Minimally Invasive Management in CHD

Overview of Minimally Invasive Management in CHD

• Interventional cardiac catheterization and hybrid procedures have fundamentally transformed the management of congenital heart disease (CHD), offering effective alternatives to open-heart surgery while minimizing trauma, shortening hospitalizations, and avoiding cardiopulmonary bypass.
• These techniques encompass balloon dilations of stenotic valves and vessels, transcatheter device closure of septal defects and shunts, and the percutaneous implantation of prosthetic valves.

Patent Ductus Arteriosus (PDA)

Pathophysiology and Clinical Findings

• A hemodynamically significant PDA results in left-to-right shunting, which leads to left atrial and left ventricular volume overload, pulmonary overcirculation, and congestive heart failure.
• Auscultation classically reveals a continuous "machinery-like" murmur.
• The electrocardiogram (ECG) is often normal with a small ductus but may demonstrate left ventricular hypertrophy or biventricular hypertrophy if pulmonary hypertension develops.
• Echocardiography is crucial for identifying the ductal ampulla, measuring the minimal diameter, and determining the total length of the ductus.

Transcatheter Interventions and Devices

• Transcatheter closure is the standard of care for patients beyond the neonatal period, indicated to treat volume overload or to prevent endarteritis.
• Small PDAs are routinely closed using catheter-delivered intravascular coils.
• Moderate to large PDAs are occluded using plug-like or umbrella devices, including the Amplatzer Duct Occluder (I and II), Nit-Occlud PDA system, Amplatzer Vascular Plug (II, IV), and the Medtronic Microvascular Plug.
• The Amplatzer Piccolo Occluder is specifically FDA-approved for PDA closure in extremely premature and low-birth-weight infants (<1000g).
• In premature infants, arterial access is strictly avoided to prevent vascular injury; the device is delivered via the femoral vein utilizing real-time transthoracic echocardiography instead of angiography to evaluate the branch pulmonary arteries and aortic arch.

Atrial Septal Defect (ASD)

Pathophysiology and Clinical Findings

• Secundum ASDs create a pre-tricuspid left-to-right shunt resulting in right atrial and right ventricular volume overload.
• Auscultation features an ejection systolic murmur originating from increased flow across the pulmonary valve, and potentially a soft delayed diastolic rumble at the lower left sternal border representing increased flow across the tricuspid valve.
• Echocardiography combined with balloon sizing in the catheterization laboratory is used to measure the stretched defect diameter and evaluate the adequacy of septal rims.
• Transesophageal echocardiography (TEE) bicaval views and subcostal views are critical for confirming the defect type and ruling out anomalous pulmonary venous connections.

Transcatheter Interventions and Devices

• Percutaneous closure is the preferred method for secundum ASDs provided there are sufficient septal rims; the absence of a posteroinferior rim significantly increases the risk of device embolization.
• The Amplatzer Septal Occluder consists of a self-expanding, double-disc nitinol wire mesh encasing Dacron fabric and is approved for defects up to 40 mm in diameter.
• The Gore Cardioform Septal Occluder utilizes a nitinol frame attached to expanded polytetrafluoroethylene (ePTFE) and is approved for defects up to 17 mm.
• The Gore Cardioform ASD Occluder features a conforming central waist and is utilized for closing defects up to 35 mm.
• Procedures are performed under TEE or intracardiac echocardiography (ICE) guidance to ensure proper deployment of the left and right atrial discs without impinging on the atrioventricular valves, pulmonary veins, or aortic root.

Ventricular Septal Defect (VSD)

Pathophysiology and Clinical Findings

• VSDs cause a left-to-right shunt of oxygenated blood at the ventricular level, leading to left ventricular volume overload.
• Auscultation reveals a harsh pansystolic murmur, frequently accompanied by a palpable thrill.
• Cardiac MRI and echocardiography are utilized to quantify the left atrial and ventricular dilation and to estimate the Qp:Qs shunt ratio.

