Surgical management of infants with mitral valve stenosis or atresia without diminutive ascending aorta Tetsuya Kitagawa, Takaki Hori, Yutaka Masuda, Tomohisa Kawahito, Fumio Chikugo, Takashi Kitaichi, Yasushi Fukuta, Reiko Nakagawaa, Kazuhiro Moria, Suguru Matsuokaa, and Itsuo Katoh Department of Cardiovascular Surgery, and aDepartment of Pediatrics, The University of Tokushima School of Medicine, Tokushima, Japan Abstract:The surgical strategy in infants with mitral valve stenosis or atresia without diminutive ascending aorta remains to be established, including the potential for biventricular repair as a definitive operation. Our surgical experience of six infants with mitral valve stenosis (4patients) or atresia (2patients) without diminutive ascending aorta was evaluated based on three important factors:left ventricular volume;the nature of the systemic outflow obstruction; and the type of mitral valve anomaly. Two patients with systemic outflow tract diameter less than 65% of normal underwent systemic outflow tract reconstruction, and the other patients with outflow tract diameter more than 68%of normal were able to maintain systemic circulation without repair. Only one patient with mitral valve stenosis without left ventricular outflow tract obstruction underwent a successful open mitral valvotomy as a biventricular repair after first-stage palliation. The left ventricle of the other patients did not grow after first-stage palliation. Due to progressive subaortic narrowing, pulmonary artery banding should be avoided in patients with mitral atresia due to absent atrioventricular connection who are future Fontan candidates. Most patients with this lesion can be expected to become candidates for safe Fontan-type repair. J. Med. Invest. 46:59-65, 1999 Keywords:congenital mitral stenosis, mitral atresia, left ventricular volume, systemic outflow tract obstruction, Fontan-type repair INTRODUCTION Recently, advances in the surgical strategy for Fontan circulation in infants with the classical hypo-plastic left heart syndrome characterized by a diminu-tive ascending aorta have been achieved based on the experience of Norwood, Bove, and their colleagues (1-4). However, the surgical strategy for infants with mitral valve stenosis or atresia without diminutive ascending aorta remains to be established, including the potential for biventricular repair as a definitive operation (5). The strategy should be determined based on three important factors:left ventricular volume, the nature of the systemic outflow obstruc-tion, and the type of mitral valve anomaly. On the basis of this concept, we have retrospectively evalu-ated our surgical experience. PATIENTS AND METHODS Between December 1986 and December 1994, 6 consecutive infants with mitral valve stenosis or atresia without diminutive ascending aorta and ex-cessive pulmonary blood flow underwent surgical treatment at our institution (Table1). Echocardio-graphic examinations were performed on all patients before the first-stage palliative surgery. 1) Left ventricular volume Left ventricular volume was assessed by measure-ment of the left ventricular internal dimension and left ventricular-right ventricular cross-sectional area ratio at end-diastole from the parasternal short axis view. The left ventricular internal dimension at end-diastole was compared with normal values (6). For standardization of the latter, the ratio was mea-sured in 7 healthy infants (age:10-44 days [mean, 31 days], body weight:2.5-4.4kg [mean, 3.6kg]). The normal value of the left ventricular-right ven-tricular cross-sectional area ratio was 0.96±0.14. 2) Nature of systemic outflow obstruction Ventriculoarterial connections, the diameters of the aortic annulus and the aortic root, and subaortic narrowing were evaluated echocardiographically. The diameters of the aortic annulus and the aortic root were obtained at end-systole from the parasternal long axis view. The results were compared with normal values (6). 3) Type of mitral valve anomaly The type of mitral valve anomaly was assessed based on the number and position of papillary mus-cles. The diameter of the mitral annulus was measured at end-diastole from the apical four-chamber view. The results were compared with normal values (6). RESULTS 1) Left ventricular volume All patients except for patient 4 could be evaluated before the first-stage of palliation (Table2). The left ventricular internal dimension at end-diastole ranged from 4 to 12mm (24% to 77% of normal). The left ventricular-right ventricular cross-sectional area ratio ranged from 0.05 to 0.42. The left ventricle of all patients except for patient 5 (left ventricular internal dimension=77% of normal value, left ventricular-right ventricular cross-sectional area ratio=0.42) was diag-nosed as hypoplastic. We defined a hypoplastic left ventricle as one with a left ventricular internal di-mension at end-diastole less than 70% of the normal value (6). 