinical Implications
The degree of cyanosis in TOF with pulmonary stenosis depends on the severity of the RVOTO. When the obstruction is severe, less blood reaches the lungs, resulting in more pronounced cyanosis. Conversely, if the obstruction is less severe, there may be minimal cyanosis or even a “pink” TOF variant, where the patient has relatively normal oxygen levels.
Management may include medications to manage cyanosis and surgical repair. Surgical correction typically involves closing the VSD and relieving the RVOTO, which allows for normal blood flow to the lungs and reduces right ventricular hypertrophy.
Pathophysiology of Tetralogy of Fallot (TOF)
Tetralogy of Fallot (TOF) is a complex congenital heart defect that arises due to abnormal development of the right ventricular outflow tract (RVOT) during fetal development. The primary structural problem in TOF is the underdevelopment of the right ventricular infundibulum, which is the area just below the pulmonary valve, along with the anterior and superior displacement of the outlet septum. These structural abnormalities contribute to the four characteristic features of TOF:
-
Ventricular Septal Defect (VSD):
- The VSD is typically large and located just below the aortic valve (subaortic). However, it can also be found beneath the pulmonary valve (subpulmonary). The size of the defect allows for equalization of pressures between the right and left ventricles. Therefore, both ventricles contract with the same pressure, facilitating the shunting of blood across the VSD.
-
Right Ventricular Outflow Tract Obstruction (RVOTO):
- The severity of the RVOTO directly influences the clinical presentation and degree of cyanosis. When the obstruction is severe, it limits blood flow to the lungs, leading to decreased pulmonary blood flow. This causes blood from the right ventricle to shunt right-to-left across the VSD into the systemic circulation, resulting in cyanosis. Conversely, if the obstruction is mild, there is more blood flow to the lungs, and the shunting is primarily left-to-right, leading to what is termed “pink TOF,” where the patient may not exhibit significant cyanosis.
-
Right Ventricular Hypertrophy:
- Due to the increased workload imposed on the right ventricle by the RVOTO, the right ventricular muscle thickens (hypertrophies). This adaptation is necessary for the ventricle to generate sufficient pressure to pump blood through the obstructed outflow tract to the lungs.
-
Overriding Aorta:
- The aorta is positioned directly above the VSD, receiving blood from both the left and right ventricles. This results in the mixing of oxygenated and deoxygenated blood that is then delivered to the systemic circulation, contributing to systemic hypoxemia and cyanosis.
What are the Impact of Right Ventricular Outflow Tract Obstruction
&
Complications During exertion
- The degree of RVOTO is a major factor in determining the severity of the disease:
- Severe RVOTO: This leads to significant right-to-left shunting, reduced pulmonary blood flow, and pronounced cyanosis. Patients may develop secondary effects such as erythrocytosis (increased red blood cell production) and hyperviscosity due to chronic hypoxemia.
- Mild RVOTO: In cases where the obstruction is less severe, pulmonary blood flow is adequate, and shunting may be left-to-right. These patients may exhibit a “pink TOF” phenotype with minimal or no cyanosis.
Complications During Exertion: Hypercyanotic Spells (“Tet Spells”)
- In patients with severe RVOTO, increased oxygen demand during exertion (e.g., crying, feeding, or physical activity) can trigger infundibular muscle spasm, further narrowing the right ventricular outflow tract. This exacerbates right-to-left shunting, leading to a sudden increase in cyanosis and hypoxemia, known as a “hypercyanotic spell” or “Tet spell.”
- Symptoms of a Tet spell can include intense cyanosis, shortness of breath, loss of consciousness (syncope), seizures, and in severe cases, sudden death due to extreme hypoxia.
Clinical Presentation and Diagnosis
- Age of Diagnosis: Most patients with TOF are diagnosed in infancy or early childhood due to the characteristic presentation of cyanosis. However, milder forms (such as “pink TOF”) may present later in childhood or even adulthood.
