Discrete Subaortic Stenosis: Incidence, Morphology and Surgical Impact of Associated Subaortic Anomalies

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1 Discrete Subaortic Stenosis: Incidence, Morphology and Surgical Impact of Associated Subaortic Anomalies Maurizio Marasini, MD, Lucio Zannini, MD, Gian Paolo Ussia, MD, Robin Pinto, MD, Rodolfo Moretti, MD, Franco Lerzo, MD, and Giacomo Pongiglione, MD, FACC Laboratory of Interventional Cardiology, Division of Cardiovascular Surgery, and Intensive Care Unit, Department of Pediatric Cardiology and Cardiovascular Surgery, Giannina Gaslini Institute, Children s Hospital, Genova, Italy Background. The association between discrete subaortic stenosis and other subaortic anomalies is a well known but rarely reported occurrence. The aim of this study is to define the incidence, morphology, and surgical impact of associated anomalies of the left ventricular outflow tract in children operated on for discrete subaortic stenosis. Methods. Between 1994 and 2000, 45 consecutive children were operated on for discrete subaortic stenosis. Patients were divided in two groups according to the obstructive lesion detected by echocardiography. Results. A localized shelf was found as an isolated lesion in 31 patients (group A), whereas additional subaortic anomalies were found in 14 cases (31%) and were multiple in 5 cases (group B). The anomalies included anomalous septal insertion of mitral valve (7 cases); accessory mitral valve tissue (2 cases); anomalous papillary muscle (2 cases); anomalous muscular band (8 cases); and muscularization of the anterior mitral valve leaflet (1 case). Cardiopulmonary bypass and aortic crossclamping times were significantly shorter in group A. There were no operative deaths nor major complications or deaths during follow-up. A gradient of 15 mm Hg or more was found at follow-up in 5 cases whereas aortic regurgitation was estimated to be not clinically significant in all but 1 patient. Six cases of recurrent subaortic stenosis were found in our series, 3 of them with other subaortic anomalies. Conclusions. This study shows that discrete subaortic stenosis can often be associated with other subaortic abnormalities. Surgical treatment of these anomalies produces excellent early and mid-term relief of obstruction without any increase in mortality and morbidity. (Ann Thorac Surg 2003;75:1763 8) 2003 by The Society of Thoracic Surgeons Discrete subaortic stenosis remains a surgical challenge for the relatively high incidence of recurrence of stenosis or progression of aortic regurgitation [1, 2]. Recent reports suggest that surgery must be aimed at the removal of all structures causing flow turbulence in the left ventricular outflow tract (LVOT) in order to reduce the incidence of these complications [3 6]. We reviewed our experience to evaluate the incidence, morphology, and impact of LVOT associated anomalies on the surgical treatment and early outcome of patients operated on for discrete subaortic stenosis. Patients and Methods From January 1994 through December 2000, 45 consecutive patients (26 male and 19 female) underwent surgery for discrete subaortic stenosis defined as a localized shelf of fibrous or fibromuscular tissue beneath the aortic valve [1, 7]. Patients with long segment stenosis, hypertrophic obstructive cardiomyopathy, or associated major Accepted for publication Dec 17, Address reprint requests to Dr Marasini, Laboratory of Interventional Cardiology, Giannina Gaslini Institute, Largo Gerolamo Gaslini, Genova, Italy; mauriziomarasini@istituto-gaslini.ge.it. anomalies such as transposition of the great arteries, univentricular heart, or double outlet right ventricle were excluded. Patients having previous cardiac surgery for ventricular septal defect (VSD) or atrioventricular septal defect (AVSD) and developing subaortic stenosis were included in the study as well as those with recurrent discrete subaortic stenosis. Preoperative and postoperative assessment was performed by transthoracic and transesophageal ultrasonography examination alone (Sonos 2500 or 5500; Hewlett-Packard) in all cases. Six patients who had previous cardiac operations also underwent preoperative cardiac catheterization to rule out any residual defect. Patients were placed into two groups according to preoperative echocardiographic evidence of an obstructive lesion: a localized shelf with moderate to severe septal hypertrophy was found as an isolated lesion in 31 patients (group A), whereas additional anomalies of the LVOT were found in 14 patients (31%), 5 of them with multiple lesions (group B). These anomalies included anomalous septal insertion of mitral valve (7 cases; Fig 1); accessory mitral valve tissue (2 cases; Fig 2); accessory papillary muscle (2 cases; Fig 3); anomalous muscular bands within the LVOT (8 cases; Fig 4); muscularization 2003 by The Society of Thoracic Surgeons /03/$30.00 Published by Elsevier Inc PII S (02)