2) Nature of systemic outflow obstruction A concordant ventriculoarterial connection was found in5patients, and a transposed connection in one patient. The diameter of the aortic annulus at end-systole ranged from 4 to7mm (59% to103%of normal) (Table3). The aortic valvular movements of all patients were normal. The diameter of the aortic root at end-systole ranged from3to6.6mm(43% to 82% of normal). No significant subaortic narrowing before the first-stage palliative surgery was seen in any patient. Two patients were diag-nosed with aortic stenosis of annular hypoplasia and the remaining 4 patients had normal systemic outflow tracts (we defined stenosis of the systemic outflow tract as a systemic outflow tract diameter at end-systole of less than 70% of normal values). 3) Type of mitral valve anomaly Mitral valve atresia of an absent atrioventricular connection was detected in 2 patients (Table4).The diameter of the mitral annulus in the other 4patients ranged from 6 to 10mm (56% to 85% of normal). Patients 1, 2, and 3 had two pa-pillary muscles in the normal position, and patient 4 had one papillary muscle. The mitral valve of patients 1 and 2 showed normal valvular movement. Patients 1and 2 were diagnosed with mitral valve stenosis of an-nular hypoplasia (we defined annular hypo-plasia as a diameter of the mitral annulus at end-diastole of less than 70% of normal values). The mitral valve of patient 3 showed ballooning of leaflets despite a bilateral commissural fusion and slight thickening. Patient 3 was diagnosed with mitral stenosis with shortened chordae. Patient 4 was diag-nosed with mitral valve stenosis with a para-chute valve. 4) First-stage palliation First-stage palliative surgery was performed be-tween 9 and 117 days (mean, 40days) after birth. Body weight at first-stage palliative surgery ranged from 2.5 to 4.2kg (mean, 3.3kg). In the patients with aortic annulus or aortic root diameter less than 65% of the normal value, re-construction of the systemic outflow tract was indicated based on our experience in the surgical treatment of infants with interrupted aortic arch, small ascending aorta, and ventricular septal defect separate from future definitive repair (Fig. 1).Patients 1 and 2, who had aortic annulus and aortic root diameters less than 65% of normal values underwent placement of a main pulmonary artery to the descending aorta conduit (in the earliest patient in our series) or a modified Norwood op-eration. An aortic annulus and aortic root with a diameter greater than 68% of the normal value could maintain the systemic circulation without repair in the early postoperative period. It was difficult to estimate on admission whether patient3would be a candidate for biventricular or Fontan-type repair, but the patient eventually under-went only repair of coarctation of the aorta. Patient4,with a parachute mitral valve, double-outlet right ventricle, small muscular ventricular septal defect, and apparently significantly hypoplastic left ventricle, was judged to be a candidate for Fontan-type repair and underwent surgical atrial septal defect creation and pulmonary artery banding. Patients 5 and 6, with mitral atresia of the absent atrioventricular connection, were originally diagnosed as candidates for Fontan-type repair and under-went repair of coarctation of the aorta, balloon atrial septostomy, and pulmonary artery banding. 5) Outcomes After first-stage palliation the left ventricle did not grow due to insufficient preload to the left ventricle in all patients except for patient 3. Patient1died because of inadequate regulation of the pulmonary blood flow after first-stage pallia-tive surgery resulting in postoperative congestive heart failure. Patient 2, who survived the Norwood operation, is now 9 years old, and shows good hemodynamics. However, he did not undergo a Fontan-type operation because of other physical anomalies. Patient3improved temporarily after repair of coarctation of the aorta but deteriorated gradually due to spontaneous closure of the foramen ovale. However, the left ventricle developed because of reduction of the afterload following repair of coarctation of the aorta and increased