Embryology and Surgical Anatomy of A V Septal defects

Dr Gopi krishna

• Atrioventricular septal defects (AVSD) are a group of anomalies that share a defect of the atrioventricular septum and abnormalities of the atrioventricular valves.

• The terms atrioventricular canal defects or �endocardial cushion defects also describe �these lesions.

• These lesions are divided into partial and complete forms

Demographics

• AVSDs account for 4% to 5% of congenital heart disease and an estimated occurrence of 0.19 in 1,000 live births .

• In a large fetal echocardiography experience, AVSD was the most common anomaly detected, constituting 18% of abnormal fetal hearts .

• Gender distribution is approximately equal or may show a slight female preponderance

• About 40% to 45% of children with Down syndrome have congenital heart disease, and among these, approximately 40% have an AVSD, usually the complete form .

• Complete AVSDs also occur in patients with heterotaxy syndromes (more common with asplenia than with polysplenia).

• Common atrium has been associated with Ellis van Creveld syndrome.

partial AVSD

• Primum atrial septal defect (ASD) is always present

• There are two distinct mitral and tricuspid valve annuli.

• The mitral valve invariably is cleft.

The complete AVSD

• This includes a primum ASD, but it is contiguous with an inlet ventricular septal defect (VSD).

• Common atrioventricular valve has a single annulus.

• The clinical manifestations and management of these patients depend on the extent and severity of the lesions present.

The arterial trunk will divide to separate the pulmonary and systemic supply.The bulbus and the ventricle will differentiate into the right and left ventricles.

The primitive cardiac tube has five zones:

the arterial trunk

the bulbus cordis ) } some would call these two togetherthe ventricle ) the primitive ventricle, with inlet

and outlet portions

the atrium

and the sinus venosus

Embryologic development of the the spectrum of AVSD

Anatomical Abnormalities• Faulty development of the endocardial

cushions and of the atrioventricular septum is thought to be responsible for the broad range of AVSDs.

• In partial AVSDs, incomplete fusion of the superior and inferior endocardial cushions results in a cleft in the midportion of the anterior mitral leaflet, often associated with mitral regurgitation.

• The primum atrial septal component of this defect is usually large.

• This results in downward displacement of the anterior mitral leaflet to the level of the septal tricuspid leaflet .

• In AVSDs, the atrioventricular valves have the same septal insertion level in contrast to the leaflet arrangement in the normal heart.

• The distance from the cardiac crux to the left ventricular apex is foreshortened, and the distance from the apex to the aortic valve is increased in contrast to normal heart.

• In AVSDs the disproportion between the two distances causes anterior displacement of the left ventricular outflow tract (LVOT).

• As a result, the LVOT is longer and narrower than normal and produces the gooseneck deformity.�

• After surgical repair of the defect, progressive subaortic stenosis may develop .

• In the normal heart, the aortic valve is wedged between the mitral and tricuspid annuli.

• In AVSD the aortic valve is displaced or sprung anteriorly .

• This anterior displacement creates an elongate, so-called gooseneck deformity of the LVOT.

• LVOT obstruction may occur in all forms of AVSD.

• It is more frequent when two atrioventricular valve orifices are present than when there is a common orifice.

Other causes that can exacerbate subaortic stenosis.

• The superior bridging leaflet attaches to the crest of the ventricular septum, causing the outflow tract to become elongated and consequently narrowed.

• Discrete subaortic fibromuscular ridges.• Septal hypertrophy,• Abnormal left atrioventricular valve chordal

attachments.• Abnormally oriented papillary muscles.• can exacerbate subaortic stenosis.

• . LVOT obstruction may be subtle and therefore not appreciated during preoperative echocardiographic assessment.

• Obstruction may develop de novo after initial repair of the AVSD and closure of the mitral valve cleft .

• The LVOT obstruction often is progressive.

Mitral valve abnormalities

• Cleft. • parachute mitral valve . • Double-orifice mitral

valve al.

• In partial AVSD, the mitral and tricuspid annuli are separate.

• The most frequent form of partial AVSD consists of a primum ASD and a cleft anterior mitral valve leaflet .

• Most primum ASDs are large and located anteroinferiorly to the fossa ovalis.