2 1764 MARASINI ET AL Ann Thorac Surg SUBAORTIC STENOSIS AND ASSOCIATED ANOMALIES 2003;75: Fig 1. Biplane transesophageal long axis view through the left ventricular outflow tract demonstrating multiple subaortic chordal attachment (arrows) of the anterior mitral valve leaflet to the interventricular septum. of the anterior mitral valve leaflet (1 case; Fig 5). Eight patients in both groups had undergone previous surgery (Table 1): 4 had repair of a partial or complete AVSD and 1 was operated on twice for subaortic stenosis and severe mitral valve regurgitation; 1 patient had closure of a perimembranous VSD; and 7 had aortic coarctation repair. Finally, reoperation was required in 4 patients for recurrent subaortic stenosis. Aortic valve was found bicuspid in 9 patients, 7 in group A and 2 in group B (Table 1). Subaortic gradient was estimated by continuous wave Doppler and mean pressure gradient was obtained [8]. Doppler color flow mapping was used to grade aortic valve regurgitation as described by Parry and colleagues [9]. Patients were scheduled for surgery when a mean pressure gradient of 25 mm Hg or more was recorded or when, irrespective of LVOT gradient, a new appearance of aortic regurgitation was found [10 12]. Fig 3. Cross-sectional parasternal long axis echocardiographic view showing attachment of an accessory papillary muscle to the anterior leaflet of the mitral valve (arrow). Operations were always performed with hypothermic cardiopulmonary bypass and myocardial protection was obtained by anterograde blood cardioplegia repeated at 20-minute intervals. The obstructive lesions were approached through an oblique aortotomy, which was extended to the noncoronary sinus. The surgical procedure included membranectomy and deep myectomy in all patients and additional resection of the associated anomalies in group B, consisting of transection of anomalous papillary muscle or muscular band and resection of accessory chordal attachment or valvular tissue. When necessary a prolapsed or redundant aortic cusp was repaired using a standard pledget-reinforced technique. Residual gradient and aortic valve competence after cardiopulmonary bypass were evaluated by direct pressure recording and transesophageal echocardiography. All patients were regularly followed up by echocardiography to evaluate residual or recurrent subaortic obstruction and aortic valve function. Recurrence of subaortic stenosis was defined as the new echocardiographic ap- Fig 2. Two dimensional transesophageal long axis view of the left ventricular outflow tract showing accessory mitral valve tissue (white arrow) below the subaortic membrane (black arrow). Fig 4. Cross-sectional apical long axis view of the left ventricle demonstrating an anomalous muscular band (arrow) from the anterolateral papillary muscle to the interventricular septum.

3 Ann Thorac Surg MARASINI ET AL 2003;75: SUBAORTIC STENOSIS AND ASSOCIATED ANOMALIES 1765 Fig 5. Parasternal short axis view of the left ventricular outflow tract showing an anomalous muscularization of the anterior mitral valve leaflet (arrows). pearance of a previously undetected lesion causing subaortic flow acceleration. Left ventricular outflow tract peak flow velocity 1.8 m/s or less was considered within normal range and the estimated pressure gradient was set equal to zero [8]. The obstruction was considered significant when a Doppler mean pressure gradient of 15 mm Hg or more was recorded. A one-step increase in the degree of aortic valve regurgitation was considered a sign of worsened diastolic aortic valve function. Data are expressed as median, range, and mean standard deviation. Comparison of means and proportions for continuous variables were based on standard t test. For each of the analyses a p value of 0.05 or less was considered statistically significant. Results All the patients but 1 were symptom free. No significant difference in age at operation and in preoperative Doppler mean pressure gradient was found between the two groups (Table 2). Moderate to severe aortic regurgitation was present preoperatively in 5 patients of group A and in 3 patients of group B (Fig 6); in 3 of them cusp resuspension was performed at operation. Associated anomalies of the left ventricular outflow tract detected by preoperative ultrasonography examination were confirmed intraoperatively in all cases and treated at the first operation in all but 2 cases. In these 2 latter patients, both previously operated on for AVSD, anomalous septal insertion of the mitral valve leaflet was considered untreatable without mitral valve replacement. This procedure was performed 3 years later in 1 case for recurrent subaortic stenosis associated with persistent severe mitral valve regurgitation. In another 2 patients first undergoing only ridge resection and deep myectomy, a significant residual gradient at the end of cardiopulmonary bypass was recorded (Table 3). Intraoperative transesophageal