test 4 part 2 Flashcards
Three names for the same type of defect dealing with the AV sulcus
- AVSD: Atrio-ventricular septal defect
- ECD: Endocardial cushion defect
- AVC: Atrio-ventricular canal defect
Definition: AVC/ECD/AVSD Defects
- A deficiency or absence of septal tissue immediately above and/or below the normal plane of A-V valves. The valves are abnormal in shape and/or function
- Incomplete fusion of the endocardial cushions which form the primum atrial septum, the A-V valves, and the inlet ventricular septum
- AV valves fail to separate leaving common AV valve
- Common valve may be insufficient
- Pulmonary vascular obstructive disease secondary to high pulmonary flow usually occurs early
Lower part of atrial septum deficient / missing results in
• Left to right shunt
Upper part of ventricular septum deficient / missing results in
• Left to right shunt
Epidemiology: A-V Canal
- Prevalenc of all congenital heart disease is approximately 8 per 1000 live births
- AVSD is the 5th most common occurring CHD
* 4% to 5% total congenital cases; prevalence of 0.3 to 0.4 per 1000 live births - Can be assessed with more complex problems
- It is also present in 60% of patients with heterotaxy syndrome
* Disorder where some organs form on opposite side of body
* Often associated with asplenia (increased chance of infection) (might not have a spleen)
Morbidity and Mortality A-V Canal
- Children with a complete AV canal fail to thrive in the first few months of life
- Patients may survive the first few years of life if the PVR is high
- High PVR decreases left to right shunting which increases LVEF
- If AV canal is repaired between 4-6 months of life, survival is >80%
Day of Outflow tract septation and days of atrial and Ventricular septation and development
- Day 27-37: Atrial and Ventricular septation and development
- Day 29: Outflow tract septation
Embryology of AVSD
- AV septal defects occur at the embryonic age of 34-36 days when fusion of the endocardial cushions fails
- This occurs when the endocardial cushion fibroblasts fail to migrate normally to form the septum of the atrio-ventricular canal
What are the end results of developmental problems of the AV canal
- Deficiency of the:
* Primum atrial septum
* Ventricular septum
* Septal leaflet of the tricuspid valve
* Anterior leaflet of the mitral valve - AV valves becomes offset
- Anterior leaflet of the AV valve extends across septum
- If the leaflet opens preferentially toward a ventricle
* Limits flow to other ventricle (one ventricle bigger than the other)
* Hypoplasia occurs creating an unbalanced AV Canal
Atrioventricular septal defects can be classified into one of three categories:
- Complete (CAVSD)
* Balanced (how the common valve is postitioned in the ventricles)
* Unbalanced (how the common valve is postitioned in the ventricles) - Transitional (TAVSD)
- Partial (PAVSD)
Complete AVSD: Balanced
- most common
- Ventricles are equal in size
- Size is relatively normal
- Both left and right AV valves may equally share the common AV valve orifice. This arrangement is termed a balanced defect.
Complete AVSD: Unbalanced
- One of the ventricles may be hypoplastic
* Size will be different
Complete AV Canal
• Complete AVC has defects in all structures formed by the endocardial cushions. • ASD • VSD • Common AV valve - Blood in ALL 4 chambers can mix
Transitional AV Canal
• Normal ASD present
• Bridge of tissue forms anterior to posterior dividing common valve into right and left component
• Mitral valve has cleft (additional commissure)
• Only small VSD remains
- STILL HAVE ASD BUT A SMALL VSD
• A transitional atrioventricular septal defect behaves more like a partial
atrioventricular septal defect, even thought it looks more like a complete atrioventricular septal defect (i.e. has a VSD).
Partial AV Canal
• A partial atrioventricular septal defect is one in which the part of the ventricular septum formed by the endocardial cushions has filled in
• NO VSD
• Primum ASD
• Cleft mitral valve
• Geometry of valve may be affected – usually leads to MR
- Only partial mixing of the blood through the ostium primum ASD (limits amount of mixing because it must go through ASD)
Partial AV Canal Considerations
- Conduction system disruption (because AV node is being shifted)
* A-V node displaced inferiorly between coronary sinus and ventricular crest - Coronary sinus ostium often displaced
- Associated anomalies
* PDA, Persistent Left SVC
Surgical Interventions for AV Canal
- It’s all about pulmonary blood flow
• Flow can be too high or too low
• Depends on size of septal defects – normally left to right
• Pulmonary damage will lead to right to left (IF NOT FIXED)
• Large VSD or unbalanced ventricles could produce right to left
• Keep flow as “normal” as possible - Choice of palliation versus complete repair depends on many variables. TIMING OF INTERVENTION IS IMPORTANT.
