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Obstruction of the left ventricular outflow tract by the mitral valve due to a muscle band
938
Brief communications
Obstruction of the left ventricular outflow tract by the mitral valve due to a muscle band Philip W. Wright, M.D., and Richard S. Wittner, M.D., Long Beach. Calif. From the Sections of Thoracic Surgery and of Pediatric Cardiology, Earl and Loraine Miller Children's Hospital, Long Beach, Calif.
This paper details a rare cause of subaortic obstruction-a muscle band tethering the anterior leaflet of the mitral valve to the ventricular septum. Excision of this band released the leaflet and cured the obstruction. The patient also had a discrete subaortic membranous obstruction. the membrane being excised. Clinically significant subaortic obstruction to left ventricular outflow in the child is most frequently due to a discrete membrane. Hypertrophic muscular obstruction and fibromuscular tunnel are less common causes, and obstructive mitral valve conditions, consisting of mitral web, cleft, and bleb, are rare.' We report a unique example of obstruction resulting from an anomalous muscle band inserting into the anterior mitral valve leaflet and attached to the septal wall in the outflow tract. Case report. An II-year-old boy was referred for surgical relief of subaortic obstruction. A systolic murmur had been present since infancy. Initial heart catheterization at 8 years of age had disclosed a discrete subaortic membrane with only a modest (35 mm Hg) peak systolic gradient across the left ventricular outflow tract. When 10 years old, the boy began to complain of exertional chest pain and diminished exercise tolerance. Physical examination now revealed a thrusting and sustained apical impulse, and a precordial thrill was palpable over the base of the heart. A long, Grade 4/6 systolic ejection murmur could be heard maximally in the left third and fourth intercostal spaces, and was also well heard in the aortic area with low-intensity radiation to the base of the neck. On chest roentgenograms, the heart size was at the upper limits of normal with prominence of the left ventricle. The lung fields were normal. The electrocardiogram showed left ventricular hypertrophy with strain pattern. Treadmill electrocardiographic stress tests obtained since the age of 8 years were compared, and results were now abnormal, with ischemic changes at a heart rate of 110 beats/min. An echocardiogram revealed septal thickening, but the posterior wall was also thickened, such that the ratio between them was more in keeping with concentric rather than asymmetric septal hypertrophy. The septum moved normally. The left ventricular outflow was somewhat narrowed, measuring 1.5 em, and the suggestion of a gooseneck deformity was reported. The mitral valve was unremarkable. Recatheterization at this time revealed an average peak Address for reprints: Philip W. Wright, M.D., 701 E. 28th St., Suite 217, Long Beach, Calif. 90806.
The Journal of Thoracic and Cardiovascular Surgery
systolic gradient of 85 mm Hg across the left ventricular outflow tract, and the pressure trace showed the pattern of subaortic stenosis. Left ventricular pressure was 195/12 mm Hg. The left ventricular angiocardiogram showed a wellmarked area of radiolucency high in the outflow tract, characteristic of a subaortic membrane (Fig. I). There was no evidence of intracardiac shunt or of any other lesion or functional abnormality of the aortic or mitral valves. The preoperative diagnosis was discrete left ventricular outflow obstruction resulting from a subaortic membrane. The patient was operated upon with the aid of cardiopulmonary bypass for resection of this subaortic membrane. The approach was through an aortotomy and the aortic valve. The aortic valve appeared normal. In the subvalvular area, a typical subaortic membrane was found and excisedcompletely with a rim of muscle along its attachment. After closure of the aortotomy and discontinuation of cardiopulmonary bypass,the pressure gradient across the left ventricular outflow tract was found to be virtually unchanged. Cardiopulmonary bypass was resumed and, with combined myocardial protection of topical cooling and cold potassium cardioplegic arrest, the aortotomy was reopened to reexamine the subaortic area. A fiberoptic endoscopic light was introduced to illuminate the cavity of the left ventricle. The remaining obstruction appeared to be caused by a short anomalous muscle band (6 mm in diameter) which arose from the middle of the ventricular surface of the anterior mitral leaflet and crossed the outflow tract to insert high into the ventricular septum (Fig. 2). The muscle band was encircled with a ligature and, by traction and displacement, its pointsof attachment were carefully studied. This band appeared to tether the anterior mitral leaflet close to the septum, narrowing the outflow tract. The end of the band at its attachment to the mitral valve splayed out somewhat linearly up and down, marking the midline of the leaflet. The chordal attachments along the margin of the leaflet and papillary muscle apparatus appeared to be normal and entirely separate from this band. The band was excised by cutting it away nearly flush, without injury to the integrity of the valve leaflet, and from its pointof attachment high on the anterior ventricular septum. Thus released, the anterior leaflet assumed a normal position and appeared unobstructive, and the gradient across the outflow tract was found to be completely abolished following excision of the band. Histologically, the band was composed only of cardiac muscle. The patient had no residual gradient or mitral dysfunction at recatheterization 20 months later and has done well during a follow-up period of over 5 years.
