Ann Thorac Surg 1996;62:1858-1860
© 1996 The Society of Thoracic Surgeons
Case Report
Subaortic Stenosis Caused by Anomalous Papillary Muscle of the Mitral Valve
Yutaka Imoto, MD,
Hideaki Kado, MD,
Hiroyuki Yasuda, MD,
Ryuji Tominaga, MD,
Hisataka Yasui, MD
Division of Cardiovascular Surgery, Kyushu University, and Department of Cardiovascular Surgery, Fukuoka Children's Hospital, Fukuoka, Japan
Accepted for publication June 21, 1996.
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Abstract
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We report on a rare case of subaortic stenosis caused by an anomalous posteromedial papillary muscle inserting directly into the anterior mitral leaflet, which had muscular extension to the subaortic region. Resection of the muscular extension alone was ineffective. A second operation including entire resection of the anomalous papillary muscle and mitral valve replacement resulted in successful relief of the obstruction. Microscopic findings of the resected tissue were compatible with those of hypertrophic cardiomyopathy.
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Introduction
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Most cases of subaortic stenosis in children are caused by a discrete membrane, hypertrophic muscular obstruction, or a fibromuscular tunnel [1, 2]. We experienced a rare case in which subaortic stenosis was caused by an anomalous papillary muscle inserting directly into the anterior mitral leaflet with subaortic muscular extension.
A 9-year-old girl was referred to us for increasing pressure gradient in the left ventricular (LV) outflow tract during follow-up by Doppler echocardiography. On auscultation, a grade 3/6 systolic murmur maximal at the left sternal border in the third intercostal space was audible, which had first been noted at 6 months of age. Electrocardiogram showed LV hypertrophy with exercise-induced ST depression. Echocardiography showed that the LV outflow tract was obstructed by the hypertrophic posteromedial papillary muscle, which inserted directly into the anterior mitral leaflet and had muscular extension to the subaortic region (Fig 1
). The ventricular septum and the LV posterior wall was mildly thickened. Neither systolic anterior motion of the anterior mitral leaflet nor localized hypertrophy of the ventricular septum was recognized. The aortic valve had three cusps and was normal in size. Cardiac catheterization revealed a systolic pressure gradient of 75 mm Hg between the left ventricle and the ascending aorta.
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Fig 1. Parasternal long-axisechocardiogram beforethe first operation. The anomalous posteromedial papillary muscle (APMPM) with severe hypertrophy, which inserts directly into the anterior mitral leaflet (AML), has subaortic extension. (Ao= aorta; IVS = interventricular septum;LA= left atrium.)
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In the first operation, the abnormal muscle in the LV outflow tract, ie, subaortic extension of the posteromedial papillary muscle, was resected as much as possible through an aortotomy with special care to avoid mitral regurgitation. Postoperative catheterization revealed a residual pressure gradient of 63 mm Hg in the LV outflow tract and trivial mitral regurgitation. Echocardiography showed that the subaortic extension of the papillary muscle had been almost removed, but the rest of the papillary muscle still obstructed the LV outflow tract by making contact with the ventricular septum during the systolic phase (Fig 2).
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Fig 2. Left ventricular anatomy after the first operation. A pressure gradient was left in the outflow tract although subaortic extension of the anomalous posteromedial papillary muscle had been resected(star). (ALPM =anterolateral papillary muscle;AML =anterior mitral leaflet;Ao =aorta;IVS =interventricular septum.)
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The second operation was performed 18 months after the first operation. The left atrium was entered along the interatrial groove, and the posteromedial papillary muscle and the anterior mitral leaflet were resected (Fig 3). Residue of the subaortic extension of the anomalous papillary muscle was excised through aortotomy. A prosthetic valve, St. Jude Medical (St. Paul, MN) no. 23, was sewn to the mitral annulus with pledgeted 2-0 polyester mattress sutures. The postoperative course was uneventful, and cardiac catheterization 1 month after the operation showed that the pressure gradient was greatly reduced to 11 mm Hg. Microscopic examination of the excised papillary muscle revealed disarray and abnormal branching of muscle fibers in addition to hypertrophic changes of myocytes, which are compatible with the findings in hypertrophic cardiomyopathy.