- Presentation: Patients may present with varying degrees of cyanosis depending on the severity of the RVOTO, heart murmur, or signs of heart failure.
Summary
Tetralogy of Fallot is a congenital defect characterized by a combination of structural abnormalities that affect the right ventricular outflow tract and lead to varying degrees of cyanosis. The pathophysiology revolves around the extent of right ventricular outflow tract obstruction, which influences the direction and magnitude of shunting through the ventricular septal defect. Understanding the dynamics of these changes is crucial for effective management and treatment, which often involves surgical correction to improve blood flow to the lungs and reduce cyanosis.
What are the Clinical Features of Tetralogy of Fallot (TOF)
The clinical manifestations of TOF are largely influenced by the degree of right ventricular outflow tract obstruction and the resultant cyanosis. Here’s a detailed look at the typical clinical features:
-
Dyspnea and Fatigue
- Patients commonly experience shortness of breath (dyspnea) and fatigue, which worsen with physical exertion. These symptoms occur because the body’s demand for oxygen increases during activity, but due to the obstructed blood flow, the oxygen supply is limited.
- To alleviate symptoms after exertion, patients may instinctively adopt a squatting posture. This maneuver increases systemic vascular resistance, which temporarily reduces the right-to-left shunting, thereby improving oxygenation by redirecting more blood flow to the lungs.
-
Cyanosis
- Cyanosis, a bluish discoloration of the skin and mucous membranes due to low oxygen levels in the blood, is a hallmark of TOF. It is usually evident by 6 weeks to 6 months of age. The severity of cyanosis can vary depending on the extent of the obstruction in the right ventricular outflow tract.
-
Clubbing of Fingers and Toes
- Symmetrical clubbing, characterized by the enlargement of the distal ends of the fingers and toes, is commonly observed in older children and adults with TOF. This is a response to chronic hypoxemia. However, clubbing is typically not seen in infants.
-
Growth and Developmental Delays
- Due to the chronic hypoxemia and reduced oxygen delivery to tissues, physical growth is often impaired. Developmental milestones may also be delayed compared to children without congenital heart defects.
-
Jugular Venous Pressure (JVP)
- In TOF, the jugular venous pressure is usually within normal limits, as there is no significant left-sided heart failure. However, the pulse volume tends to be low due to reduced cardiac output, and blood pressure may be normal or slightly lower than average.
-
Cardiac Examination Findings
- A midsystolic thrill may be palpable along the left sternal border, due to turbulent blood flow across the obstructed right ventricular outflow.
- A grade III or IV mid-systolic murmur, best heard over the 2nd and 3rd intercostal spaces, is often present. This murmur results from the flow of blood through the narrowed pulmonary outflow tract.
Laboratory Findings
-
Neonates:
- There is often a marked reduction in arterial oxygen saturation due to right-to-left shunting across the VSD, leading to low systemic oxygen levels. This can sometimes result in metabolic acidosis, a condition where the blood becomes more acidic due to inadequate oxygenation.
- Polycythemia (an increased number of red blood cells) is typically rare in neonates with TOF, and some may even present with anemia.
-
Older Children and Adults:
- Patients often exhibit high hematocrit levels (70-80%) and elevated hemoglobin concentrations. These findings are due to the body’s compensatory mechanism to produce more red blood cells in response to chronic low oxygen levels (hypoxia).
Summary
The clinical picture of TOF includes a combination of symptoms like dyspnea, fatigue, and cyanosis, which worsen with physical activity. Patients may adopt certain postures, such as squatting, to alleviate symptoms. Growth and developmental delays are also common. The physical examination often reveals specific heart murmurs and clubbing in older patients. Laboratory findings indicate reduced oxygen levels and increased red blood cell production, especially in older children and adults, as a response to chronic hypoxia.
