SECTION III - ATRIOVENTRICULAR SEPTAL DEFECT

Part I - Background Information

Definition

The terms atrioventricular (septal) defects, atrioventricular canal defects and endocardial cushion defects can be used interchangeably to describe this group of defects. Atrioventricular septal defects (AVSD) cover a spectrum of anomalies caused by abnormal development of the endocardial cushions. The defect may be only at the atrial level (ostium primum ASD) or may include an inlet-type ventricular septal defect (intermediate AVSD when the VSD is restrictive or complete form of AVSD when the VSD is non-restrictive). The atrioventricular valves are fundamentally abnormal being derived from five leaflets (a right antero-superior leaflet, a right inferior leaflet, a superior bridging leaflet, an inferior bridging leaflet and a left mural leaflet). This may result in separate right and left AV valves (with the left AV valve having a "cleft" at the junction of the superior and inferior bridging leaflets) or a common valve. (See classification below)

Classification:

Partial AVSD:	The ventricular septum is intact. There is almost always a primum ASD. 'Cleft' in the left AV (mitral) valve. There are two separate AV valve annuli.
Intermediate AVSD:	This is the rarest form and a part of a spectrum between complete and partial AVSD. It is characterized by a restrictive VSD, a primum ASD and a cleft mitral valve. The anterior and posterior bridging leaflets are fused giving 2 distinct AV valve components.
Complete AVSD:	There is a non-restrictive inlet-type VSD. There is usually a primum ASD but rarely the atrial septum may be intact. There is a common AV orifice.

 
Part II - Prevalence and Genetics

AVSD may coexist with other lesions, both cardiac and non-cardiac. Down syndrome occurs in 35% of patients with AVSD. Most complete AVSDs occur in Down syndrome patients (> 75%). Patients with Down syndrome have a premature tendency for pulmonary vascular disease irrespective of the type of AVSD. Most partial AVSDs occur in non-Down syndrome patients (> 90%). AVSD may occur in association with tetralogy of Fallot and other forms of complex CHD.

 
Part III - History and Management of Unoperated Patients

Clinical presentation of these patients will depend on the presence and size of the ASD and VSD and competence of the left AV ("mitral") valve.

Clinical presentation may take several forms:

• Symptoms of heart failure or pulmonary vascular disease.
• Atrial arrhythmias, nodal rhythm, or complete heart block.
• Subaortic stenosis may or may not be present initially but may develop or progress.
• No symptoms.

Partial/Intermediate AVSD :

Presentation of an unrepaired partial (ostium primum ASD) or intermediate AVSD as an adult is not uncommon. Symptoms include decreased exercise tolerance, fatigue, dyspnea, arrhythmias, and recurrent chest infections. Symptoms increase with age and most adults are symptomatic by 40 years of age.

Complete AVSD :

Most patients with complete defects will have been repaired in infancy although some may have been palliated in the past with pulmonary artery bands and have variable degrees of pulmonary vascular obstructive disease. The history of unoperated complete AVSD is that of Eisenmenger syndrome to be discussed in Section XV. AVSD with Eisenmenger syndrome seems to have a worse prognosis than ASD, VSD or PDA with Eisenmenger. Poor prognostic features are felt to be atrial flutter/fibrillation, syncope, heart failure and hemoptysis.

 
Part IV - Diagnostic Recommendations

An adequate diagnostic workup:

• Documents the presence of each component of the AVSD and whether or not the ventricular chamber sizes are "balanced" (although this is usually a pediatric issue).
• Assesses the magnitude and direction of intracardiac shunting.
• Documents the pulmonary artery pressure.
• Documents abnormalities of the atrioventricular valves and their connections (straddling of the AV vales/overriding of the AV annulus) and assesses the severity of AV valve regurgitation, if any.
• Documents the presence/absence of subaortic stenosis. This may occasionally require provocative testing with isoproterenol although it may be impossible to document a gradient in the presence of a non-restrictive VSD.
• Identifies the presence of associated abnormalities (cardiac and non-cardiac) which may impact upon management (e.g. pulmonary hypertension, tetralogy of Fallot, PDA, muscular VSDs, aortic coarctation or Down syndrome).

The initial workup should include at minimum:

• A thorough clinical assessment paying particular attention to AV valve regurgitation.
• ECG.
• Chest x-ray.
• Transthoracic echo-Doppler evaluation by an appropriately trained individual.