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Fig 3. Photographs of the mitral value specimen. Atrial aspect (A) and ventricular aspect (B) of a part of the anterior mitral leaflet with anomalous posteromedial papillary muscle are shown.
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Comment
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Subaortic stenosis is a complex subject because of the peculiarities of the anatomic features of the LV outflow tract [3]. Although abnormalities of the mitral valve or papillary muscles are uncommon causes of subaortic stenosis [4, 5], Klues and associates [6] reported that malformation of the mitral valve is frequently seen in patients with hypertrophic obstructive cardiomyopathy. Of 78 mitral valve specimens from patients with hypertrophic obstructive cardiomyopathy, 10 (13%) were identified as having direct insertion of one or both left ventricular papillary muscles into the anterior mitral leaflet. They also reported that because the anomalous papillary muscle inserts into the commissural region of the mitral valve (and not in the central portion of the anterior leaflet), standard parasternal long-axis view in the echocardiographic study usually fails to image this abnormality. Awareness of this rare anomaly is important in the preoperative and intraoperative diagnosis. Inspection of the mitral valve and papillary muscles through a left atriotomy is recommended when this type of abnormality is suspected.
In the surgical treatment of hypertrophic obstructive cardiomyopathy, obstruction is usually reduced by myotomy/myectomy of the ventricular septum (Morrow procedure [7]). Mitral valve replacement is indicated in selected patients such as those with a relatively thin ventricular septum, severe mitral regurgitation secondary to an intrinsic abnormality of the valve or infectious endocarditis, or inadequate relief of the obstruction after myotomy/myectomy procedure. In the present case, resection of the subaortic muscular extension of the papillary muscle performed in the first operation was ineffective. Postoperative echocardiography showed that residual obstruction was caused by the papillary muscle itself. Therefore, complete resection of the anomalous papillary muscle and mitral valve replacement seem essential in this type of obstruction.
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Footnotes
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Address reprint requests to Dr Imoto, Division of Cardiovascular Surgery, Research Institute of Angiocardiology, Kyushu University, Faculty of Medicine, 3-1-1 Maidashi, Higashi-ku, Fukuoka, 812, Japan.
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References
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- Penkoske PA, Collins-Nakai RL, Duncan NF. Subaortic stenosis in childhood: frequency of associated anomalies and surgical options. J Thorac Cardiovasc Surg 1989;98:852–60.[Abstract]
- Kirklin JW, Barratt-Boyes BG. Cardiac surgery. 2nd ed. New York: Churchill Livingstone, 1993:1212–l24.
- Edwards JE. Pathology of left ventricular outflow tract obstruction. Circulation 1965;31:586–99.[Abstract/Free Full Text]
- Del Guzzo L, Sherrid MV. Anomalous papillary muscle insertion contributing to obstruction in discrete subaortic stenosis. J Am Coll Cardiol 1983;2:379–82.[Abstract]
- Wright PW, Wittner RS. Obstruction of the ventricular outflow tract by the mitral valve due to a muscle band. J Thorac Cardiovasc Surg 1983;85:938–40.[Abstract]
- Klues HG, Roberts WC, Maron BJ. Anomalous insertion of papillary muscle directly into anterior mitral leaflet in hypertrophic cardiomyopathy. Circulation 1991;84:1188–97.[Abstract/Free Full Text]
- Morrow AG, Reitz BA, Epstein SE, et al. Operative treatment in hypertrophic subaortic stenosis: techniques and the results of pre- and postoperative assessments in 83 patients. Circulation 1975;52:88–102.[Abstract/Free Full Text]
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Abstract
Introduction
