• In partial AVSD, there are distinct mitral and tricuspid annuli. In complete AVSD, there is a common AV valve with a single annulus.
  • Transitional AVSD is a partial AVSD with a small VSD.
  • Intermediate AVSD is a complete AVSD with separate mitral and tricuspid orifices due to a connecting tongue.


  • Slight female preponderance.
  • Down syndrome- 40% have congenital heart disease of which 40% is AVSD, usually complete.
  • Heterotaxy especially asplenia.


  • Incomplete fusion between superior and inferior endocardial cushions.
  • Cleft in midportion of AML causes MR.
  • Mitral and tricuspid valves are at the same level because AML is displaced apically by the primum ASD.
  • Distance between apex and aortic valve is more than that from apex to crux causing LVOT to be long and narrow – called gooseneck deformity- and predisposing to subaortic stenosis.
  • The common AV valve may be disproportionately connected to one ventricle.

Partial AV septal defect


  • Most frequent form is a large primum ASD with cleft AML.
  • Primum ASD is anteroinferior to fossa ovalis and extends to the AV valves.
  • Inlet ventricular septum has scooped-out appearance.
  • AML cleft is directed towards IVS (isolated clefts are directed towards aortic annulus).
  • Mitral orifice is triangular (normally it is elliptical).
  • Commonest associations are secundum ASD and LSVC.

Clinical features

  • Unlike usual ASDs, symptoms of increased pulmonary blood flow and growth failure in childhood. These are more likely if there is MR.
  • Examination findings of a typical ASD + PSM at apex.


  • In transitional AVSD, an aneurismal part of IVS, called a tricuspid pouch, prevents significant ventricular shunting through the VSD.
  • Aortic valve is displaced anteriorly as it is now not wedged between mitral and tricuspid annuli.
  • LVOT obstruction may develop after repair of AVSD.


  • Cardiomegaly and prominent pulmonary vasculature.
  • RA may be enlarged instead of LA if MR is directed to RA.


  • PR interval is prolonged in half of cases; due to increased intra-atrial conduction time.
  • QRS axis from -30 to -120 degrees.
  • RAE, LAE or BAE.
  • RVH. LVH if MR.


  • Qp/Qs is often more than 1.5.
  • Gooseneck deformity of LVOT.