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

Initial repair of AVSD by the one-patch technique is approached in the same manner as for all types of repairs. Figure 7.8 shows aortobicaval cardiopulmonary bypass with aortic cross-clamping and antegrade cardioplegia. The right atrium is exposed, and a sucker is placed into the left ventricle, which shows the crest of the interventricular septum and the Rastelli Type A common AV valve with developed commissures dividing the right and left AV valve components. The repair is commenced by approximating the central cleft, which is to become the anterior leaflet of the left AV valve, as in Fig. 7.9. Figure 7.10 shows individual pledgeted sutures being placed on the right interventricular septal crest to avoid any injury to the conduction system. These individual sutures are placed into a pericardial or prosthetic patch, as in Fig. 7.11. Figure 7.12 shows the patch being cut to formation and size, and Fig. 7.13 demonstrates the patch anchored to the septum by the pledgeted sutures. Once the patch is in place, the zone of apposition in the anterior leaflet of the left AV valve is exposed and closed with interrupted suture technique, as in Figs. 7.14 and 7.15. Also shown in Fig. 7.15 is the reattachment of the left AV valve leaflets to the common patch that effectively closes the VSD and defines the height of the AV valve leaflets. This is accomplished with interrupted suture technique. Figure 7.16 shows the rest of the reconstruction, and Fig. 7.17 demonstrates the right AV valve being attached to the common patch, thereby completing the repair of both the right and left AV valves. Figure 7.18 demonstrates the closure of the cleft of the right AV valve, and Fig. 7.19 shows the closure of the ostium primum defect, using running suture technique. The valves are tested with a saline-filled bulb syringe; the atrium is closed and de-aired, and the cross-clamp is removed. After rewarming, the patient is weaned from cardiopulmonary bypass and transesophageal echocardiography interrogation is accomplished to assess the quality of the repair.

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.

7.2.2 Two-Patch Technique

The two-patch technique is approached in the same manner as noted for the one-patch technique. Figure 7.20 shows the relevant anatomy and demonstrates the atrial exposure, the crest of the interventricular septum, and the common AV valve. Figure 7.21 shows sharp incision of the common posterior leaflet to expose the extent of the interventricular septum. This incision is performed to clearly visualize the crest of the septum and safely place the sutures. Figure 7.21 also shows pledgeted sutures being placed on the crest of the septum in anticipation of VSD closure using a pericardial or prosthetic patch. The pledgeted sutures are completed along the crest of the interventricular septum, as noted in Fig. 7.22, making sure to extend the interrupted sutures to the annulus of the aortic valve and the annulus of the common AV valve. Figure 7.23 demonstrates placement of the pledgeted sutures through the patch as it is being lowered into the heart. Notice that the superior edges of the patch are being anchored to their respective common valve annulus locations to decrease the incidence of residual VSD. Figure 7.24 shows the VSD patch anchored in place. The zone of apposition of the left AV valve is now being approximated to align the leaflets, the patch, and the pericardium, which is noted in Fig. 7.25. Interrupted mattress sutures are placed from the top of the VSD patch through the left AV valve leaflets and through the pericardial patch. The thin leaflets are being anchored to the top of the VSD patch, with the knots being placed on the pericardium, thereby interposing the leaflets between the patch and the pericardium for a more secure repair; because the knots are not placed in the valve leaflets, the chance of tearing and disruption is decreased. Figure 7.26 demonstrates the closure of a VSD and the proposed shaping of the pericardial patch for the eventual ASD closure. The pericardial patch is now reflected medially to expose the zone of apposition, which is approximated with interrupted suture technique, as noted in Fig. 7.27. Figure 7.28 shows the pericardial patch being configured for the ASD closure. The patch is sutured to the edges of the defect, with special care to avoid any injury to the conduction system, which is close to the coronary sinus, as noted in Fig. 7.29. Often, the sutures are placed within the left atrium close to the septum, to avoid injury to the conduction system. Other surgeons have avoided injuring the conduction system by using a larger patch to incorporate the coronary sinus, with drainage into the left atrium. Because a left superior caval vein is present in approximately 5% of patients with AVSD, primum ASD closure with normal coronary sinus drainage into the right atrium is essential. Consequently, we prefer to leave the coronary sinus draining normally on the right atrial side and apply it in all cases. Figure 7.30 shows the completed repair with attachment of the right AV valve leaflets to the top of the VSD patch and closure of the zone of apposition of the right AV valve. The result can be tested with a saline-filled bulb syringe.

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