test 4 part 2

Question 1

Three names for the same type of defect dealing with the AV sulcus

Answer 1

• AVSD: Atrio-ventricular septal defect
• ECD: Endocardial cushion defect
• AVC: Atrio-ventricular canal defect

Question 2

Definition: AVC/ECD/AVSD Defects

Answer 2

• 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

Question 3

Lower part of atrial septum deficient / missing results in

Answer 3

• Left to right shunt

Question 4

Upper part of ventricular septum deficient / missing results in

Answer 4

• Left to right shunt

Question 5

Epidemiology: A-V Canal

Answer 5

• 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)

Question 6

Morbidity and Mortality A-V Canal

Answer 6

• 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%

Question 7

Day of Outflow tract septation and days of atrial and Ventricular septation and development

Answer 7

• Day 27-37: Atrial and Ventricular septation and development
• Day 29: Outflow tract septation

Question 8

Embryology of AVSD

Answer 8

• 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

Question 9

What are the end results of developmental problems of the AV canal

Answer 9

• 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

Question 10

Atrioventricular septal defects can be classified into one of three categories:

Answer 10

• 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)

Question 11

Complete AVSD: Balanced

Answer 11

• 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.

Question 12

Complete AVSD: Unbalanced

Answer 12

• One of the ventricles may be hypoplastic

* Size will be different

Question 13

Complete AV Canal

Answer 13

• Complete AVC has defects in all structures formed by the endocardial cushions.
• ASD
• VSD
• Common AV valve
- Blood in ALL 4 chambers can mix

Question 14

Transitional AV Canal

Answer 14

• 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).

Question 15

Partial AV Canal

Answer 15

• 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)

Question 16

Partial AV Canal Considerations

Answer 16

• 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

Question 17

Surgical Interventions for AV Canal

Answer 17

• 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

Question 18

PA Banding – Excess Pulmonary Flow

Answer 18

• 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

Question 19

PA Banding - Complications

Answer 19

• 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

Question 20

Insufficient Pulmonary Flow

Answer 20

• 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

Question 21

Palliation for Insufficient pulmonary Flow

Answer 21

• 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

Question 22

The treatment of choice for an AV Canal is

Answer 22

• complete surgical repair.

Question 23

Two Types of Complete Repair of the AV canal

Answer 23

• 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

Question 24

Bi-ventricular Repair

Answer 24

• 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.

Question 25

Surgical Goals of Univentricular Repair

Answer 25

* 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.

Question 26

Stage One: Blalock-Taussig (BT) shunt

Answer 26

• 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

Question 27

Stage Two: Bi-Directional Glenn Procedure or Hemi-Fontan

Answer 27

• 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

Question 28

Stage 3: Fontan Completion

Answer 28

• 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

Question 29

Fontan

Answer 29

``` - Connect IVC to PA • Intracardiac • Atrial baffle • Lateral tunnel • Extracardiac - sometimes add a fenestration as a pop off valves to maintain acceptable pulmonary pressures ```

Question 30

Why is atrioventricular canal a concern?

Answer 30

- 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

Question 31

Palliation Stage

Answer 31

- 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

Question 32

Surgical Repair: Bi-ventricular

Answer 32

• 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

Question 33

Surgical Repair: Univentricular

Answer 33

* Bi-Directional Glenn * Can be done off-bypass * Single atrial cannula * Aortic arterial cannula * Fontan * Single atrial cannula * Aortic arterial cannula