The LAVV in AVSD is not a mitral valve with a cleft in it. It is a trifoliate valve made of the superior bridging, inferior bridging and mural leaflets. The “cleft” is the zone of apposition between the left halves of the two bridging leaflets. Morphologically it is neither a true cleft nor a commissure, it varies considerably between patients, and it has poor subvalvar support compared with a normal mitral valve. After septal repair, LAVV regurgitation is the dominant long-term problem. In one series of 202 children, 13. 4% needed reoperation for LAVV failure over a median follow-up of 5. 9 years. In a 40-year review of partial AVSD by the Mayo Clinic, closing the LAVV cleft was associated with better survival. Similar work found that closing the cleft improved outcomes even when the valve was not incompetent at the time of surgery.^1,2 Experimental models show that regurgitant volume falls as more of the cleft is closed, and rises with later annular dilatation, even after closure.³ Closure is therefore preventive, aimed at the valve’s future behaviour.

           A competent valve at baseline does not predict a durable valve. The unsupported zone of apposition tends to fail with time and annular dilation. Under general anesthesia, reduced preload and afterload lead to underestimation of mitral regurgitation (MR) severity by TEE,  so “trace” may understate the true lesion. Thus, option ‘a’ is incorrect.

           As explained earlier, Leaving the cleft open is a recognized risk factor for LAVV reoperation. Cleft closure is therefore routine. The extent of cleft closure is tailored to the anatomy. Even with routine closure, late failures in complete AVSD were mostly due to residual or recurrent deficits at the cleft, which underlines that this is the vulnerable site. Thus, option ‘b’ is correct.

           Post-bypass TEE is essential for checking the repair, but should not be used to decide whether to close the cleft. Anesthetic loading conditions mask regurgitation, a second pump run adds risk, and absence of MR early on does not protect against late LAVV regurgitation. Thus, decision of closure of the cleft must be made with the initial pre-bypass echocardiography itself. Pre-bypass echocardiography should be used to define anatomy that determines how much of the cleft to close. Thus, option ‘c’ is incorrect.

           The TEE findings are those of AVSD with same-level atrioventricular  valve insertion, and a cleft pointing toward the septum. Isolated anterior leaflet clefts point toward the left ventricular  outflow tract, whereas AVSD “clefts” point toward the ventricular septum and lie between the bridging leaflets. A conservative strategy for isolated clefts without significant  MR does not apply to AVSD. Thus, option ‘d’ is incorrect.

            Complete closure however is not done routinely. A small mural leaflet, a single papillary muscle (parachute arrangement) or a double-orifice LAVV can cause stenosis after complete closure. In these cases, surgeons close the cleft partially, and post-bypass TEE should measure the mean inflow gradient as well as the residual MR.

 The characteristic TEE features of the AVSD “mitral cleft” include:

1. Trifoliate LAVV with superior bridging, inferior bridging and mural leaflets, best seen en-face in the transgastric basal short-axis view or on 3D TEE from the atrial side.
2. Cleft pointing toward the inlet ventricular septum. In an isolated cleft, it points toward the left ventricular outflow tract or aortic root.
3. Common atrio-ventricular junction with loss of offset as both valves insert at the same level in the mid-esophageal four-chamber view. The atrioventricular septum is absent and there is a primum defect.
4. Small mural leaflet which covers a smaller share of the annulus than the normal posterior mitral leaflet. The smaller the mural leaflet is, the higher the stenosis risk after closure.
5. Rotated papillary muscles which are displaced counterclockwise and placed closer together.
6. “Goose-neck” left ventricular outflow tract where the outflow tract is elongated and narrowed because the aorta is unwedged, which predisposes to left ventricular outflow tract obstruction (visible in the midesophageal  long-axis view).
7. Regurgitant jet typically originating from the cleft, near the septal end of the zone of apposition.

REFERENCES

1. El-Najdawi EK, Driscoll DJ, Puga FJ, et al. Operation for partial atrioventricular septal defect: a forty-year review. J Thorac Cardiovasc Surg 2000;119:880-9; discussion 889-90.
2. Bové T, Strubbe I, Vandekerckhove K, et al. Surgical repair of atrioventricular septal defects: incidence and mode of failure of the left atrioventricular valve. Interact Cardiovasc Thorac Surg 2018;27:42-7.
3. Padala M, Vasilyev NV, Owen JW Jr, et al. Cleft closure and undersizing annuloplasty improve mitral repair in atrioventricular canal defects. J Thorac Cardiovasc Surg 2008;136:1243-9.