Journal of The Indian Academy of Echocardiography & Cardiovascular Imaging

: 2022  |  Volume : 6  |  Issue : 3  |  Page : 216--221

Role of Echocardiography in Catheter Interventions for the Right Ventricular Outflow Tract

Supratim Sen 
 Department of Pediatric Cardiology, NH SRCC Children's Hospital, Mumbai, Maharashtra, India

Correspondence Address:
Dr. Supratim Sen
Department of Pediatric Cardiology, NH SRCC Children's Hospital, Mumbai, Maharashtra


The treatment strategies and timing of corrective or palliative procedures for patients with right ventricular outflow tract (RVOT) obstruction vary depending on the lesion and also on the severity of the patient's symptoms. A wide variety of right heart obstructive lesions ranging from severe valvar pulmonary stenosis, pulmonary atresia with intact ventricular septum, and tetralogy of Fallot can be treated effectively with corrective or palliative interventions in the catheterization laboratory. Interventional procedures to relieve right ventricular outflow obstruction and/or to augment antegrade pulmonary blood flow include balloon pulmonary valvotomy, pulmonary valve perforation, and RVOT stenting. In all these interventions, echocardiography plays an essential role, not only in the preprocedural assessment and case selection but also during the actual procedure in the catheter laboratory. With proper use, a transthoracic echocardiogram can minimize radiation exposure, help in stent positioning in the RVOT, and even detect complications instantaneously. This manuscript reviews the role of echocardiography in transcatheter interventions of the RVOT.

How to cite this article:
Sen S. Role of Echocardiography in Catheter Interventions for the Right Ventricular Outflow Tract.J Indian Acad Echocardiogr Cardiovasc Imaging 2022;6:216-221

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Sen S. Role of Echocardiography in Catheter Interventions for the Right Ventricular Outflow Tract. J Indian Acad Echocardiogr Cardiovasc Imaging [serial online] 2022 [cited 2023 Mar 20 ];6:216-221
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Right ventricular outflow tract (RVOT) obstruction can occur in isolation, as seen in valvar pulmonary stenosis (PS), or in association with other intracardiac lesions such as ventricular septal defects (VSDs) and tetralogy of Fallot (TOF) physiology. The treatment strategies and timing of corrective or palliative interventions for patients with RVOT obstruction vary depending on the lesion and also on the severity of the patient's symptoms. Balloon pulmonary valvotomy (BPV) is the standard treatment modality for critical or isolated severe PS. Palliative interventional procedures in the RVOT include pulmonary valve perforation, palliative BPV, and RVOT stenting. In all these interventions, echocardiography plays an integral role in the choice and planning of the procedure, as well as during and immediately after the procedure.

This manuscript reviews the role of echocardiography in transcatheter interventions of the RVOT.

 Advantages of Echocardiography over Other Imaging Modalities for Structural Heart Interventions

Although transthoracic echocardiography remains the primary imaging modality for diagnosis of congenital heart disease (CHD) in the outpatient clinic, contemporary pediatric cardiac care often involves multi-modality imaging to better understand the anatomy and physiology of the CHD. A multi-slice computed tomography (CT) pulmonary angiogram gives invaluable information to delineate the anatomy of extracardiac structures such as the aorta and pulmonary arteries. Cardiac magnetic resonance imaging (MRI) has also gained importance, especially in assessing right ventricular (RV) volume, function, and regurgitant fractions, for example, in patients after repair of TOF with transannular patch. Over time, advanced catheter-laboratory technologies such as three-dimensional (3D) rotational angiography, fusion imaging, and EchoNavigator (EchoNavigator, Philips Healthcare, Eindhoven, the Netherlands) have found their way into mainstream clinical work. The CT images can also be overlayed on the catheter laboratory monitors to achieve optimal angulations and orientations for complex cardiac interventions.

