MMCTS
(July 23, 2007). doi:10.1510/mmcts.2006.002303
Copyright © 2007 European Association for Cardio-thoracic Surgery
Procedure
Surgery for subvalvar aortic stenosis – resection of discrete subvalvar aortic membrane
Viktor Hraska*,
Joachim Photiadis and
Claudia Arenz
Department of Pediatric Cardiac Surgery, German Pediatric Heart Center, Asklepios Clinic Sankt Augustin, Arnold Janssen Str. 29, 53757 Sankt Augustin, Germany
* Corresponding author: * Tel.: +49-2241-249 603; fax: +49-2241-249 602 v.hraska{at}asklepios.com
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Summary
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Discrete subvalvar aortic membrane is characterized by a fibromuscular shelf located at the area of aortomitral continuity with the extension toward the interventricular septum. As compared to other congenital heart defects, discrete subvalvar aortic membrane is virtually never recognized in early infancy, but appears to be an ‘acquired’ lesion, typically seen in patients with a more acute angle between the long axis of the left ventricle and the aorta. This angulation leads to imbalance in shear forces, which causes the proliferation of tissue that forms the membrane. The surgical intervention is considered when the gradient across the left ventricular outflow tract is 30 mmHg or more. Surgery is also advocated in infants and children in the presence of aortic regurgitation even when there is no significant gradient. The circumferential excision of the fibrous ridge with septal myectomy is safe and provides efficient relief of obstruction. Aggressive resection of all structures causing flow turbulence and removal of pathological tissue from the valve leaflets might prevent development or progression of aortic regurgitation and might eliminate the substrate for recurrent obstruction. Nevertheless, recurrence still remains a problem, especially in the presence of a predisposing associated congenital heart defect.
Key Words: Congenital heart disease • Discrete subvalvar aortic membrane • Subvalvar aortic stenosis • Surgery
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Introduction
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Discrete subvalvar aortic membrane (DSAM) is characterized by a thin, fibromuscular shelf located at the area of aortomitral continuity with the extension toward the interventricular septum. This condition occurs in patients with associated congenital heart disease, including ventricular septal defect, coarctation of the aorta, interrupted aortic arch, atrioventricular canal and others. The lesion may develop in patients with these defects before operation, but also may appear and progress significantly after surgical correction of the associated defects. In addition, DSAM can present as a primary defect [1]. It is typically seen in patients with a more acute angle between the long axis of the left ventricle and the aorta. This angulation leads to imbalance in shear forces, which causes the proliferation of tissue that forms the membrane [2, 3]. The membrane, which results, creates more turbulence, further accelerating the process of proliferation and fibrosis. The turbulence can also cause injury to the aortic valve leaflets, with subsequent thickening and distortion resulting in aortic insufficiency. There is some evidence that this type of DSAM is not congenital but an acquired obstruction, secondary to flow disturbances in the left ventricular outflow tract [4].
Our treatment protocol
Symptoms associated with left ventricular outflow tract obstruction (syncope, angina, diminished exercise tolerance, etc.) are indications for surgery. The surgical intervention is indicated when the peak Doppler gradient across the left ventricular outflow tract is 30 mmHg or more. Patients with peak gradient <30 mmHg and no significant left ventricle hypertrophy are followed closely for progression, especially in the first several years of life. Surgery is also advocated in infants and children in the presence of aortic regurgitation regardless of gradient (Schematic 1).
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Schematic 1 Treatment protocol of the German Heart Center, Sankt Augustin for discrete subvalvar aortic membrane. AR – aortic regurgitation.
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Surgical technique
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Resection of a discrete subvalvar aortic membrane
The operation is performed on cardiopulmonary bypass (CPB) with mild hypothermia (32 °C). After systemic heparinization, the aorta is cannulated as high as possible to leave enough space for working on the ascending aorta. One venous cannula usually provides optimal venous drainage without interfering with the operative field. The bypass is commenced and the left atrial vent is placed to keep the operating field bloodless. The aortic cross-clamp is applied and antegrade cold crystalloid cardioplegia is delivered. The aorta is incised 5–10 mm above the origin of the coronary artery by a longitudinal aortotomy which is extended into the non-coronary sinus like an inverted hockey stick (Video 1).
