For the Patients and Families

TOC

• Catheter Intervention for congenital heart
• Development of Catheter Intervention for Congenital Heart Disease
• Percutaneous transluminal pulmonary valvuloplasty
• Patent Ductus Arteriosus
• Atrial Septal Defect
• Vascular Dilation Procedures in Congenital Heart Disease
• Catheter Embolization for Abnormal Vessels
• Transcatheter Pulmonary Valve Implantation（TPVI）
• Catheter Ablation for Pediatric Cardiovascular Diseases

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Catheter Intervention for congenital heart

This section provides explanations about catheter-based treatments for congenital heart disease. We hope that this information will be helpful to you.
For questions or concerns regarding an individual patient, we strongly encourage you to consult your primary physician. Seeking a second opinion may also be beneficial.

Japanese Society of Congenital Interventional Cardiology (JCIC) Surveillance Committee, Planning Subcommittee

Kenji Baba, MD

Interventional Radiology (IVR) Center, Medical Development Field, Okayama University

Seiji Asagai, MD

Department of Pediatric Cardiology and Adult Congenital Cardiology, Tokyo Women’s Medical University

Hideaki Kanazawa, MD

Department of Cardiology, Tokyo Medical University

Takuro Kojima, MD

Department of Pediatric Cardiology, Saitama Medical University International Medical Center

Mitsuru Seki, MD

Department of Pediatrics, Jichi Medical University

Tomohiro Nawa, MD

Department of Pediatric Cardiology, Hokkaido Medical Center for Child Health and Rehabilitation

Jun Yoshimoto, MD

Department of Electrophysiology, “Mt. Fuji” Shizuoka Children’s Hospital

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Development of Catheter Intervention for Congenital Heart Disease

Catheter-based interventions for congenital heart disease (CHD) have made remarkable progress over the past half century and are now established as therapeutic options comparable to surgical procedures. The history of interventional cardiology in CHD began in 1966, when Dr. William Rashkind and Dr. Miller reported balloon atrial septostomy for complete transposition of the great arteries. This innovative technique, which allowed creation of an interatrial communication without thoracotomy, marked the beginning of catheter-based therapy for congenital heart disease. (Figure 1)

In the 1970s, attempts were made to close atrial septal defects (ASD) percutaneously without surgery. In 1974, Dr. King and Dr. Mills first reported transcatheter closure of ASD. Subsequently, in 1979, Dr. Rashkind introduced a device for the transcatheter closure of patent ductus arteriosus (PDA). These pioneering attempts laid the foundation for clinical applications that expanded rapidly through the 1980s, alongside continued refinement of device designs.

In 1982, Dr. Kan first reported percutaneous balloon pulmonary valvuloplasty for pulmonary valve stenosis. Around the same period, Dr. Lock and colleagues popularized balloon angioplasty for pulmonary and aortic stenoses, establishing catheter-based therapy as a standard approach for stenotic lesions. In the late 1980s, Dr. Palmaz and Dr. Schatz introduced intravascular stents, revolutionizing the management of vascular stenoses. Stent implantation soon became widely used for postoperative anastomotic or pulmonary arterial stenoses and remains an essential interventional technique in the field of congenital cardiology. (Figure 2)

In the field of occlusion devices, significant structural advances were achieved during the 1990s. In 1997, Dr. Kurt Amplatz developed the Amplatzer Septal Occluder (ASO) for ASD closure. Its double-disc nitinol mesh design offered superior stability, safety, and retrievability, leading to worldwide adoption. In Japan, the Amplatzer Septal Occluder was approved and introduced in 2006, rapidly becoming the standard device. (Figure 3) Subsequently, the Occlutech Figulla Flex II (approved in 2016) and the Gore Cardioform ASD Occluder (approved in 2021) were introduced, expanding therapeutic options. Furthermore, the Amplatzer Duct Occluder (ADO), reported in 1998, became the standard treatment for PDA, replacing coil embolization. The ADO was approved and introduced in Japan in 2009, and remains widely used today. (Figure 4)

A major breakthrough occurred in 2000, when Dr. Philipp Bonhoeffer and colleagues reported the first Transcatheter Pulmonary Valve Implantation (TPVI). In this pioneering procedure, a bioprosthetic valve sewn into a stent was implanted via a venous approach, providing an innovative, less invasive alternative to repeat open-heart surgery. This technique was later commercialized as the Melody valve. More recently, next-generation devices such as the Sapien valve and Harmony valve have been developed. In Japan, Sapien 3 was approved in 2021, followed by the Harmony valve in 2022, leading to widespread clinical adoption of TPVI. (Figure 5)

In summary, catheter-based interventions for congenital heart disease began as life-saving palliative procedures and have evolved into minimally invasive therapies that complement or replace surgical repair. Ongoing advancements in device design and delivery systems continue to expand the boundaries of what can be achieved through catheter-based therapy. Further innovation aimed at achieving less invasive, more durable, and patient-tailored treatment strategies is eagerly anticipated in the years to come.

