Live three-dimensional transthoracic echocardiographic identification of discrete subaortic membranous stenosis

We describe an adult patient in whom live three-dimensional transthoracic echocardiography illustrated the exact site and full extent of the subaortic membrane as well as the narrow opening within the membrane, indicative of severe stenosis. To our knowledge this has not been reported previously.     

Rheology of discrete subaortic stenosis

The discrete form of subaortic stenosis is thought to be an acquired lesion, the aetiology of which may be a combination of factors which include an underlying genetic predisposition, turbulence in the left ventricular outflow tract, and various geometric and anatomical variations of the left ventricular outflow tract. A review of hypotheses relating to its aetiology is provided     

Two-dimensional echocardiographic evaluation of discrete subaortic stenosis from the apical long axis view

M-mode and standard two-dimensional (2DE) left parasternal long axis echocardiographic examination of the left ventricular outflow tract (LVOT) was evaluated exclusively with respect to its utility in identifying discrete subaortic stenosis (SUB-AS). Important details of the anatomy of the subaortic area may also be obtained from 2DE apical long axis imaging. Accordingly, 18 patients with discrete SUB-AS were prospectively evaluated by M-mode and 2DE. The M-mode findings included narrowing of the LVOT and early systolic closure of the aortic valve. However, these findings were variable and highly dependent upon scan speed, fluid flow dynamics, and beam angulation. 2DE findings varied using the standard long axis view at the left parasternal border, depending upon the type of obstruction present. A discrete membrane produced linear echoes adjacent and parallel to the interventricular septum beneath the aortic valve. Fibromuscular obstruction produced a localized dense ridge of echoes in the LVOT. These findings were not apparent in five patients studied. In these patients, the 2DE apical long axis view was employed to image the subaortic area. From this tomographic crosssection a fibrous membrane was imaged as a linear echo parallel to the aortic valve. The membrane extended across the LVOT from the ventricular septum to the anterior leaflet of the mitral valve. The 2DE apical long axis view therefore provides an additional approach in the evaluation of patients with discrete SUB-AS.     

Early systolic closure of the aortic valve in patients with hypertrophic subaortic stenosis and discrete subaortic stenosis. Correlation with preoperative and postoperative hemodynamics

Patterns of motion of the aortic valve were analyzed with echocardiography in 9 patients with discrete subaortic stenosis and 31 patients with idiopathic hypertrophic subaortic stenosis, 22 with and 9 without a resting intraventricular pressure gradient. The intention was to determine whether the early systolic closure of the aortic valve was a sensitive indicator of a resting pressure gradient across the left ventricular outflow tract. All 9 patients with discrete subaortic stenosis and the 22 patients with idiopathic hypertrophic subaortic stenosis with a resting pressure gradient showed early systolic closure of the aortic valve; however, the 9 patients without a resting gradient had normal motion of the aortic valve. Measured values for O-ESC (the interval from the opening point of the aortic valve to the point of early systolic closure of the aortic valve) in 9 patients with discrete subaortic stenosis and in 22 with idiopathic hypertrophic subaortic stenosis averaged 0.05 ± 0.01 (standard deviation) second and 0.14 ± 0.04 second for each group, respectively (P < 0.01). Twelve patients with idiopathic hypertrophic subaortic stenosis underwent operation to alleviate left ventricular outflow tract obstruction. In eight of these patients the resting pressure gradient was completely abolished and early systolic closure of the aortic valve was no longer present. The results indicate that in idiopathic hypertrophic subaortic stenosis, early systolic closure of the aortic valve is recorded only when there is a significant intraventricular pressure gradient at rest. The time of occurrence of early systolic closure differentiated patients with discrete subaortic stenosis from those with idiopathic hypertrophic subaortic stenosis in all observations.     

