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Atrioventricular Septal Defect

Atrioventricular Septal Defect

1. Definition

Deficiency or absence of septal tissue immediately above and/or below the normal level of the AV valves. The AV valves are abnormal.

2. General Morphologic Considerations

A. Deficiency or absence of atrioventricular septum
B. Ostium primum defect immediately above the AV valves
C. Deficiency (scooped out area) in the inlet portion of the ventricular septum
D. Five or more atrioventricular valve leaflets of variable size

3. A spectrum of malformations

A. Simplest type = partial AV canal defect or ostium primum ASD
B. Complex type = complete AV septal defect
1) Large deficiency in the atrial and ventricular septa
2) Common AV valve orifice

4. Associated Cardiac Anomalies

A. PDA - 10%
B. TET - 10%
1) 1% of TET have AV septal defect
C. DORV - 2%
D. TGA - Rare
E. Completely unroofed coronary sinus with left SVC - 3%

5. Pathophysiology

A. Shunts--Atrial or ventricular level
B. AV Valve incompetence
1) Moderate 20%
2) Severe 15%
C. Partial AV defect
1) Atrial shunt only - present as ASD
2) Atrial shunt + AV valve incompetence = CHF
D. Complete AV defect
Progressive CHF with tachypnea, tachycardia, poor peripheral perfusion, and failure to grow

6. Natural History

A. Extremely variable depending on morphology
B. Obstructive pulmonary vascular disease with pulmonary hypertension inevitable in complete AV septal defect
1) 30% at 7-12 months
2) 90% at 3-5 years

7. Plan of Operation

A. Close ASD
B. Close VSD if present (one or two patch)
C. Avoid injury to conduction system
D. Maintenance or reconstruction of AV valves
1) The "cleft" - to close or not is controversial
2) Annuloplasty

8. Results

A. Survival
1) Ostium primum ASD - mortality is very low
2) Complete AV septal defect -3%
B. Incremental Risk Factors
1) Earlier date of operation
2) Higher NYHA classification
3) Important systemic AV valve incompetence
4) Ventricular septal defect
5) Accessory valve orifice
6) Young age

EXTENDED OUTLINE

1. Embryology

A. Endocardial cushions
1) Anterior and posterior margins of A-V canal
2) Fusion results in septation of primitive heart (10mm embryo)
3) Left and right endocardial cushions close secondary interventricular foramen, forming inlet septum
B. A-V septal (canal) defects
1) Failure of fusion of major endocardial cushions
2) Free borders of septum primum have nothing with which to fuse interatrial communication
3) Abnormalities of 3 aspects of A-V canal:
a) Atrial portion of A-V canal septum
b) Ventricular portion of A-V canal septum
c) A-V valves

2. Anatomy

A. “Wedge” position of aorta (between TV and MV) absent
1) Aortic valve is elevated and deviated anteriorly
2) LVOT narrowed, but rarely hemodynamically significant
3) LV-gram - “gooseneck” LVOT
B. Ventricular dominance
1) Balanced = A-V junction evenly shared between RV and LV
2) Dominant = valve orifice committed to that side- opposite side is hypoplastic
C. 40-45% of Downs pts have A-V septal defects
D. Associated anomalies are common

3. Partial A-V septal defect

A. Ostium primum ASD
B. Left A-V valve abnormalities
1) Cleft in midportion of anterior leaflet (septal cleft or commisure)
2) Others define L A-V valve as tricuspid
3) Left lateral, superior and inferior leaflets
C. R A-V valve: superior, lateral, inferior
D. Conduction system
1) CS ostium often displaced inferiorly
2) A-V node displaced inferiorly between CS and ventricular crest-nodal triangle
E. Associated anomalies: PDA, unroofed CS, persistent LSVC

4. Complete A-V septal defect

A. Primum ASD, common A-V valve orifice, VSD
B. 6-leaflet A-V valve - see 3 b,c above
C. Rastelli classification (based upon anatomy of anterior bridging leaflet)
1) A: Common leaflet but cordae attached to crest of interventricular septum
2) B: Papillary muscle attached to left part of leaflet from right of septum - rare
3) C: Free floating common anterior leaflet without cordal attachment to ventricular crest
D. Dominance - LV usually smaller in unbalanced
E. Conduction
1) A-V node displaced inferiorly (as in partial defect)
2) His bundle
a) Travels anteriorly and superiorly from A-V node, reaching ventricular crest where it fuses posteriorly with common A-V valve annulus
b) Passes along crest of septum, giving off left bundle branches, then becomes RBB, runs toward muscle of Lancisi
F. Associated anomalies
1) DORV - unique to complete
2) TOF - see below
3) TGA - rare

