Echocardiography in discrete subaortic stenosis

Computational Assessment of Valvular Dysfunction in Discrete Subaortic Stenosis: A Parametric Study

PURPOSE

Discrete subaortic stenosis (DSS) is a left-ventricular outflow tract (LVOT) obstruction caused by a membranous lesion. DSS is associated with steep aortoseptal angles (AoSAs) and is a risk factor for aortic regurgitation (AR). However, the etiology of AR secondary to DSS remains unknown. This study aimed at quantifying computationally the impact of AoSA steepening and DSS on aortic valve (AV) hemodynamics and AR.

METHODS

An LV geometry reconstructed from cine-MRI data was connected to an AV geometry to generate a unified 2D LV-AV model. Six geometrical variants were considered: unobstructed (CTRL) and DSS-obstructed LVOT (DSS), each reflecting three AoSA variations (110°, 120°, 130°). Fluid-structure interaction simulations were run to compute LVOT flow, AV leaflet dynamics, and regurgitant fraction (RF).

RESULTS

AoSA steepening and DSS generated vortex dynamics alterations and stenotic flow conditions. While the CTRL-110° model generated the highest degree of leaflet opening asymmetry, DSS preferentially altered superior leaflet kinematics, and caused leaflet-dependent alterations in systolic fluttering. LVOT steepening and DSS subjected the leaflets to increasing WSS overloads (up to 94% increase in temporal shear magnitude), while DSS also increased WSS bidirectionality on the inferior leaflet belly (+ 0.30-point in oscillatory shear index). Although AoSA steepening and DSS increased diastolic transvalvular backflow, regurgitant fractions (RF < 7%) remained below the threshold defining clinical mild AR.

CONCLUSIONS

The mechanical interactions between AV leaflets and LVOT steepening/DSS hemodynamic derangements do not cause AR. However, the leaflet WSS abnormalities predicted in those anatomies provide new support to a mechanobiological etiology of AR secondary to DSS.

Impact of Aortoseptal Angle Abnormalities and Discrete Subaortic Stenosis on Left-Ventricular Outflow Tract Hemodynamics: Preliminary Computational Assessment

Discrete subaortic stenosis (DSS) is an obstruction of the left ventricular outflow tract (LVOT) due to the formation of a fibromuscular membrane upstream of the aortic valve. DSS is a major risk factor for aortic regurgitation (AR), which often persists after surgical resection of the membrane. While the etiology of DSS and secondary AR is largely unknown, the frequent association between DSS and aortoseptal angle (AoSA) abnormalities has supported the emergence of a mechanobiological pathway by which hemodynamic stress alterations on the septal wall could trigger a biological cascade leading to fibrosis and membrane formation. The resulting LVOT flow disturbances could activate the valve endothelium and contribute to AR. In an effort to assess this hypothetical mechano-etiology, this study aimed at isolating computationally the effects of AoSA abnormalities on septal wall shear stress (WSS), and the impact of DSS on LVOT hemodynamics. Two-dimensional computational fluid dynamics models featuring a normal AoSA (N-LV), a steep AoSA (S-LV), and a steep AoSA with a DSS lesion (DSS-LV) were designed to compute the flow in patient-specific left ventricles (LVs). Boundary conditions consisted of transient velocity profiles at the mitral inlet and LVOT outlet, and patient-specific LV wall motion. The deformation of the DSS lesion was computed using a two-way fluid-structure interaction modeling strategy. Turbulence was accounted for via implementation of the k-ω turbulence model. While the N-LV and S-LV models generated similar LVOT flow characteristics, the DSS-LV model resulted in an asymmetric LVOT jet-like structure, subaortic stenotic conditions (up to 2.4-fold increase in peak velocity, 45% reduction in effective jet diameter vs. N-LV/S-LV), increased vorticity (2.8-fold increase) and turbulence (5- and 3-order-of-magnitude increase in turbulent kinetic energy and Reynolds shear stress, respectively). The steep AoSA subjected the septal wall to a 23% and 69% overload in temporal shear magnitude and gradient, respectively, without any substantial change in oscillatory shear index. This study reveals the existence of WSS overloads on septal wall regions prone to DSS lesion formation in steep LVOTs, and the development of highly turbulent, stenotic and asymmetric flow in DSS LVOTs, which support a possible mechano etiology for DSS and secondary AR.

Discrete subaortic stenosis in adults: increased prevalence and slow rate of progression of the obstruction and aortic regurgitation

OBJECTIVES

We sought to determine the prevalence and rate of progression of left ventricular outflow tract obstruction (LVOTO) and aortic regurgitation (AR) in adults with discrete subaortic stenosis (DSS).