Echocardiographic manifestations of discrete subaortic stenosis

The echocardiographic manifestations of discrete membranous subaortic stenosis are described in three cases. The diagnosis was confirmed by cardiac catheterization in all and at operation in two. The characteristic finding in these patients was abnormal movement of the aortic valve leaflets. The leaflets opened rapidly with the onset of systole, then exhibited abrupt premature closure shortly after ventricular ejection. The valve remained partially closed throughout the remainder of systole. This premature leaflet closure Is believed to be caused by obstruction to aortic valve flow produced by the band-like fibrous subaortic tissue. The valve leaflets also exhibited a gross fluttering motion possibly caused by a jet stream effect of the turbulent blood hitting the leaflets. In the two patients treated surgically, postoperative echograms continued to show premature leaflet closure but the degree of closure was decreased. The echocardlogram of one patient had the characteristic systolic anterior bulge of the mitral valve observed in muscular subaortic stenosis or idiopathic hypertrophic subaortic stenosis. Our data suggest that the following echocardiographic findings are suggestive if not specific for discrete subaortic stenosis: aortic valve closure early in systole, persistent valve closure throughout the remainder of systole, coarse fluttering of the leaflets, and absence of asymmetric septal hypertrophy.     

Two-dimensional echocardiography in discrete subaortic stenosis

Thirty-seven patients with discrete subaortic stenosis (DSS) underwent 2-dimensional echocardiography (2-D echo) and cardiac catheterization. The peak systolic pressure gradients ranged from 0 to 150 mm Hg. Thirty-two patients had membranous DSS and 5 had fibromuscular DSS. Of 37 patients with DSS, 2-D echo diagnosed the presence and type in 35; in 2, a membrane was demonstrated by angiography. Of the 35 patients accurately diagnosed by 2-D echo, angiography corroborated the diagnosis in 33, but failed to show the membrane in 2. Subsequent cardiac surgery confirmed the accuracy of the echocardiographic diagnosis in these 2 patients. In all patients with membranous DSS, the anterior insertion of the membrane was demonstrated. In 9 of them the posterior insertion was demonstrated by tilt of the transducer but the anterior insertion disappeared. In 4 patients both insertions were demonstrated simultaneously and in 3 patients the membrane was demonstrated as a continuous line. In 4 of the 5 patients with fibromuscular DSS, both insertions of the lesion were demonstrated simultaneously. However, 2-D echo was unsuccessful in assessing the severity of obstruction. In only 1 patient did demonstration of the whole subaortic membrane as a continuous line below the aortic valve correlate with severe obstruction. Thus, the presence and type of DSS, but not the degree and severity, can be accurately and reliably diagnosed by means of 2-D echo.     

Mitral valvar anomalies and discrete subaortic stenosis

On the basis of our clinical experience, we hypothesized that the role of mitral valvar anomalies in the development and recurrence of discrete subaortic stenosis might be underestimated. From January 1994 to October 2000, the anatomy of the mitral valve and its relationship to the other components of the left ventricular outflow tract were studied by echocardiography in a series of 73 consecutive patients referred to our institution for surgical correction of discrete subaortic stenosis. In all patients for whom it was considered advisable, surgical correction of the mitral anomaly was performed, together with resection of the fibro-muscular subaortic stenosis. One or more mitral valvar anomalies were found in 35 patients (48%). They could be grouped into five categories: insertion of a papillary muscle into the aortic leaflet, insertion of a papillary muscle into the ventricular wall, "muscularization" of the subaortic portion of the aortic leaflet, anomalous insertion of the valvar tissue into the ventricular wall, and accessory valvar tissue. In all cases with anomalous mitral valvar anatomy, surgical correction was feasible. It consisted of transection of the anomalous papillary muscle or its attachment, resection of accessory valvar tissue, and/or patch enlargement of the aortic leaflet. The incidence of mitral valvar anomalies associated with subaortic stenosis is probably underestimated. Our data suggest that they should be systematically searched for during the evaluation of all cases of subaortic stenosis. Their surgical correction is generally feasible, and might improve the mid and long term results.     