• The defect is bordered by a crescentic rim of atrial septal tissue posterosuperiorly and by mitral-tricuspid valvular continuity anteroinferiorly.

• These defects are not amenable to transcatheter device closure because of their proximity to the atrioventricular valves.

• The cleft in the anterior mitral leaflet is directed toward the midportion of the ventricular septum, along the anteroinferior rim of the septal defect .

• In contrast, isolated mitral clefts (not otherwise associated with AVSD) are directed toward the aortic valve annulus .

• The mitral orifice is triangular rather than elliptical as in a normal heart and resembles a mirror-image tricuspid orifice.

• The cleft mitral valve usually is regurgitant and, with time, becomes thickened and exhibits secondary hemodynamic alterations in morphology that resemble mitral valve prolapse.

common associated anomalies

• secundum ASD and persistence of a left superior vena cava connecting to the coronary sinus.

• Less frequently, pulmonary stenosis, tricuspid stenosis or atresia, cor triatriatum, coarctation of the aorta, patent ductus arteriosus, membranous VSD, pulmonary venous anomalies, hypoplastic left ventricle

Transitional form of partial AVSD

• There is aneurysmal replacement of a portion of the inlet ventricular septum .

• Although small shunts may occur, tricuspid pouch usually obstructs any shunting at the ventricular level.

• The dextrodorsal conus cushion contributes to the development of the right atrioventricular valve and the outflow tracts lie adjacent to their respective inflow tracts.

• So AVSDs may be associated with conotruncal anomalies, such as tetralogy of Fallot and double-outlet right ventricle.

• Shift of the atrioventricular valve orifice may result in connection of the valve primarily to only one ventricle, creating disproportionate or unbalanced ventricles.

Complete AVSD• complete AVSD is

associated with lack of fusion between the superior and inferior cushions .

• consequently, with the formation of separate anterior and posterior bridging leaflets along the subjacent ventricular septum .

Three types of straddling

Complete AVSD• complete AVSD is

associated with lack of fusion between the superior and inferior cushions .

• consequently, with the formation of separate anterior and posterior bridging leaflets along the subjacent ventricular septum .

• The type of complete AVSD has some bearing on the likelihood of associated lesions.

• Type A usually is an isolated defect and is frequent in patients with Down syndrome.

• Type C is encountered with other complex anomalies, such as tetralogy of Fallot, double-outlet right ventricle, complete transposition of the great arteries, and heterotaxy syndromes.

• Coronary artery anomalies, when they occur, tend to be associated with coexistent conotruncal malformations rather than the AVSD.

• The combination of type C complete AVSD with tetralogy of Fallot is observed in patients with Down's syndrome, whereas double-outlet right ventricle is a feature of patients with asplenia.

Orientation commissures and papillary muscles.• Beneath the five commissures are five papillary muscles.• The two left-sided papillary muscles are oriented closer

together than in a normal heart, such that the lateral leaflet is smaller than a normal posterior mitral leaflet.

• The two papillary muscles often are rotated counterclockwise, such that the posterior muscle is farther from the septum than normal and the anterior muscle is closer to the septum.

• This papillary muscle arrangement, in conjunction with prominence of an anterolateral muscle bundle, may contribute to progressive LVOT obstruction.

Double-orifice left A.V. valve

• Double-orifice left atrioventricular valve occurs rarely in AVSDs.

• This abnormality is more common when two distinct right and left atrioventricular valve orifices are present.

• The combined effective valve area of a double-orifice valve is always less than the valve area of a single-orifice valve.

• This predisposes the valve to postoperative stenosis.

single left ventricular papillary muscle

• Similar to the double-orifice valve, a single papillary muscle will reduce the effective valve area.

• In patients with a single left ventricular papillary muscle, valve repair may be compromised owing to relative leaflet hypoplasia

Unbalanced Defect

• One ventricle and its corresponding atrioventricular valve are hypoplastic while the other ventricle receives the larger portion of the common atrioventricular valve.

• The most common arrangement is a dominant right ventricle with a hypoplastic left ventricle.

• The left-sided component of the common atrioventricular valve may be stenotic after two-ventricle repair has been performed.

• When left ventricular hypoplasia and right ventricular dominance occur ,the associated malformations such as aortic arch hypoplasia and coarctation are common.

