A 43-year-old woman was referred to our institution for surgical resection of a subaortic stenosis. Her medical history included the repair of a transitional atrioventricular (AV) septal defect (AVSD) at the age of 14 years, consisting of an ostium primum AVSD and a restrictive muscular ventricular septal defect (VSD), associated with a cleft anterior mitral leaflet. After her surgery, she remained asymptomatic until she was 34 years old, when she experienced progressive fatigue. A transthoracic echocardiography showed no residual shunt, mild tricuspid and aortic regurgitation, moderate mitral regurgitation, and subaortic stenosis with a fixed left ventricular outflow tract (LVOT) peak gradient of 52 mm Hg. The subaortic stenosis worsened over the years, reaching a systolic peak gradient of 100 mm Hg. She remained active, but experienced more frequent diaphoretic episodes with mild activity.
After induction of general anesthesia, a transesophageal echocardiography (TEE) was performed. In the midesophageal long-axis view, remnants of mitral valve chordae originating from the base of the thickened anterior mitral leaflet and attached to the interventricular septum were seen (Fig. 1) (Video 1, see Supplemental Digital Content 1, http://links.lww.com/AA/A283; see Appendix for video legends), and a distinct subvalvular membrane (Fig. 2), both causing deformation and narrowing of the LVOT, and associated with turbulent flow (Video 2, see Supplemental Digital Content 2, http://links.lww.com/AA/A284; see Appendix for video legends). A common AV junction (same septal insertion of the AV valves), mild regurgitations of both AV valves, and hypertrophy of the interventricular septum were also visualized. Intraoperative findings correlated well with the structures seen with TEE. A subvalvular membrane and mitral valve chordae inserted into the LVOT were resected in addition to a septal myectomy. Postoperative TEE showed no significant residual obstruction in the LVOT with a systolic peak gradient reduced to 14 mm Hg and the mitral regurgitation decreased to trivial. The mild aortic regurgitation was still present. No shunt at the ventricular level was found after the septal myomectomy.
AVSDs account for 7% of congenital heart diseases.1 Joffe and Oxorn2 previously described intraoperative TEE findings before and after correction of a transitional AV canal. In this Echo Round, we describe the occurrence of subaortic stenosis after AVSD repair, its incidence, and discuss the factors contributing to the development of the obstruction and the TEE evaluation of this pathology.
In partial AVSD, the mitral and tricuspid annulus are separated but achieve the same septal insertion level because the mitral annulus is displaced toward the apex, whereas in complete AVSD the valve itself is also shared. The most frequent form of partial AVSD consists of a primum atrial septal defect associated with a cleft anterior mitral valve leaflet. Transitional defects are a form of partial AVSD in which a restrictive (small) inlet VSD is also present.
Subaortic stenosis may occur after AVSD repair because of many predisposing factors. In the normal heart, the aortic valve (AoV) occupies a central position, wedged between the mitral and tricuspid annuli. In AVSD, the AoV is displaced anteriorly because of the deficiency of the ventricular septum, and the AV valves are displaced toward the ventricular apex, resulting in a shorter distance from the left ventricular apex to the AV valves than the apex to the aortic annulus. This anterior displacement creates an elongation (gooseneck deformity) of the LVOT, predisposing to LVOT obstruction (Fig. 3). Additional abnormalities may convert the potential stenosis to an actual one. The most frequent causes are discrete subaortic fibromuscular ridges, abnormal left AV valve chordae attachments, septal hypertrophy, anomalous insertion of left ventricular papillary muscles, and generalized hypoplasia of the LVOT.3 The obstruction is usually progressive and may be undetected at the time of the initial repair. Autopsy and echocardiographic studies have demonstrated that the anatomy of patients with an AVSD leads to an “at-risk” configuration for the development of LVOT obstruction in up to 75% of patients.4–6 However, although only approximately 5% to 10% will ultimately develop clinically significant LVOT obstruction, patients with a partial AVSD may be up to 3 times more likely to develop this complication compared with patients with a complete AVSD.5
As previously reported, TEE examination using multiple planes, mainly midesophageal short- and long-axis views, as well as in deep transgastric (TG) long-axis view using color flow Doppler, should be used to identify the location of the subaortic lesion in relationship to the AoV.7 Continuous wave Doppler can be used to evaluate the pressure gradient between the left ventricle and aorta in either the TG long-axis view or the deep TG view. Compared with the typical tracing of aortic stenosis, which displays the lower LVOT velocities embedded in the aortic velocity profile (“double-envelope” tracing), the LVOT obstruction is characterized by late-peaking flow velocity leading to a “dagger-shaped” velocity profile. Pulsed wave Doppler placed in the LVOT, however, will result in aliasing, unlike valvular stenosis, because of the high LVOT velocities. In the absence of AoV abnormalities by TEE examination, the maximal gradient obtained with continuous wave Doppler is most likely caused by subaortic stenosis. AoV insufficiency could result from repetitive trauma caused by high-velocity turbulent blood flow jets impinging on the valve.
