- Atrioventricular septal defects (AVSDs): a spectrum of congenital cardiac malformations involving the atrioventricular septum and atrioventricular valves
- Atrioventricular septum: a layer of tissue that separates the atria from the ventricles, composed of cardiac tissues
- Atrioventricular valves (AVVs): mitral and tricuspid valves
- Atrioventricular valve annulus: fibrous ring to which valve leaflets attach
- Ostium primum: a kind of atrial septal defect located near the AVVs
Classification of AVSD is based on anatomy of defect:
- Partial: atrial septal defect (ASD) + single AVV annulus with separate tricuspid/mitral valve openings
- Complete: ASD + VSD + single/fused mitral and tricuspid annulus and openings
- Intermediate or transitional: ASD + small VSD + usually a single mitral and tricuspid annulus
- Unbalanced: hypoplasia of 1 ventricle + single/fused mitral and tricuspid annulus opening mainly into the other ventricle
- 5%–8% of all congenital heart defects
- Prevalence: 1 out of 3,000–4,000 live births
- Strong association with Down’s syndrome, especially the complete type
- Normally, endocardial cushions close off atrial and ventricular septa during fetal cardiac development.
- Underlying genetic defects → abnormal development of endocardial cushions → AVSD
- ASD in AVSD involves most inferior part of atrial septum (ostium primum defect).
Symptoms of AVSD (cyanosis, heart failure, and pulmonary hypertension) are due to excessive blood flow in the pulmonary system.
- Left-to-right shunt through ostium primum defect (usually significant) + regurgitation through mitral and/or tricuspid valve defects (usually moderate) + minimal to no pulmonary vascular resistance
- With large defects, mixing of right and left atrial blood causes cyanosis.
- Usually, symptoms are not evident until adulthood because of the low pulmonary pressure.
- Gerbode defect: Mitral regurgitation often occurs through the mitral valve cleft directly into the right atrium (RA), causing RA enlargement.
- Significant left-to-right shunt through both atrial and ventricular septal defects
- Some degree of right-to-left shunt with larger defects
- Significant AVV regurgitation with development of congestive heart failure
- Progressive pulmonary vascular disease and higher pulmonary vascular resistance (PVR)
- Symptoms arise within the 1st year of life.
- Eisenmenger physiology: Gradual increase in right-to-left shunt causes central cyanosis.
- Mild shunt with minimal AVV regurgitation: asymptomatic; discovered during a general physical exam later in life
- Large shunt and severe AVV regurgitation:
- History of exercise intolerance, easy fatigability, and/or recurrent pneumonia
- Physical examination:
- Moderate to severe cardiac enlargement
- Hyperdynamic precordium
- Accentuated 1st heart sound, wide-fixed splitting of 2nd heart sound, a pulmonary systolic ejection murmur, mid-diastolic rumble at lower left sternal border due to increased flow through the AVVs, and an apical holosystolic murmur radiating to the axilla due to mitral regurgitation
- Usually presents during infancy with failure to thrive and history of recurrent pneumonia
- Physical examination:
- Cardiac and liver enlargement, a precordial bulge, and a palpable systolic thrill at lower left sternal border
- Heart sounds are similar to those in severe forms of partial AVSD.
- Milder cases may occasionally present with cyanosis later during childhood or adolescence.
Severe partial or complete atherosclerotic cardiovascular disease (ASCVD): large cardiac silhouette with a prominent pulmonary artery arch and increased pulmonary vascularity
Significant changes seen with complete ASCVD:
- Left axis deviation (negative QRS complex in inferior leads) or superior axis deviation (negative QRS complex in inferior leads plus Q waves in I and aVL)
- Biventricular or isolated right ventricular hypertrophy
- Right ventricular conduction delay
- Tall P waves
- Prolongation of PR interval
- Confirms the diagnosis: performed either prenatally or soon after birth
- RV enlargement
- Abnormally low AVVs with “gooseneck” deformity of LV outflow tract
- Tricuspid valve is at same level as mitral valve instead of normal, more apical insertion.
- A VSD and a single AVV is seen in complete AVSD.
- Doppler: used to detect blood flow in the defect
- Left-to-right shunt at atrial, ventricular, and/or LV-to-right atrial levels
- Degree of AV regurgitation
- May show associated anomalies such as patent ductus arteriosus or coarctation of aorta
Surgery is performed through a right atrial incision and is highly successful.
- Surgery is more complicated, but still highly successful.
- Must be performed early (during infancy) due to higher risk of pulmonary hypertension with delayed surgery
- Heart block
- Narrowed LV outflow tract
- Residual AVV regurgitation
- Most patients with mild partial AVSD are asymptomatic and only develop symptoms in the 3rd or 4th decade of life.
- Complete AVSD has a high mortality rate during infancy without corrective surgery.
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