• In contrast, if left ventricular dominance is present, pulmonary valve stenosis or atresia is a common associated defect.

• classification scheme from Bharati and Lev

• From van Son, JAM, Phoon CK, Silverman NH, et al. Predicting feasibility of biventricular repair of right-dominant unbalanced atrioventricular canal. Ann Thorac Surg 1997;63:1657

• )

Down Syndrome and Atrioventricular Septal Defect

• Children with Down syndrome are more likely to have complete AVSD than children without Down syndrome.

• They are also more likely to have associated tetralogy of Fallot .

• Sidedness (situs) and splenic anomalies are rare in patients with Down syndrome.

• Patients with Down syndrome usually do not have associated LVOT obstruction, left ventricular hypoplasia, coarctation of the aorta, or additional muscular VSDs .

• The extent and progression of pulmonary vascular changes in children with Down syndrome and complete AVSD remain controversial.

• Histologic studies have failed to reveal any differences in the extent of pulmonary vascular changes when patients with Down syndrome were compared with normal children who also had AVSD.

• Other studies have suggested that children with Down syndrome have relative pulmonary parenchyma hypoplasia.

• Surgical results for patients with Down syndrome are similar to those of the general population .

?surgical anatomy importance• Surgical repair of AVSD has been one of the great

successes of the last several decades of congenital cardiac surgery.

• Studer et al. reported average operative mortality <2%.

• Long-term survival has been excellent. A cumulative 20-year survival of 95% .

• However, at least 25% of patients await reoperation, most commonly because of progressive left atrioventricular valve regurgitation or relief of left ventricular outflow tract obstruction.

Surgical Treatment of Partial Atrioventricular Septal Defect

• The objectives of surgical repair include closure of the interatrial communication and restoration and preservation of left atrioventricular valve competence.

• These objectives can be accomplished by careful approximation of the edges of the valve cleft with interrupted nonabsorbable sutures.

• On occasion, it is necessary to add eccentric annuloplasty sutures to correct persistent central leaks.

• The repair is completed by closure of the interatrial communication (usually with an autologous pericardial patch), avoiding injury to the conduction tissue.

• This repair results in a two-leaflet valve .

• Danielson GK. Endocardial cushion defects. In: Ravitch MM, Welch KJ, Benson CD, et al., eds. Pediatric Surgery. 3rd ed. Vol. 1. Chicago: Year Book Medical, 1979:720–726

• ,

• Alternatively, if the left atrioventricular valve is to be considered a trileaflet valve, with the cleft viewed as a commissure, surgical repair demands that this commissure be left unsutured and that various annuloplastic sutures be placed to promote coaptation of the three leaflets.

• These morphologic concepts and surgical methods, favored by Carpentier and Piccoli et al, have not yet provided superior results.

The risk of hospital death for the surgical repair of partial AVSD is approximately 3%.

• Determinants of hospital mortality include• Congestive heart failure.• Cyanosis.• Failure to thrive.• Age at operation of <4 years.• Moderate to severe left atrioventricular valve

regurgitation.

• In a series of 334 patients from Mayo Clinic, 20- and 40-year survivals after repair of partial AVSD were 87% and 76%, respectively.

• Closure of the mitral cleft and age <20 years at time of operation were associated with better survival. Reoperation was performed for 11% of these patients.

• Repair of residual/recurrent mitral valve regurgitation or stenosis was the most common reason for reoperation.

• A low frequency of postoperative arrhythmias has been noted.

• Bradyarrhythmias, including severe sinus node dysfunction, may occur.

• The finding of surgical complete heart block has been rare.

• Permanent pacemaker implantation has been required for these patients.

• Late onset of atrial flutter has been rare.

Surgical Treatment of Complete Atrioventricular Septal Defect

• Surgical repair of complete forms of AVSD is indicated earlier in life than for the partial forms of AVSD.

• Repair of complete AVSD must be done prior to the development of irreversible pulmonary vascular obstructive disease.

• Repair should be done electively before 6 months of age.

• Earlier repair should be considered for infants with failure to thrive.

• For the symptomatic infant, surgical options include palliative pulmonary artery banding and complete repair of the anomaly.