However, the regular transthoracic two-dimensional (2D) echocardiogram still has important utility during transcatheter interventions in the catheter laboratory. First and perhaps most importantly, it is real-time, unlike a CT pulmonary angiogram or cardiac MRI. Second, there is no radiation exposure to the patient or the catheter-laboratory staff. Hence, a detailed echocardiogram can be done safely rather than multiple cineangiograms to delineate anatomy. Third, it provides instantaneous physiological information such as ventricular function and residual stenosis following valvotomy or stenting. And finally, an echocardiogram can quickly rule out or identify adverse complications such as pericardial tamponade or valve rupture/regurgitation.[1]

 Balloon Pulmonary Valvotomy for Isolated Severe Pulmonary Stenosis and Critical Pulmonary Stenosis

The incidence of PS is reported as 0.6–0.8/1000 live births and 5.8% of all congenital heart defects.[2]

Neonates with critical PS are dependent on left-to-right shunting across the arterial duct for maintenance of pulmonary blood flow and oxygenation. These neonates present with desaturation at birth, and prostaglandin E1 infusion is required for stabilization and to maintain ductal patency. Emergency BPV is usually curative in these patients unless there is associated RV hypoplasia.

Older patients with isolated valvar PS have normal saturations and are often diagnosed on the evaluation of an ejection systolic murmur. Severe PS can present with signs of RV hypertrophy along with symptoms of RV failure such as hepatomegaly and ascites. In older children and adolescents, long-standing severe pulmonary valve stenosis can cause associated RV infundibular hypertrophy and right-to-left shunting across a patent foramen ovale or atrial septal defect, which would manifest as cyanosis.

Echocardiography in preprocedural decision-making

During the echocardiographic assessment of a patient with isolated valvar PS [Figure 1], [Figure 2], [Figure 3], it is important to define the level of obstruction (whether isolated valvar or also infundibular and supravalvar),[2] measure the pulmonary annulus, and assess the pliability and appearance of the pulmonary valve leaflets. Isolated valvar PS is associated with poststenotic dilation of the main pulmonary artery [Figure 1]b. Care must be taken to measure the pulmonary annulus in end-systole, to decide whether there is annular hypoplasia (pulmonary annulus z-score <−2), and also to choose the appropriate-sized balloon for valvotomy. A balloon-annulus ratio of 1–1.2 is recommended for BPV.[3]{Figure 1}{Figure 2}{Figure 3}

In neonates and infants with severe PS, often there may be associated severe tricuspid regurgitation (TR) and/or RV hypoplasia. Entering the RV and crossing the pulmonary valve in these small patients from the femoral venous access may be challenging due to the TR jet. The right internal jugular venous access in these patients gives an easy ingress into the RV and simplifies the procedure. While the quantum of TR with a morphologically normal tricuspid valve should decrease once the RV pressures subside on successful BPV, an abnormal Ebsteinoid tricuspid valve may continue to have severe regurgitation even after an effective balloon valvotomy.[2] Hence, careful preprocedure evaluation of the tricuspid valve morphology, TR, and RV cavity during echocardiography helps plan the procedure.

Pulmonary stenosis in a syndromic patient

PS is described in association with Noonan syndrome, William's syndrome, Alagille syndrome, and congenital Rubella syndrome. Noonan syndrome is an autosomal dominant condition commonly associated with valvar PS.[2] However, the valve leaflets in these patients are often dysplastic with tethering to the main pulmonary artery [Figure 3] and [Video 1]. Dysplasia is defined as thick, immobile valve leaflets with the absence of poststenotic dilation.[4] These valves respond poorly to BPV, and relief of the stenosis is suboptimal. Hence, the dysplastic appearance of pulmonary valves with the absence of poststenotic dilation on echocardiography, especially in a syndromic child, indicates that the stenosis may not be adequately relieved with balloon valvotomy.


Video 1: Dysplastic pulmonary valve. Modified parasternal view with clockwise rotation from parasternal short-axis showing the cross-section of the pulmonary valve en face throughout the cardiac cycle. The thickened leaflets are well delineated.

Imaging tips

The pulmonary annulus needs to be carefully and accurately measured on the preprocedural echocardiogram. The parasternal short-axis (PSAX) view, parasternal long-axis view with an anterior tilt, and the apical 5-chamber view with an anterior tilt will profile the pulmonary valve opening [Figure 1]. The annulus is measured between the hinge points in systole.[2] To measure the peak systolic pressure gradient across the pulmonary valve, a continuous wave Doppler measurement with good alignment is required [Figure 2]. The operator must ensure a good Doppler envelope to accurately measure the peak systolic pressure gradient. The best alignment may be achieved in the subcostal sagittal view, parasternal long-axis view with anterior tilt, or apical 5-chamber view with anterior tilt. Hence, it is prudent to take measurements in multiple views to estimate the PS gradient accurately.

