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 Table of Contents  
REVIEW ARTICLE
Year : 2022  |  Volume : 6  |  Issue : 3  |  Page : 197-208

Role of Echocardiography in Balloon Dilatation of Aortic Valve


Department of Pediatric Cardiac Sciences, Krishna Institute of Medical Sciences, Secunderabad, Telangana, India

Date of Submission19-Apr-2022
Date of Decision11-Jun-2022
Date of Acceptance14-Jun-2022
Date of Web Publication12-Nov-2022

Correspondence Address:
Dr. Sudeep Verma
Krishna Institute of Medical Sciences, Secunderabad - 500 004, Telangana
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jiae.jiae_21_22

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  Abstract 

Aortic valve obstruction accounts for majority of left ventricular outflow tract obstruction. When present in neonatal age group, presentation is more severe and is mostly due to unicomissural aortic valve while at later age, bicuspid aortic valve is the most common cause for aortic stenosis. Echocardiography plays an importance role in the diagnosis and to assess the anatomy for suitability for balloon valvuloplasty. Its role also extends to assess the left ventricle size and function, to diagnose associated lesions and to suggest the suitable plan of management. Echocardiography also plays an important role immediately after balloon dilatation and during follow up to assess adequacy of dilatation and resultant complications. Balloon dilation of bicuspid aortic valves is associated with better outcome and lesser need for reinvention as compared to unicuspid valves.

Keywords: Aortic stenosis, balloon valvuloplasty, echocardiography


How to cite this article:
Verma S, Gouthami V. Role of Echocardiography in Balloon Dilatation of Aortic Valve. J Indian Acad Echocardiogr Cardiovasc Imaging 2022;6:197-208

How to cite this URL:
Verma S, Gouthami V. Role of Echocardiography in Balloon Dilatation of Aortic Valve. J Indian Acad Echocardiogr Cardiovasc Imaging [serial online] 2022 [cited 2023 Feb 4];6:197-208. Available from: https://jiaecho.org/text.asp?2022/6/3/197/361059

Aortic valve obstruction accounts for 60%–75% of all cases of left ventricle (LV) outflow tract obstruction.[1],[2] Bicuspid aortic valve (BAV) with or without stenosis occurs in up to 2% of the general population.[2],[3] It can cause pressure overload of LV causing hypertrophy without increase in the cardiac size. If unaddressed, it leads to decompensation in the form of LV dysfunction and cardiomegaly with congestive heart failure. Only 2% of the patients with congenitally abnormal aortic valve will experience significant stenosis/regurgitation by adolescence[4] Ten percent of the patients of aortic stenosis (AS) during infancy presents with congestive heart failure.[5] AS diagnosed during infantile age has more severe stenosis and higher mortality with or without treatment.[5],[6],[7] Patients diagnosed to have AS after 2 years of age have 25-years survival in the range of 85%. Even with mild stenosis, ultimate progression to the severe stenosis is the rule.[6],[7],[8] This review describes the pathophysiologial characteristics of congenital AS and the role of echocardiography in the balloon dilatation of aortic valve.


  Normal Anatomy of Aortic Valve Top


Normal aortic valve is formed of three thin leaflets of equal size attached to aortic root and supporting ventricular muscle. These leaflets are separated from each other by three commissures which lie in apposition from center to periphery [Figure 1]. Aortic annulus is the fibrous structure defined as the area of ventriculoarterial junction but actually aortic valve tissue extends beyond the annulus level into the LV outflow tract. Free edge of the leaflets curve upward from the commissure to form slight thickening at the tip/midpoint which is known as the 'node of Aranticus'.
Figure 1: Normal aortic valve as seen in the closed and open position during diastole and systole respectively in the parasternal long-axis (a and b) and the parasternal short-axis (c and d) views

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  Etiologies for Aortic Valve Stenosis Top


Various morphological patterns seen with congenital aortic valve stenosis are described in [Table 1]. With morphological patterns from 1 to 3, abnormal commissure morphology is seen.
Table 1: Morphological patterns of aortic valve anatomy seen with congenital aortic stenosis

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Overall the most common abnormality is BAV due to commissural pathology. However, during the neonatal age, the most common pathology associated with AS is unicuspid unicommissural aortic valve.

