1. Clarifying the Surgical Morphology of Inlet Ventricular Septal Defects
Diane E. Spicer, BS, Robert H. Anderson, MD, Carl L. Backer, MD 
The Annals of Thoracic Surgery 
Volume 95, Issue 1, Pages (January 2013)
DOI: /j.athoracsur
Copyright © 2013 The Society of Thoracic Surgeons Terms and Conditions

2. Fig 1
(A) The heart shown, with a perimembranous ventricular septal defect, has been opened through the left ventricle. It is the presence of fibrous continuity between the leaflets of the aortic and tricuspid valves that defines the defect as being perimembranous. Note the remnant of the membranous septum, forming the membranous flap, and the location of the atrioventricular conduction axis (dotted line). When viewed from the right ventricle, however, it can be seen that, depending on the deficiency of the septal musculature making up the margins of the holes, the defects can open predominantly to (B) the outlet or to (C) the inlet of the right ventricle. In B, we show the right ventricular view of the defect illustrated in A. The oval shape shows the location of the atrioventricular node, at the apex of the triangle of Koch. The conduction axis runs posteroinferiorly relative to the defect, which in this heart opens mostly to the outlet of the right ventricle. A similar defect is shown in C, but one that opens mostly to the inlet of the right ventricle. The apex of the triangle of Koch along with the atrioventricular node, are deviated inferiorly, but the conduction axis still runs posteroinferiorly relative to the defect itself. This axis is positioned to the right hand of the surgeon operating through the tricuspid valve.
The Annals of Thoracic Surgery  , DOI: ( /j.athoracsur )
Copyright © 2013 The Society of Thoracic Surgeons Terms and Conditions

3. Fig 2
(A, B) The images show two hearts with muscular defects opening to the inlet of the right ventricle. The defect shown in A is closer to the atrioventricular (AV) junction, but in both, because of the integrity of the muscular septum relative to the membranous septum, the AV conduction axis, shown by the oval shape and the black dotted line, runs anterocephalad relative to the defects. In this case, the AV conduction axis runs to the left hand of the surgeon operating through the tricuspid valve.
The Annals of Thoracic Surgery  , DOI: ( /j.athoracsur )
Copyright © 2013 The Society of Thoracic Surgeons Terms and Conditions

4. Fig 3
This drawing shows the view obtained by the surgeon working through the tricuspid valve. It illustrates the fundamental difference in the location of the atrioventricular conduction axis when ventricular septal defects opening to the inlet of the right ventricle are perimembranous as opposed to muscular.
The Annals of Thoracic Surgery  , DOI: ( /j.athoracsur )
Copyright © 2013 The Society of Thoracic Surgeons Terms and Conditions

5. Fig 4
The images show two of the hearts with straddling and overriding of the tricuspid valve, with (A) showing the view from the right and (B) showing the view from the left ventricle. Note that the malaligned ventricular septum runs along the full width of the overriding orifice of the tricuspid valve. As shown in A, the regular atrioventricular node, at the apex of the triangle of Koch (oval shape), is unable to make contact with the atrioventricular conduction axis (black dotted line). The axis arises from an anomalous posteroinferior atrioventricular node (second oval shape). As shown in B, the valve opening to the left ventricle from the left atrium is morphologically mitral, and the aorta is deeply wedged between the mitral valve and the overriding component of the tricuspid valve. This patient has two separate atrioventricular junctions and clear straddling of the tricuspid valve (TV) into the left ventricle. (VSD = ventricular septal defects.)
The Annals of Thoracic Surgery  , DOI: ( /j.athoracsur )
Copyright © 2013 The Society of Thoracic Surgeons Terms and Conditions

6. Fig 5
The images show the salient feature of hearts having an atrioventricular (AV) septal defect, but with shunting confined at the ventricular level. (A) The view through the opened right atrium is shown. Note that the leading edge of the atrial septum extends to the level of the AV junction, with bridging leaflets seemingly disappearing from the right ventricle. They would appose the septum during ventricular systole, confining shunting at the ventricular level. The star shows the anticipated location of the AV node. It is located within an inferior nodal triangle, rather than at the apex of the triangle of Koch. (B) As expected, and as shown by the view from the left ventricle, the left AV valve is trifoliate, with the zone of apposition between the left ventricular components of the bridging leaflets pointing toward the ventricular septum.
The Annals of Thoracic Surgery  , DOI: ( /j.athoracsur )
Copyright © 2013 The Society of Thoracic Surgeons Terms and Conditions