Discrete subaortic stenosis. Surgery in children based on two-dimensional and Doppler echocardiography

Discrete subaortic stenosis: incidence, morphology and surgical impact of associated subaortic anomalies

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 cross-clamping 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.

Echocardiographic, morphologic, and geometric variations of the left ventricular outflow tract: possible role in the pathogenesis of discrete subaortic stenosis

Although the clinical features and natural course of discrete subaortic stenosis (DSS) are well defined, the etiology remains speculative. The purpose of this study was to identify the echocardiographic, morphologic, and geometric variations of the left ventricular outflow tract associated with DSS in children and to determine whether these variations have a role in the pathogenesis of DSS. The aortoseptal angle (ASA), mitral-aortic valve separation (MAS), and the size of the aortic annulus were determined in two groups of children. Group 1 comprised 11 patients with isolated DSS, who were compared with an age- and body surface area- (BSA) matched healthy children (Group 1A, n: 20). Group 2 comprised 10 patients with DSS and ventricular septal defect (VSD). Group 2 was compared with an age- and BSA-matched patients with isolated perimembranous VSD (Group 2A, n: 22). Measurements were carried out from previously recorded echocardiographic studies. The ASA was steeper (119.3 +/- 6.1 degrees vs 137.5 +/- 5.6 degrees , p < 0.001), and the MAS was wider (6.1 +/- 1.6 vs 3.2 +/- 0.7 mm, p < 0.001) in patients with isolated DSS than in healthy control subjects. Similar differences were found between patients in Group 2 and Group 2A; the ASA was steeper (122.2 +/- 6.5 degrees vs 141.3 +/- 5.0 degrees, p < 0.001), and the MAS was wider (5.8 +/- 1.5 vs 3.8 +/- 1.1 mm, p < 0.001). The size of the aortic annulus was not different among the four study groups. Although the MAS was significantly wider in patients with DSS, there was significant overlap in MAS between patients and controls. However, if an ASA < or = 130 degrees was chosen as a predictive variable, it was found to be a highly sensitive, specific, and positive predictive marker for the development of DSS. This study demonstrates that DSS is associated with a steeper ASA, and a wider MAS, in patients with or without associated VSD. These morphologic abnormalities, especially a steeper ASA, may be risk factors for the development of DSS.

Morphology and dynamic change of discrete subaortic stenosis can be imaged and quantified with three-dimensional transesophageal echocardiography

This report describes three-dimensional transesophageal echocardiographic findings in three consecutive patients with discrete subaortic stenosis. The discrete subaortic stenosis lesions included a circumferential, a remnant crescent, and a broken fibrotic subaortic membrane. The lesions were best imaged by using a three-dimensional transesophageal echocardiography-generated "aortotomy view" of the left ventricular outflow tract immediately below the plane of the aortic valve. The three-dimensional images correlated well with surgical and pathologic findings. The three-dimensional surface areas of the left ventricular outflow tract at the level of discrete subaortic stenosis during systole (0.8 +/- 0.5 cm2) and diastole (1.7 +/- 0.7 cm2) were measured by planimetry of the three-dimensional transesophageal echocardiographic images. The novel "aortotomy view" offered by three-dimensional transesophageal echocardiography provided direct visualization and quantification of discrete subaortic stenosis in a dynamic fashion. In summary, three-dimensional transesophageal echocardiography can accurately display and quantify discrete subaortic stenosis and could be a new clinically useful tool for assessing discrete subaortic stenosis and guiding surgical and transcatheter interventions.

Potential role of mechanical stress in the etiology of pediatric heart disease: septal shear stress in subaortic stenosis

OBJECTIVES

The objective of this study was to show elevations in septal shear stress in response to morphologic abnormalities that have been associated with discrete subaortic stenosis (SAS) in children. Combined with the published data, this critical connection supports a four-stage etiology of SAS that is advanced in this report.

BACKGROUND

Subaortic stenosis constitutes up to 20% of left ventricular outflow obstruction in children and frequently requires surgical removal, and the lesions may reappear unpredictably after the operation. The etiology of SAS is unknown. This study proposes a four-stage etiology for SAS that I) combines morphologic abnormalities, II) elevation of septal shear stress, III) genetic predisposition and IV) cellular proliferation in response to shear stress.

METHODS

Morphologic structures of a left ventricular outflow tract were modeled based on measurements in patients with and without SAS. Septal shear stress was studied in response to changes in aortoseptal angle (AoSA) (120 degrees to 150 degrees), outflow tract convergence angle (45 degrees, 22.5 degrees and 0 degree), presence/location of a ventricular septal defect (VSD) (3-mm VSD; 2 and 6 mm from annulus) and shunt velocity (3 and 5 m/s).

RESULTS

Variations in AoSA produced marked elevations in septal shear stress (from 103 dynes/cm2 for 150 degrees angle to 150 dynes/cm2 for 120 degrees angle for baseline conditions). This effect was not dependent on the convergence angle in the outflow tract (150 to 132 dynes/cm2 over full range of angles including extreme case of 0 degree). A VSD enhanced this effect (150 to 220 dynes/cm2 at steep angle of 120 degrees and 3 m/s shunt velocity), consistent with the high incidence of VSDs in patients with SAS. The position of the VSD was also important, with a reduction of the distance between the VSD and the aortic annulus causing further increases in septal shear stress (220 and 266 dynes/cm2 for distances of 6 and 2 mm from the annulus, respectively).