What are the investigations for a Tetralogy of Fallot (TOF) patient
Evaluation of TOF includes various diagnostic tests that help assess the severity of the condition and guide surgical management. Here are the commonly used investigations and their findings:
-
Pulse Oximetry
- Pulse oximetry is a simple, non-invasive method used to measure the oxygen saturation in the blood and assess the degree of hypoxemia (low oxygen levels).
- In TOF, a resting oxygen saturation below 80% indicates severe hypoxemia, warranting prompt surgical intervention.
- Oxygen saturation can decrease even further during hypercyanotic (tet) spells, which are episodes of acute worsening of cyanosis.
-
Full Blood Count (FBC)
- FBC reveals erythrocytosis, which is characterized by a high hemoglobin level and an elevated hematocrit (HCT). This occurs as the body compensates for chronic hypoxemia by producing more red blood cells to improve oxygen transport.
- Chronic cyanosis in TOF can also cause abnormalities in platelet number and function, which may affect blood clotting.
-
Chest X-ray
- In older children and adults, the heart may appear boot-shaped due to the upward displacement of the cardiac apex caused by right ventricular hypertrophy. Additionally, the normal contour of the pulmonary artery segment may be absent.
- In neonates, the heart can appear unusually small on the chest X-ray.
- The lung fields may show signs of oligemia, which refers to reduced blood flow to the lungs, leading to a decreased pulmonary vascular pattern.
- If there is a noticeable difference between the lungs, with one appearing more vascular (plethora) than the other, this may suggest an anomalous origin of a pulmonary artery from the ascending aorta.
-
Electrocardiography (ECG)
- The ECG commonly shows signs of right ventricular hypertrophy and right axis deviation, reflecting the elevated pressure in the right ventricle due to the outflow tract obstruction.
- These findings correspond to the increased workload on the right ventricle.
-
Echocardiography
- Two-dimensional color Doppler echocardiography is a critical diagnostic tool for TOF. It helps visualize the anatomy and severity of the defects.
- It can clearly show the ventricular septal defect (VSD), overriding aorta, and the degree of right ventricular outflow tract narrowing.
- Echocardiography is usually sufficient to provide all the necessary information for preoperative planning.
-
Cardiac Catheterization
- Although echocardiography typically provides enough detail, cardiac catheterization may be performed in certain cases to obtain additional information. It can be used to:
- Detect the presence of additional muscular VSDs, which may be multiple.
- Assess the morphology of the pulmonary trunk and its branches to evaluate any abnormalities or stenosis.
- Examine the structure of the pulmonary valve, especially if there is uncertainty about the level of obstruction.
- Identify any associated cardiac abnormalities, such as abnormal coronary artery anatomy or other congenital defects that may influence surgical planning.
- Although echocardiography typically provides enough detail, cardiac catheterization may be performed in certain cases to obtain additional information. It can be used to:
Summary
The diagnostic workup for TOF includes non-invasive and invasive tests to evaluate the degree of cyanosis, cardiac structure, and pulmonary blood flow. Pulse oximetry and FBC help assess the severity of hypoxemia and blood characteristics. Chest X-rays and ECG provide insight into cardiac size and hypertrophy. Echocardiography is the cornerstone for detailed visualization of the heart’s structure, while cardiac catheterization offers additional anatomical information when needed.
What are the treatments you will recommend for TOF?
Medical & Surgical (also indications for surgery)
Treatment for Tetralogy of Fallot (TOF)
Management of TOF involves both medical and surgical approaches, aimed at relieving symptoms, preventing complications, and ultimately repairing the structural heart defects.
Medical and Interventional Management
-
Beta-Blockers for Hypercyanotic Spells
- Beta-blockade, such as propranolol (2-6 mg/kg/day), is commonly used to manage paroxysmal hypercyanotic spells, also known as “tet spells.” These are episodes where there is a sudden worsening of cyanosis due to increased right-to-left shunting across the VSD.
- Propranolol works by reducing dynamic right ventricular outflow tract obstruction, which helps alleviate the infundibular spasm (muscle contraction in the outflow tract of the right ventricle).