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Percutaneous transluminal pulmonary valvuloplasty

1. Overview

Congenital pulmonary valve stenosis is the most common form of right ventricular outflow tract obstruction in pediatric cardiology, occurring in approximately 0.5–0.8 per 1,000 live births. Most cases present with a domed pulmonary valve and commissural fusion, resulting in right ventricular pressure overload from stenosis at the valve annulus.
Since the initial report by Kan et al. in 1982, percutaneous transluminal pulmonary valvuloplasty (PTPV) has rapidly gained widespread acceptance. Multiple large-scale studies have demonstrated efficacy equivalent to that of surgical treatment, with superior invasiveness. Currently, PTPV is positioned as the first-line treatment in international guidelines and plays a crucial role as a fundamental technique in pediatric catheter interventions.
However, in cases of dysplastic pulmonary valves associated with genetic disorders such as Noonan syndrome, the primary pathology is valve leaflet thickening and reduced mobility, making it difficult to split fused commissures by balloon dilatation. In such cases, treatment effectiveness is limited, and careful assessment of anatomical features is necessary to determine appropriate indication.

2. Severity Assessment and Treatment Indication

The most reliable method for assessing the severity of pulmonary valve stenosis is right ventricular systolic pressure measured during cardiac catheterization. Patients with pulmonary valve stenosis are classified as mild when pressure is less than 50 mmHg, moderate when 50 mmHg or higher but below systemic blood pressure, and severe when equal to or exceeding systemic blood pressure. In clinical practice, the estimated pressure gradient calculated using continuous wave Doppler echocardiography is often used as a guide for determining treatment indication, but caution is required in cases of severe stenosis, as this method may underestimate the severity.
Current guidelines recommend PTPV for cases with a pressure gradient across the pulmonary valve of 40 mmHg or higher on cardiac catheterization or echocardiography, or for cases with a gradient less than 40 mmHg but with evidence of right ventricular dysfunction. Even in asymptomatic cases with moderate or greater severity, aggressive intervention is recommended, considering the risk of future right ventricular dysfunction and arrhythmias. After treatment, a rapid reduction in right ventricular pressure and improvement in ECG changes are expected, leading to significant improvements in exercise tolerance and clinical symptoms. Therefore, timely intervention significantly affects prognosis.

3. Balloon Catheter Selection

For device selection in PTPV, standard-pressure semi-compliant balloons are routinely used. Moderate flexibility and uniform expansion characteristics enable safe and reliable splitting of fused valve commissures. Although non-compliant balloons offer excellent control with consistent expansion diameter, their high rigidity poses a risk of annular injury, requiring careful consideration of indications.
Balloon diameter selection is the most critical factor directly affecting treatment outcomes and complication rates. Previously, 140–150% of the annulus diameter was used, but due to the high risk of annular injury and excessive pulmonary regurgitation, current recommendations specify a balloon diameter of 120% of the annulus diameter. Accurate assessment through lateral or oblique angiography is essential for measuring the annulus diameter, with comprehensive evaluation incorporating echocardiographic measurements.
When the annulus diameter is large or when the available sheath size is limited, the double balloon technique is selected. The target effective diameter is calculated using Narang's formula (effective diameter = sum of two balloon diameters × 0.82, and an appropriate balloon combination is determined. The advantages of the double balloon technique include the ability to accommodate large annuli with smaller sheath sizes and the maintenance of blood flow between the two balloons during dilatation. However, the procedure becomes somewhat more complex due to the need to manipulate two guidewires and balloons.

