Overview
Definition:
An atrioventricular septal defect (AVSD), also known as an atrioventricular canal defect (AVC) or endocardial cushion defect, is a congenital heart anomaly characterized by a deficiency in the atrial septum, ventricular septum, and the endocardial cushions
This results in a spectrum of defects, ranging from a partial AVSD (ostium primum atrial septal defect with mitral valve cleft) to a complete AVSD (a large central defect involving both atria and ventricles with a common AV valve)
Complete AVSD is the most common congenital heart defect seen in individuals with Down syndrome (Trisomy 21).
Epidemiology:
Approximately 40-50% of infants with Down syndrome have congenital heart disease, and AVSD accounts for 20-30% of these cardiac anomalies, making it the most frequent heart defect in this population
The incidence of complete AVSD in the general population is about 1 in 2,300 live births
In children with Down syndrome, the prevalence is significantly higher, estimated at 1 in 100 to 1 in 200 live births.
Clinical Significance:
AVSD in Down syndrome is clinically significant due to its high prevalence and the potential for severe hemodynamic consequences if left untreated
The defect leads to significant left-to-right shunting at both atrial and ventricular levels, resulting in volume overload of the pulmonary circulation and both ventricles
This can progress to pulmonary hypertension, Eisenmenger syndrome, and ultimately, heart failure
Early diagnosis and appropriate timing of surgical intervention are crucial for improving long-term outcomes and preventing irreversible pulmonary vascular disease.
Clinical Presentation
Symptoms:
Symptoms often present in infancy and are related to congestive heart failure
Tachypnea
Poor feeding
Failure to thrive
Recurrent respiratory infections
Sweating with exertion
Cyanosis is usually absent in complete AVSD unless pulmonary hypertension develops.
Signs:
A loud, single second heart sound (S2) due to pulmonary hypertension
A systolic ejection murmur at the left upper sternal border (pulmonary flow murmur)
A holosystolic murmur best heard at the apex or lower left sternal border (mitral or tricuspid regurgitation)
A mid-diastolic rumble at the lower left sternal border (increased flow across AV valves)
Signs of heart failure such as hepatomegaly, peripheral edema, and crackles in the lungs may be present.
Diagnostic Criteria:
Diagnosis is primarily based on echocardiography, which provides detailed anatomical and functional assessment of the AVSD
Cardiac catheterization may be used in complex cases or when there is suspicion of significant pulmonary hypertension
Clinical suspicion is high in all infants with Down syndrome, given the high association.
Diagnostic Approach
History Taking:
Focus on gestational age at birth, maternal health during pregnancy, and any prenatal diagnoses
Inquire about the infant's feeding patterns, weight gain, respiratory status (frequency of colds, difficulty breathing), and activity tolerance
Family history of congenital heart disease is important
History of chromosomal abnormalities or dysmorphic features suggestive of Down syndrome is critical.
Physical Examination:
Perform a thorough cardiovascular examination, including inspection for cyanosis, palpation for thrills, and auscultation for murmurs, gallops, and heart sounds
Assess for signs of respiratory distress and volume overload (e.g., hepatomegaly, edema)
Assess for dysmorphic features characteristic of Down syndrome.
Investigations:
Transthoracic echocardiography is the gold standard for diagnosis and evaluation, demonstrating the size and type of AVSD, valve morphology (mitral and tricuspid), presence and severity of regurgitation, and ventricular size and function
Electrocardiogram (ECG) may show evidence of biventricular hypertrophy and right atrial enlargement
Chest X-ray can reveal cardiomegaly and pulmonary venous congestion
Cardiac catheterization is reserved for select cases to precisely measure pressures and assess pulmonary vascular resistance
Genetic testing for Trisomy 21 should be performed if Down syndrome is suspected clinically.
Differential Diagnosis:
Other types of congenital heart defects that can cause heart failure in infancy, such as ventricular septal defect (VSD), atrial septal defect (ASD), patent ductus arteriosus (PDA), and atrioventricular re-entry tachycardia (AVRT)
Differentiating between partial and complete AVSD is crucial
The presence of significant tricuspid regurgitation or a cleft mitral valve can sometimes mimic other valvular abnormalities.
Management
Initial Management:
Medical management focuses on stabilizing the infant and managing heart failure symptoms
Diuretics (e.g., furosemide) to reduce fluid overload
Digoxin for inotropic support
Nutritional support with high-calorie formula to optimize growth
Prophylaxis against respiratory infections with vaccinations and prompt treatment of any respiratory illness.
