Overview
Definitions
- 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
Complete atrioventricular septal defect: Notice the simultaneous flow of blood from the left atrium and ventricle to their right counterparts.
Image by Lecturio.Classification
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
Forms of atrioventricular septal defect
Image by Lecturio.Epidemiology
- 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
Etiology
- 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).
Pathophysiology
Symptoms of AVSD (cyanosis, heart failure, and pulmonary hypertension) are due to excessive blood flow in the pulmonary system.
Partial AVSD
- 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.
Complete AVSD
- 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.
Anatomy of the atrioventricular septation complex in a human 4-chambered heart with normal anatomy and in hearts with AVSDs.
Image: “Anatomy of the atrioventricular septation complex” by US National Library of Medicine. License: CC BY 4.0
(A) shows a properly septated heart with a complete atrial and ventricular septum;
(B) depicts a heart with an incomplete AVSD; and in
(C) a heart with a complete AVSD is shown.
Note that when a primary atrial septal defect is observed, the muscular rim at the base of the atrial septum is missing.
IVS = interventricular septum,
pAS = primary atrial septum,
pASD = primary atrial septal defect,
LA = left atrium,
LV = left ventricle,
RA = right atrium,
RV = right ventricle,
VSD = ventricular septal defect.
Clinical Presentation
Partial AVSD
- 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
Complete AVSD
- 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.
Diagnosis
Chest X-ray
Severe partial or complete atherosclerotic cardiovascular disease (ASCVD): large cardiac silhouette with a prominent pulmonary artery arch and increased pulmonary vascularity
Electrocardiogram
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
Echocardiography
- Confirms the diagnosis: performed either prenatally or soon after birth
- Findings:
- 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
An apical 4-chamber 3-D echocardiogram in a patient with AVSD. Arrowheads mark the hinges of the common atrioventricular junction. The bridging leaflets divide the defect into an interatrial (ASD) and interventricular (VSD) component. Note the posterior location of the inferior vena caval orifice (IVC) relative to the septal structures. L, left; S, superior.
Image: “Three dimensional echocardiography in congenital heart defects” by Department of Pediatrics, Medical University of South Carolina, USA. License: CC BY 2.0
Atrioventricular septal defect with 2 separate atrioventricular valves.
Image: “Understanding atrioventricular septal defect” by Echocardiography in Out Patients Clinic, Instituto Nacional de Cardiología Ignacio Chávez, Juan Badiano N degrees 1, Colonia Sección XVI, Mexico City, Mexico. License: CC BY 2.0
(A): Internal view of right chambers, left (1) and right (2) atrioventricular valves, ostium primum (asterisk), and arrow pointing to the insertion of the septal leaflets of the left valve in the crest of the interventricular septum. Note the confluence of the ostium primum with the atrioventricular septal defect (upper asterisk), the commissure that separates those leaflets, the ample commissure between the septal leaflets, and the anterior leaflet of the right atrioventricular valve (lower asterisk).
(B): The 2 separate atrioventricular valves (1 and 2) and the fusion of the septal leaflets to the crest of the interventricular septum that closes the ventricular septal defect (arrow) can be seen. IAS: interatrial septum.
Management
Partial AVSD
Surgery is performed through a right atrial incision and is highly successful.
Complete AVSD
- Surgery is more complicated, but still highly successful.
- Must be performed early (during infancy) due to higher risk of pulmonary hypertension with delayed surgery
Surgical complications
- Heart block
- Narrowed LV outflow tract
- Residual AVV regurgitation
Prognosis
- 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.
References
- Yue, E. L., & Meckler, G. D. (2020). Congenital and acquired pediatric heart disease. In J. E. Tintinalli, O. J. Ma, D. M. Yealy, G. D. Meckler, J. S. Stapczynski, D. M. Cline & S. H. Thomas (Eds.), Tintinalli’s emergency medicine: A comprehensive study guide, 9e (). New York, NY: McGraw-Hill Education. accessmedicine.mhmedical.com/content.aspx?aid=1166594605
- Cunningham, F. G., Leveno, K. J., Bloom, S. L., Dashe, J. S., Hoffman, B. L., Casey, B. M., & Spong, C. Y. (2018). Fetal imaging. Williams Obstetrics. New York, NY: McGraw-Hill Education. accessmedicine.mhmedical.com/content.aspx?aid=1160773294
- Kliegman, R. M., M.D., St Geme, Joseph W., MD, Blum, N. J., M.D., Shah, Samir S., M.D., M.S.C.E., Tasker, Robert C., M.B.B.S., M.D., & Wilson, Karen M., M.D., M.P.H. (2020). Acyanotic congenital heart disease: Left-to-right shunt lesions. In R. M. Kliegman MD et al. Nelson textbook of pediatrics. https://www.clinicalkey.es/#!/content/3-s2.0-B9780323529501004533
- Park, Myung K., MD, F.A.A.P., F.A.C.C. (2015). Fisiopatología de las lesiones con cortocircuito izquierda-derecha. In Park, Myung K., MD, FAAP, FACC (Ed.), Cardiología pediátrica. https://www.clinicalkey.es/#!/content/3-s2.0-B9788490228333000096
- Davidson, M. A., M.D. (2008). Primary care for children and adolescents with down syndrome. Pediatric Clinics of North America, 55(5), 1099-1111. DOI:http://dx.doi.org/10.1016/j.pcl.2008.07.001