Discussion. To our knowledge, no previous reports of a similar case of subaortic obstruction have appeared in the literature. In personal communication, Lev has reported observing similar abnormal muscle bundles and smaller bands in his large autopsy series of congenital heart disease; however, these have not caused clinically or hemodynamically significant obstruction. Heretofore, such bands have been significant only in that they may produce murmurs (personal communications from JE Edwards and RV Lucas, Jr.). Although they are uncommon causes of subaortic stenosis, several abnormalities of the mitral valve responsible for left ventricular outflow obstruction have
Volume 85 Number 6 June, 1983
Brief communications
939
av 8m
-=ttt=:~~~~ ommb almv -
Fig. 2. Diagram of the relationships in systole of the aortic valve leaflets (av), the discrete subaortic membrane (sm), the obstructing mitral muscle band (ommb), and the latter's attachments to anterior leaflet of the mitral valve (almv) and ventricular septum in the outflow tract. Ao, Aorta. LA, Left atrium. LV, Left ventricle. RV, Right ventricle. Fig. I. Cineangiocardiogram demonstrating the subaortic membrane (arrow).
been described. Abnormal cushion development affecting leaflet or septal formation, or both, has been held responsible.!" We believethe muscular band in this case is developmentally related to these and, more particularly, comparable to the mitral web. In our review, reported descriptions of mitral web have been helpful in explaining the possibleorigin of this mitral muscle band. I.2. S Mitral web is a term describing a fibromembranous structure inserting into the intact anterior mitral leaflet along a mid-mitral line and extending across the outflow tract to attach where the developmental fusion of conal and sinus septa occurs. The structure thus has the potential to obstruct left ventricular outflow.I.5 The mitral band in this case also arose in the anterior mitral leaflet in the same vertical linear central zone 'wherein the web develops when fusion of superior and inferior endocardial cushion contributions occurs. This is the familiar area in which a cleft of the leaflet exists when normal fusion has failed to occur. Like the web, the band was attached to the ventricular septum high in the outflow tract. In addition to these points of attachment which appear to be in common, mitral web has been reported to arise only from an intact leaflet as an accessory development, and the web has also been
associated with subaortic membrane.' Functionally, both band and web possess a similar potential to obstruct the left ventricular outflow by restraining the anterior leaflet near the septum. Additionally, the web may obstruct by means of the diaphragm it presents in the outflow tract. Should the mitral band and mitral web be considered variants of one condition? We believe they are. One might logically propose that what is common to mitral cleft and web as well as to this muscle band is maldevelopment in the zones of fusion of endocardial cushion elements, particularly as they relate to formation of the anterior mitral valve leaflet and ventricular septum. In the case of mitral web and band, an accessory rest of tissue of endocardial cushion origin appears in one instance to differentiate into a fibrous web and, in the other instance, into a compact muscular band. The coexistence of a subaortic membrane in this case deserves further comment. Not only in this case but in two of the original cases of mitral web reported by Sellers, Lillehei, and Edwards,' a subaortic membrane was also present of the classical high discrete type (Kelly Type I), with which associated anomalies are not particularly common." Van Praagh and associates? stated that typical fibrous ring subaortic stenosis results from maldevelopment of endocardial cushion tissue of the atrioventricular canal which usually forms the ante-