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Video 1 An oblique, inverted hockey stick type of incision is made from the anterior aspect of the aorta towards the non-coronary sinus of Valsalva.
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Holding sutures are placed on the edges of the aortotomy. The aortic valve and subvalvar area are carefully examined (Video 2).
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Video 2 The morphology of the valve, the orifices of the coronaries and the extent and relationship of the membrane to the surrounding structures, especially the encroachment of the membrane onto the leaflets of the aortic and mitral valves, are carefully assessed.
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The right coronary cusp is retracted anteriorly, exposing the subvalvular area. The membrane is identified. Caution should be exercised not to damage the aortic valve by instruments. The incision is made through the white fibrous tissue only to its junction with the muscle (Video 3).
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Video 3 The membrane is grasped with forceps and/or stabilized by a stay suture. Under the right coronary cusp, close to the intercoronary commissure, a radial incision is made into the membrane.
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Combination of sharp and blunt dissection is used to peel the membrane off the muscle all the way round the entire circumference of the subaortic region. Great care is employed to avoid any deep, sharp resection at the area of conduction system, immediately adjacent to the membranous septum (Videos 4, 5, 6, Photo 1).
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Video 4 A combination of blunt and sharp dissection is used to enucleate the membrane of the ventricular septum and the anterior leaflet of the mitral valve.
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Video 5 If the membrane is attached to the anterior leaflet of the mitral valve and to the aortic valve cusps, careful blunt dissection is performed to peel it off the undersurface of the valves. The goal is to remove any fibrous tissue which could obstruct the left ventricular outflow tract and limit the movement of the valves.
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Video 6 The location of the conduction tissue near the membranous septum should be identified and any deep, sharp dissection must be avoided. Blunt dissection is preferable.
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Photo 1 The whole extent of the membrane was removed distally down the septum and onto the anterior leaflet of the mitral valve.
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A myectomy is routinely performed to enlarge the left ventricular outflow tract and to reduce the likelihood of recurrence. A wedge of muscle under the left half of the right coronary cusp is excised (Video 7).
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Video 7 The ridge of muscle projecting into the left ventricular outflow tract is excised as widely as possible without interfering with the aortic valve integrity and the conduction system. Two parallel incisions are made into the anterolateral aspect of the ventricular outflow tract. The first incision is made beneath the intercoronary commissural triangle and the second one is made beneath the belly of the right coronary cusp. The incisions are extended apical as far down as needed and the chunk of muscle in between is excised with scissors.
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Having completed the membranectomy and myectomy, the leaflets of the aortic valve are inspected. If they appear thickened, thinning of leaflets is performed. Aortotomy is closed (Video 8).
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Video 8 A final assessment of the opening of the valve and mobility of the leaflets is performed and the aortotomy is closed with a running suture.
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The left part of the heart is de-aired through the vent, using retrograde filling of the left ventricle with saline. The aortic cross-clamp is removed and de-airing is completed. After re-warming, the patient is weaned from the CPB. Transesophageal echocardiographic assessment of the left ventricle function, aortic valve function and flow characteristic in the left ventricle outflow tract should be carried out routinely.
Complications of this procedure include the creation of an iatrogenic ventricular septal defect, if resection is excessively deep, damage to the conduction system, if the resection is made under the non-coronary leaflet and damage to the aortic leaflets, or mitral valve due to careless manipulation with instruments.
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Results
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Early mortality is low, less than 3% with a survival rate above 90% at 15 years. Late mortality is influenced by anatomic factors, namely by hypoplastic aortic annulus and concomitant mitral stenosis [5].
Early postoperative complications (complete heart block, etc.) are associated with too aggressive approach during extended, circumferential myectomy [6]. Circumferential excision of the fibrous ridge by sharp and blunt dissection with concomitant myectomy appears to provide the most efficient relief of obstruction [7]. Nevertheless, recurrence still remains a problem, especially in the presence of a predisposing associated congenital heart defect.