BACKGROUND

Discrete subaortic stenosis is an uncommon form of LVOTO, with rapid hemodynamic progression in children, but the prevalence and rate of progression in adults have not been studied so far.

METHODS

The prevalence of DSS was determined in 2,057 consecutive adults diagnosed with congenital heart disease (CHD). The relationship between LVOTO on Doppler echocardiography and patient age was analyzed. Sequential changes in LVOTO and AR were determined for patients with two or more Doppler echocardiograms obtained with at least a two-year interval.

RESULTS

A total of 134 adults (mean age 31 +/- 17 years) were diagnosed with DSS. The prevalence was 6.5% for all adults with CHD. Sixty patients (44%) had other associated CHD. The mean age of 29 patients who had undergone an operation for DSS during their adult life (56 +/- 15 years) was significantly higher than that of 64 patients (27 +/- 13 years) who had not required a surgical intervention (p < 0.0001). A significant relationship between LVOTO and patient age (r = 0.61, p < 0.0001) was found: 21 +/- 16 mm Hg in patients <25 years old, 51 +/- 47 mm Hg for those between 25 and 50 years old, and 78 +/- 36 mm Hg for those >50 years old. The LVOTO increased from 39.2 +/- 28 to 46.8 +/- 34 mm Hg (p = 0.01) during a mean follow-up of 4.8 +/- 1.8 years in 25 patients. The slope of the change in LVOTO was 2.25 +/- 4.7 mm Hg per year of follow-up. Aortic regurgitation was detected by color Doppler imaging in 109 patients (81%), but it was hemodynamically significant in <20%. An increase in the mean degree of AR over time was not significant (baseline: 1.3 +/- 0.8; follow-up: 1.5 +/- 0.9; p = 0.096).

CONCLUSIONS

The prevalence of DSS is increasing in adults due to the greater number of repaired CHDs that develop into evolutive DSS. In contrast to infants and children, adults with DSS show a slow rate of LVOTO progression. Aortic regurgitation is a common but usually mild and nonprogressive consequence. The current indications for surgical intervention should be revised.

[Echocardiographic evaluation in unoperated congenital heart disease in adults]

Echo and Doppler echocardiographic procedures have gained special importance in the diagnostics of congenital diseases in adults. These procedures permit detailed visualization of the pathomorphology of the heart as well as reliable evaluation of the hemodynamic changes. There are differentiated indications for the various procedures, such as transthoracic and transesophageal echocardiography, Doppler and color-Doppler echocardiography, contrast echocardiography and 3-dimensional echocardiography. This article discusses the opposition of the various echo and Doppler echocardiographic procedures with respect to the diagnostics of the most frequent non-operated congenital diseases in adults. The pathomorphology of the various congenital diseases will be summarized and then the important echocardiographic criteria presented which are decisive for the diagnostic procedure. In simple congenital malformation of cardiac valves, such as bicuspid aortic valve (Figure 1: aortic ring abscess), pulmonary valve stenosis (Figure 2), Ebstein's anomaly (Figure 3) or malformations of the mitral valve (Figure 4: cleft in the anterior mitral cusp), the diagnosis can often be made using transthoracic echo and Doppler echocardiography, and the severity of the defect determined. However, the sonographic conditions, especially in adults, are frequently too limited to permit recognition of detailed smaller changes, so that transesophageal examination is required to finally confirm the diagnosis in these patients. In the diagnostics of diseases of the left ventricular outflow tract and the thoracic aorta, such as subvalvular aortic valve stenosis (Figure 5), the sinus of Valsalva aneurysm or the coarctation of the aorta (Figure 6), the left ventricular outflow tract can be evaluated morphologically from a transthoracic procedure and the accelerations of flow can be recorded by continuous wave Doppler. If there is no sclerosis of the fibrous membrane, these can often not be depicted by transthoracic procedures, so that a supplementary transesophageal examination is meaningful. This is required in any case for diseases of the descending thoracic aorta. In the case of congenital lesions, such as atrial septal defects (Figure 7: anomalous pulmonary venous return, Figure 8: 3-dimensional visualization of an atrial septal defect, Figure 9: sinus venosus defect), ventricular septal defect or a patent ductus arteriosus Botalli (Figure 10), color-Doppler and contrast echocardiography have become especially important. Transesophageal examination is also indicated for these congenital diseases for direct depiction of the defect as well as for precise evaluation of the shunt. Moreover, in atrial septal defects, it has been shown that a 3-dimensional echocardiography provides additional advantage with respect to spatial relationship of the defect to the other cardiac structures, as well as presenting dynamic changes during a heart cycle. Extensive knowledge of complex congenital heart disease, such as tetralogy of Fallot (Figure 11), complete transposition of the great arteries, congenitally corrected transposition of the great arteries (Figure 12), the double-outlet right ventricle, truncus arteriosus communis, the cor triatriatum, tricuspid atresia (Figure 13) or the univentricular heart (Figure 14) usually requires performance of a transthoracic echo- and Doppler echocardiographic examination to assess the pathomorphological changes and to examine hemodynamics. In the majority of patients, supplementary transesophageal echocardiography and an echo contrast examination are important. Initial examinations using 3-dimensional echocardiography are very promising in this connection and with respect to the exact spatial presentation of pathoanatomical structures.