Transcatheter and Hybrid Interventions

• Percutaneous transcatheter closure is highly successful for muscular VSDs using devices like the Amplatzer Muscular VSD Occluder.
• Transcatheter closure of perimembranous VSDs remains challenging due to the defect's proximity to the aortic valve and the conduction system; older devices carried an unacceptably high risk of complete atrioventricular block (up to 22%), making surgical closure the preferred approach.
• Newer devices, such as the modified double-disk occluder and the Nit-Occlud Le VSD coil, have demonstrated improved success in minimizing conduction tissue damage.
• For small infants (<5 kg) with difficult-to-reach muscular or multiple "Swiss cheese" VSDs, a hybrid perventricular approach is utilized.
• The hybrid approach involves a subxiphoid or median sternotomy to provide direct access to puncture the right ventricular free wall, allowing device deployment via a short sheath under continuous TEE guidance without the need for cardiopulmonary bypass.

Pulmonary Valve Stenosis (PS)

Pathophysiology and Clinical Findings

• Valvar PS causes right ventricular outflow tract (RVOT) obstruction, leading to right ventricular hypertrophy and increased right ventricular systolic pressures.
• Auscultation demonstrates a pulmonary ejection systolic murmur and a thrill in the left second interspace.
• Echocardiography reveals thickened, restricted leaflets with systolic "doming" and post-stenotic dilation of the main pulmonary artery.
• A continuous wave Doppler peak systolic gradient of >40-50 mmHg typically indicates the need for intervention.

Transcatheter Interventions

• Balloon pulmonary valvuloplasty is the gold standard and initial treatment of choice for moderate to severe isolated valvar PS.
• The procedure utilizes a balloon 1.2 to 1.4 times the diameter of the pulmonary valve annulus to selectively tear the fused commissures.
• In older patients or those with a large pulmonary annulus, a double-balloon technique (simultaneous inflation of two smaller balloons) is employed to minimize systemic hypotension during balloon inflation.

Aortic Valve Stenosis (AS)

Pathophysiology and Clinical Findings

• Valvar AS increases left ventricular afterload, resulting in compensatory left ventricular hypertrophy.
• Severe critical AS in the neonate presents as ductal-dependent systemic circulation, requiring prostaglandin E1 infusion to maintain systemic perfusion.

Transcatheter Interventions

• Balloon aortic valvuloplasty is indicated for children with a peak-to-peak gradient >50-60 mmHg, or those with depressed left ventricular function.
• Vascular access is typically achieved via the femoral artery, or the umbilical or carotid artery in neonates.
• The intervention is generally considered palliative to delay surgical intervention (e.g., the Ross procedure) and must be performed carefully to minimize the creation of severe iatrogenic aortic insufficiency.

Coarctation of the Aorta (CoA)

Pathophysiology and Clinical Findings

• CoA is a discrete narrowing at the aortic isthmus resulting in upper-body hypertension and diminished or absent femoral pulses.
• Cardiac CT and MR angiography are essential for obtaining high-resolution 3D reconstructions, defining the narrowing, and identifying associated anomalies like a bicuspid aortic valve.
• An upper-to-lower extremity resting blood pressure gradient >20 mmHg is the primary indication for intervention.

Transcatheter Interventions and Devices

• Balloon Angioplasty: Serves as the procedure of choice for recoarctation following previous surgery, but remains controversial for primary native coarctation in infants due to high restenosis rates and the risk of aneurysm formation.
• Stent Implantation: This is the preferred modality over balloon angioplasty or surgery for older children and adults (>25 kg) due to a lower complication rate and superior sustained gradient reduction.
• Both bare-metal and covered stents are utilized; covered stents offer an added layer of safety against acute vascular tears and can treat established pseudoaneurysms.
• Stents implanted in children must possess the capacity to be expanded to adult dimensions via serial balloon dilations or intentional longitudinal stent fracture to accommodate somatic growth.

Transcatheter Valve Implantation

Interventions and Devices

• Transcatheter pulmonary valve (TPV) replacement provides a competent valve without requiring open-heart surgery for patients with dysfunctional RV-PA conduits or severe pulmonary regurgitation following prior RVOT reconstructions (e.g., Tetralogy of Fallot repair).
• Melody Valve: A bovine jugular vein valve sewn into a balloon-expandable stent, expandable up to 22 mm.
• Sapien Valve: A bovine pericardial valve housed in a balloon-expandable stent, expandable up to 29 mm.
• Harmony TPV & Alterra Adaptive Prestent: Newer, self-expanding devices designed to remodel and treat large, dilated native right ventricular outflow tracts previously deemed unsuitable for balloon-expandable valves.

Summary of Devices and Procedures