- It is more effective in older children than in infants.
-
Management of Established Hypercyanotic Spells
When a child experiences a hypercyanotic spell, several immediate interventions are used:-
Knee-Chest Position: Placing the infant in the knee-chest position involves holding the baby upright against the mother’s shoulder while tucking the knees under the chest. This maneuver:
- Provides a calming effect.
- Reduces systemic venous return to the heart.
- Increases systemic vascular resistance, which helps direct more blood towards the lungs.
-
Morphine Administration (0.1-0.2 mg/kg intramuscularly or subcutaneously):
- Morphine helps to reduce ventilatory drive (lower the rate of breathing), which in turn decreases systemic venous return to the heart.
-
Phenylephrine (0.02 mg/kg intravenously):
- Phenylephrine increases systemic vascular resistance, which encourages more blood flow to the lungs by decreasing the amount of right-to-left shunting.
-
Correction of Acidosis:
- Acidosis can worsen hypercyanotic spells by stimulating the respiratory center and increasing oxygen demand. It is treated with sodium bicarbonate to buffer the excess acid.
-
Knee-Chest Position: Placing the infant in the knee-chest position involves holding the baby upright against the mother’s shoulder while tucking the knees under the chest. This maneuver:
Surgical Management
Surgery is essential for all patients with TOF to correct the underlying heart defects.
-
Indications for Surgery
- Definitive repair is needed for all patients, ideally within the first year of life.
- Symptomatic infants (especially those with severe cyanosis, small pulmonary arteries, multiple VSDs, or a coronary artery crossing the right ventricular outflow tract) may require palliative surgery before undergoing the complete repair. This is to stabilize the patient and allow time for growth.
-
Types of Surgical Interventions
-
Palliative Procedures: Used when immediate complete repair is not possible. These may include:
- Blalock-Taussig shunt: A connection between a systemic artery (like the subclavian artery) and the pulmonary artery to increase blood flow to the lungs.
-
Definitive Intracardiac Repair:
- This is the surgical correction of the defects and involves:
- Closing the VSD with a patch.
- Relieving the right ventricular outflow tract obstruction (e.g., widening the pulmonary valve or infundibulum).
- Repairing any associated anomalies if present.
- This is the surgical correction of the defects and involves:
-
Palliative Procedures: Used when immediate complete repair is not possible. These may include:
Summary
TOF treatment focuses on both immediate relief from hypercyanotic spells and long-term correction of heart defects. Beta-blockers like propranolol help manage spells by reducing outflow tract obstruction, while positioning and medication such as morphine and phenylephrine are used during acute episodes. Surgical repair is crucial for long-term management, with some patients needing palliative procedures before the definitive repair.
Define Complete Transposition of the Great Arteries (CTGA)
Definition and Anatomy
Complete transposition of the great arteries (CTGA) is a serious congenital heart defect where the aorta arises from the right ventricle and the pulmonary artery arises from the left ventricle, which is the opposite of the normal heart anatomy. Normally, the pulmonary artery should carry deoxygenated blood from the right ventricle to the lungs, and the aorta should carry oxygenated blood from the left ventricle to the body. However, in CTGA:
- The pulmonary artery arises posteriorly from the left ventricle and sends oxygenated blood back to the lungs.
- The aorta arises anteriorly from the right ventricle, sending deoxygenated blood to the body.
Circulatory Consequences
In a healthy heart, the blood circulates in series:
1. Deoxygenated blood goes from the body to the lungs for oxygenation.
2. Oxygenated blood is then sent from the lungs to the body.
In CTGA, the circulation is parallel rather than in series:
- Oxygenated blood continuously cycles between the lungs and left side of the heart.
- Deoxygenated blood cycles between the body and right side of the heart.
What are the Clinical Implications and Cyanosis
Clinical Implications and Cyanosis
- Cyanosis (bluish discoloration of the skin) is typically present at birth because the systemic circulation is being supplied with deoxygenated blood.