Fixed subaortic stenosis: the value of cross-sectional echocardiography in evaluating different anatomical patterns

We present a study using cross-sectional echocardiography in 39 patients (29 male and 10 female) with discrete subaortic stenosis. Five parameters were evaluated in the study: the morphology of the obstruction, the distance of the stenosis from the aortic valve, the type of insertion, the base of implantation, and any associated anomalies. The lesion could be divided into groups with either fibrous or fibromuscular shelves. In the group of 14 patients with fibrous shelves, the distances from the stenotic lesion to the aortic valve was less than 15% of the length of the left ventricle. The obstructive fibrous tissue was inserted on the septum and extended onto the aortic leaflet of the mitral valve (circumferential lesion) in 12 cases. The base of implantation was narrow in all 14 of them. In the 25 patients having fibromuscular lesions, the distance between obstruction and valve was greater than 18.4% of the length of the left ventricle. The insertion of the obstructive lesion was circumferential in 18 cases and its base of implantation was wide in 20 of the patients. Nineteen patients, 16 of whom had fibromuscular lesions, showed associated anomalies. Statistical analysis showed a good correlation between the type of stenosis and the base of implantation of the stenotic lesion (P less than 0.001) or associated anomalies (less than 0.01), but there was no distinction between the groups with regard to the type of insertion (less than 0.38). Twenty-five patients underwent surgical correction which was carried out between the ages of 4-14 years. Prosthetic valves (3 aortic and 1 mitral) were inserted in 4 patients.(ABSTRACT TRUNCATED AT 400 WORDS)

Discrete sub-aortic stenosis and ventricular septal defect

We present details of 15 children, aged 3 months to 11 years, with discrete sub-aortic stenosis and ventricular septal defect. We emphasise a high index of clinical suspicion and echocardiography as the best means of diagnosing this dangerous combination. Physical signs were those of ventricular septal defect in all patients, with auscultatory evidence of additional sub-aortic stenosis in only one. Five patients had a short early diastolic murmur of mild aortic incompetence. The electrocardiograph showed isolated left ventricular hypertrophy in eight patients. Cardiac catheterisation and angiography identified the ventricular septal defect in all cases but detected the sub-aortic stenosis in only eight. Cross sectional echocardiography showed both lesions in all 11 patients to whom it was available.

Combined discrete subaortic stenosis and ventricular septal defect in infants and children

Eight patients, aged 1 to 8 years, with discrete subaortic stenosis (DSS) and ventricular septal defect (VSD) were studied by 2-dimensional (2-D) and M-mode echocardiography. Initial cardiac catheterization and angiocardiography showed VSD and other associated cardiac lesions, including coarctation of the aorta and patent ductus arteriosus. None had evidence of DSS. Six patients underwent surgical repair of the associated lesions, but none required closure of the VSD. Ultimately, 6 patients had spontaneous closure of VSD, and 2 had a residual small VSD. Subsequent serial echocardiography showed evidence of subaortic membrane, prompting repeat cardiac catheterization, which confirmed moderate to severe peak systolic pressure gradients between the left ventricle and ascending aorta. Surgical resection of the membrane was performed in 5 patients. Thus, in patients with small or spontaneously closed VSDs, DSS may develop. Evaluation of the left ventricular outflow tract area is recommended in patients with small or closed VSD in whom a significant heart murmur or electrocardiographic abnormality remains.