Early aortic valve closure in combined idiopathic hypertrophic subaortic stenosis and discrete subaortic stenosis

A patient with idiopathic hypertrophic subaortic stenosis (90 mm Hg resting intraventricular gradient) and discrete subaortic stenosis was found to have two separate systolic closing movements of the aortic valve on M mode echocardiography, each movement being associated with a separate systolic ejection murmur. The first closing movement occurred early in systole and was attributed to alterations in flow across the discrete stenosis. The second closing movement coincided with a later systolic murmur and systolic anterior motion of the mitral valve. This case supports the concept that timing of early closing movements of the aortic valve is useful in the diagnosis of subvalvular obstruction.     

Percutaneous balloon dilatation of discrete subaortic stenosis

Discrete subaortic stenosis is an uncommon congenital cardiac disorder in which the left ventricular outflow tract is narrowed. We report about the diagnostic procedures and the successful balloon dilatation of a 49-year old, highly symptomatic male patient suffering from discrete subvalvular aortic stenosis.     

Pulmonary hypertension associated with echocardiographic pseudohypertrophic subaortic stenosis

An echocardiographic study of a 67-year-old patient with pseudoidiopathic hypertrophic subaortic stenosis due to secondary pulmonary hypertension is reported. Autopsy revealed findings consistent with pulmonary hypertension, and no evidence of idiopathic subaortic stenosis was found.     

Transluminal balloon dilatation for discrete subaortic stenosis

Ten children, 10 weeks to 18 years old, with discrete subaortic stenosis (DSS) underwent transluminal balloon dilatation of the subaortic obstruction. The DSS was visualized by 2-dimensional echocardiography and cineangiography. Six patients had a thin discrete "membrane" immediately below the aortic valve (group I) and 4 patients had a thicker fibromuscular ring about 1 cm below the aortic valve (group II). In group I, the mean gradient decreased from 82 +/- 49 mm Hg (range 35 to 164) to 22 +/- 15 mm Hg (range 5 to 40); in group II, it decreased from 155 +/- 18 mm Hg (range 132 to 177) to 85 +/- 44 mm Hg (range 60 to 150). Three patients had follow-up cardiac catheterization 1 year later. Their mean gradient soon after the procedure was 37 +/- 23 mm Hg. On follow-up, it was still 37 +/- 19 mm Hg, indicating persistence of relief of the obstruction. Because of the high residual gradient in group II, 3 patients had surgical relief of the obstruction. The degree of aortic regurgitation present before the dilatation in all 10 patients did not change after the procedure. The mechanism of relief of the obstruction was by tearing of the subaortic membrane. Our data suggest that relief of subaortic obstruction is more favorable in the thin, membranous DSS.     

Long-term pediatric outcome of isolated discrete subaortic stenosis

Background

The management of pediatric discrete subaortic stenosis remains controversial.

Objectives

Document the natural history and surgical outcomes for discrete subaortic stenosis to adolescence.

Methods

Retrospective review of clinical and echocardiographic findings in 74 patients diagnosed in childhood between 1985 and 1998.

Results

Twenty-five patients were followed only medically for 9.4 ± 0.9 years to 15.9 ± 0.6 years of age. Their echocardiographic left ventricular outflow peak gradient did not progress, 19 ± 1.4 (SEM) vs 20 ± 2.3 mm Hg. The proportion with aortic insufficiency (AI) increased (4% to 52%). Forty-nine patients were operated for discrete subaortic stenosis at 7.8 ± 0.6 years. Their peak gradient at diagnosis was 36 ± 3 mm Hg with AI in 33%. Preoperatively their peak gradient progressed to 60 ± 5 mm Hg with AI in 82%. Assessment 6.2 ± 0.5 years postoperativly showed a peak gradient of 14 ± 2 mm Hg with AI in 88%. Ten patients required reoperation for recurrent discrete subaortic stenosis, 3 acquired complete heart block, and 1 developed endocarditis. There was no mortality. At diagnosis, surgical patients were younger, had greater peak gradients, and greater incidence of AI, than those followed only medically. The progression of discrete subaortic stenosis was positively associated with severity of obstruction and negatively associated with older age at diagnosis. The risk of having surgery over time was associated with greater preoperative obstruction and presence of AI.