4. Procedural Technique

1) Pulmonary Valve Stenosis (Figure 1)
Cardiac catheterization and treatment are usually performed via the femoral vein approach. If both femoral veins are occluded, the internal jugular vein approach is also feasible. As mentioned above, right heart catheterization is performed to accurately measure right ventricular pressure, pulmonary artery pressure, and pressure gradient, followed by measurement of the annulus diameter through right ventriculography or pulmonary artery angiography. A particularly important consideration in guidewire placement is avoiding injury to the tricuspid valve chordae tendineae. If the wire enters the interchordal space, withdrawal of the balloon can damage the chordae, potentially causing severe tricuspid regurgitation.
Therefore, the recommended method is to first advance a balloon-tipped catheter such as a wedge pressure catheter from the right ventricle to the pulmonary artery, then insert the guidewire after the catheter tip reaches the distal pulmonary artery. A flexible guidewire should be selected and positioned stably in the peripheral pulmonary artery. If the balloon-tipped catheter cannot be advanced into the pulmonary artery, a right Judkins or Multipurpose catheter may be used. Alternatively, after guidewire placement, switching to a balloon-tipped catheter and confirming resistance-free passage through the right ventricle with the balloon inflated can serve as verification.
Balloon dilatation must be performed rapidly and reliably. Contrast medium is diluted 3–4 times with normal saline and loaded into the indeflator. Diluting the contrast medium reduces viscosity and enables rapid inflation/deflation. After accurately positioning the balloon at the stenosis site, rapid inflation is performed while observing the waist, with prompt deflation once the waist disappears. Balloon inflation time is usually within a few seconds, and careful attention should be paid to hemodynamic changes such as bradycardia and blood pressure drop through arterial pressure monitoring. To prevent bradycardia, atropine may be administered intravenously immediately before PTPV.
After dilatation, angiography, and pressure measurement are repeated to evaluate the degree of gradient improvement and the extent of pulmonary regurgitation. If insufficient gradient reduction is achieved, additional dilatation with a slightly larger balloon may be performed, but the risk of annular injury and severe pulmonary regurgitation from over-dilatation must always be kept in mind. Additionally, immediately after PTPV, rapid reduction of right ventricular afterload often causes right ventricular hypercontractility, which may create a pressure gradient in the right ventricular outflow tract. This hypercontractility usually improves relatively quickly, but β-blocker administration should be considered if right ventricular outflow tract obstruction is severe.

2) Pulmonary Atresia
In cases of pulmonary atresia, if the pulmonary valve is membranous atretic, the tricuspid annulus and right ventricle have adequate size and maintain the structure of the inlet, apical, and outlet portions, and there is no right ventricle-dependent coronary circulation, pulmonary valve balloon valvuloplasty can be performed after perforation of the atretic pulmonary valve.
After confirming the valve position and morphology through right ventriculography, the tip of a right Judkins catheter is fixed against the pulmonary valve, and careful perforation is attempted using a thin guidewire (0.014 inch or 0.018 inch). Recently, the Nykanen RF wire, equipped with an electrode at the catheter tip capable of delivering radiofrequency output, has become available for perforating atretic pulmonary valves. This advancement allows perforation without physical force, whereas conventional methods relied on the operator's pushing force. Although the risk of peripheral tissue injury has been reduced, meticulous attention is required during perforation with either technique to accurately identify the annulus position under fluoroscopy and avoid myocardial perforation.
After valve perforation, gradual dilatation is performed using small balloon catheters (approximately 2–4 mm), progressively increasing the balloon size. The final balloon diameter is targeted at 120% of the annulus diameter, like conventional pulmonary valve stenosis, but in neonatal cases, careful determination is made considering right ventricular size and tricuspid annulus diameter.
In pulmonary atresia, the right ventricle is small and right ventricular compliance is reduced due to myocardial hypertrophy, requiring several days for antegrade flow from the right ventricle to the pulmonary artery to increase. Therefore, prostaglandin infusion, which was used preoperatively, is continued to maintain ductal patency and gradually reduced and discontinued based on oxygen saturation and echocardiographic findings.

5. Complications and Countermeasures

Major complications associated with PTPV include pulmonary regurgitation, annular injury, tricuspid chordae tendineae damage, and arrhythmias. Additionally, in neonatal and infant cases, cardiac perforation may occur during catheter and wire manipulation in the right ventricular outflow tract, requiring careful operation.
Pulmonary regurgitation is a relatively common complication, but most cases are mild to moderate with limited clinical significance. Appropriate balloon sizing can minimize the occurrence of severe pulmonary regurgitation. In cases of dysplastic valves or when oversized balloons are used, pulmonary regurgitation tends to worsen, making long-term follow-up important.
Tricuspid chordae tendineae injury is directly related to procedural manipulation as described above, and appropriate guidewire handling is the most effective preventive measure. If it occurs, severe tricuspid regurgitation may lead to right heart failure, potentially requiring surgical repair. Arrhythmias may occur due to right ventricular stimulation during the procedure, but most are transient and do not require special treatment. For persistent arrhythmias or those affecting hemodynamics, antiarrhythmic medication or electrical cardioversion should be considered.