940
The Journal of Thoracic and Cardiovascular Surgery
Brief communications
rior leaflet of the mitral valve; they also cited numerous works of others to support this new view. Although at variance with the traditional and still widely held view that subaortic membrane represents persistent, malincorporated subaortic conal tissue (Keith" theory), this newer concept would account for the association of subaortic membrane with mitral band and web. Coincidentally, in both of Sellers' cases, it was only after excision of the subaortic membrane, for which the patients underwent operation, that the mitral web obstruction was recognized---once intraoperatively and once at necropsy. The fact that operation failed in each case emphasized the paramount importance of recognizing the potentially associated causes of left ventricular outflow obstruction, particularly when resection of the subaortic membrane fails to relieve the obstruction. Some causes of left ventricular outflow obstruction, such as a discrete subaortic membrane, are both well demonstrated by preoperative studies and easily confirmed by operative findings. Under operative conditions, the flaccid state of the heart may obscure other significant obstructions of left ventricular outflow, particularly those which are partly functional, such as idiopathic hypertrophic subaortic stenosis, bands, or abnormalities of mitral valve position. Therefore, operation must be guided by pressure determinations. The concluding operative pressure determination may be of paramount importance and should confirm relief of obstruction. Such pressure determinations have been controversial and belittled as misleading and even unnecessary in operations for simple subaortic membrane. This case illustrates their usefulness and impor-
tance, for it was solely on the basis of this finding that reexploration of the subaortic area and the possibility of a second cause of obstruction was considered. When a mitral band obstruction of the type we have described is found, resection of the band, releasing the obstructing anterior mitral leaflet in the outflow tract, should be corrective. REFERENCES Goor DA, Lillehei CW: Congenital malformation of the heart, Malformations of the Aortic Pathway. New York, 1975, Grune & Stratton, Inc., p 237 2 Bjork VO, Hulquist G, Lodin H: Subaortic stenosis produced by an abnormally placed anterior mitral leaflet. J THORAC CARDIOVASC SURG 41:659-669, 1961 3 McLean LD, Culligan JA, Kane DJ: Subaortic stenosis due to accessory tissue on the mitral valve. J THORAC CARDIOVASC SURG 45:382-388, 1963 4 Nanton MA, Belcourt CL, Gillis DA, Krauss VW, Roy DL: Left ventricular outflow tract obstruction owing to accessory endocardial cushion tissue. J THORAC CARDIOVASC SURG 78:537-541, 1979 5 Sellers R, Lillehei CW, Edwards JE: Subaortic stenosis caused by anomalies and atrioventricular valves. J THORAC CARDIOVASC SURG 48:289-301, 1964 6 Kelly DT, Wulfberg BA, Rowe RD: Discrete subaortic stenosis. Circulation 46:309-322, 1972 7 Van Praagh R, Corwin RD, Dahlquist EH Jr, Freeman RM, Mattioli L, Nebesar RA: Tetralogy of Fallot with severe left ventricular outflow tract obstruction due to anomalous attachment of the mitral valve to the ventricular septum. Am J Cardiol 26:93-101, 1970 8 Keith A: Schorstein lecture on the fate of the bulbus cordis in the human heart. Lancet 2:1267-1273, 1924
Notice of correction In the article by Laschinger and associates, entitled "Myocardial Cooling: Beneficial Effects of Topical Hypothermia" (J THoRAc CARDIOVASC SURG 84:807-814, 1982), an error has been noted. Figs. 2 and 4 are correctly referenced and their legends are correct. However, the graph now shown in Fig. 2 should be transposed to the location above the legend to Fig. 4, and the graph now shown in Fig. 4 should be moved to the position above the legend to Fig. 2.