Conclusions

Many pediatric patients with mild discrete subaortic stenosis exhibit little progression of obstruction and need not undergo immediate surgery. Others with more severe stenosis may progress precipitously and will benefit from early resection.     

Echocardiographic assessment of discrete subaortic stenosis in childhood

The validity of Laplace's relation for assessing peak left ventricular pressure has previously been demonstrated in children with congenital aortic valve $\text{s}$tenosis by using the echocardiographically determined end-diastolic $\text{h}\text{r}$ ratio (that is, the ratio of mean left ventricular septal and posterior wall thicknesses to half the minor left ventricular cavity axis). This report examines the applicability of this ratio to the preoperatlve assessment of left ventricular pressure in 17 children with discrete subaortic stenosis. Because the regression equation derived from previously published data on patients with aortic valve stenosis and the present data on children with subaortic stenosis were similar, a pooled estimate of peak left ventricular pressure (LVP) in children $\text{w}$ith left ventricu$\text{l}$ar outflow tract obstruction is presented: $\text{LVP}\text{= 312.23 (}\text{h}\text{r}\text{) ± 28.01 (}\text{h}\text{r}\text{)}$.Additionally, the left ventricular outflow tract was measured as the anteroposterior dimension between the first recognizable closure point of the mitral valve and the interventricular septum and expressed as the left ventricular outflow tract/aortic root dimension ($\text{LVOT}\text{Ao}$) ratio. This ratio was tower in patients with subaortic stenosis than in control subjects and was helpful in differentiating patients with mild stenosis from those with more severe stenosis. The prevalence of echocardiographically observed features such as early systolic closure of the aortic valve and fluttering of the aortic valve leaflets could not be correl$\text{a}$ted with the severity of stenosis. It is concluded that the end-diastolic $\text{h}\text{r}$ ratio and the $\text{VOT}\text{Ao}$ ratio are quantitatively useful in the assessment of subaortic stenosis, whereas the commonly present motion abnormalities of the aortic valve are not indicative of the severity of the subaortic lesion.     

Regional myocardial function in idiopathic hypertrophic subaortic stenosis. An echocardiographic study.

To assess regional contractility in idiopathic hypertrophic subaortic stenosis (IHSS), a primary myopathic disorder with documented hyperdynamic ventricular contractions, systolic wall thickening and velocity of contraction of the septum and left ventricular posterior wall were measured in echocardiograms from 16 patients with IHSS and 16 normal subjects. The average thickening of the normal septum and posterior wall was 75.9+/-8.8% and 84.8+/-6.3%, respectively. The posterior wall in IHSS thickened by 75.1+/-6.8%. None of these values differed significantly. However, the increase in thickness of the IHSS septum averaged 22.5+/-2.4%, significantly less than that of either the IHSS posterior wall or the normal septum. Velocity measurements confirmed the impression of diminished septal function. The mean velocity of normal septal contraction averaged 37.0+/-2.3 mm/sec, normal posterior wall 42.3+/-2.0 mm/sec and IHSS posterior wall 55.7+/-3.5 mm/sec, whereas the septum in IHSS contracted at the rate of 26.0+/-2.5 mm/sec. Thus, the IHSS septum contracted significantly more slowly than the normal septum or IHSS posterior wall. However, the posterior wall velocity in IHSS was significantly more rapid than that measured in normal ventricles--perhaps to compensate for the septum. Normalization of all velocities for left ventricular end-diastolic internal diameter did not alter the sifnificance of the results. Consideration of IHSS as an asymmetric myopathy based on prior observations of predominantly septal hypertrophy and distorted septal cellular architecture is now supported by the above evidence of functional left ventricular asymmetry. Although the total left ventricular function in IHSS may be hyperdynamic, regional function is not uniform. The septum appears to be hypodynamic, while the contractile capacity of the posterior wall is increased.