6. Treatment Outcomes and Prognosis

The acute success rate of PTPV is extremely high, with reports showing that over 90–95% of cases achieve more than 50% gradient reduction, with final right ventricular pressure falling to 50% or less of systemic blood pressure. Excluding post-procedural pulmonary regurgitation, the incidence of serious complications is less than 5%, establishing excellent safety. Long-term prognosis is also favorable, with most cases maintaining right ventricular outflow tract patency and right ventricular function recovering to the normal range. Follow-up studies of 10 years or longer demonstrate that over 90% of cases do not require reintervention. However, in cases treated in early infancy (especially under 6 months of age) or cases with dysplastic pulmonary valves, restenosis occurs in approximately 15–30%, making regular echocardiographic follow-up essential. When restenosis occurs, good results can often be achieved with repeat balloon treatment. Transition to surgical treatment is required in less than 5% of all cases, representing a limited proportion.
Overall, PTPV is a standard and safe catheter intervention for pediatric congenital heart disease, and with appropriate patient selection, an accurate understanding of the technique, and meticulous postoperative management, excellent short- and long-term outcomes can be expected.

7. Summary

PTPV is a standard and safe catheter intervention method for pediatric congenital heart disease. The keys to procedural success include appropriate balloon size selection, avoidance of tricuspid chordae tendineae injury, rapid balloon inflation/deflation, and appropriate management of complications. For pediatric cardiologists, PTPV is a fundamental catheter intervention technique that must be mastered, and its principles and techniques provide important knowledge that can be applied to the treatment of other structural heart diseases.

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Patent Ductus Arteriosus

1. Patent Ductus Arteriosus (PDA)

In low-birth-weight infants, failure the ductus arteriosus to close can lead to respiratory failure and cardiac failure, resulting in severe complications such as poor weight gain, necrotizing enterocolitis, and sepsis. The first-line treatment for this disease is closure with medications such as indomethacin or ibuprofen. However, there are cases where the ductus arteriosus fails to close due to drug resistance, or complications such as acute renal failure and necrotizing enterocolitis occur due to drug therapy. In such cases, ligation or clipping of the ductus arteriosus via a lateral thoracotomy has traditionally been performed. While surgical treatment has shown good outcomes, complications such as bleeding, lung injury, infection, chylothorax, and recurrent laryngeal nerve palsy have been reported.

2. Ductus Arteriosus Closure

In 1994, catheter-based closure of patent ductus arteriosus was approved using the Flipper coil, and it has gradually become a common treatment for PDA in Japan. The introduction of the AMPLATZER Duct Occluder (ADO), a percutaneous arterial duct closure set, in 2009 greatly expanded the scope of treatment. At the same time, JCIC established facility and operator standards for the use of ADO in accordance with the "Institutional Standards and Educational Program for the Use of Percutaneous Arterial Duct Closure Sets" and has led the country's introduction, safe treatment, and widespread use, revising them as necessary. By adhering to these standards, catheter closure is now performed in most cases except for early infancy and low birth weight infants. Furthermore, the AMPLATZER Duct Occluder II (ADO II) was introduced in 2019, and the AMPLATZER Piccolo Occluder was introduced in 2020, making it a treatment option for low-birth-weight infants weighing less than 2.5 kg, who previously required surgical treatment. With the introduction of these three types of percutaneous ductal closure devices in Japan, catheter-based treatment for patent ductus arteriosus, a common congenital heart disease, is now available to patients of all ages, from preterm and low birth weight infants and newborns to adults and the elderly.

3. Implementation System

In Japan, the ADO family can only be used in facilities that meet the facility standards, by doctors who meet the operator standards and have completed the educational programs established by the JCIC Society and the CVIT Society. Furthermore, to use the AMPLATZER Piccolo Occluder in patients weighing less than 2.5 kg at the time of the procedure, the facility, operator, and appropriate use criteria set forth in the "Guidelines for the Use of Percutaneous Duct Closure Sets for Patent Ductus Arteriosus in Patients Weighing Less than 2.5 kg" must be met.

4. Closure Devices Available in Japan

There are three types of occluders: ADO, ADO II, and the Piccolo Occluder (Figure1-3). The occluder is made of a mesh woven from nitinol wire. The ADO consists of a unilateral disk and tubular section, while the ADO II and Piccolo Occluder consist of a central waist and disks on both sides. Only the ADO is internally filled with a polyester patch. Its self-expanding properties make it relatively easy to manipulate and allow for retraction and redeployment. The ADO is available in seven sizes and can be placed only from the pulmonary artery side using a 5-7 Fr long sheath. The ADO II is available in eight sizes and can be placed from both the pulmonary artery and aorta using a 4-5 Fr delivery catheter, while the Piccolo Occluder is available in nine sizes and can be placed from both the pulmonary artery and aorta using a 4 Fr delivery catheter.