[Table 2] summarizes key differences between the AS seen in the neonatal age and that seen in the older age group [Figure 2] and [Figure 3].
Table 2: Differentiation in aortic valve pathology and presentation seen with aortic valve stenosis in neonatal and other age groups

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Figure 2: Aortic valve stenosis as seen with (a) Unicommissural unicuspid aortic valve and (b) Bicuspid aortic valve due to commissural fusion. LCC: Left coronary cusp, NCC: Non-coronary cusp, RCC: Right coronary cusp

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Figure 3: Diagram showing various pattern of valve anatomy as seen with aortic stenosis (a) Unicuspid. (b) Bicupsid. (c) Dysplastic. BAV: Bicuspid aortic valve

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  Echocardiographic Assessment Before Balloon Dilatation of Aortic Valve Top


Valve has to be assessed in detail from various views to get proper information regarding anatomy and mechanism of stenosis [Box 1]. Parasternal short- axis (PSAX) view is best for delineation of valve anatomy including commissure, raphe, and margins while parasternal long-axis (PLAX) is the view for annular measurement.



Valve anatomy- leaflet and commissural morphology

One of the important roles of echocardiography is to assess the morphology of the aortic valve [Figure 3],[Figure 4],[Figure 5],[Figure 6],[Figure 7],[Figure 8],[Figure 9],[Figure 10],[Figure 11],[Figure 12],[Figure 13],[Figure 14]. Valve anatomy and morphology determines the natural history and the outcome of the procedure [Box 2]. PSAX is the best view to assess the valve pathology and mechanism.
Figure 4: Unicommissural unicuspid aortic valve with eccentric opening. Thickened aortic valve margins are seen

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Figure 5: Unicommissural aortic valve as seen in two planes. (a) PLAX view showing doming aortic valve with thickened valve margin on left side toward mitral valve. (b) PSAX view showing eccentric aortic valve opening with thickened margins involving non-coronary cusp, and partly the right coronary cusp. PLAX: Parasternal long-axis, PSAX: Parasternal short-axis

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Figure 6: 3D picture of the same patient with unicommissural unicuspid valve. 3D: Three-dimensional

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Figure 7: Bicuspid valve with aortic stenosis. (a) PSAX view showing fish mouth opening. (b) PLAX- doming valve. (c and d) Normal aortic valve shown for comparison. PSAX: Parasternal short axis, PLAX: Parasternal long axis

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Figure 8: Raphe as seen in most common morphological pattern of the bicuspid aortic valves. Fused commissure can be appreciated as a raphe between the RCC and NCC, creating a vertical opening. NCC: Noncoronary cusp, RCC: Right coronary cusp

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Figure 9: Two patients with aortic stenosis having horizontal opening. (a) absence of any raphe (b) Raphe/fused commissure between RCC and LCC. LCC: Left coronary cusp, RCC: Right coronary cusp

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Figure 10: Vertical aortic valve opening as seen in a BAV. (a and b) Raphe seen due to fused RCC and NCC- in closed and opened position of aortic valve. (c) Bicuspid valve with vertical opening without raphe (commissure not seen- absent raphe). BAV: Bicuspid aortic valve, LCC: Left coronary cusp, NCC: Noncoronary cusp, RCC: Right coronary cusp

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Figure 11: Quadricuspid aortic valve with aortic regurgitation and stenosis. (a) Shows valve anatomy and cusp description of qaudricuspid valve. (b) Associated regurgitation as seen with quadricuspid valve

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Figure 12: LV hypoplasia as seen with aortic stenosis. (a) Mild. (b) Significant LV hypoplasia not forming apex. (c and d) 6 days old with severe aortic stenosis and small aortic annulus associated with hypo plastic LV not forming apex. LV: Left ventricle

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Figure 13: Various leaflet morphologies as seen with bicuspid aortic valve with stenosis. (a) Nodule seen on the RCC, fused commissure seen. (b) Unequal cusps. (c) Thickened leaflet margins. (d) Thickened raphe with nodular appearance. RCC: Right coronary cusp

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Figure 14: Severe aortic stenosis with severe pulmonary valve stenosis. Aortic valve seems to be tethered at ST junction. ST: Sinotubular