• Age; Patient health; Severity disease; Patient tolerance of treatment; Expectations for course of disease
PA Banding – Excess Pulmonary Flow
- Palliation for excessive pulmonary blood flow
• Increases PVR (without affecting pulmonary vasculature)
• Decreases Pulmonary Flow
• Decreases Pulmonary Over-circulation - Reduce the potential for development of pulmonary vascular damage
- used more with balance
PA Banding - Complications
• Band migration and distortion of PA branches (could effect flow to one side or the other)
• Erosion of band into the lumen of the PA (could go through PA tissue and go into the artery)
• Distortion of pulmonary valve
• Subannular ventricular hypertrophy and thickening of the outflow tract
- when the band is removed and the hypertrophy and outflow track are changed permanently which increases life long pulmonary pressure
- damage to the pulmonary vasculature happens before damage to the ventricle
Insufficient Pulmonary Flow
- Insufficient flow can be caused by combination of congenital problems
• Combination of Tetralogy of Fallot (TOF) and AV canal
• Left unbalanced AV canal (small right ventricle) - Purpose of palliation
• Ensure adequate pulmonary blood flow using arterial to pulmonary artery shunt
• Does not require CPB but it is a SHUNT that steals arterial blood flow
Palliation for Insufficient pulmonary Flow
- Blalock-Tausig Shunt
* Subclavian artery to pulmonary artery (direct connection, no artificial graft)
* Modified using any systemic artery to the pulmonary artery (direct connection or via artificial graft) - Central Shunt
* Connect aortic root / ascending aorta to pulmonary artery usually with graft
The treatment of choice for an AV Canal is
- complete surgical repair.
Two Types of Complete Repair of the AV canal
- Bi-ventricular Repair
* RV and LV normal and functional - Univentricular Repair
* Single ventricle (i.e. VSD so large there is no separation)
* AV canal combined with TOF
* Left unbalanced AV canal with small RV
Bi-ventricular Repair
- True repair of defect – Returns flow patterns to normal – Requires CPB
• The VSD is often closed with a synthetic patch (Dacron, Gore Tex), or bovine pericardium
• The ASD is often closed with a pericardial patch
• Valve repair technique:
• Attempt to repair the abnormal valve. This is accomplished by suturing/cutting the cleft to recreate a two-leaflet mitral valve.
• The tricuspid valve may also be repaired.
Surgical Goals of Univentricular Repair
- The eventual goal of surgical repair is to separate pulmonary and venous outflow – ensure venous blood goes through pulmonary system
- Usually done with staged procedures, culminating in the Fontan Procedure.
Stage One: Blalock-Taussig (BT) shunt
• Usually performed within the first few days after birth
• Establishes a systemic-to-pulmonary artery shunt between the brachiocephalic artery (or the right subclavian artery) and the right pulmonary artery via (usually) a tubed homograft or synthetic graft.
- Does not require CPB
Stage Two: Bi-Directional Glenn Procedure or Hemi-Fontan
• Usually performed at 4-6 months after birth as a bridge to Fontan completion
• BT shunt and pulmonary artery band is usually removed
• The superior vena cava is then attached to right pulmonary artery, creating a systemic venous-to-pulmonary connection.
- Starts process of diverting venous flow through pulmonary system –
Removes the A-V shunt – Can be completed without CPB
Stage 3: Fontan Completion
• Usually performed at 2-3 years of age
• The inferior vena cava is connected to the right pulmonary artery via a tunnel like patch within the right atrium
• (Lateral Tunnel Fontan)
• OR by creating a conduit for IVC flow outside the right atrium
• (Extracardiac Fontan)
Completes replumbing so all venous return goes through the pulmonary system – Requires CPB
Fontan
- Connect IVC to PA
• Intracardiac
• Atrial baffle
• Lateral tunnel
• Extracardiac
- sometimes add a fenestration as a pop off valves to maintain acceptable pulmonary pressuresWhy is atrioventricular canal a concern?
- If not treated, this heart defect can cause lung disease.
• Larger volume of blood than normal must be handled by the right side of the heart.
• Causes higher volume than normal and higher pressure than normal in the blood vessels in the lungs.
• The lungs are able to cope with this extra volume of blood at high pressure for a while
• Lungs become damaged by this extra volume of blood at high pressure
• The blood vessels in the lungs get thicker
• With time, these changes in the lungs become irreversible
• CHF will eventually ensue
Palliation Stage
- Shunts: Usually done early with small size to prevent damage caused by flow and pressure
- PA Band: off CPB
- BT shunt: off CPB
- Central Shunt: both on and off CPB
Surgical Repair: Bi-ventricular
• Cannulation
• Arterial: Aortic cannulation
• Venous: Bicaval cannulation
• LV Vent: Flexible vent when the heart is open
• Aortic Cross-Clamp w/ multiple antegrade CP dosing depending
on solution
• CPB time is moderate in length
Surgical Repair: Univentricular
- Bi-Directional Glenn
* Can be done off-bypass
* Single atrial cannula
* Aortic arterial cannula - Fontan
* Single atrial cannula
* Aortic arterial cannula