Production of the Flipper PDA Coil (Cook Medical), a detachable coil commonly used for ductal arteries, was discontinued in June 2022 (sales will continue until 2027), and the ADO family is expected to become the dominant product going forward.

5. Treatment Considerations

(1) Indications for the Prevention of Infective Endocarditis
The annual risk of developing infective endocarditis in PDA patients has been reported to be 0-4.5%, but this risk is dramatically reduced through surgical and catheter treatment. Patients with a continuous murmur are considered to be at higher risk for infective endocarditis, but the indications for treatment in silent PDAs, i.e., whether they cause infective endocarditis, remain controversial.

(2) PDA Closure in Neonates and Infants
For PDA closure in early infancy and beyond, catheterization is the first choice because it has fewer complications and a higher success rate than surgical treatment. With the introduction of the Amplatzer Piccolo Occluder, which is compatible with newborns aged 3 days or older and weighing 700g or more, catheterization in neonates and early infants is expected to become more widespread nationwide.

(3) PDA Closure in Adults (Including the Elderly)
PDAs in adults have unique anatomical and hemodynamic characteristics. It has also been reported that PDA closure is possible without the use of contrast agents due to renal dysfunction. When treating elderly patients with PDA who have comorbid conditions, a multidisciplinary team approach is important, including not only catheterization specialists but also heart failure teams, congenital heart disease teams (including pediatric cardiologists), echocardiologists, cardiac surgeons, anesthesiologists, and paramedical staff.

6. Summary
Various types of PDA can be closed by selecting the appropriate device, size, and placement technique. If a PDA is found, regardless of age, we recommend consulting a pediatric cardiologist to consider the possibility of catheterization.

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Atrial Septal Defect

1. Overview of Atrial Septal Defect

Atrial septal defect (ASD) occurs in approximately 1 per 1,000–1,500 live births and is more common in females, with a male-to-female ratio of about 1:2. The main pathophysiology involves left-to-right shunting through the defect, leading to increased blood flow to the right atrium, right ventricle, and pulmonary artery—resulting in right-sided volume overload. Although most patients remain asymptomatic during childhood, ASD closure is indicated—regardless of symptoms—when echocardiography or cardiac catheterization demonstrates significant right-sided volume overload. In 2024, the Japanese Congenital Interventional Cardiology (JCIC) published updated guidelines, including recommendations and evidence levels for transcatheter ASD closure.

2. ASD Closure

In 1974, Dr. King and Dr. Mills in the United States performed first transcatheter ASD closure in the world. Since then, various occluder devices have been developed worldwide; however, due to concerns regarding procedural success and safety, none achieved widespread use. This situation changed in 1997 with the introduction of the AMPLATZER™ Septal Occluder (ASO). Its efficacy and safety were established, leading to FDA approval. ASO has since been widely used globally, supported by extensive clinical experience and accumulating evidence, and is now regarded as one of the most reliable closure devices. Transcatheter closure is currently the first-line therapy for ASD worldwide due to its proven efficacy and safety. Compared with surgical repair, catheter-based closure is associated with lower complication rates, shorter procedure times, and shorter hospital stays. However, surgical closure remains necessary in anatomically unsuitable cases. In recent years, minimally invasive cardiac surgery (MICS) techniques have also been increasingly adopted.

3. Implementation System in Japan

In Japan, transcatheter ASD closure was introduced in 2005 under the leadership of JCIC. Since 2010, The Japanese Association of Cardiovascular Intervention and Therapeutics (CVIT)-accredited institutions have also participated. Currently, approximately 1,500 procedures—including both pediatric and adult cases—are performed annually in Japan.

4. ASD Occluder Devices Available in Japan

Three ASD occluder devices are currently approved for use in Japan:
AMPLATZER™ Septal Occluder (Abbott Medical Japan LLC) (Figure 1A)
Figulla® Flex II Septal Occluder (Japan Lifeline Co.) (Figure 1B)
GORE® CARDIOFORM ASD Occluder (W. L. Gore & Associates Japan), reimbursed since August 2021 (Figure 1C)
Each device has unique characteristics, and the appropriate occluder is selected based on defect morphology and anatomy. Transcatheter ASD closure is typically performed under general anesthesia in children, in an angiography suite or hybrid operating room, using imaging guidance such as transesophageal echocardiography or intracardiac echocardiography. Venous access is obtained through the right femoral vein, and the procedure takes approximately one hour, making it a minimally invasive therapy (Figure 2).