Brief communications
Obstruction of the left ventricular outflow tract by the mitral valve due to a muscle band Philip W. Wright, M.D., and Richard S. Wittner, M.D., Long Beach. Calif. From the Sections of Thoracic Surgery and of Pediatric Cardiology, Earl and Loraine Miller Children's Hospital, Long Beach, Calif.
This paper details a rare cause of subaortic obstruction-a muscle band tethering the anterior leaflet of the mitral valve to the ventricular septum. Excision of this band released the leaflet and cured the obstruction. The patient also had a discrete subaortic membranous obstruction. the membrane being excised. Clinically significant subaortic obstruction to left ventricular outflow in the child is most frequently due to a discrete membrane. Hypertrophic muscular obstruction and fibromuscular tunnel are less common causes, and obstructive mitral valve conditions, consisting of mitral web, cleft, and bleb, are rare.' We report a unique example of obstruction resulting from an anomalous muscle band inserting into the anterior mitral valve leaflet and attached to the septal wall in the outflow tract. Case report. An II-year-old boy was referred for surgical relief of subaortic obstruction. A systolic murmur had been present since infancy. Initial heart catheterization at 8 years of age had disclosed a discrete subaortic membrane with only a modest (35 mm Hg) peak systolic gradient across the left ventricular outflow tract. When 10 years old, the boy began to complain of exertional chest pain and diminished exercise tolerance. Physical examination now revealed a thrusting and sustained apical impulse, and a precordial thrill was palpable over the base of the heart. A long, Grade 4/6 systolic ejection murmur could be heard maximally in the left third and fourth intercostal spaces, and was also well heard in the aortic area with low-intensity radiation to the base of the neck. On chest roentgenograms, the heart size was at the upper limits of normal with prominence of the left ventricle. The lung fields were normal. The electrocardiogram showed left ventricular hypertrophy with strain pattern. Treadmill electrocardiographic stress tests obtained since the age of 8 years were compared, and results were now abnormal, with ischemic changes at a heart rate of 110 beats/min. An echocardiogram revealed septal thickening, but the posterior wall was also thickened, such that the ratio between them was more in keeping with concentric rather than asymmetric septal hypertrophy. The septum moved normally. The left ventricular outflow was somewhat narrowed, measuring 1.5 em, and the suggestion of a gooseneck deformity was reported. The mitral valve was unremarkable. Recatheterization at this time revealed an average peak Address for reprints: Philip W. Wright, M.D., 701 E. 28th St., Suite 217, Long Beach, Calif. 90806.
The Journal of Thoracic and Cardiovascular Surgery
systolic gradient of 85 mm Hg across the left ventricular outflow tract, and the pressure trace showed the pattern of subaortic stenosis. Left ventricular pressure was 195/12 mm Hg. The left ventricular angiocardiogram showed a wellmarked area of radiolucency high in the outflow tract, characteristic of a subaortic membrane (Fig. I). There was no evidence of intracardiac shunt or of any other lesion or functional abnormality of the aortic or mitral valves. The preoperative diagnosis was discrete left ventricular outflow obstruction resulting from a subaortic membrane. The patient was operated upon with the aid of cardiopulmonary bypass for resection of this subaortic membrane. The approach was through an aortotomy and the aortic valve. The aortic valve appeared normal. In the subvalvular area, a typical subaortic membrane was found and excisedcompletely with a rim of muscle along its attachment. After closure of the aortotomy and discontinuation of cardiopulmonary bypass,the pressure gradient across the left ventricular outflow tract was found to be virtually unchanged. Cardiopulmonary bypass was resumed and, with combined myocardial protection of topical cooling and cold potassium cardioplegic arrest, the aortotomy was reopened to reexamine the subaortic area. A fiberoptic endoscopic light was introduced to illuminate the cavity of the left ventricle. The remaining obstruction appeared to be caused by a short anomalous muscle band (6 mm in diameter) which arose from the middle of the ventricular surface of the anterior mitral leaflet and crossed the outflow tract to insert high into the ventricular septum (Fig. 2). The muscle band was encircled with a ligature and, by traction and displacement, its pointsof attachment were carefully studied. This band appeared to tether the anterior mitral leaflet close to the septum, narrowing the outflow tract. The end of the band at its attachment to the mitral valve splayed out somewhat linearly up and down, marking the midline of the leaflet. The chordal attachments along the margin of the leaflet and papillary muscle apparatus appeared to be normal and entirely separate from this band. The band was excised by cutting it away nearly flush, without injury to the integrity of the valve leaflet, and from its pointof attachment high on the anterior ventricular septum. Thus released, the anterior leaflet assumed a normal position and appeared unobstructive, and the gradient across the outflow tract was found to be completely abolished following excision of the band. Histologically, the band was composed only of cardiac muscle. The patient had no residual gradient or mitral dysfunction at recatheterization 20 months later and has done well during a follow-up period of over 5 years.