- The severity of cyanosis depends on whether there is mixing of oxygenated and deoxygenated blood, which can occur through:
- An atrial septal defect (ASD), allowing blood to mix between the right and left atria.
- A ventricular septal defect (VSD), allowing blood to mix between the ventricles.
- A patent ductus arteriosus (PDA), which is a connection between the aorta and pulmonary artery that usually closes shortly after birth.
If ASD is restrictive or VSD is absent, minimal blood mixing occurs, leading to severe cyanosis and making the situation critical when the ductus arteriosus closes.
What are the Importance of Maintaining Ductus Arteriosus Patency
- Prostaglandin E1 (PGE1) is used to keep the ductus arteriosus open, allowing some mixing of blood between the parallel circulations. This temporary measure is essential to maintain systemic oxygenation.
Coronary Arteries and Myocardial Oxygenation
- The coronary arteries, which arise from the aorta, supply deoxygenated blood to the myocardium in CTGA. This means the heart muscle, like other tissues, suffers from severe hypoxia, affecting its function and potentially leading to heart failure.
Prognosis
- Systemic hypoxia is usually profound, and without prompt intervention, most affected infants do not survive beyond three months.
- The prognosis is especially poor in regions with limited access to neonatal care, where timely medical and surgical interventions may not be available.
Summary
CTGA is a critical congenital heart condition requiring urgent intervention. Survival depends on maintaining blood mixing through congenital heart defects or a patent ductus arteriosus. Prompt administration of PGE1 to keep the ductus open and surgical correction are often needed to manage this life-threatening anomaly.
What are the Clinical Features of Complete Transposition of the Great Arteries (CTGA)
-
Cyanosis
- Cyanosis is present at birth due to the circulation of deoxygenated blood in the systemic system. The severity of cyanosis can worsen with age as the mixing of blood becomes inadequate or as the ductus arteriosus closes.
-
Anoxic Spells
- Episodes of severe oxygen deprivation, known as anoxic spells, may occur. These spells are marked by rapid breathing (tachypnea) and deepening cyanosis, indicating significant hypoxemia.
-
Growth and Development Impairment
- Children with CTGA often experience delays in physical growth and development due to chronic hypoxia and poor oxygen delivery to tissues.
-
Recurrent Respiratory Infections
- Frequent respiratory infections are common and can worsen the patient’s condition, potentially leading to heart failure. Once heart failure develops, it may progressively deteriorate.
-
Heart Murmurs
- On auscultation, various systolic murmurs may be heard. These murmurs can be associated with additional congenital shunts, such as VSDs or ASDs, which allow for blood mixing.
-
Clubbing and Polycythemia
- Clubbing of the fingers and toes, as well as polycythemia (increased red blood cell count), are common in older patients. These changes occur as the body tries to compensate for chronic low oxygen levels by producing more red blood cells.
What investigations for CTGA would you do?
-
Chest X-rays
- Chest X-ray findings typically show an enlarged cardiac shadow due to the dilation of all four heart chambers. The cardiac silhouette in CTGA is often described as having an “egg-shaped” appearance due to the abnormal position of the great vessels.
-
Electrocardiography (ECG)
- ECG findings can vary, but they generally reveal enlargement of the right atrium and right ventricle, reflecting the high pressures on the right side of the heart.
-
Echocardiography
- Two-dimensional color Doppler echocardiography is the key diagnostic tool for CTGA. It visualizes the anatomy of the great arteries, ventricular septal defects, and any associated shunts. Echocardiography typically provides enough information for diagnosis and surgical planning.
-
Cardiac Catheterization
- Although not always necessary, cardiac catheterization can be performed to further evaluate the anatomy. This test is particularly important for assessing the coronary artery anatomy, which can have significant variations in TGA. Understanding these variations is crucial when planning an arterial switch operation (Jatene’s Operation), which involves reconnecting the great arteries to their correct ventricles.