5. Summary

The efficacy and safety of transcatheter ASD closure are well established.
However, ASD presents considerable anatomical variation among patients. Therefore, individualized assessment—including anatomical evaluation, defect morphology, risk stratification, and careful selection of device type and size—is critically important for determining the optimal treatment strategy.

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Vascular Dilation Procedures in Congenital Heart Disease

Vascular dilation procedures for congenital heart disease in children have been performed for more than 40 years, ever since Lock and colleagues first reported the efficacy of balloon angioplasty for pulmonary artery stenosis in 1983. Today, they are among the most well-established interventional cardiac catheterization procedures. The anatomical targets are diverse and include the pulmonary arteries, aorta, venae cavaes, and pulmonary veins, as well as stenotic lesions following shunt operations or conduit implantation. In congenital heart disease, vascular dilation refers to balloon angioplasty and stent implantation, in which a balloon catheter or stent is advanced to the target vessel and expansion is performed. In clinical practice, the choice between balloon angioplasty and stent implantation is made after comprehensive consideration of patient age, body size, target vessel characteristics, and clinical status.

There are many types of balloon catheters, which vary in material and size, and the appropriate type and size differ greatly depending on the anatomical site and vessel diameter. Each balloon catheter has a manufacturer-specified rated burst pressure, and dilation is recommended at pressures not exceeding this limit. To apply appropriate dilation pressure and ensure procedural safety, the use of an indeflator during balloon expansion is recommended. Compared with stent implantation, balloon angioplasty is technically less complex, and vessel growth can be expected after dilation (Figure 1). However, its limitations include insufficient dilation in some cases and a higher likelihood of restenosis compared with stents.

In Japan, no stents have been specifically developed for pediatric use; thus, adult peripheral stents—such as those designed for the renal arteries or other peripheral vessels—are commonly used. Stent implantation carries higher risks than balloon angioplasty, including stent migration, and requires greater technical expertise; therefore, these procedures are generally performed by experienced interventional cardiologists. Once deployed, the stent expands the target vessel to the stent’s diameter, resulting in a low risk of acute restenosis, and if an adequately sized stent is implanted, the need for subsequent reintervention is reduced (Figure 2). However, because the vessel cannot be expanded beyond the stent’s maximum diameter, the indication for small-diameter stents in smaller children must be carefully evaluated, taking into account somatic growth.

Guidewires are essential for delivering balloon catheters and stents to the target vessel. Their purposes include guiding the balloon or stent to the lesion and maintaining stability during dilation. Safe and effective vascular dilation cannot be achieved without guidewires. As with balloons and stents, various types and sizes of guidewires exist, and appropriate selection must be made according to the planned balloon angioplasty or stent implantation.

Vascular dilation procedures are among the most established catheter-based treatments for congenital heart disease in children. However, as with other catheter interventions, careful evaluation of safety and efficacy is essential before proceeding. We hope that this article will encourage more healthcare professionals to develop an interest in vascular dilation procedures for congenital heart disease in the pediatric population.

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Catheter Embolization for Abnormal Vessels

Sometimes, blood vessels that are not supposed to exist can develop around the heart, lungs, or liver. These abnormal vessels are collectively called collateral vessels or shunts. When they are present, oxygen-poor blood may circulate through the body, or the heart and lungs may receive extra workload.
Catheter embolization is a minimally invasive procedure in which these abnormal vessels are closed using plugs or coils. It does not require open-chest surgery and generally places less stress on the body.

Below are several common types of abnormal vessels and how embolization is used to treat them.

1. Major Aortopulmonary Collateral Arteries

New blood vessels may form from the body’s arteries toward the lungs. These are called aortopulmonary collateral arteries. When they carry too much blood into the lungs, they can lead to pulmonary hypertension and increased strain on the heart (Fig. 1A). Embolization is used to place plugs or coils inside these extra vessels to reduce unnecessary blood flow and maintain appropriate pulmonary circulation (Fig. 1B). It may be performed before or after surgery as part of overall treatment planning.

2. Veno-venous Collaterals

These abnormal connections are often seen after Glenn or Fontan surgery for single-ventricle conditions. A high-pressure systemic vein can connect to a low-pressure pulmonary vein, allowing oxygen-poor blood to flow directly into the body. This can cause cyanosis and increase stress on the heart (Fig.1C). Before closing the vessel, doctors may temporarily block it with a balloon catheter to assess whether closure is safe. If closure is judged to be beneficial, embolization with plugs or coils is performed (Fig.1C).