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As explained above, the most common pathology is commissural fusion, in which two of the three leaflets are fused together/one of the commissure is underdeveloped. The fused/underdeveloped commissure appears as an echogenic line of demarcation between the two involved leaflets, known as raphe [Figure 8]. Raphe is seen in 75% of the BAVs.[1],[9],[10] Most commonly involve leaflets are right coronary cusp (RCC) and left coronary cusp (LCC) (70%–86%) and the raphe is usually present between the origin of the two coronary arteries. Here the orientation of valve opening is horizontal [Figure 9]. The second most common is the fusion of RCC and noncoronary cusp (NCC) accounting for 12%–28% of cases. Here the opening is more vertical/oblique in nature [Figure 10]. The least common is the fusion of NCC and LCC. The pattern of fusion has clinical significance as the RCC/NCC fusion is more commonly associated with stenosis and regurgitation.[9],[10] [Table 3] shows the associated abnormalities in relation to the involved leaflets [Figure 9] and [Figure 10].
Table 3: Associated cardiovascular abnormalities in relation to leaflets fusion in aortic stenosis

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Another determinant is the length/size of the involved leaflets in comparison to unaffected leaflet/annulus size. Usually, the size of the combined leaflet is more than the size of the unaffected leaflet. If the size is more than twice the size of the uninvolved leaflet, it is more suggestive of developmental problem rather than just fusion.[1] If the commissures are congenitally fused or if the free edges of the cups are not longer than the diameter of the aorta ring, the valve is inherently obstructed. Nodules on the leaflets and the leaftlet margins should also be assessed as they have an impact on the successful outcome of the procedure [Figure 13] and [Figure 14].

In neonates, more slit like eccentric opening is seen and is more commonly associated with significant stenosis [Figure 3] and [Figure 4].[1],[4],[5]

Dysplastic valve is seen as tricommissural with irregular thickened margins with lumpy appearance [Figure 3]c.

Aortic annular hypoplasia is observed with a spectrum of neonatal AS/hypopalstic left heart syndrome/ventricular septal defect with posterior malalignment [Figure 12].

Valve annulus measurement

Accurate measurement of the aortic annulus size is the single-most important determinant of the success of percutaneous balloon aortic valvuloplasty (PBAV). Balloon to aortic annulus ratio should not be more than 0.9-1. Beyond this ratio, the risk of valve injury and aortic regurgitation (AR) increases. The annulus can be best measured during echocardiography in the parasternal long-axis view [Figure 15] and [Figure 16]. The measurement should be performed from leading edge-to- leading edge, in systole when the valve is fully opened. The annulus size is reconfirmed with aortic root angiogram during the procedure.
Figure 15: Doming aortic valve with annulus measurement for PBAV. LVH is also seen. Inset showing aortic root angiogram with doming valve with measurement of aortic annulus. AOV: Aortic valve annulus, LVH: Left ventricular hypertrophy, PBAV: Percutaneous balloon aortic valvuloplasty

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Figure 16: Aortic valve annulus measurement to decide the size of balloon to be used for PBAV. Inset picture shows angiogram with doming aortic valve and rechecking of the aortic annulus size. AOV: Aortic valve annulus, PBAV: Percutaneous balloon aortic valvuloplasty

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Degree of obstruction (severity)

Gradient across the aortic valve should be measured by aligning continuous wave (CW) Doppler beam parallel to the high velocity jet of AS. In most patients, this can be achieved in the apical five-chamber view. However, in some patients, better alignment of the Doppler beam can be achieved in the suprasternal view or in the right high parasternal view with the patient turned to the right side [Figure 17]. Without proper alignment, gradient may be underestimated [Figure 17].
Figure 17: Gradient across the aortic valve. (a) The gradient is underestimated due to improper alignment of CW Doppler (apical five-chamber view). (b) Correct measurement of peak and mean gradient across stenotic aortic valve with proper alignment of CW Doppler parallel to the stenotic jet (suprasternal/right parasternal view). CW: Continuous wave