Postoperative TEE has an important role in detecting and quantifying immediate postoperative regurgitation, because the AoV and mitral valve may have been injured as a result of their close proximity with the resected area. The adequacy of the resection and the integrity of the neighboring ventricular septum should also be evaluated for residual obstruction or iatrogenic VSD.
Subaortic stenosis may develop after initial repair of a partial AVSD. Transthoracic echocardiography has an important role in following disease progression whereas TEE is warranted during surgery to confirm the diagnosis and document additional abnormalities such as subaortic membranes or the presence of mitral valve chordae in the LVOT, and after surgery to identify mitral and AoV regurgitation, iatrogenic VSD, or any residual obstruction or persistent gradient across the LVOT.
1. Chassot PG, Bettex DA. Anesthesia and adult congenital heart disease. J Cardiothorac Vasc Anesth 2006;20:414–37
2. Joffe CD, Oxorn CD. Transitional atrioventricular canal. Anesth Analg 2009;2:358–60
3. Cetta F, Minich L, Edwards WD, Dearani JA, Puga FJ. Atrioventricular septal defects. In: Allen HD, Driscoll DJ, Shaddy RE, Feltes TF, eds. Moss and Adams' Heart Disease in Infants, Children, and Adolescents: Including the Fetus and Young Adult. 7th ed. Philadelphia: Lippincott Williams & Wilkins, 2008:646–67
4. Gallo P, Formigari R, Hokayem NJ, D'Offizi F, D'Alessandro, Francalanci P, d'Amati G, Colloridi V, Pizzuto F. Left ventricular outflow tract obstruction in atrioventricular septal defects: a pathologic and morphometric evaluation. Clin Cardiol 1991;14:513–21
5. Piccoli GP, Ho SY, Wilkinson JL, Macartney FJ, Gerlis LM, Anderson RH. Left-sided obstructive lesions in atrioventricular septal defects: an anatomic study. J Thorac Cardiovasc Surg 1982;83:453–60
6. Ebels T, Meijboom EJ, Anderson RH, Schasfoort-van Leeuwen MJ, Lenstra D, Eijgelaar A, Bossina KK, van der Heide JN. Anatomic and functional “obstruction” of the outflow tract in atrioventricular septal defects with separate valve orifices (“ostium primum atrial septal defect”): an echocardiographic study. Am J Cardiol 1984;54:843–7
7. Nepveu ME, Cogan J, Cartier R, Denault AY. Severe subaortic stenosis. Anesth Analg 2007;105:34–5
APPENDIX: VIDEO LEGENDS
Video 1. Midesophageal long-axis view showing remnants of mitral valve chordae originating from the base of the anterior mitral leaflet and attached to the interventricular septum.
Video 2. Midesophageal long-axis view with color Doppler showing a distinct subvalvular membrane (arrow) causing deformation and narrowing of the left ventricular outflow tract (LVOT), and associated with a turbulent flow in the LVOT.
Clinician's Key Teaching Points By Roman M. Sniecinski, MD, Nikolaos J. Skubas, MD, and Martin J. London, MD
- A transitional atrioventricular septal defect (AVSD) consists of a primum atrial septal defect, a cleft mitral valve, and a small ventricular septal defect (VSD). This congenital heart defect is typically repaired in infancy. However, because the mitral valve insertion point is more apical than normal, the left ventricular outflow tract (LVOT) is elongated and prone to obstruction later in life.
- The mechanisms of LVOT obstruction after AVSD repair include hypertrophy of the interventricular septum (IVS), abnormal chordae tendinae insertions to the IVS, and development of LVOT membranes or ridges proximal to the aortic valve (AV). Clues to LVOT obstruction on transesophageal echocardiography (TEE) (midesophageal and transgastric longaxis (TG LAX) and deep TG LAX views) include aliasing of pulsed wave Doppler and turbulent systolic flow on color flow Doppler proximal to a normal AV, and a late-peaking, “dagger-like” velocity tracing on continuous wave Doppler.
- In this case of subaortic stenosis in a patient with a repaired AVSD, the authors visualized a distinct membrane in the LVOT as well as septal hypertrophy. TEE was used to ensure the LVOT gradient decreased after resection of the membrane, and an iatrogenic VSD was not created during myectomy of the thickened interventricular septum.
- Stenosis of the AV is not the only cause of high gradients between the left ventricle and aorta. When such a gradient is encountered on Doppler in the face of a normal-appearing AV on 2-dimensional examination, causes of subvalvular stenosis should be considered.