The diagnostic work-up may require:

• TEE to determine the exact anatomy (if unclear after TTE); the presence of intracardiac shunts; chordal attachments; the presence and severity of left AV ("mitral") valve regurgitation (or stenosis if previous valve repair has been undertaken); the presence and severity of right AV valve regurgitation and subaortic stenosis.
• Heart catheterization to determine: the presence and magnitude of intracardiac shunts; pulmonary artery pressures and resistances; the severity of pulmonary vascular disease (± reversibility using oxygen, nitric oxide and/or prostaglandins); the presence and severity of left AV ("mitral") valve regurgitation (or stenosis, if previous valve repair has been undertaken); the presence and severity of subaortic stenosis (provocative testing may be necessary).
• Coronary angiography in patients at risk of coronary artery disease or in patients over the age of 40 years if a surgical repair is planned.
• Open lung biopsy should only be considered when the reversibility of the pulmonary hypertension is uncertain from the hemodynamic data. It is potentially hazardous and should be done only at centres with substantial relevant experience in CHD.
• Holter monitoring to assess AV block or other arrhythmia.
• MRI to help define the anatomy. MRI can also be used to estimate Qp/Qs.

 
Part V - Indications for Intervention/Reintervention

The following situations warrant intervention/reintervention: The unoperated AVSD with any sustained atrial arrhythmias, impaired ventricular function, right ventricular volume overload, attributable symptoms, heart failure, presumed paradoxic embolism or reversible pulmonary hypertension. Persisting or new hemodynamically significant defects arising after the original repair. Left AV ("mitral") valve regurgitation (or stenosis from previous repair) causing symptoms, atrial arrhythmia or deterioration in ventricular function. Significant subaortic obstruction (cath gradient or mean echo gradient > 50mmHg at rest or on provocative testing with isoproterenol) may require intervention.
Grade: C	Level: V	Refs: 35-37

Transvenous pacing should be avoided if there are residual inter-atrial or inter-ventricular communications since paradoxical emboli may occur. For the same reason, venous thromboemboli from any source are a potential hazard.
Grade: C	Level: V	Ref: 11

 
Part VI - Surgical Technical Options

AVSD patients, including those with ostium primum ASD, left AV ("mitral") valve repair, subaortic stenosis or residual defects should be operated on by congenital heart surgeons.
Grade: C	Level: V	Refs: 18-19

When "mitral" valve repair is not possible, "mitral" valve replacement may be necessary. It should have a similar operative risk as routine mitral valve replacement although the risk of complete AV block may be higher.

 
Part VII - Surgical Outcomes

In the short term, the results of repair of partial AVSD are similar to those following closure of secundum ASD, but sequelae of left AV ("mitral") valve regurgitation, subaortic stenosis and AV block may develop or progress. (38-42)

In general, late results after "mitral" valvuloplasty for these patients have been excellent with the need for surgical revision in about 5-10% of patients. (39-41) Occasionally, repair of the abnormal left AV ("mitral") valve may result in a stenotic valve, which will usually necessitate reoperation.

The likelihood of a residual left-to-right shunt from left atrium or left ventricle to right atrium is small.

Subaortic stenosis will develop or progress in up to 5% of patients after repair, particularly in patients with primum ASD and some complete defects, especially if the left AV (mitral) valve has been replaced.

The long-term results of repair of complete AVSD are not well known but similar problems as with partial AVSD are likely.

 
Part VIII - Arrhythmias

First degree AV block is common and complete AV block may occur spontaneously or after repair. Sinus node dysfunction may also occur especially after repair and lead to brady- or tachyarrhythmias. Atrial flutter or fibrillation in the adult are not uncommon.

 
Part IX - Pregnancy

Pregnancy is well tolerated in patients with complete repair and no significant residual lesions.

Women in NYHA class I and II with unoperated partial AVSD usually tolerate pregnancy very well, but have an increased risk of paradoxical embolization.

Consideration should be given to closure of any significant AVSD prior to pregnancy in order to minimize the risk of paradoxical emboli.
Grade: Consensus

Pregnancy is contraindicated in Eisenmenger syndrome because of the high maternal (up to 50%) and fetal (up to 60%) mortality.
Grade: C	Level: V	Ref: 22

 
Part X - Follow Up

All patients with AVSD require periodic follow up by an ACHD cardiologist because of the possibility of progressive AV valve regurgitation (or stenosis); the development of subaortic stenosis; the development of significant atrial arrhythmias, or progression of the commonly present 1st degree AV block. Particular attention should be paid to those with pulmonary vascular disease present pre-operatively. Endocarditis prophylaxis is recommended for 6 months following AVSD closure or for life if any residual defect persists.
Grade: Consensus