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Mean gradient is measured by tracing the Doppler spectral profile [Figure 17] and [Figure 18]. Mean gradient correlates better with the catheter based peak-to-peak gradient across the aortic valve. Other indirect indicators of severity are LV hypertrophy and increased LV mass [Figure 19] and [Figure 20]. These values have to be compared with the values for the normal children with the same age and body surface area (BSA) using the Z -score. Mean gradient of more than 50 mmHg and peak instantaneous gradient of 70 mmHg or more are considered as significant stenosis requiring balloon valvuloplasty.[4],[11],[12] For patients who desire to go for competitive sports or are contemplating pregnancy, PBAV is advised at a gradient of 50-70 mm Hg. Using catheter-based peak-to-peak gradient, the thresholds for intervention would be 60 mmHg for general population and 50 mmHg for for athletes.[4],[11],[12] Subendocardial fibroelastosis is a feature of severe AS as seen in neonatal age. It can be localized to mitral valve papillary muscle or may involve almost complete endocardium [Figure 20]. Gradient is influenced by a variety of hemodynamic parameters which may change in the same patient at different point of time. Gradient may increase with increase in contractility or stroke volume. Gradient may differ during activity, with anxiety or with sedation or anesthesia. [Figure 21] shows pictorial diagram showing severity indicators in AS.
Figure 18: (a) A 5-year-old with PDA and aortic stenosis. (b) Doppler interrogation showing exaggerated peak and mean gradient across the aortic valve in the presence of PDA. This patient underwent PDA closure followed by percutaneous balloon aortic valvuloplasty. PDA: Patent ductus arteriosus

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Figure 19: Indirect indicators of severity of aortic stenosis. (a and b) concentric LVH with hypertrophied interventricular septum and the LV posterior wall in the parasternal long-axis view; (c) hyperechogenic papillary muscles; and (d and e) echogenic subendocardium with LVH. IV: Interventricular, LV: Left ventricular, LVH: Left ventricular hypertrophy

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Figure 20: A 7‑day‑old neonate with symptoms of breathing difficulty. Echocardiography shows aortic stenosis and MR without significant LVH (a and b). Radiograph shows granular pattern suggestive of PVH due to high LV filling pressures (c). MR: Mitral regurgitation, LV: Left ventricle, LVH: Left ventricular hypertrophy, PVH: Pulmonary venous hypertension

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Figure 21: Line diagram showing various parameters for assessment of severity of aortic stenosis. MR: Mitral regurgitation, LA: Left atrium, LV: Left ventricular, LVEDP: Left ventricular end-diastolic pressure, LVH: Left ventricular hypertrophy

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Aortic valve area measurement

As explained earlier, the transvalvular gradient may change with the changes in the hemodyanmic conditions; hence, the aortic valve area should be measured to assess AS severity. Although cumbersome, it can be used in place of or as complimentary to the Doppler gradient. Principal of continuity equation considering equal flow across the aortic valve and left ventricular outflow tract (LVOT) is applied. Area of the aortic valve can be calculated by multiplying LVOT cross sectional area (cm2) with the mean LVOT velocity (cm/s), divided by the mean velocity across the aortic valve orifice (cm/s) [Figure 22]. Resultant area in children should be indexed to BSA. Severe stenosis in children is considered when valve area is lesser than 0.5 cm2/m2. Normal area in children is approximately 2 cm2/m2 while in adults it is 3-4 cm2.
Figure 22: Steps for calculation of aortic valve area. CW: Continuous-wave, LVOT: Left ventricular outflow tract; PW: Pulsed-wave: VTI: Velocity time integral

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Left ventricle function and utility of dobutamine stress echocardiography

In the presence of LV systolic dysfunction, the peak aortic valve gradient may be low despite severe AS, due to decrease aortic valvular flow and low cardiac output. In such cases, mean gradient is also affected but to a lesser degree, as compared to the peak instantaneous gradient. Dobutamine stress echocardiography (DSE) may have a role in such cases, in assessing the true gradient before and after the procedure to assess the adequacy of dilatation [Figure 23] and [Figure 24]. In low gradient AS, DSE is useful in assessing contractile reserve and the true gradient to formulate the treatment plan. Dobutamine infusion is started start at 5 mcg/kg/min and gradually increased at 3 min interval to 10, 20, 30, 40, and 50 mcg/kg/min up to the point to achieved maximal target heart rate (85% of the maximal heart rate) for that age.
Figure 23: Severe valvar aortic stenosis with LV dysfunction. (a) Aortic valve stenosis with turbulence seen at the level of aor tic valve. (b) significant MR secondary to LV dysfunction and annular dilatation. (c) PLAX view with LV dysfunction and MR. (d) Doming aortic valve. LV: Left ventricle, MR: Mitral regurgitation, PLAX: Parasternal long axis