Echographic early systolic partial closure (notching) of the aortic valve in congestive cardiomyopathy

We investigated the prevalence and significance of aortic valve early systolic partial closure (notching) in congestive cardiomyopathy by reviewing clinical and M-mode echocardiographic findings in 33 patients. We also compared their echocardiographic aortic root and valve findings to those in 17 aortic regurgitation patients and 24 normal subjects. Thirteen cardiomyopathy patients (39%) exhibited aortic valve partial closure--similar to the prevalence in the aortic regurgitation (41%) and normal (33%) groups. However, patients with dilated cardiomyopathy and aortic valve notching exhibited a higher mean percentage of partial closure (18% +/- 10) than those with notching in either the aortic regurgitation (8% +/- 9) or normal (5% +/- 2) group. There was no significant difference in age, body surface area, left ventricular dimension, systolic function, or presence of mitral regurgitation between cardiomyopathy patients with and without aortic valve notching, but the former had slightly greater aortic root dimensions and maximal aortic leaflet separation. Although the reason for this difference is unknown, a wider aortic root may result in low-pressure areas bordering the aortic flow stream during early systole, which may favor partial aortic valve closure.

Discrete subaortic stenosis: the value of cross-sectional sector echocardiography in evaluating different types of obstruction

The value of cross-sectional sector echocardiography in the visualization of discrete subaortic stenosis (DSS) was investigated using an 80 degrees phased-array sector scanner with simultaneously derived M-mode outputs. Thirty-three patients (including 22 postoperative patients) with proven DSS were investigated and divided into two groups: group I--discrete membranous type; and group II--diffuse fibromuscular type. In group I (15 patients), two isolated subaortic ridges were identified as discrete linear echoes in the long axis of the outflow tract in five patients. A single distinct and isolated linear echo was observed in three patients, whereas in another five the ridges appeared to be attached to the ventricular septum and/or to the base of the anterior mitral leaflet. In two patients with mild DSS, a false-negative diagnosis was made. Only 2 out of 12 patients in this group showed a short remnant of the ridge after surgical revision. In group II, a more generalized or long-segment narrowing was present in 18 patients; in 14 of them the ridges were continuous with the walls of the outflow tract. Eight out of ten patients reexamined following resection of fibromuscular tissue still had residual obstruction. Analysis of the simultaneous M-mode recordings revealed that the transient appearance of the ridge in the outflow tract depended on the normal movement of the heart within the chest, on the lengthening of the membrane itself, and on the angle between the ultrasound beam and the membrane during different cardiac cycles. Our study shows that a spectrum of one- and two-dimensional patterns exists depending on the nature of the obstructing lesion. Cross-sectional sector echocardiography provides more direct visualization and characterization of various types of DSS than M-mode echocardiography does.

Discrete membraneous sub-aortic stenosis in adult patient obtained by echocardiography and not proved by catheterization

A case of a 60-year-old patient with discrete membranous sub-aortic stenosis is described. The diagnosis was established bases on echocardiographic evaluation by demonstration of a premature aortic valve closure and a sub-aortic membrane. No evidence of the sub-aortic membrane was noticed on cardiac catheterization. At operation, a discrete sub-aortic membrane was found 9 mm below the aortic valve, leaving an aperture of 1 cm diameter and a mildly deformed stenotic aortic valve. We stress the importance of careful pre-operative echocardiographic evaluation of every patient suspected of having any kind of left ventricular outflow tract obstruction, even if catheterization data are not contributory.

Systolic closure of aortic valve in patients with prosthetic mitral valves

Systolic closure of the aortic valve was found in 10 of 36 patients who underwent mitral valve replacement. Eight patients had early systolic closure, and two had mid-systolic closure. The left ventricular outflow tract dimension on M-mode and two dimensional echocardiograms, left ventricular posterior wall and septal thickness, left ventricular dimensions in systole and diastole, aortic valve opening, and mitral to aortic valve distance were not significantly different between patients with and without systolic closure of the aortic valve. Two of the 10 patients with systolic aortic valve closure were catheterised and in neither was there a gradient between the left ventricle and the aorta. The two patients with mid-systolic closure, however, were the patients who had the narrowest left ventricular outflow tract which could cause significant distortion of blood flow. Systolic closure of the aortic valve in patients with mitral valve replacement is probably not caused by left ventricular outflow tract obstruction, though abnormalities in laminar flow from the left ventricular outflow tract may be involved.

