Definition

  • One-third have Down’s syndrome. One-third of Down’s syndrome have AVCD.
  • 10% recurrence rate in first degree relatives – higher than for other congenital heart diseases.
  • 14% recurrence rate in offspring- higher than for other congenital heart diseases- half have AVCD while half have TOF.
  • No sex predilection

Embryology

  • Lack of fusion of superior and inferior endocardial cushions

Pathology

  • Both AV valves are at same level.
  • Lack of atrioventricular septum.
  • Annulus of AV valves is convex towards apex.
  • LVOT is anteriorly displaced.
  • Common AV valve has five leaflets-
    • Superior bridging
    • Inferior bridging
    • Right anterosuperior
    • Right inferior
    • Left mural
  • When there is a connecting tongue, the left sided gap between superior and inferior bridging leaflet appears as the mitral cleft which is directed towards the IVS.
  • Ostium primum ASD in the lower anterior part of IAS.
  • Inferior bridging leaflet is often attached to IVS. Superior bridging leaflet is often not attached to the IVS and this produces the VSD which is of inlet type.
  • Distance from LV apex to aortic valve is more than that from LV apex to mitral valve.
  • Rastelli classification-
    • Type A- SBL is attached to the crest of the IVS. Small inlet VSD which does not extend to aortic cusps. Association with Down’s syndrome.
    • Type B- SBL is attached to an RV papillary muscle at the RV side of IVS. The VSD extends to the aortic cusps.
    • Type C- SBL is attached to an RV papillary muscle which is present at the apex of the RV. Association with other congenital heart diseases like TOF and DORV.
  • Inlet VSD can occur in AVCD without primum ASD.
  • Unbalanced AVCD- one ventricle receives most of the common AV valve, the other one is hypoplastic. This is rare in Down’s syndrome.
  • LVOT is narrowed, but not commonly obstructed.
  • The AV node is displaced inferiorly to near the crux.

Associated anomalies

  • LSVC to LA
  • CS ASD
  • PS or TOF
  • DORV (this combination suggests situs ambiguous)
  • Double inlet ventricles

Hemodynamics

  • Partial AVCD- In ostium primum ASD, if MR is absent, the hemodynamics resembles a large secundum ASD while if MR is present, the left to right shunt is increased. Even primum ASD without MR becomes symptomatic in infancy due to large flow.
  • Complete AVCD- Both the VSD and the MR produces LV volume overload. Thus, heart failure occurs early. Complete AVCD becomes symptomatic earlier than a large VSD.
  • Down’s syndrome- Earlier onset of PVOD.

Clinical features-

  • See hemodynamics

Radiography-

  • See hemodynamics

ECG-

  • Left axis deviation
  • Counterclockwise depolarization- as initial left to right septal depolarization does not occur
  • Prolonged PR interval in about half cases- due to prolonged atrial conduction rather than AV block
  • RAE in primum ASD, BAE in complete AVCD. In primum ASD with MR, the MR jet is directed towards RA producing RAE rather than LAE
  • RVH in primum ASD and BVH in complete AVCD.

Echo-

  • See pathology and hemodynamics

Cardiac catheterization-

  • LV angiogram shows goose neck deformity of LVOT.

Surgery-

  • Usually done at 2 to 4 months. Refractory heart failure may necessitate an earlier surgery.