Freedom from re-operation is about 85% at 15 years (Table 1).
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Discussion
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On the basis of the underlying physiology and morphology of a DSAM [3], any surgical treatment should, in addition to relieving the subaortic stenosis, address the anatomic abnormality causing increased septal shear stress [5]. DSAM can be cured in most patients by membranectomy accompanied by myectomy. Aggressive resection of all structures causing flow turbulence (anomalous septal insertion of the mitral valve, accessory mitral valve tissue, anomalous papillary muscle, anomalous muscular band, etc.) and removal of pathological tissue from the valve leaflets and from the sub-commissural trigones, might prevent development or progression of aortic regurgitation and might eliminate the substrate for recurrent obstruction [6, 7, 8]. In patients without a myectomy, the left ventricle outflow tract gradient increased postoperatively at a greater rate than those with concomitant myectomy [9]. Recurrence of significant re-stenosis is associated with the immediate postoperative gradient across the left ventricle outflow tract  30 mm, with the mean delay for reappearance of a gradient leading to surgery at approximately 4 years [7, 9, 10]. The mild or moderate aortic insufficiency preoperatively has a negative impact on the progression of aortic insufficiency postoperatively. Therefore, in the presence of aortic regurgitation, surgery is recommended regardless of gradient to prevent the development of aortic regurgitation or to improve aortic valve function [6, 11].
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References
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- Kleinert S, Geva T. Echocardiographic morphometry and geometry of the left ventricular outflow tract in fixed subaortic stenosis. J Am Coll Cardiol 1993;22:1501–1508.[Abstract]
- Cape EG, Vanauker MD, Sigfusson G, Tracy TA, del Nido PJ. Potential role of mechanical stress in the etiology of pediatric heart disease: septal shear stress in subaortic stenosis. J Am Coll Cardiol 1997;30:247–254.[Abstract]
- Gewillig M, Daenen W, Dumoulin M, Van der Hauwaert L. Rheologic genesis of discrete subvalvular aortic stenosis: a Doppler echocardiographic study. J Am Coll Cardiol 1992;19:818–824.[Abstract]
- Serraf A, Zoghby J, Lacour-Gayet F, Houel R, Belli E, Galleti L, Planche C. Surgical treatment of subaortic stenosis: a seventeen-year experience. J Thorac Cardiovasc Surg 1999;117:669–678.[Abstract/Free Full Text]
- Parry AJ, Kovalchin JP, Suda K, McElhinney DB, Wudel J, Silverman NH, Reddy VM, Hanley FL. Resection of subaortic stenosis: can a more aggressive approach be justified? Eur J Cardiothorac Surg 1999;15:631–638.[Abstract/Free Full Text]
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- Marasini M, Zannini L, Ussia GP, Pinto R, Moretti R, Lerzo F, Pongiglione G. Discrete subaortic stenosis. Incidence, morphology and surgical impact of associated subaortic anomalies. Ann Thorac Surg 2003;75:1763–1768.[Abstract/Free Full Text]
- Barkhordarian R, Uemura H, Rigby ML, Sethia B, Shore D, Goebells A, Ho YS. A retrospective review in 50 patients with subaortic stenosis and intact ventricular septum: 5-year surgical experience. Interac CardioVasc Thorac Surg 2007;6:35–38.[Abstract/Free Full Text]
- Lupinetti FM, Pridjian AK, Callow LB, Crowley DC, Beekman RH, Bove EL. Optimum treatment of discrete subaortic stenosis. Ann Thorac Surg 1992;54:467–470.[Abstract]
- Brauner R, Laks H, Drinkwater DC Jr, Shvarts O, Eghbali K, Galindo A. Benefits of early surgical repair in fixed subaortic stenosis. J Am Coll Cardiol 1997;30:1835–1842.[Abstract]
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Summary
Introduction