Ventricular septal defect with silent discrete subaortic stenosis

Subaortic stenosis is rarely mentioned as a lesion that may be associated with a ventricular septal defect. We have encountered 4 patients with discrete subaortic stenosis adjacent to a ventricular septal defect, all of whom posed significant problems in diagnosis. In all 4 patients the subaortic stenosis was silent clinically and in 3 cases the obstruction was also not detected at the initial cardiac catheterization and angiocardiography. In the latter 3 cases, after surgical closure of the ventricular septal defect, there was a loud systolic murmur initially thought to be due to a small residual ventricular septal defect. In time, the clinical findings became more typical of isolated subaortic stenosis. In each of these cases the obstruction was verified at cardiac catheterization with peak systolic pressure gradients of 145, 45, and 70 mmHg. During reoperation, a discrete subaortic shelf was found opposite the patch used to close the ventricular septal defect. In the 4th case, the subaortic stenosis was unsuspected by clinical evaluation but was diagnosed by echocardiography as well as at cardiac catheterization, and both the ventricular septal defect and subaortic stenosis were corrected at the initial operation. A discrete subaortic shelf situated adjacent to a ventricular septal defect may be "silent," producing minimal, if any, pressure gradient and may pose diagnostic difficulties. Failure to recognize such a shelf and to remove it at the time of surgical closure of the ventricular septal defect, may result in the creation of a severe subaortic obstruction.

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

M-mode 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. According, 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 corss-section 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.

Echocardiography in combined discrete and hypertrophic subaortic stenosis

A 10-year-old boy with discrete subaortic stenosis had coexisting abnormal systolic anterior motion of the mitral valve, demonstrated by echocardiography, a sign normally taken as indicating the presence of idiopathic hypertrophic subaortic stenosis. Surgical removal of a fibromuscular diaphragm abolished the echocardiographic signs of discrete subaortic stenosis but abnormal systolic anterior motion of the mitral valve persisted. A severe low cardiac output state complicated immediate recovery after removal of the left ventricle outflow obstruction, and was overcome only with considerable difficulty. The presence of hypertrophied septal muscle, and the associated small left ventricular cavity size, was thought to be the immediate cause of these problems, so that recognition of marked septal hypertrophy, together with abnormal anterior systolic movement of the mitral valve, should serve as a warning that similar difficulties are likely to bae encountered by other patients, after removal of the obstruction in subaortic stenosis. In our experience other forms of left ventricle outflow tract obstruction have not been found to show such a marked degree of asymmetric septal hypertrophy, but this does not mean it may not occur.

Results of intraventricular baffle procedure for ventricular septal defect and double outlet right ventricle or d-transposition of the great arteries

Thirty patients with ventricular septal defect and d-transposition of the great arteries or double outlet right ventricle underwent placement of an intraventricular baffle to achieve physiologic correction. Eighteen of these patients also required an external conduit to establish continuity between the right ventricle and the pulmonary artery. There was an overall 22 percent early mortality rate, although the rate was 63 percent in patients who weighed less than 10 kg. There was an additional 20 percent late mortality rate, primarily related to conduction disturbances and pulmonary vascular obstructive disease, problems that have not occurred in patients operated on since 1974. Of the survivors, all are asymptomatic and as a group have achieved a significant weight gain. Many have residual hemodynamic abnormalities that required cardiac catheterization for precise assessment. Four patients have been reoperated on, with no additional mortality.

Early systolic closure of the aortic valve

Six patients with early systolic closure of the aortic valve are described with mitral regurgitation, double outlet right ventricle, left ventricular diverticulum, congestive cardiomyopathy, Eisenmenger ventricular septal defect, and aortic regurgitation with an aneurysmal ascending aorta, respectively. None had evidence of subaortic stenosis. Early sytolic closure of the aortic valve is thus not diagnostic of subvalvular aortic stenosis but is a non-specific finding.

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. The case supports the concept that timing of early closing movements of the aortic valve is useful in the diagnosis of subvalvular obstruction.

Echocardiographic recognition of atrioventricular valve stenosis associated with endocardial cushion defect: pathologic and surgical correlates

The association of either mitral or tricuspid stenosis with endocardial cushion defects has been well recognized pathologically but is infrequenctly diagnosed clinically. M mode echocardiographic features such as markedly disproportionate ventricular size, abnormal mitral or tricuspid diastolic echoes or failure to define adequately an atrioventricular (A-V) valve are strongly suggestive of associated stenosis of that valve. In this study mitral stenosis in association with endocardial cushion defect was correctly diagnosed in four of five patients. In the fifth patient (the first seen) the condition was easily diagnosed retrospectively. Tricuspid stenosis was similarly diagnosed prospectively in three of four patients. Significant stenosis was not overlooked or misdiagnosed in any patient with an endocardial cushion defect. Significant stenosis of an A-V valve in association with endocardial cushion defect carries a high mortality. It is important to recognize the combined lesion clinically because infants with it are not suitable for total surgical correction. Palliative surgical procedures with aggressive medical therapy probably offer the infant the best chance of surviving until ventricular growth may render corrective surgery feasible.