Discussion. To our knowledge, no previous reports of a similar case of subaortic obstruction have appeared in the literature. In personal communication, Lev has reported observing similar abnormal muscle bundles and smaller bands in his large autopsy series of congenital heart disease; however, these have not caused clinically or hemodynamically significant obstruction. Heretofore, such bands have been significant only in that they may produce murmurs (personal communications from JE Edwards and RV Lucas, Jr.). Although they are uncommon causes of subaortic stenosis, several abnormalities of the mitral valve responsible for left ventricular outflow obstruction have
Volume 85 Number 6 June, 1983
Brief communications
939
av 8m
-=ttt=:~~~~ ommb almv -
Fig. 2. Diagram of the relationships in systole of the aortic valve leaflets (av), the discrete subaortic membrane (sm), the obstructing mitral muscle band (ommb), and the latter's attachments to anterior leaflet of the mitral valve (almv) and ventricular septum in the outflow tract. Ao, Aorta. LA, Left atrium. LV, Left ventricle. RV, Right ventricle. Fig. I. Cineangiocardiogram demonstrating the subaortic membrane (arrow).
been described. Abnormal cushion development affecting leaflet or septal formation, or both, has been held responsible.!" We believethe muscular band in this case is developmentally related to these and, more particularly, comparable to the mitral web. In our review, reported descriptions of mitral web have been helpful in explaining the possibleorigin of this mitral muscle band. I.2. S Mitral web is a term describing a fibromembranous structure inserting into the intact anterior mitral leaflet along a mid-mitral line and extending across the outflow tract to attach where the developmental fusion of conal and sinus septa occurs. The structure thus has the potential to obstruct left ventricular outflow.I.5 The mitral band in this case also arose in the anterior mitral leaflet in the same vertical linear central zone 'wherein the web develops when fusion of superior and inferior endocardial cushion contributions occurs. This is the familiar area in which a cleft of the leaflet exists when normal fusion has failed to occur. Like the web, the band was attached to the ventricular septum high in the outflow tract. In addition to these points of attachment which appear to be in common, mitral web has been reported to arise only from an intact leaflet as an accessory development, and the web has also been
associated with subaortic membrane.' Functionally, both band and web possess a similar potential to obstruct the left ventricular outflow by restraining the anterior leaflet near the septum. Additionally, the web may obstruct by means of the diaphragm it presents in the outflow tract. Should the mitral band and mitral web be considered variants of one condition? We believe they are. One might logically propose that what is common to mitral cleft and web as well as to this muscle band is maldevelopment in the zones of fusion of endocardial cushion elements, particularly as they relate to formation of the anterior mitral valve leaflet and ventricular septum. In the case of mitral web and band, an accessory rest of tissue of endocardial cushion origin appears in one instance to differentiate into a fibrous web and, in the other instance, into a compact muscular band. The coexistence of a subaortic membrane in this case deserves further comment. Not only in this case but in two of the original cases of mitral web reported by Sellers, Lillehei, and Edwards,' a subaortic membrane was also present of the classical high discrete type (Kelly Type I), with which associated anomalies are not particularly common." Van Praagh and associates? stated that typical fibrous ring subaortic stenosis results from maldevelopment of endocardial cushion tissue of the atrioventricular canal which usually forms the ante-