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Figure 24: DSE in the presence of aortic stenosis and severe LV dysfunction. (a) Baseline dobutamine study to assess the true gradient (b) After the balloon dilatation to assess the adequacy of procedure (c) Measurements and calculations involved in DSE. CW: Continuous-wave, DSE: Dobutamine stress echocardiography, EF: Ejection fraction, LVOT: Left ventricular outflow tract, PBAV: Percutaneous balloon aortic valvuloplasty, PW: Pulsed-wave, VTI: Velocity time integral

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Associated aortic regurgitation

Mild AR associated with AS is not a contraindication for PBAV. Instead, in such cases, the balloon chosen should not exceed the require diameter.

Presence of mitral regurgitation and left atrial dilatation

MR is a direct indicator of LV dysfunction seen with severe AS [Figure 20] and [Figure 23]. Left atrial dilation also indicates high LV filling pressure as seen with severe AS [Figure 23]. MR may develop after PBAV due to chordal damage.

Subvalvar and supravalvar assessment

Subvalvar area has to be assessed for septal hypertrophy or the presence or ridge/membrane. After PBAV, dynamic subvalvar obstruction may develop. Associated supravalvar tethering has to be assessed in relation to the aortic valve stenosis [Figure 14].

Adequacy of left ventricle

Adequacy of LV in severe AS in infants determines the success of PBAV. Four anatomical variables that were found to have the most significant independent relation to survival with AS as described by Rhodes et al. in 1991 are: (1) a left ventricular long-axis to heart long-axis ratio of 0.8 or less; (2) an indexed aortic root diameter of 3.5 cm/m2 or less; (3) an indexed mitral valve area of 4.75 cm2/m2 or less and 4) an LV mass index of 35 g/m2 or less.[13]


  Post Procedure Echocadiographic Assessment Top


It is important to perform echocardiography during and after the procedure to assess adequacy of balloon dilatation and complications. Postballoon residual stenosis [Figure 25],[Figure 26],[Figure 27] and regurgitation [Figure 28] have to be assessed along with any visible valve injury. Immediately after balloon dilatation, with development of significant AR an high LV end diastolic pressure, the child may develop features of left heart failure and pulmonary edema [Figure 29] and [Figure 30]. Aortic flow reversal as seen in suprasternal view gives fair assessment of severity of AR [Figure 31]. A major objective of the post-procedure assessment is to decide the need for surgical intervention. Older patients more often have postdilation AR.[14] In presence of small LV/LV hypoplasia, development of AR has greater detrimental effect causing early and profound left heart failure. Failure symptoms also get aggravated in the presence of restrictive interatrial communication in the presence of borderline small LV [Figure 32]. [Box 3] shows factors associated with suboptimal outcome after PBAV.
Figure 25: Doppler interrogation (a) before and (b) after ballon dilatation of severe aortic stenosis

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Figure 26: A 10-year old underwent PBAV, but had persistent gradient as shown by Doppler interrogation of the jet. PBAV: Percutaneous balloon aortic valvuloplasty

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Figure 27: Valve morphology as seen at the baseline and after balloon dilatation. (a) Fused commissure between RCC‑NCC with nodule seen on RCC. (b) After PBAV demonstrating splitting of commissure as a result of balloon dilatation. NCC: Noncoronary cusp, PBAV: Percutaneous balloon aortic valvuloplasty, RCC: Right coronary cusp

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Figure 28: Splitting of commissure and development of AR after PBAV. Origin of jet clearly seen from the area of commissure tear resulting in AR with good relief of stenosis. AR: Aortic regurgitation, PBAV: Percutaneous balloon aortic valvuloplasty

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Figure 29: Avulsion of one of the leaflets seen after PBAV. (a) PLAX view showing valve redundancy as it lies in a plane below the plane of aortic valve annulus. (b) Thickened rolled up leaflet margins seen after PBAV. (c) Color interrogation showing thick jet of AR almost occupying full LVOT and reaching up to left ventricular apex. AR: Aortic regurgitation, LVOT: Left ventricular outflow tract, PBAV: Percutaneous balloon aortic valvuloplasty, PLAX: Parasternal long axis