preload to the left ventricle following spontaneous closure of the foramen ovale. The left ventricular internal dimension at end-diastole in patient 3 increased from 6mm (41% of normal) on admission to14mm (95% of normal) before mitral valvotomy (Fig. 2).The left ventricular-right ventricular cross-sectional area ratio in patient3also increased from 0.23on admission to 0.59 before mitral valvotomy (Fig. 3).At that time we assessed the left ventricle as able to function as a systemic ventricle and performed a successful open mitral valvotomy 40 days after birth. However, cardiac catheterization at 26months old showed residual mitral valve stenosis of the subvalvular lesion and moderate pulmonary artery hypertension. Patient 4 had a good postoperative course. Cardiac catheterization at 3 years of age revealed low pul-monary vascular resistance by appropriate control of the pulmonary blood flow and normal right ventricular function. This patient is waiting for the Fontan-type operation. Patients 5 and 6required subsequent conversion to a Damus-Kaye-Stansel anastomosis, shunt op-eration, and creation of atrial septal defect due to progressive subaortic narrowing resulting from pul-monary artery banding in the first-stage palliative surgery and restrictive foramen ovale. However, patient 5 died on the first postoperative day because of limited pulmonary blood flow resulting from pulmonary venous and artery hypertension due to the delayed second-stage palliation (at13months of age). Patient 6 underwent a 4-mm modified Blalock-Taussig shunt between an innominate artery and the right pulmonary artery which caused exces-sive pulmonary blood flow and reduced systemic perfusion (at 6 months of age). The shunt was re-placed with a bidirectional Glenn shunt. However, he died because of the pulmonary thromboembolism 6 days after the operation. DISCUSSION Although the surgical strategy for patients with mitral valve stenosis or atresia without diminutive ascending aorta should be determined based on three factors, it seems unusual for them to become candidates for future biventricular repair. Therefore, most patients are expected to be candidates for safe Fontan-type repair. 1) Fontan-type repair A hypoplastic aortic valve is defined as having a di-ameter of less than 5 or 6 mm by echocardiographic assessment (5, 7), and a hypoplastic aortic root as having a diameter of less than 6mm by the same method (8). In our patient series, a systemic outflow tract with a diameter greater than 68% of normal was capable of maintaining the systemic circulation without repair, with sufficient feeding and weight gain. We experienced that one patient from another series with an interrupted aortic arch, ventricular septal defect, and aortic root with a diameter of 64% of normal values showed low cardiac output syndrome after complete repair and died. Gen-erally speaking, in infants with body weight of 3 kg, an aortic annulus diameter of 4.3mm and aortic root diameter of4.5mm are65%of normal values and correspond to about42%of the normal cross-sectional area of the aortic annulus and aortic root. We think that an aortic annulus or aortic root with a diameter of less than65%of normal might be a reasonable criterion for performing the Norwood procedure as a first-stage palliative surgery. In patients with mitral valve stenosis after the Norwood-type operation, the left ventricle appears not to grow due to insufficient preload. Therefore, to perform an optimal Fontan-type op-eration by achieving low pulmonary vascular resistance and prevention of myocardial hypertrophy, it is important to proceed swiftly with a second-stage hemi-Fontan procedure (2). An unusual patient with mitral atresia of the imperforate membrane might be better corrected by resection of the imperforate membrane and the insertion of a prosthetic valve in the mitral position. However, in most patients with mitral valve atresia of the absent atrioventricular connection, normally related great arteries, and muscular ven-tricular septal defect, the left ventricle appears to function as the outlet chamber of the main right ven-tricle through a muscular ventricular septal defect, and not to grow even if it is not hypoplastic. We think that patients with such complex lesions should be treated from the start in anticipation of a future Fontan-type repair. Therefore, pulmonary artery banding, which causes subaortic narrowing and reduction of myocardial compliance, should be avoided as first-stage palliation for patients with such complex lesions (9, 10). A palliative arterial switch operation (11, 12) or modified Norwood/Damus-Kaye-Stansel procedure are advocated as first-stage palliative surgery for neonates with such complex lesions, which have the potential to result in systemic ventricular outflow tract obstruction (7,13-16). If pulmonary artery banding is performed reluctantly, such detrimental long-term effects should be monitored closely and be relieved by the above procedures or hemi-Fontan operation/bidirectional Glenn shunt as early as possible. 