Medical Management:
Aggressive management of congestive heart failure is paramount
Diuretics are typically started at birth or shortly thereafter
Digoxin may be used for symptoms of poor cardiac output
Careful monitoring of fluid balance, weight, and urine output is essential
Prophylactic antibiotics for recurrent respiratory infections may be considered.
Surgical Management:
Surgical repair is the definitive treatment for AVSD
The timing of repair is controversial and depends on several factors, including the degree of left-to-right shunting, pulmonary artery pressure, growth of the child, and the presence of other associated anomalies
Generally, repair is recommended when pulmonary to systemic blood flow ratio (Qp:Qs) is greater than 1.5:1 or when the child develops symptoms of heart failure
In complete AVSD, repair is often performed between 4 and 6 months of age
In children with Down syndrome, some centers advocate for earlier repair (as early as 3 months) if significant symptoms are present or if pulmonary hypertension is developing rapidly, to prevent irreversible pulmonary vascular changes
Complete AVSD repair involves closure of the atrial and ventricular septal defects and reconstruction of the common AV valve
This is typically done using a synthetic patch for septal closure and prosthetic material for valve repair or replacement.
Supportive Care:
Comprehensive supportive care includes vigilant monitoring of vital signs, cardiac function, and respiratory status
Nutritional counseling and support are crucial for adequate weight gain
Parents require significant education regarding the child's condition, management plan, and signs of worsening heart failure
Psychological support for the family is also important, given the implications of Down syndrome.
Complications
Early Complications:
Arrhythmias (supraventricular tachycardia, heart block)
Residual or recurrent AV valve regurgitation (mitral or tricuspid)
Bleeding
Sternal wound infection
Neurological complications
Pulmonary hypertension.
Late Complications:
Progressive AV valve dysfunction requiring reoperation
Residual or recurrent shunt
Pulmonary vascular obstructive disease
Growth and developmental delay
Late arrhythmias
Extracardiac malformations related to Down syndrome.
Prevention Strategies:
Meticulous surgical technique to minimize valve injury and ensure complete septal closure
Careful anesthetic management
Postoperative hemodynamic monitoring and management of fluid balance
Judicious use of inotropic support and vasodilators
Prompt treatment of infections and arrhythmias
Regular echocardiographic follow-up to assess valve function and detect residual shunts.
Prognosis
Factors Affecting Prognosis:
The presence and severity of associated extracardiac anomalies
The degree of pulmonary hypertension preoperatively
The success of surgical repair, particularly AV valve function
The overall health and chromosomal status of the child
The presence of significant residual shunt or regurgitation post-repair.
Outcomes:
With timely and successful surgical repair, the prognosis for AVSD in Down syndrome is generally good
Most children achieve a functional cure and have a normal or near-normal life expectancy
However, long-term follow-up is essential due to the potential for late complications
Children with complete AVSD and Down syndrome may have a slightly higher risk of mortality and morbidity compared to those without Down syndrome, particularly if repair is delayed or if there are significant associated anomalies.
Follow Up:
Lifelong cardiac follow-up is recommended
This includes regular clinical assessments and serial echocardiography to monitor AV valve function, detect residual shunts or regurgitation, and assess for pulmonary hypertension
Older children and adults should also be monitored for potential late complications such as arrhythmias or valve deterioration
Genetic counseling and support should be available for the family.
Key Points
Exam Focus:
Complete AVSD is the most common congenital heart defect in Down syndrome
Early diagnosis and surgical repair are critical to prevent pulmonary hypertension
Timing of repair is between 4-6 months for Qp:Qs > 1.5:1 or symptomatic heart failure, but may be earlier in Down syndrome if rapid progression of pulmonary hypertension is observed
Postoperative AV valve regurgitation is a significant concern.
Clinical Pearls:
Always consider AVSD in an infant with Down syndrome presenting with failure to thrive or respiratory distress
Early echocardiographic evaluation is paramount
Multidisciplinary team approach involving pediatric cardiologists, cardiac surgeons, geneticists, and nurses is essential for optimal management.
Common Mistakes:
Delaying surgical repair in symptomatic infants with Down syndrome leading to irreversible pulmonary vascular disease
Underestimating the severity of AV valve regurgitation
Inadequate postoperative monitoring for residual shunts or arrhythmias.