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Figure 30: Development of severe AR after balloon dilatation. (a) Angiogram shows opacification of LV on aortic root injection. (b) Echocardigram shows to-and-fro Doppler flow patten across the aortic valve and AR jet reaching up to the left ventricular apex. This patient developed severe AR as a result of high balloon to aortic annulus ratio exceeding 1. Ao: Aorta, AR: Aortic regurgitation, LV: Left ventricle

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Figure 31: (a) Diastolic reversal seen after percutaneous balloon aortic valvuloplasty suggestive of development of AR. (b) Pandiastolic reversal as seen using pulsed-wave Doppler interrogation with velocity as high as 50 cm/sec. AR: Aortic regurgitation

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Figure 32: A 5-day-old presented with severe aortic stenosis due to dysplastic valve and borderline LV systolic function (a and b). (c) Doppler interrogation shows peak gradient of 40 mm Hg across the valve (underestimated). (d) Doppler across IAS shows continuous pattern with mean gradient of 7 mmHg suggestive of high LA pressure. (e) After balloon dilatation of aortic valve, the flow across aortic valve improved but the noenate continued to have PVH due to high LA pressure as a result of hypoplastic LV and MV pathology as evident by restricted PFO with mean gradient of 11 mm Hg (f and g). This patient underwent BAS followed by IAS stent and turned out to be an HLHS substrate. HLHS: Hypopalstic left heart syndrome, IAS: Interatrial septum, LA: Left atrial, LV: Left ventricle, MV: Mitral valve, PFO: Patent foramen ovale, PVH: Pulmonary venous hypertension, RA: Right atrium

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  Follow-Up Top


During follow-up after balloon valvotomy, evaluation should be done for restenosis, appearance and progression of AR along with assessment of LV function and aortic root dilatation.[15] If there is development of AR, the patient has to be assessed for the need for surgical correction. If associated anomalies are present, they should also be evaluated in detail. Pedra et al. in their study followed 87 children who underwent PBAV at a median age of 6.9 years and who were followed up for an average of 6.3 years. The freedom from reintervention was 86% after 1 year, 67% after 5 years, and 46% at 12 years.[16] For newborns who undergo valve dilatation for critical AS, the reintervention rate is higher during follow-up. McCrindle et al. and McElhinney et al. showed reintervention-free survival rate of 48% at 5 years in this population.[17],[18],[19] Brown et al. in their paper with intermediate and long-term follow-up showed 44% patients underwent aortic valve reintervention in the form of repeat balloon vavuloplasty in 23%, aortic valve repair in 13% and aortic valve replacement in 23%.[14] Lower postdilation AS gradient and lower grade of postdilation AR were associated with longer freedom from aortic valve replacement, but age, era, and predilation AS severity were not.


  Conclusion Top


Echocardiographic assessment is crucial for the diagnosis of AS and planning balloon valvotomy procedure. Its importance remains even in the periprocedural period to assess the adequacy of procedure and to identify the complications related to the procedure. During follow up, echocardiography is crucial to decide the need for reintervention in the form of repeat dilatation or surgical correction.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Eidem WB, Cetta F, O'leary WP. Echocardiography in Pediatric and Adult Congenital Heart Disease. 1st ed. Philadelphia, USA: Wolters Kluwer, Lippincott Williams and Wilkins; 2009.  Back to cited text no. 1
    
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Hoffman JI, Kaplan S. The incidence of congenital heart disease. J Am Coll Cardiol 2002;39:1890-900.  Back to cited text no. 2
    
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Roberts WC. The congenitally bicuspid aortic valve. A study of 85 autopsy cases. Am J Cardiol 1970;26:72-83.  Back to cited text no. 3
    
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Allen HD, Driscoll DJ, Shaddy RE, Feltes TF. Moss and Adams' Heart Disease in Infants, Children and Adolescents Including the Foetus and Young Adult. 9th ed. Philadelphia: Wolters Kluwer, Lippincott Williams and Wilkins; 2016.  Back to cited text no. 4
    
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Hastreiter AR, Oshima M, Miller RA, Lev M, Paul MH. Congenital aortic stenosis syndrome in infancy. Circulation 1963;28:1084-95.  Back to cited text no. 5
    