940
The Journal of Thoracic and Cardiovascular Surgery
Brief communications
rior leaflet of the mitral valve; they also cited numerous works of others to support this new view. Although at variance with the traditional and still widely held view that subaortic membrane represents persistent, malincorporated subaortic conal tissue (Keith" theory), this newer concept would account for the association of subaortic membrane with mitral band and web. Coincidentally, in both of Sellers' cases, it was only after excision of the subaortic membrane, for which the patients underwent operation, that the mitral web obstruction was recognized---once intraoperatively and once at necropsy. The fact that operation failed in each case emphasized the paramount importance of recognizing the potentially associated causes of left ventricular outflow obstruction, particularly when resection of the subaortic membrane fails to relieve the obstruction. Some causes of left ventricular outflow obstruction, such as a discrete subaortic membrane, are both well demonstrated by preoperative studies and easily confirmed by operative findings. Under operative conditions, the flaccid state of the heart may obscure other significant obstructions of left ventricular outflow, particularly those which are partly functional, such as idiopathic hypertrophic subaortic stenosis, bands, or abnormalities of mitral valve position. Therefore, operation must be guided by pressure determinations. The concluding operative pressure determination may be of paramount importance and should confirm relief of obstruction. Such pressure determinations have been controversial and belittled as misleading and even unnecessary in operations for simple subaortic membrane. This case illustrates their usefulness and impor-
tance, for it was solely on the basis of this finding that reexploration of the subaortic area and the possibility of a second cause of obstruction was considered. When a mitral band obstruction of the type we have described is found, resection of the band, releasing the obstructing anterior mitral leaflet in the outflow tract, should be corrective. REFERENCES Goor DA, Lillehei CW: Congenital malformation of the heart, Malformations of the Aortic Pathway. New York, 1975, Grune & Stratton, Inc., p 237 2 Bjork VO, Hulquist G, Lodin H: Subaortic stenosis produced by an abnormally placed anterior mitral leaflet. J THORAC CARDIOVASC SURG 41:659-669, 1961 3 McLean LD, Culligan JA, Kane DJ: Subaortic stenosis due to accessory tissue on the mitral valve. J THORAC CARDIOVASC SURG 45:382-388, 1963 4 Nanton MA, Belcourt CL, Gillis DA, Krauss VW, Roy DL: Left ventricular outflow tract obstruction owing to accessory endocardial cushion tissue. J THORAC CARDIOVASC SURG 78:537-541, 1979 5 Sellers R, Lillehei CW, Edwards JE: Subaortic stenosis caused by anomalies and atrioventricular valves. J THORAC CARDIOVASC SURG 48:289-301, 1964 6 Kelly DT, Wulfberg BA, Rowe RD: Discrete subaortic stenosis. Circulation 46:309-322, 1972 7 Van Praagh R, Corwin RD, Dahlquist EH Jr, Freeman RM, Mattioli L, Nebesar RA: Tetralogy of Fallot with severe left ventricular outflow tract obstruction due to anomalous attachment of the mitral valve to the ventricular septum. Am J Cardiol 26:93-101, 1970 8 Keith A: Schorstein lecture on the fate of the bulbus cordis in the human heart. Lancet 2:1267-1273, 1924
Notice of correction In the article by Laschinger and associates, entitled "Myocardial Cooling: Beneficial Effects of Topical Hypothermia" (J THoRAc CARDIOVASC SURG 84:807-814, 1982), an error has been noted. Figs. 2 and 4 are correctly referenced and their legends are correct. However, the graph now shown in Fig. 2 should be transposed to the location above the legend to Fig. 4, and the graph now shown in Fig. 4 should be moved to the position above the legend to Fig. 2.