5. Complete A-V septal defect without atrial communication (rare)

6. Diagnosis

A. Presentation a fxn of: degree of Left to Right shunting and A-V valve incompetence
B. A-V valve incompetence (common)=> pulmonary vascular dz early
C. RV=LV pressure => high PA pressure
D. Partial defect
1) Symptoms of increased pulmonary flow- dyspnea, failure to thrive, repeated respiratory infections
2) PE: active precordium, prominent pulmonic flow murmur, widely split S2
3) ECG: often diagnostic
a) Left axis deviation
b) Prominent P waves
c) Prolonged PR interval
4) CXR
a) Cardiac enlargement
b) Increased pulmonary flow
5) 2-D echo
6) Cardiac catheterization - may be unnecessary
a) Confirm diagnosis
b) Assess degree of pulmonary vascular disease
c) LV-gram - MV regurgitation, “gooseneck” LVOT
7) Natural history
a) Survival (w/o tx) unusual beyond 40 yo
b) Dysrhythmias common
E. Complete defect
1) Present earlier, usually w/severe CHF
2) PE
a) Thin, breathless
b) Marked precordial activity, prominent thrill
c) Cyanosis in 15%
d) Split S1 due to pulm HTN
e) Holosystolic murmur along LSB from VSD
f) High-pitched apical murmur from MV regurgitation
g) Mid-diastolic flow murmur across common A-V valve
3) Echo: attachment of pap. muscles and cordae
4) Cath
a) Assess degree of pulmonary vascular disease
b) Angio shows long, narrow LVOT
5) Natural history
a) 96% 5-yr mortality w/o treatment
b) Surgery recommended at 3-4 months
c) Associated abnormalities may preclude biventricular repair - need PA band early in infancy
6) Complete A-V septal defect without atrial communication

7. Surgical technique

A. General
1) SVC and IVC cannulation
2) +/- hypothermic circulatory arrest - 18-20C (up to 45 min is “safe”)
3) LSVC
a) If pressure remains < 25mm Hg (IJ), clamp
b) If pressure > 25mm Hg
(1) Cannulate
(2) Low flow + sump sucker in CS
(3) Circ arrest
4) Open RA close to AV groove
5) Test A-V valve w/cold saline - “float” leaflets
B. Partial A-V septal defect
1) Valve repair
a) Approximate tips (kissing edge) of left superior and inferior leaflets with a suture - do not tie
b) This defines septal commisure (cleft)
c) Close cleft with interrupted 5-0 or 6-0 sutures
d) Some (Carpentier) recommend leaving three-leaflet valve - can become severe regurgitation
e) Size valve according to BSA
2) Closure of ASD
a) Pericardial patch
b) Close CS into LA or RA
C. Complete A-V septal defect
1) L A-V valve repair as above
2) Two-patch technique (Carpentier)
a) Superior bridging leaflet is not divided
b) VSD patch (dacron)
(1) Interrupted or running suture along right side of ventricular septum
(2) Suture top edge of patch to middle of bridging leaflets
(3) Now close septal cleft
(4) Measure valve orifice
c) ASD patch (pericardium)
(1) Close CS into LA or RA
2) One-patch technique
a) Superior common (bridging) leaflet is divided to annulus (veering a bit to the right to increase Left A-V valve orifice
b) Divide inferior bridging leaflet
c) Suture patch (Dacron or PTFE)to right side of septum, staying 3-5mm from crest
d) Valve leaflets attached to patch w/ interrupted sutures +/- pledgets
e) Closure of ASD as above (CS to LA or RA)
D. Complete A-V septal defect and tetralogy of Fallot
1) Present in nearly 10% of AVSD - especially w/Down’s
2) Small PA’s - BT shunt to allow PAs to grow - complete repair at 3-5 yrs - pulmonary bed is protected
3) VSD extends to subaortic area
4) Valved conduit if PV excised (and TV incompetent)
E. Complete A-V septal defect without atrial communication
1) Repair L A-V valve via secundum ASD (existing or surgical)
2) Top edge of patch sutured to bridging leaflet

8. Post-op care

A. Pulmonary HTN
B. Reactive pulmonary vasculature
1) Fentanyl prophylaxis
2) Phenoxybenzamine
3) Prostacyclin
4) Nitric oxide
5) pO2 > 150mmHg
6) pCO2 < 35mmHg

9. Results

A. Risks for premature sudden death:
2) Severe pre-op Leeft A-V valve incompetence
3) Poor status
4) Accessory A-V valve orifice
5) Down’s syndrome
B. 98% 1-yr, 96% 20-yr survival (Mayo)
1) Reoperation in 18 (9%)
C. Down’s syndrome
1) Survival not influenced
2) Fewer associated cardiac anomalies
D. Age - controversial
E. Date of operation - earlier = worse
F. Hanley - 7% re-operation for Left A-V valve problems
G. Higher mortality for complete w/o VSD

10. Timing of operation

A. Complete
1) Complete repair by 3-6 months
2) By 1yr for asymptomatic (Boston = 6 months)
B. Partial (pulmonary HTN rare)
1) Elective repair at 3-5 yrs (Boston = by 1yr)
2) Significant Left A-V valve regurgitation occurs earlier