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Freedom RM, Too SJ, Mikailian H, Williams WG, editors. The Natural History and Modified History of Congenital Heart Disease. Toronto: Blackwell Publishing, Futura Divison; 2004.  Back to cited text no. 6
    
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Campbell M. The natural history of congenital aortic stenosis. Br Heart J 1968;30:514-26.  Back to cited text no. 7
    
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Cohen LS, Friedman WF, Braunwald E. Natural history of mild congenital aortic stenosis elucidated by serial hemodynamic studies. Am J Cardiol 1972;30:1-5.  Back to cited text no. 8
    
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Rudolph A. Congenital Diseases of the Heart Clinical – Physiological Considerations. 3rd ed. West Sussex, UK: Wiley-Blackwell; 2009.  Back to cited text no. 9
    
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Fernandes SM, Sanders SP, Khairy P, Jenkins KJ, Gauvreau K, Lang P, et al. Morphology of bicuspid aortic valve in children and adolescents. J Am Coll Cardiol 2004;44:1648-51.  Back to cited text no. 10
    
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Feltes TF, Bacha E, Beekman RH 3rd, Cheatham JP, Feinstein JA, Gomes AS, et al. Indications for cardiac catheterization and intervention in pediatric cardiac disease: A scientific statement from the American Heart Association. Circulation 2011;123:2607-52.  Back to cited text no. 11
    
12.
Saxena A, Relan J, Agarwal R, Awasthy N, Azad S, Chakrabarty M, et al. Indian guidelines for indications and timing of intervention for common congenital heart diseases: Revised and updated consensus statement of the Working group on management of congenital heart diseases. Ann Pediatr Cardiol 2019;12:254-86.   Back to cited text no. 12
    
13.
Rhodes LA, Colan SD, Perry SB, Jonas RA, Sanders SP. Predictors of survival in neonates with critical aortic stenosis. Circulation 1991;84:2325-35.  Back to cited text no. 13
    
14.
Brown DW, Dipilato AE, Chong EC, Lock JE, McElhinney DB. Aortic valve reinterventions after balloon aortic valvuloplasty for congenital aortic stenosis: Intermediate and late follow-up. J Am Coll Cardiol 2010;56:1740-9.  Back to cited text no. 14
    
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Reich O, Tax P, Marek J, Rázek V, Gilík J, Tomek V, et al. Long term results of percutaneous balloon valvoplasty of congenital aortic stenosis: independent predictors of outcome. Heart 2004;90:70-6.  Back to cited text no. 15
    
16.
Pedra CA, Sidhu R, McCrindle BW, Nykanen DG, Justo RN, Freedom RM, et al. Outcomes after balloon dilation of congenital aortic stenosis in children and adolescents. Cardiol Young 2004;14:315-21.  Back to cited text no. 16
    
17.
McElhinney DB, Lock JE, Keane JF, Moran AM, Colan SD. Left heart growth, function, and reintervention after balloon aortic valvuloplasty for neonatal aortic stenosis. Circulation 2005;111:451-8.  Back to cited text no. 17
    
18.
McCrindle BW, Blackstone EH, Williams WG, Sittiwangkul R, Spray TL, Azakie A, et al. and the members of the Congenital Heart Surgeons Society. Are outcomes of surgical versus transcatheter balloon valvotomy equivalent in neonatal critical aortic stenosis? Circulation 2001;104:I-152–I-158.  Back to cited text no. 18
    
19.
Lofland GK, McCrindle BW, Williams WG, Blackstone EH, Tchervenkov CI, Sittiwangkul R, et al. Critical aortic stenosis in the neonate: A multi-institutional study of management, outcomes and risk factors. J Thorac Cardiovasc Surg 2001;121:10-27.  Back to cited text no. 19
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11], [Figure 12], [Figure 13], [Figure 14], [Figure 15], [Figure 16], [Figure 17], [Figure 18], [Figure 19], [Figure 20], [Figure 21], [Figure 22], [Figure 23], [Figure 24], [Figure 25], [Figure 26], [Figure 27], [Figure 28], [Figure 29], [Figure 30], [Figure 31], [Figure 32]
 
 
    Tables

  [Table 1], [Table 2], [Table 3]



 

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