CONCLUSIONS

Small changes in AoSA produce important changes in septal shear stress. The levels of stress increase are consistent with cellular flow studies showing stimulation of growth factors and cellular proliferation. Steepened AoSA may be a risk factor for the development of SAS. Evidence exists for all four stages of the proposed etiology of SAS.

Primary repair of isolated ventricular septal defect in infancy guided by echocardiography

Between 1989 and 1995, 96 consecutive infants affected by isolated ventricular septal defect (VSD) were submitted for primary correction at a median age of 4 months. Of the 96, 60 (group I) underwent surgery on the base of a 2-dimensional Doppler echocardiographic (DD echo) test alone. The preoperative DD echo anatomic definition of the type of VSD was confirmed at surgery in all 60 patients without false-positive results in terms of additional cardiac anomalies. There were 2 false-negatives: in 2 patients an associated cardiac anomaly was not detected by DD echo and required a second surgical procedure after postoperative cardiac catheterization. During the same period 36 infants (group II) underwent surgical closure of isolated VSD on the basis of cardiac catheterization and angiocardiography in addition to DD echo. The retrospective comparison between the 2 groups revealed no significant difference in terms of sensitivity and specificity of the diagnostic tools, early and late mortality after surgical correction, postoperative hospital stay, and need for late cardiac catheterization and surgery. We conclude that after an accurate selection, most of the infants with uncomplicated VSD can safely undergo primary repair on the basis of DD echo alone.

The Usefulness of Transesophageal Echocardiography in the Surgical Management of Older Children with Subaortic Stenosis

Subaortic stenosis is a complex lesion that often presents in older children and adolescents. A clear depiction of the lesion is required for optimization of surgery. Due to the large size of these patients, is not always possible from surface echocardiography. Intraoperative multiplane echocardiography (MTEE) has been performed at our institute in older children for several different congenital heart lesions including many patients with subaortic stenosis. A retrospective analysis of our experience with MTEE in patients with subaortic stenosis was performed to assess its usefulness in the preoperative diagnosis and postoperative assessment of repair. Our results show that intraoperative MTEE was useful preoperatively by correcting or confirming suspected diagnosis, and giving additional details of the lesion in many patients. Postoperatively, MTEE was highly useful in the assessment of repair. We strongly recommend the use of intraoperative MTEE in older children and adolescents with subaortic stenosis. (ECHOCARDIOGRAPHY, Volume 13, November 1996)

Echocardiographically guided repair of tetralogy of Fallot

Although 2-dimensional, Doppler, color flow echocardiography is accepted as a safe diagnostic method to guide the surgical treatment of certain heart defects, cardiac catheterization remains mandatory for patients with tetralogy of Fallot. Based on the excellent diagnostic correlation between echocardiography and angiocardiography, a policy of echo-guided primary repair of uncomplicated, selected cases of tetralogy of Fallot was introduced at Ospedale Bambino Gesù. In the last 5 years, of 139 patients who had surgery for tetralogy of Fallot, 105 underwent primary repair. In 56 patients (53.3%), surgery was guided only by echocardiography (group I). In the remaining 49 patients (46.7%) (group II), unclear imaging of cardiovascular anatomy (n = 23), or echo-suspected associated malformations (n = 26) prompted cardiac catheterization. The 2 groups did not differ in age and weight at surgery. Intraoperative examination did not show diagnostic errors in patients of group I; cardiac catheterization and surgery confirmed the suspected associated anomalies in 16 of 26 patients of group II (38.4% false-positive). Echocardiography showed an overall sensitivity of 100% and specificity of 85% for detection of associated malformations. In conclusion, echocardiography proved to be adequate for selection of patients with uncomplicated forms of tetralogy of Fallot for primary repair.

"Acquired" subvalvular aortic stenosis after repair of a ventricular septal defect

Of 353 children who underwent surgical repair of a congenital heart defect, including closure of a ventricular septal defect (VSD), 12 patients (four with tetralogy of Fallot, five with a VSD, and three with a double-outlet right ventricle) developed subaortic stenosis, which was diagnosed one to six years after the surgical procedure. Five patients required surgical treatment of the subaortic stenosis, and one required percutaneous balloon angioplasty. Postsurgical subaortic stenosis appears to be an uncommon progressive acquired disease.

Pediatric cardiac surgery guided by echocardiography. Established indications and new trends

Cardiac surgery in 602 children was not preceded by cardiac catheterization, the diagnosis being based on clinical findings and two-dimensional and Doppler echocardiography. In the 355 operations without cardiopulmonary bypass there were nine major and seven minor diagnostic errors (2.5% and 2%). Among the 247 cases with open-heart surgery there were no major and eight (3.2%) minor errors. The malformations most suitable for nonbypass surgery without catheterization seem to be those with reduced pulmonary blood flow requiring systemic-pulmonary artery shunt, aortic coarctation and patent ductus arteriosus. For open-heart surgery without invasive investigation, atrial septal defect, partial atrioventricular canal, aortic and pulmonary stenosis, cardiac tumor and isolated valve disorder are 'classic' candidates. Recent experience indicated that selected cases of complete atrioventricular canal, tetralogy of Fallot, truncus arteriosus, total anomalous pulmonary venous connection and transposition of the great arteries may safely undergo primary repair without cardiac catheterization. Because of its diagnostic potentialities, pediatric cardiac surgeons must become familiar with echocardiography.