3. Pulmonary Arteriovenous Malformations (PAVMs)

PAVMs occur when a pulmonary artery connects directly to a pulmonary vein without the normal capillary network in between (Fig.2A). No oxygen exchange occurs in this area, leading to low blood oxygen levels. Severe cases may cause headaches, shortness of breath, or even neurological complications.
PAVMs can be associated with genetic conditions, liver disease, or may appear after Glenn surgery. Embolization is a highly effective treatment, improving oxygen levels by closing the abnormal connection (Fig.2B).

4. Coronary Artery Fistulas

A coronary artery fistula is an abnormal connection between a coronary artery (which supplies oxygen to the heart muscle) and a heart chamber or vessel, bypassing the capillary system (Fig.2C). Blood may “leak” away from the heart muscle, causing reduced oxygen supply, arrhythmias, or heart enlargement. When the fistula is large or causes symptoms, it should be closed. Catheter-based embolization using plugs or coils is a less invasive alternative to surgical closure and is often preferred when suitable (Fig.1D).

5. Porto-systemic Shunts

The portal vein normally carries blood from the intestines to the liver. When it connects abnormally to a large vein in the body, substances that should be processed by the liver circulate throughout the body instead. This can lead to liver tumors, encephalopathy, or pulmonary hypertension (Fig.3A, B). Embolization can reduce or close the shunt to restore proper liver blood flow. However, closing the shunt can increase portal pressure, so doctors first perform a test occlusion and carefully evaluate the risks. Treatment is carried out under the guidance of a specialized team (Fig.3C, D).

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Transcatheter Pulmonary Valve Implantation（TPVI）

Repair outcomes for tetralogy of Fallot (TOF) and related conditions have improved dramatically, and approximately 90% of patients now reach adulthood. However, most patients in this disease group undergo treatment to the pulmonary valve (PV) at the time of their initial repair, and subsequently develop pulmonary regurgitation (PR) or pulmonary stenosis (PS) after surgery. When severe PV dysfunction persists long-term, right ventricle (RV) enlargement and elevated RV pressures worsen. Many patients 20–40 years after their initial repair who are left untreated experience repeated hospitalizations for heart failure (HF) and go on to develop advanced HF, life-threatening arrhythmias, or sudden death, resulting in poor prognosis. Therefore, reintervention for PR or PS becomes necessary.

In the 2025 revision of the Adult Congenital Heart Disease Treatment Guidelines, surgical pulmonary valve replacement (SPVR) or TPVI is given a Class I recommendation for patients with significant PR (regurgitant fraction ≥ 25%) who have symptoms of HF or reduced exercise capacity. A Class IIa recommendation is given for asymptomatic patients who show at least moderate RV dilation (RV end-diastolic volume index > 160 mL/m² or RV end-systolic volume index > 80 mL/m²), those with RV dysfunction, or those with progressive symptomatic atrial or ventricular arrhythmias. For PS, a Class IIa recommendation is given to consider SPVR or TPVI based relief of the obstruction when RV systolic pressure exceeds 70% of left ventricular (LV) systolic pressure, or when the pressure gradient across the right ventricular outflow tract (RVOT) is ≥ 50–60 mmHg.

Historically, SPVR was the standard treatment. However, many patients remain under observation without intervention because re-entering the chest after prior childhood thoracotomy is difficult and surgical risk increases with advanced age.
At present in Japan, two types of transcatheter bioprosthetic valves are available. The Harmony valve (Figure 1a and b) is a self-expanding stented valve that contains a porcine pericardial valve. The Sapien 3 valve (Figure 2a and b) is a balloon-expandable stented valve that contains a bovine pericardial valve. Both are delivered via a catheter inserted through a femoral or jugular vascular access and positioned to the RVOT for valve deployment (Figure 3a and b).

Indications differ between the two devices. The Harmony valve is indicated for patients in whom the native PV has been preserved after RV patch augmentation, and it is used for PR alone. The Sapien3 valve is indicated for patients after conduit replacement or prior bioprosthetic valve replacement and may be used for PR or PS.

For the prevention of infective endocarditis, patients must take preventive antibiotics lifelong when undergoing procedures that involve tooth extraction or other interventions associated with bleeding. In addition, after stented valve implantation, lifelong antiplatelet or anticoagulant therapy is required for thrombosis prevention.

TPVI reduces PR, increases forward blood flow, and lowers right ventricular pressure, resulting improvement of heart failure symptoms such as exertional dyspnea. Even in asymptomatic patients, the procedure can prevent future development of HF, reduce the occurrence or progression of life-threatening arrhythmias, and potentially improve survival. Because the procedure is less invasive than SPVR, patients can often return to normal activities sooner.