Echocardiography during the procedure

Echocardiography is not strictly required during the BPV in the catheter laboratory. However, after the balloon inflation, it is prudent to deflate and withdraw the balloon leaving the guidewire in situ across the pulmonary valve and perform a transthoracic echocardiogram to confirm the adequacy of the pulmonary valve opening, decrease in the PS gradient, and to also assess the pulmonary regurgitation (PR). The absence of significant PR and more than mild residual PS after balloon inflation would be an indication for repeating BPV with a larger balloon.

 Pulmonary Atresia-Intact Ventricular Septum

Patients with pulmonary atresia-intact ventricular septum (PA-IVS) require a transcatheter intervention in the neonatal period. In those patients with tripartite RV without any evidence of the RV-dependent coronary circulation [Figure 4], the procedure of choice is pulmonary valve perforation with BPV and/or an additional patent ductus arteriosus stenting to augment and maintain pulmonary blood flow till the RV compliance improves.{Figure 4}

Echocardiography in preprocedural decision-making

In any patient with PA-IVS, echocardiography is essential to rule out RV-dependent coronary circulation, assess RV adequacy, and to decide whether decompressing the RV will allow adequate antegrade pulmonary blood flow [Figure 4]a. Once a decision for pulmonary valve perforation has been made, the RVOT needs to be evaluated in detail. In India, most pediatric cardiac centers do not have access to radiofrequency catheters (Baylis Medical Company Inc., Montreal, Canada) for pulmonary valve perforation. In the absence of radiofrequency perforation, pulmonary valve perforation is generally done with chronic total occlusion (CTO) coronary wires or even the stiff end of a workhorse coronary wire. In PA-IVS, coronary wire perforation of the pulmonary valve should only be attempted for membranous pulmonary atresia. The shape and orientation of the RVOT can be clearly assessed by transthoracic echocardiography to predict the stability of the Judkins right (JR) catheter in the RVOT. A tapering RVOT with membranous pulmonary atresia [Figure 4]b and [Figure 4]c is conducive to stable catheter position to enable passage of a CTO wire for pulmonary valve perforation. A horizontal RVOT on echocardiography may also require a microcatheter through the JR catheter, to improve stability of the CTO wire before perforation, as the JR catheter alone may not remain stable at the tip of the pulmonary valve.

In contrast, a broad RVOT in the setting of a dilated RV and Ebsteinoid tricuspid valve would usually not allow stable positioning of the JR catheter. Without stable catheter position in the RVOT, there are increased risks of inadvertent perforation of anterior RV wall instead of the membranous pulmonary valve plate during attempted perforation.

Imaging tips

The apical 4-chamber view will delineate the adequacy of the RV cavity [Figure 4]a. Anterior tilt on the 5-chamber view and also the PSAX view [Figure 4]b will help image the pulmonary valve plate and RVOT. The PSAX view is also needed to image the coronary arteries and to look for any RV to coronary fistulae.

Echocardiography during the procedure

Once the CTO wire has perforated the pulmonary valve, a microcatheter is passed over it into the branch pulmonary artery and exchanged for a workhorse coronary wire over which BPV can be done with a Tyshak-mini balloon (NuMED Inc., Orlando, FL, USA). After each balloon dilation, echocardiography is used to assess the antegrade flow and PR. Based on this imaging, the operator can decide whether adequate antegrade flow has been achieved or whether repeat balloon valvotomy with a larger balloon is indicated.

Echocardiography for managing complications

Often, if the CTO or workhorse coronary wire has perforated the anterior wall of the RVOT instead of perforating the membranous pulmonary valve plate, it would have entered the pericardial space. Quick echocardiography can be done at this stage to look for pericardial effusion or tamponade. Once incorrect wire position/perforation is confirmed, the wire is withdrawn and removed, and echocardiography can be repeated to rule out a worsening pericardial collection, which would need emergency surgery. Most often, fortunately, wire perforation of the RV anterior wall gets sealed off spontaneously on the removal of the coronary wire.