Summary
The clinical features of CTGA primarily result from severe systemic hypoxia due to parallel circulation, with signs such as cyanosis, growth delay, and anoxic spells. Investigations like chest X-ray, ECG, and echocardiography are critical for diagnosis, while cardiac catheterization is important for preoperative planning, especially in understanding coronary artery anatomy.
Indications for Surgery in Complete Transposition of the Great Arteries (CTGA)
Most infants with CTGA experience severe cyanosis at birth, necessitating surgical intervention to correct the circulation. Surgical procedures for CTGA can be classified as palliative or definitive, aimed at redirecting blood flow to establish a more normal circulatory pattern. The surgical approaches can be divided into two main types:
-
Physiological Correction at the Atrial Level
- Atrial-level repairs, such as the Mustard or Senning operations, are designed to redirect systemic and pulmonary venous blood flows to facilitate better oxygenation. These procedures involve the use of a cardiopulmonary bypass to reroute the flow of blood at the level of the atria.
- In these surgeries, the systemic venous return (blood coming from the body) is directed into the left ventricle, while pulmonary venous return (blood coming from the lungs) is channeled to the right ventricle. This rerouting allows oxygenated blood to be pumped to the body, despite the anatomical abnormality.
-
Mustard Operation:
- In this procedure, the atrial septum (wall between the atria) is removed, and a patch made of autologous pericardium (patient’s own tissue) or another suitable material is used to create a pathway (baffle) that directs caval venous blood across the mitral valve into the left ventricle, and pulmonary venous blood across the tricuspid valve into the right ventricle.
-
Senning Operation:
- Unlike the Mustard procedure, the Senning operation uses as much of the patient’s native heart tissue as possible to create the baffle. In both operations, the right ventricle remains the systemic ventricle, meaning it continues to pump blood to the body.
-
Limitations of Atrial-Level Repairs:
- Although effective, the long-term outlook for these operations is limited because the right ventricle, which was originally designed to handle low-pressure pulmonary circulation, is now supporting the high-pressure systemic circulation.
- Anatomic Correction: Arterial Switch Operation
- Anatomic correction involves an arterial switch operation, which is considered a more definitive approach. In this surgery, the aorta and pulmonary artery are transected (cut and repositioned) to re-establish normal anatomical relationships.
-
Steps of the Arterial Switch Operation:
- Cardiopulmonary bypass is utilized during the procedure.
- The aorta and pulmonary artery are cut and repositioned.
- The coronary arteries are carefully harvested as buttons from the original aortic sinuses and are transferred to their corresponding locations on the newly positioned pulmonary root.
- Any defects in the aortic sinuses left after the transfer are repaired using pericardial patches.
- The aorta is then reconnected to the pulmonary artery root, and the pulmonary trunk is reattached to the aortic root.
-
Advantages of the Arterial Switch Operation:
- This procedure allows the left ventricle to function as the systemic ventricle, which is its natural role in normal circulation. As a result, the long-term prognosis is superior compared to atrial-level repairs.
- By restoring the normal circulatory pattern, this surgery ensures that oxygen-rich blood is delivered to the body and oxygen-poor blood is sent to the lungs.
-
Timing Considerations:
- The arterial switch operation is most effective when performed during the neonatal period or shortly afterward. This timing is crucial to ensure that the left ventricle retains its capacity to support the systemic circulation, as a delay could cause the left ventricle to weaken and lose its ability to handle systemic pressure.
Summary
Surgical intervention for CTGA is essential due to the severe cyanosis and risk of early mortality. The choice of surgery depends on several factors, including the patient’s age and the presence of associated defects. Atrial-level corrections (Mustard or Senning) reroute blood flow but leave the right ventricle as the systemic pump, while the arterial switch operation (anatomic correction) repositions the great arteries, allowing the left ventricle to function as the systemic ventricle, providing a better long-term prognosis. Timing is critical for the arterial switch to be successful, ideally occurring soon after birth.