echocardiography confirmed the complete excision of the subaortic ridge and suggested that residual obstruction was related to the persistence of an anomalous muscular band. Cardiopulmonary bypass was then restarted and the associated anomalies were removed, with disappearance of the subaortic gradient. Cardiopulmonary bypass and aortic cross-clamping times were significantly lower in group A when compared with group B (p 0.001; Table 2). No significant difference in the early postoperative gradient as well as in the degree of residual aortic valve regurgitation was observed between the two groups (Table 2). There were no operative deaths nor major complications or deaths during a median follow-up of 24 months in both groups. Doppler mean pressure gradient at the last control scan was significantly lower compared with the preoperative gradient in both groups (p 0.001; Tables 2 and 3). A gradient of 15 mm Hg or more was found in 5 patients (11%), 3 in group A and 2 in group B; 1 was associated with aortic valve stenosis, the remaining 4 with discrete subaortic stenosis recurrence. There were 6 cases of recurrent subaortic stenosis in our series: 1 with dominant aortic valve stenosis, 2 with recurrence of isolated shelf, and 3 with other anomalies of the LVOT either undetected or not corrected at operation. There was no clinically significant aortic regurgitation at follow-up and it was found trivial or absent in 25 of 31 patients in group A and in all but 1 patient in group B (Fig 6). Finally, mitral valve regurgitation was ruled out by color Doppler examination in all but 4 patients previously operated on for AVSD, and in 3 of them it was mild. One patient underwent reoperation for discrete subaortic stenosis associated with persistent severe mitral valve regurgitation and another had balloon percutaneous valvuloplasty for aortic valve stenosis; both patients are doing well at more than 1 year of follow-up. Table 1. Associated Heart Defects and Previous Operations in 45 Patients Anomalies Group A Group B Bicuspid aortic valve 7 2 Atrioventricular septal defect 0 4 a Aortic coarctation 5 2 Ventricular septal defect 1 0 Subaortic stenosis 2 2 a a One patient was initially operated on once for atrioventricular septal defect and twice for discrete subaortic stenosis and mitral valve regurgitation. Comment Discrete subaortic stenosis is a progressive and probably acquired cardiac abnormality in which the left ventricular outflow tract is obstructed by a subvalvular fibromuscular ring [7, 10]. This condition may occur as a primary defect or be associated with other congenital heart diseases [1, 2, 5, 7]. Similarly to previously reported series, we included in our study patients with discrete subaortic stenosis having previous surgery for VSD or AVSD but not patients with subaortic stenosis associated with univentricular heart, transposition of the great arteries, dou-

4 1766 MARASINI ET AL Ann Thorac Surg SUBAORTIC STENOSIS AND ASSOCIATED ANOMALIES 2003;75: Table 2. Preoperative and Postoperative Variables of the Two Groups Mean SD Group A Median (Range) Mean SD Group B Median (Range) p Value Age (years) ( ) (0.8 9) ns MG1 (mm Hg) (15 70) (15 80) ns a CPB (min) (41 142) (63 170) ACC (min) (20 75) (42 144) Follow-up (months) (6 72) (8 72) ns MG2 (mm Hg) (0 65) (0 70) ns a a p MG1 versus MG2. ACC aortic cross clamping time; Age age at operation; CPB cardiopulmonary bypass; MG1 mean aortic gradient before surgery; MG2 mean aortic gradient at follow-up. ble outlet right ventricle, or Shone s anomaly [3 5, 10, 11]. In these latter patients, subaortic obstruction is usually more complex and often requires other surgical procedures. Surgery is widely accepted as a reliable means to relieve obstruction and to prevent complications secondary to long-standing ventricular hypertrophy, aortic valve damage, or infective endocarditis [3, 5, 7, 11 13]. However, major concerns remain on the indications for and timing of intervention [7, 11 15]. Significant LVOT gradient before surgery is still recommended by most centers but more rapid intervention is advocated by others especially for infants and children [3, 5, 7, 13]. Almost all patients in our series were children and consequently we chose to treat patients with a mean pressure gradient of 25 mm Hg or more and, irrespective of LVOT gradient, patients with a new appearance of aortic regurgitation. Mean Doppler gradient was preferred to the instantaneous peak Doppler gradient because of better correlation with the invasive gradient, particularly for the lower values [8]. Surgical excision of the subaortic ridge with resection of underlying LVOT muscle can now be accomplished with a very low mortality rate and minimal complications [1 5]. However this apparently simple surgical issue was found to be associated with a relatively high incidence of Fig 6. Preoperative (hatched bars) and postoperative (dotted bars) distribution of aortic valve regurgitation in 