Imaging tips in the catheter laboratory

With the patient supine, acoustic windows may not be as good as in the preprocedural transthoracic echocardiogram. The subcostal view can be used for a quick assessment of ventricular function and to rule out pericardial tamponade [Figure 5].{Figure 5}

 Tetralogy of Fallot: Balloon Pulmonary Valvotomy versus Right Ventricular Outflow Tract Stenting

In the present era, corrective surgery (intracardiac repair) for TOF is usually undertaken between 3 and 9 months of age at most international centers, as the surgical mortality and morbidity are the least in this age group.[5],[6] Neonatal corrective repair has been described,[5],[7] although the morbidity and hospital stay are significantly higher than surgery in older infants. Palliative options such as surgical modified Blalock-Taussig (BT) shunt, RVOT stenting, ductal stenting, and BPV are often chosen when the institutional policy precludes early intracardiac repair in the neonates and infants with TOF with low saturation or frequent cyanotic spells.[8] With increasing expertise of complex structural neonatal interventions, many pediatric cardiac centers now prefer interventional palliative options in the catheter laboratory over the traditional surgical palliation with a modified BT shunt.

Echocardiography in preprocedural decision-making

In TOF, detailed echocardiographic imaging of the RVOT includes assessment of the degree of infundibular versus valvar stenosis [Figure 6]. In patients with predominantly valvar PS with an adequate-sized pulmonary annulus, BPV may be adequate palliation to increase saturation. However, the presence of significant multilevel pulmonary obstruction with prominent infundibular muscle bundles will require RVOT stenting.[9]{Figure 6}

In their early experience, the Birmingham group advocated preserving the pulmonary annulus during RVOT stenting for TOF with adequate-sized pulmonary annulus.[10] Preprocedural echocardiography is essential for detailed delineation of the pulmonary valve, to check the z-scores of the pulmonary annulus, and also to predict whether placing a stent across the infundibular muscle and not covering the pulmonary annulus will provide adequate relief of the RVOT obstruction. Stenting across the pulmonary annulus is often technically easier and gives a better immediate result as there is no risk of residual pulmonary valve stenosis. However, this approach eventually leads to a transannular patch at the time of the intracardiac repair and does not allow subsequent pulmonary valve preservation.[11]

Right ventricular outflow tract stenting for tetralogy of Fallot with major coronary crossing the right ventricular outflow tract

Echocardiogram is essential to assess for a major coronary artery crossing the RVOT anteriorly. Fortunately, RVOT stenting is considered safe even with a major coronary artery crossing the RVOT. In the Birmingham cohort, left anterior descending artery crossing RVOT was not a contraindication for RVOT stenting as the authors felt the stent addressed the anterior deviation of the conal septum by pushing it backward and did not protrude forwards to cause coronary ischemia.[10] This makes RVOT stenting preferable to total correction with a small RV to pulmonary artery conduit for small cyanosed infants with TOF with coronary artery crossing RVOT.

Contraindication to right ventricular outflow tract stenting in tetralogy of Fallot

A relative contraindication for RVOT stenting or BPV in TOF is the presence of a doubly committed VSD on echocardiogram. This is because, in the absence of muscular outlet septum in a TOF with doubly committed VSD, the facing leaflets of the aortic and pulmonary valves are in fibrous continuity. Hence, any splitting or controlled tear of the pulmonary valve leaflets during BPV or RVOT stenting in these patients has the potential to extend into the adjacent wall of the aortic valve sinus, causing aortic regurgitation.[9],[12],[13]

Imaging tips

The RVOT is best visualized from the subxiphoid sagittal view and the subxiphoid long axis–RVOT sweep [Figure 6]c and [Figure 6]d. The parasternal long-axis view with an anterior tilt will also demonstrate the entire length of the RVOT [Figure 6]b. With these views, the length of the RVOT stent required for adequate palliation of the RVOT obstruction can be estimated.

Echocardiography during the procedure

BPV or stenting of the RVOT in TOF is a high-risk procedure. The procedure is only undertaken in those patients who are too small for complete corrective surgery (hence are usually aged <3 months) and who are also severely cyanosed or have frequent cyanotic spells. Importantly, these very patients are also the most prone to refractory and severe cyanotic spells during any wire and catheter manipulation in the RVOT. Hence, even before the first RV angiogram, echocardiography can be used to choose, and sometimes keep prepared the appropriate sized balloon or stent that will be required to save time. While angiography will be required to delineate landmarks and position the stent or balloon, the sizing can be done predominantly with echocardiography.

