Baffle Closure of ASD

Overview

Why a Baffle is Needed (Not a Simple Patch)

• The superior vena cava (SVC) and right atrial junction + right upper pulmonary vein(s) [most common - superior type], or
• The inferior vena cava (IVC) and right atrial junction + right lower pulmonary veins [inferior type]

• These defects are not amenable to catheter-based device closure, and surgical repair is always required.
• Sabiston Textbook of Surgery, p. 2564; Mulholland & Greenfield's Surgery, p. 4403

Types of Sinus Venosus ASD and Repair Strategy

1. Superior Sinus Venosus ASD (most common)

• Cardiopulmonary bypass (CPB) with bicaval cannulation
• Right atriotomy is performed
• A patch (pericardial or synthetic) is positioned inside the right atrium/SVC to create a tunnel (baffle)
• The baffle directs pulmonary venous blood behind the patch, through the sinus venosus defect, and into the left atrium
• The superior vena cava is kept widely patent anterior to the baffle to drain systemic venous blood into the right atrium
• Care is taken to avoid obstruction of the pulmonary veins or SVC (the SVC is usually dilated and provides ample room)
• Schwartz's Principles of Surgery, p. 781; Mulholland & Greenfield's Surgery, p. 4403

2. When the Anomalous Vein Connects Cranially to the Right Pulmonary Artery - The Warden Procedure

1. The SVC is transected cranial to the anomalous vein connection
2. The caudal stump of the SVC is oversewn (closed)
3. The cranial end of the SVC is anastomosed to the right atrial appendage - this redirects upper body systemic venous return into the right atrium
4. Inside the atrium, a patch baffle is sewn to cover the SVC-right atrial junction and redirect anomalous pulmonary venous blood through the sinus venosus defect into the left atrium

• Schwartz's Principles of Surgery, p. 781-782; Sabiston Textbook of Surgery, p. 2564

3. Inferior Sinus Venosus ASD (scimitar syndrome)

• Associated with the scimitar vein (anomalous pulmonary vein draining to the IVC)
• Repair may involve a patch baffle within the intrahepatic IVC, which is technically more complex
• May require hypothermic circulatory arrest
• Sabiston Textbook of Surgery, p. 2564

Key Surgical Principles

Outcomes and Complications

• Operative mortality approaches zero in the absence of pulmonary hypertension
• Postoperative SVC obstruction - a major concern unique to baffle repair (not seen with simple patch)
• Pulmonary vein obstruction - can cause pulmonary hypertension and is avoided by careful patch sizing
• Atrial arrhythmias - occur in 10-40%, particularly in older patients (>40 years) or those with pre-existing arrhythmias; not completely mitigated by repair
• Baffle dehiscence - late complication; a dehisced patch after Warden procedure may be amenable to percutaneous closure using an ASD occluder (e.g., 44-mm Gore Cardioform device), guided by 3D CMR modeling
• Schwartz's Principles of Surgery, p. 782; Sabiston Textbook of Surgery, p. 2565

Key Comparison: Types of ASD and Closure Method

Atrial Septal Defect (ASD)

Definition

Embryological Basis

• Septum primum - a crescent-shaped ingrowth that partially divides the atria; the gap in front (ostium primum) closes as the septum grows, but a new opening (ostium secundum) forms posteriorly
• Septum secundum - grows to the right of septum primum and covers the ostium secundum, leaving a small channel called the foramen ovale, which normally closes at birth when lung expansion drops right atrial pressure below left atrial pressure

• Robbins, Cotran & Kumar Pathologic Basis of Disease, p. 504

Types of ASD

• Robbins, Cotran & Kumar, p. 504; Harrison's Principles of Internal Medicine 22E, p. 2114

Pathophysiology

• Normal left atrial (LA) pressure > right atrial (RA) pressure, driving a left-to-right shunt through the ASD
• Pulmonary vascular resistance is much lower than systemic, and the right ventricle is more distensible - both factors amplify the shunt
• Pulmonary blood flow may be 2 to 8 times normal (Qp:Qs up to 8:1)
• This causes right heart volume overload - right atrium and right ventricle dilate
• Over time: pulmonary hypertension, right heart failure, atrial arrhythmias
• Risk of paradoxical embolism (clot crossing from right to left via the ASD, causing stroke)
• Robbins & Kumar, p. 505

Clinical Features

Symptoms

• Usually asymptomatic until adulthood (most patients reach their 30s before symptoms)
• Exercise intolerance, dyspnea on exertion, fatigue
• Palpitations, syncope (from atrial arrhythmias)
• Stroke (from paradoxical embolism)

• 70% of patients become impaired by the fifth decade if untreated

Physical Examination Signs

• Wide and fixed splitting of S2 - the hallmark sign; the split does not vary with respiration (because increased venous return during inspiration partially equalises the shunt and offsets phasic changes)
• Soft midsystolic ejection murmur at left upper sternal border - due to increased flow across the pulmonary valve (not across the ASD itself, which is too large to generate turbulence)
• Mid-diastolic murmur at lower left sternal border - increased tricuspid flow in large shunts
• Right ventricular heave (parasternal lift)
• Dilated pulmonary artery may be palpable at the second left intercostal space
• Goldman-Cecil Medicine, p. 984

