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Ann Thorac Surg 1997;63:232-234
© 1997 The Society of Thoracic Surgeons

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Case Report

Anomalous Papillary Muscle as a Cause of Left Ventricular Outflow Tract Obstruction in an Adult

Royal Brompton Hospital and National Heart and Lung Institute, London, United Kingdom

Accepted for publication July 18, 1996.

	Abstract

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Left ventricular outflow tract obstruction may be caused by abnormalities of the various structures comprised by the outflow tract. Hypertrophic cardiomyopathy is one of the more common causes, but many are rare anomalies, a collection of which we have compiled. We present a case of left ventricular outflow tract obstruction mimicking aortic stenosis in an adult. This was found to be due to abnormal insertion of a hypertrophied papillary muscle, successfully corrected by mitral valve replacement.

	Introduction

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A 69-year-old female patient presented with recurrent syncopal episodes over a period of 2 years. She had no angina, but was short of breath on exertion. Holter monitoring showed sinus rhythm with no evidence of dysrhythmias. Blood pressure was measured at 150/90 mm Hg, and a harsh ejection systolic murmur was noted. A 12-lead electrocardiogram showed sinus rhythm with voltage criteria for left ventricular hypertrophy with strain pattern. Anteroposterior chest radiography indicated cardiomegaly. Transthoracic echocardiography showed aortic stenosis with mobile leaflets, and a peak instantaneous gradient of 100 mm Hg with concentric left ventricular hypertrophy (septal wall thickness, 2.5 cm; posterior wall, 1.0 cm). Coronary angiographic results were normal; however, the aortic valve was not transgressed. The diagnosis of aortic stenosis with left ventricular hypertrophy was made, and routine aortic valve replacement was scheduled.

The operation was performed via median sternotomy, with cardiopulmonary bypass and cardioplegic arrest. On inspection through the aortic root, the aortic valve was found to be normally tricuspid, mobile, and free from calcification. The left ventricular cavity was explored and a large muscle bar with short chordae was found extending from the anterior leaflet of the mitral valve to the apex of the left ventricle. This appeared to represent an abnormal papillary muscle of the mitral valve obstructing the outflow tract, and we decided this should be excised and the mitral valve replaced. Bicaval venous drainage was substituted and a bileaflet mechanical prosthesis was inserted via the left atrium. Cardiopulmonary bypass was discontinued easily, and the gradient across the left ventricular outflow tract measured directly was 20 mm Hg. Echocardiography on the sixth postoperation day confirmed the minor left ventricular outflow tract gradient with normal function of the mitral valve prosthesis.

On macroscopic examination of the specimen, the mitral valve was found to be slightly thickened but of normal morphology. The abnormal muscle mass inserted directly into the ventricular surface of the anterolateral commissure, with no intervening chordae. Separate short chordae arose from the muscle to attach to the free margin of the mitral leaflets (Fig 1). Histologic examination of the muscle showed hypertrophy of the myocytes, some areas of interstitial fibrosis, and prominent perivascular fibrosis. The leaflets were thickened but were of normal structure.

View larger version (81K): [in this window] [in a new window]   Fig 1. . (A) The gross specimen shows slight thickening and hooding of the mural (posterior) leaflet, and moderate thickening of the anterior leaflet (between the asterisk and the x). There are no chordae at the site of the commissure (asterisk). The abnormal papillary muscle is broad and extends to the base of the leaflets. (B) The ventricular aspect of the valve shows a layer of fibrous tissue (arrows) overlying the muscle.

	Comment

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Below the aortic valves, discrete membranous subvalvular stenosis of varying degrees of severity has been described, ranging from a simple membrane [4] to an elongated "tunnel" [5]. Anomalous insertion of hypertrophic papillary muscle into the base of the mitral valve has been reported [6]. Abnormal muscle bars arising from the ventricular septum to insert into the anterior leaflet of the mitral valve may also traverse the outflow tract [7].

Various anomalies of the atrioventricular valve apparatus have been described. Accessory tissue growth is rare, but prolapse of this tissue into the outflow tract can cause obstruction. Accessory tissue arising from the mitral valve is well recognized [8–12], sometimes in the form of balloon-like cysts. Tricuspid valve tissue has also been found protruding through a ventricular septal defect into the left ventricular outflow tract [13]. Abnormal tethering of the mitral valve due to anomalous attachment of the papillary muscle apparatus or additional muscle bars may limit its normal excursion during systole out of the outflow tract [7, 12, 14, 15]. In these cases, coaptation of the mitral valve leaflets is incomplete, and mitral regurgitation often ensues. Anomalous insertion of the mitral valve to the ventricular septum is reported [16].

Our case has a very unusual cause of left ventricular outflow tract obstruction. There was no echocardiographic evidence of hypertrophic cardiomyopathy or other forms of subaortic stenosis as previously described, nor was there mitral valve regurgitation associated with systolic anterior motion. We therefore propose an alternative mechanism of outflow tract obstruction other than systolic anterior motion, similar to that described by Klues and associates [17].

Klues and associates explored the role of anomalous papillary muscle in patients with hypertrophic cardiomyopathy, and found long areas of outflow tract narrowing in the middle of the ventricular cavity due to the apposition of anomalous papillary muscle and the hypertrophic ventricular septum. Roldan and colleagues [18] have also postulated the role of anomalous papillary muscle in the Venturi effect. We propose that septal wall hypertrophy due to hypertension rather than cardiomyopathy may have given rise to the conditions described by Klues and associates in the cavity of the left ventricle. It may be that long-standing hypertension could explain the late presentation in adulthood. We decided that the best operative treatment for this condition was excision of the papillary muscle and replacement of the mitral valve.

In conclusion, this is a rare case of left ventricular outflow tract obstruction in an adult patient mimicking closely the typical presentation of aortic stenosis. During echocardiography we concentrated on determining the severity of disease, but failed to pursue the finding of relatively thin and mobile aortic valve cusps. Furthermore, at coronary angiography, the aortic valve was not transgressed and no ventriculogram was obtained. We recognize that rare events cannot be routinely excluded, but recommend that the presence of normal aortic valve cusp movement should alert the operator to look for other causes of left ventricular outflow tract obstruction.

	Footnotes

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Address reprint requests to Mr Kon, Royal Brompton Hospital, Sydney Street, London SW3 6NP, UK.

	References

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This Article Abstract Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): J. Graeme Bennett Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Kon, M. W. S. Articles by Collins, P. D. Search for Related Content PubMed PubMed Citation Articles by Kon, M. W. S. Articles by Collins, P. D.