45 patients. gradient recurrence or progression of aortic regurgitation after surgery [1 5, 11, 12, 15]. Recent reports suggest that surgery must be aimed at removing all structures causing LVOT flow turbulence in order to reduce the incidence of these complications [3 6, 10, 16]. Therefore more aggressive surgical approaches have been proposed other than simple excision of the fibrous ring, including early operation before the appearance of severe left ventricle hypertrophy [5], extended and circumferential myectomy [3], and mobilization of the left and right fibrous trigones [4]. The association between discrete subaortic stenosis and other left ventricular outflow tract anomalies such as anomalous mitral valve insertion [17], accessory mitral valve tissue [18 20], abnormal mitral papillary muscle [21], anomalous muscular bands within the LVOT [22], and posterior displacement of the infundibular septum without VSD [23] is well known but has been only sporadically reported. In a personal communication, LeCompte referred to a more than 40% incidence of these Table 3. Preoperative and Postoperative Variables in Patients of Group B Patient Number MG1 (mm Hg) MG-EPO (mm Hg) Follow-up (months) MG2 (mm Hg) [20] a [30] a a Values in brackets were recorded at the end of the first cardiopulmonary bypass. MG-EPO mean aortic gradient early after operation; MG1 mean aortic pressure gradient before surgery; MG2 mean aortic gradient at follow-up.

5 Ann Thorac Surg MARASINI ET AL 2003;75: SUBAORTIC STENOSIS AND ASSOCIATED ANOMALIES 1767 anomalies in a series of 37 patients with discrete subaortic stenosis and more recently the same French group reported one or more valvular anomalies in 48% of 73 consecutive patients operated on for discrete subaortic stenosis [25]. This unusually high incidence of associated anomalies is similar to our experience in which 31% of patients with discrete subaortic stenosis had associated subaortic anomalies. In these patients all LVOT associated anomalies should be visualized preoperatively because it is very difficult for the surgeon to identify them in an open but relaxed and cardiopleged heart [3]. For this purpose echocardiography may be considered mandatory as it can precisely delineate LVOT obstruction through multiple scan planes in a beating heart [6, 13, 25]. However this analysis requires expertise because LVOT obstructive anomalies may remain unrecognized preoperatively when associated with a typical discrete subaortic stenosis [17]. In our experience we observed a high rate of these anomalies not only in patients with subaortic stenosis after partial or complete AVSD repair, as previously reported in the literature [24], but also in patients with isolated discrete subaortic stenosis. Although echocardiography resulted as extremely accurate in recognizing the morphologic appearance of all associated anomalies, we were unable to understand and demonstrate preoperatively which obstruction component was due to discrete subaortic stenosis and which was ascribable to other associated anomalies. This aspect should be mainly related to the close proximity of all these structures. However in the 4 patients in which all the associated anomalies were not removed at the first operation, a residual gradient was recorded at the end of cardiopulmonary bypass. Moreover 3 of 6 cases of our series with discrete subaortic stenosis recurrence had other anomalies of the LVOT either undetected or not corrected at operation. Surgical resection of these abnormal structures was finally possible at the first operation in all but 2 cases without increased risk of early mortality and morbidity, notwithstanding a significant increase in cardiopulmonary bypass and aortic cross clamping mean times. We have no experience of mitral valve regurgitation related to the resection of LVOT obstructive anomalies despite the frequent involvement of this valve in subaortic obstruction. In 2 patients, both previously operated on for AVSD, associated subaortic anomalies were considered untreatable without mitral valve replacement; in 1 of them a prosthetic valve was implanted because of persistent severe mitral valve regurgitation and subaortic stenosis and the other patient is waiting for operation. Limited follow-up time and a small number of patients characterize our experience, and further studies are required to conclude that recognition and surgical treatment of associated anomalies of LVOT may reduce the incidence of discrete subaortic stenosis recurrence and the progression of aortic regurgitation [12]. However our data support that discrete subaortic stenosis can often be associated with other abnormalities of LVOT and that their echocardiographic recognition is mandatory before operation. Surgical treatment of these anomalies produces an excellent early and mid-term relief of obstruction without any increase in mortality and morbidity. 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