Investigations

Indications for Closure

• Significant left-to-right shunt (Qp:Qs > 1.5:1) with or without symptoms
• Right heart enlargement (RA/RV dilation) on echocardiography
• Symptomatic patients at any age
• Usually performed at 3-5 years of age in children

Treatment Options

1. Percutaneous Device Closure (Transcatheter)

• Suitable for secundum ASDs with adequate rims and no associated anomalous veins
• Defects up to 3.5 cm can be closed
• Most commonly used device: Amplatzer Septal Occluder
• Currently accounts for >60% of all ASD interventions
• Avoids sternotomy and cardiopulmonary bypass

2. Surgical Closure

• Required for primum, sinus venosus, and coronary sinus ASDs (all need surgery)
• Also for large secundum ASDs not suitable for device closure
• Methods:
  • Primary suture closure - for small defects
  • Patch closure - pericardium or PTFE, sutured with polypropylene
  • Baffle repair - for sinus venosus ASDs with PAPVR (redirects anomalous pulmonary veins to LA)
• Mortality approaches zero in the absence of pulmonary hypertension
• Long-term outcomes excellent; postoperative survival comparable to normal population
• Goldman-Cecil Medicine, p. 1000; Mulholland & Greenfield's Surgery, p. 4403

Key Points Summary

• ASD = abnormal opening in the interatrial septum (not the same as PFO)
• Causes left-to-right shunt → right heart volume overload
• Most common form: secundum ASD (90%)
• Classic sign: wide, fixed splitting of S2
• ECG: incomplete RBBB pattern
• Secundum ASD - device closure preferred; all others require surgery
• Untreated, leads to right heart failure, pulmonary hypertension, arrhythmias, and paradoxical embolism

Bidirectional Glenn (BDG) Procedure

What It Is

Historical Context: Glenn Shunts

• Textbook of Clinical Echocardiography, p. classification table

Context: The Three-Stage Fontan Palliation

• Harriet Lane Handbook 23rd Ed, p. 257; Mulholland & Greenfield's Surgery, p. 4436

Indications (Diseases Requiring BDG)

• Tricuspid atresia (prototype single-ventricle lesion)
• Hypoplastic Left Heart Syndrome (HLHS) - most common indication today
• Double-inlet left ventricle
• Pulmonary atresia with intact ventricular septum (with severely hypoplastic RV)
• Heterotaxy syndromes
• Also used as "one-and-a-half ventricle repair" when the RV is judged too small or dysfunctional to support full pulmonary circulation (paired with a biventricular repair)
• Braunwald's Heart Disease; Sabiston Textbook of Surgery, p. 2584

Surgical Technique

1. Cardiopulmonary bypass may or may not be used (some centres perform it off-pump)
2. The SVC is transected at its junction with the right atrium; the SVC-RA junction is oversewn
3. The free end of the SVC is anastomosed end-to-side to the right pulmonary artery, creating a direct passive flow pathway from the upper body to both lungs
4. Any prior systemic-to-pulmonary shunts (mBTT, Sano) placed at Stage 1 are taken down at this time
5. The azygos vein is typically ligated to prevent a competing venous pathway that would cause desaturation

• Grainger & Allison's Diagnostic Radiology, p. 309; Sabiston Textbook of Surgery, p. 2588

Hemi-Fontan vs. Bidirectional Glenn

• Mulholland & Greenfield's Surgery, p. 4436

Why Stage 2 is Done at 3-6 Months

• By 3-6 months, pulmonary vascular resistance (PVR) has naturally fallen enough to allow passive (non-pulsatile) SVC flow to the lungs without a driving ventricle
• At birth, PVR is too high for passive pulmonary flow - a shunt with a ventricular pump source is still needed
• Delaying beyond 6 months prolongs the volume overload on the single ventricle, risking ventricular dysfunction

Imaging Surveillance After BDG (Pre-Fontan Assessment)

• Grainger & Allison's Diagnostic Radiology, p. 309-310

Prerequisites for Proceeding to Fontan (Stage 3)

• Pulmonary artery pressure < 20 mmHg
• PVR < 2 Wood units/m²
• Normal ventricular systolic function
• Normal or acceptable AV valve function (no significant regurgitation)
• Adequate pulmonary artery size
• Mulholland & Greenfield's Surgery, p. 4436

Complications of BDG / Living with Glenn Circulation

• Veno-venous collaterals - common; SVC-to-IVC collaterals form and shunt deoxygenated blood away from the lungs, worsening cyanosis
• Systemic-to-pulmonary collaterals - develop because the upper body is at high venous pressure; can cause pulmonary overcirculation and volume overload
• Pulmonary arteriovenous malformations (PAVMs) - can develop over time, especially if hepatic venous blood (which contains a hepatic factor that prevents PAVMs) is excluded from the pulmonary circulation. This was the major drawback of the classic unidirectional Glenn
• Superior vena cava syndrome - if the anastomosis becomes obstructed
• Pleural effusions - from elevated SVC pressure

Key Diagram

Above: Extracardiac Fontan conduit (Gore-Tex) connecting IVC directly to the pulmonary circulation - the completed Stage 3 that follows the BDG. At Stage 2 (BDG), only the upper half (SVC-to-PA) of this circuit has been created.

Summary in One Sentence