Short- to mid-term outcomes of TPVI have been reported to be favorable, with a low rate of fatal complications and therapeutic efficacy comparable to SPVR. However, similar to surgically implanted biological valves, bioprosthetic valve degeneration occurs over time; approximately 15% of patients require reintervention by 10 years and about 35% by 15 years.

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Catheter Ablation for Pediatric Cardiovascular Diseases

1. What is Catheter Ablation?
Catheter ablation is a catheter-based treatment primarily performed for tachyarrhythmias. The treatment target varies depending on the arrhythmia mechanism: for reentry tachycardias, the arrhythmia circuit is disrupted; for hyperkinetic or triggered tachycardias, the tachycardia focus is ablated.

2. Advances in Catheter Ablation
Pediatric catheter ablation began with a 1991 report of 12 PSVT cases. Over time, outcomes and safety improved through technological innovations: the introduction of 3D mapping systems, the addition of multipoint mapping modules, fusion of CT and ICE images, the introduction of cryoablation, and the introduction of contact force catheters. In recent years, the introduction of pulsed-field ablation in the field of adult atrial fibrillation has been the major topic, and knowledge regarding its application in PSVT and pediatric cases is gradually accumulating.

3. Catheter Ablation Procedure
In catheter ablation, identifying the arrhythmia mechanism is paramount. To achieve this, electrode catheters are placed intracardially. Various programmed pacing sequences are then applied while intracardiac electrocardiography is measured to elucidate the mechanism. A 3D mapping system is used concurrently to identify anatomically significant isthmuses and conduction pathways suitable for ablation. This entire sequence of procedures is termed an electrophysiological study (Figures 1, 2, 3, 4). Performing catheter ablation requires highly advanced knowledge and technical skill in electrophysiological studies. Typically, multiple electrode catheters are inserted via the femoral vein, internal jugular vein, or subclavian vein and are placed in the superior right atrium, His bundle, coronary sinus, and right ventricle. However, in pediatric patients with limited vascular access, some catheters may be omitted, or transesophageal electrode catheters may be used. Electrode catheters of 2, 4, 5, or 6 Fr are used. The transseptal technique is frequently employed to access the left atrium or the mitral annular substrate. This is performed using a long sheath and a radiofrequency transseptal needle. Concurrent use of intracardiac or transesophageal echocardiography enhances procedural safety.
Two primary treatments for arrhythmia substrates are typically employed: thermal ablation and cryoablation. Thermal ablation uses radiofrequency energy to heat the electrode catheter tip, performing ablation through thermal denaturation. Non-irrigation catheters utilize temperature control to perform ablation at 55–60°C (Figure 5). Irrigated catheters perform ablation at a fixed power output while maintaining perfusion. Cryoablation uses liquid nitrous oxide (laughing gas) to cool the catheter tip to its boiling point of −80°C. Cryoablation causes cell damage through the freezing and expansion of intracellular water and changes in intracellular and extracellular electrolyte concentrations. The choice between thermal and cryoablation is typically based on the potential risk of damaging the AV node. Cryoablation is often used for: - Standard AV nodal reentrant tachycardia (AVNRT) where ablation is performed near the AV node - Tachycardia due to right-sided twin AVN - Treatment of accessory pathways near the His bundle.

4. Indications for Catheter Ablation in Children
Arrhythmias generally considered for catheter ablation treatment include tachyarrhythmias, particularly paroxysmal supraventricular tachycardia (AV nodal reentrant tachycardia, AV nodal reentrant tachycardia associated with WPW syndrome, atrial tachycardia), ventricular tachycardia, and ventricular premature contractions. Fundamentally, the same conditions are targeted in children. Naturally, pediatric catheter ablation should be performed by experienced pediatric arrhythmia specialists. Particularly in patients weighing 15 kg or less, the risk of complications is considered higher. Therefore, careful evaluation of indications, substantial experience, and the availability of a full-time pediatric cardiovascular surgeon and emergency surgery capabilities are essential. Furthermore, paroxysmal supraventricular tachycardia in the neonatal period or early infancy is known to resolve spontaneously. Therefore, drug therapy should be the first choice, and a thorough risk assessment against the natural history must be performed. For symptomatic tachyarrhythmias in patients with adequate body size (i.e., ≥15 kg), catheter ablation is recommended for indications nearly identical to those in adults. A more conservative approach is often taken for asymptomatic WPW syndrome or outflow tract premature contractions; however, if the risk of AV block is low, the treatment plan should be determined based on thorough explanation and the principle of shared decision-making.