Care must be taken during any RVOT intervention to avoid crossing any of the tricuspid valve chordae while the catheter is manipulated from the right atrium to the RVOT and across the pulmonary annulus. It is prudent to quickly check on echocardiogram that the TR has not increased significantly after the catheter or wire is positioned in the distal branch pulmonary artery across the pulmonary valve. Severe TR at this stage often indicates entrapment of a tricuspid chorda, and it is better to withdraw the catheter and wire assembly completely and re-cross the pulmonary valve to prevent damage to the tricuspid valve chordae.

Once the desired stent size is chosen based on the angiographic measurements and taken to the desired position in the RVOT, it is again prudent to check on the echocardiogram that the proximal end of the chosen stent will not protrude into or entrap the tricuspid chordae, before deployment.

Immediately after stent deployment, echocardiography is once again used to delineate whether adequate relief of the infundibular stenosis and adequate pulmonary blood flow has been achieved.

Imaging tips

Often during RVOT stenting, the angiographic anatomy delineation may be suboptimal. Echocardiogram-guided measurements and stent positioning may help decrease fluoroscopy times and get a better stent position than with fluoroscopy alone. The best view for procedural echocardiogram during RVOT stenting is the subcostal 4-chamber and RV inflow-outflow view (subxiphoid long axis–RVOT sweep) [Figure 7] and [Figure 8].[14]{Figure 7}{Figure 8}

 General Points in the Catheter Laboratory

The echocardiography machine should be turned on with the appropriate echocardiography probes attached at the beginning of the intervention so that it is readily available in an emergency. While transesophageal echocardiography is useful for RVOT interventions in older children, most patients who require these procedures will be neonates or infants. Hence, transthoracic echocardiography is commonly employed for the majority of these interventions, and the usual probes used are 8 MHz and 12 MHz.

 Postprocedure Echocardiography

Following the RVOT intervention in early infancy, serial echocardiograms on follow-up visits are required to assess for the adequacy of pulmonary blood flow [Video 2], [Video 3], [Video 4], the growth of the branch pulmonary arteries, new appearance of in-stent restenosis, and also to decide regarding the timing of the next stage of corrective surgery.


Video 2: Courtesy Dr. Bharat Dalvi. Apical 5-chamber view with anterior tilt demonstrating good antegrade flow with pulmonary regurgitation across the right ventricular outflow tract stent in tetralogy of Fallot.


Video 3: Courtesy Dr. Bharat Dalvi. Parasternal short-axis view demonstrating good antegrade flow with pulmonary regurgitation across the right ventricular outflow tract stent in tetralogy of Fallot.


Video 4: Courtesy Dr. Bharat Dalvi. Magnified parasternal short-axis view demonstrating good antegrade stent flow and branch pulmonary artery flow with pulmonary regurgitation after right ventricular outflow tract stenting in tetralogy of Fallot.

 Role of Echocardiography in Percutaneous Pulmonary valve Implantation in the Adolescent and Adult

Percutaneous pulmonary valve implantation (PPVI) has now become the standard of care to address residual PS or PR to preserve RV function and volumes in patients previously operated for TOF with an RV to pulmonary artery conduit or homograft. The Melody™ Transcatheter Pulmonary Valve (Medtronic, Minneapolis, MN, USA) was first implanted percutaneously in 2000, and since then, this valve along with 3–4 other valve designs have become the preferred options for PPVI. For native RVOTs with a transannular patch, percutaneous valves such as the Harmony™ Transcatheter Pulmonary Valve (Medtronic, Minneapolis, MN, USA) have recently gained clinical approval. Transesophageal echocardiography is helpful during these procedures which are undertaken in adolescents and adults. However, as this is a different spectrum of CHD, it is not further discussed in this manuscript.


Echocardiography plays an essential role in corrective and palliative structural interventions in infants with isolated valvar PS, PA-IVS, and TOF physiology, not only in the preprocedural assessment and case selection but also during the actual procedure in the catheter laboratory. With proper use, a simple 2D transthoracic echocardiogram can shorten fluoroscopy times, help in stent positioning in the RVOT, and even detect complications instantaneously.

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Conflicts of interest

There are no conflicts of interest.


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