7.2 Complete Atrioventricular Septal Defect (Complete Atrioventricular Canal)
Atrioventricular septal defects are also known as AV canal defects or endocardial cushion defects . They constitute a wide spectrum and variety of anatomic substrates. The principal anatomic feature of this group of hearts is a common AV junction. There is a large VSD beneath the plane of the AV valves, and an ASD immediately superior to the plane of the AV valves. The valve anatomy is also abnormal. Instead of two AV valve orifices, a single or common AV valve orifice straddles the ventricular septum. There can be varying degrees of incomplete development of the septal tissue surrounding the AV valve, along with varying degrees of abnormalities of the AV valves themselves, leading to the broad classification of partial, intermediate, and complete AV canal defects. The partial type has been discussed above. The intermediate type of AV canal defect is characterized by fibrous fusion in the central portion of the common AV valve, with varying sizes of the VSD. In general, the VSD is small in the adult and often can be closed by direct suture technique, without a VSD patch. (This procedure is not illustrated.) The technique is similar to the modified single-patch technique as described by Nunn, which is shown later in this chapter.
Repair of complete AVSD has undergone a number of changes over the years, starting with the descriptions by Lillehei and Wilcox, who favored direct attachment of the common AV valves to the crest of the ventricular septum, thereby obliterating the VSD space without any patch material. This technique was temporarily abandoned in favor of the one-patch technique, which used a pericardial or Dacron patch to close the VSD and the ASD. The common AV valve leaflets were attached to the patch in such a way as to divide the right and left AV valve components and form the respective functioning valves. Many surgeons replaced this technique because of the difficulty in attaching the common leaflets to the AV patch, which was occasionally attended by valve disruption and residual VSDs.
A two-patch technique was introduced, whereby the VSD was closed with a patch and the left and right AV valves were divided into their right and left components by attaching them to the superior portion of the VSD patch. These sutures were anchored in place by a pericardial patch placed from above, which served as a large pledget and eventually would be used to close the primum ASD. The two-patch technique was used extensively until Nunn and associates reintroduced a modified single-patch technique that featured the direct attachment of the common AV v alves to the crest of the ventricular septum, thereby obliterating the VSD space without any patch material, and closure of the ASD with the pericardial patch that was used to bolster the VSD repair.
Adults with a primary diagnosis of complete AVSD usually have an antecedent history of operative repair during infancy or childhood (that may have been preceded by a pulmonary artery band). They come to the surgeon’s attention when important right and/or left AV valve regurgitation occurs, when there are residual ASDs or VSDs, when there is heart block or arrhythmias, or when there is LVOT obstruction or pulmonary hypertension. It is important to be familiar with all of the operations for primary repair of complete AVSD to accurately plan any subsequent reparative operation. Knowing whether a patch was used for the VSD closure and knowing the type of valvar repair and ASD closure technique can help the surgeon when a patient presents with subsequent LVOT obstruction, valvar regurgitation, or residual shunts. The following sections review the initial repairs performed in patients with AVSD and what the surgeon will encounter during a future reoperation.
7.2.1 One-Patch Technique
Failure of this operation is usually owing to disruption of the AV valve attachments to the common patch, resulting in valve regurgitation and a residual VSD. Understanding the extant anatomy and the method of repair arms the adult congenital heart surgeon, who must be aware of the mechanisms of failure to plan and perform a re-repair.