2) Biventricular repair Only a patient with mitral valve stenosis without the need for systemic outflow tract reconstruction should undergo a biventricular repair attempt. Some mitotic activity in rat cardiac myocytes was reported to persist during early neonatal life (17).Although this has not been definitely proven in humans, myocyte mitotic activity and the potential for hyperplasia allegedly persist for3to6months after birth (18). According to previous reports, only patients with a normal mitral valve who underwent a Norwood-type operation as a first-stage palliation due to subaortic obstruction have successfully under-gone a Rastelli-type biventricular procedure as a definitive repair (5). Early improvement of forward flow through the mitral valve might result in hypo-plastic left ventricle growth, as seen in the left ventricle of our patient 3. However, it is difficult to estimate the future growth potential of the left ventricle associated with congenital mitral valve stenosis before first-stage palliative surgery in neonates. Due to the volume and pressure load on the right ventricle derived from interatrial left-to-right shunt and mitral valve stenosis, the right ventricle is usually enlarged and the left ventricular-right ventricular cross-sectional area ratio is reduced. To estimate the function of the left ventricle against the volume load after repair of the mitral valve, it is important to closely follow the changes in the left ventricular internal dimension in end-diastole. Mitral valve repair is a useful palliative procedure which may provide symptomatic relief and allow growth of the child in the current absence of a satisfactory prosthetic valve substitute. However, valvotomy for most infants obviously does not result in complete reduction of the mitral valve gradient, because the obstruction of flow results mainly not from commissural fusion but from obliteration of the interchordal spaces. An innovative left ventricular apical approach for repair of subvalvular stenosis was reported by Barbero-Marcial and his coleagues (19). Although we used a modified Brawley approach (20) because of the slight subvalvular lesion in patient3, additional papillotomy would be needed to remove the residual subvalvular stenosis and to restore adequate leaflet motion. Our experience does not establish a definitive sur-gical strategy for treatment of these lesions because the number of patients was too few. However, to achieve either Fontan-type repair for most patients or biventricular repair for rare patients as a defini-tive operation, suitable first-stage palliation and additional interventions in early infancy should be performed based on changes in the three deter-minants of left ventricular volume, nature of the systemic outflow obstruction, and type of mitral valve anomaly. REFERENCES 1. Norwood WI, Lang P, Hansen DD:Physiologic repair of aortic atresia-hypoplastic left heart syndrome. N Engl J Med 308:23-26, 1983 2. Norwood WI, Jacobs ML, Murphy JD:Fontan procedure for hypoplastic left heart syndrome. Ann Thorac Surg 54:1025-1030, 1992 3. Iannettoni MD, Bove EL, Mosca RS, Lupinetti FM, Dorostkar PC, Ludomirsky A, Crowley DC, Kulik TJ, Rosenthal A:Improving results with first-stage palliation for hypoplastic left heart syndrome. J Thorac Cardiovasc Surg107:934-940, 1994 4. 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In:Alpert NR, ed. Cardiac Hyper-trophy. Academic Press, New York, 1971, pp.11 19. Barbero-Marcial M, Riso A, De Albuquerque AT, Atik E, Jatene A:Left ventricular apical approach for the surgical treatment of congeni-tal mitral stenosis. J Thorac Cardiovasc Surg106:105-110, 1993 20. Brawley RK:Improved exposure of the mitral valve in patients with a small left atrium. Ann Thorac Surg 29:179-181, 1980 Received for publication November 26, 1998 ; accepted December 17, 1998. Address correspondence and reprint requests to Dr. Tetsuya Kitagawa, Department of Cardiovascular Surgery, The University of Tokushima School of Medicine, Kuramoto-cho, Tokushima770-8503, Japan, and Fax:+81-88-633-7152.