• Although in the modern age complete repair appears to be the procedure of choice for these infants, proponents of pulmonary banding have alluded to the relatively high risk of complete repair in infants <6 months of age.

• Silverman et al. reported excellent results of pulmonary banding in 21 infants with complete AVSD who were <1 year of age.

• In this series, there was one surgical death (5%), and the remaining patients had excellent palliation.

• Williams et al. recommended pulmonary artery banding for infants weighing <5 kg who were unresponsive to medical treatment or had significant associated anomalies.

• In the modern era, most centers perform complete repair in small infants who fail to thrive.

• This approach has largely obviated the need for pulmonary artery band placement.

• The objectives of surgical repair include closure of interatrial and interventricular communications, construction of two separate and competent atrioventricular valves from available leaflet tissue, and repair of associated defects.

• Techniques for the surgical repair of complete AVSD have been standardized and are based on the use of a single patch or double patch (separate atrial and ventricular patches) to close the ASD and VSD and then reconstruction of the left atrioventricular valve as a bileaflet valve.

• Puga and McGoon (49) have described these techniques in detail.

• Piccoli et al. and Studer et al. consider the cleft of the left atrioventricular valve a true commissure and envision this valve as a trileaflet valve.

• On the basis of these concepts, Carpentier prefers the two-patch technique.

• The left atrioventricular valve remains a trileaflet structure .

• The two-patch technique has become the method of choice.

• In a series of 310 patients reported by Studer et al.

• The risk factors in the surgical repair of AVSDs were,

1. age at operation,2. severity of atrioventricular valve

regurgitation, 3. preoperative functional class.

• Chin et al, reported the results obtained with complete repair in a group of patients whose mean age at operation was 10 months.

• Hospital mortality ranged from 62% in their early experience to 17% among 30 patients who underwent operation during the period 1978 to 1980.

• Bender et al. reported 24 infants who had operation between 3 and 38 weeks of age (mean 18 weeks) and noted two operative deaths.

• Similar to repair of partial AVSD, postoperative sinus node dysfunction occurs.

• Complete heart block requiring permanent pacemaker placement is now rare.

• From Carpentier A. Surgical anatomy and management of the mitral component of atrioventricular canal defects. In: Anderson RH, Shinebourne EA, eds. Paediatric Cardiology. Edinburgh: Churchill Livingstone, 1978: 477 490

• ,

Special Problems in Complete Atrioventricular Septal Defect Surgery

• Parachute Deformity of the Mitral Valve. • Double-Orifice Mitral Valve. • Right or Left Ventricular Hypoplasia. • Tetralogy of Fallot.• Subaortic Stenosis.

Parachute Deformity of the Mitral Valve

• This problem has been addressed by David et al.

• With such a deformity, closure of the mitral cleft at the time of repair may result in an obstructed mitral orifice.

• If the patient has significant atrioventricular valve regurgitation, valve replacement may be the only suitable option.

Double-Orifice Mitral Valve

• The surgeon must resist the temptation of joining the two orifices by incising the intervening leaflet tissue.

• The combined opening of both orifices is satisfactory for adequate mitral valve function.

Right or Left Ventricular Hypoplasia

• These anomalies may be severe enough to preclude septation.

• The only option for definitive surgical treatment is the modified Fontan's procedure preceded by adequate pulmonary artery banding in infancy.

Tetralogy of Fallot

• In patients with this anomaly, all of whom have the complete form, the infundibular septum is displaced anteriorly, so that the typical inlet VSD extends anteriorly and superiorly toward the perimembranous area.

• Treat these cyanotic infants initially with a systemic-to-pulmonary artery shunt and then by complete repair at 2 to 4 years of age.

• The intracardiac repair of these hearts is best accomplished through a combined right atrial and right ventricular approach.

Subaortic Stenosis

• If discovered at the time of initial preoperative evaluation, subaortic stenosis tends to be of the fibromuscular membrane type and should be treated by appropriate resection during surgical repair.

• However, subaortic stenosis usually appears late after surgical repair of AVSD.

• The stenosis may be related to the uncorrected deficiency in the inlet septum.

• The obstruction usually is due to the formation of endocardial fibrous tags and fibromuscular ridges.

• Usually it can be treated by local resection, although in some patients a modified Konno procedure may be necessary.

Reoperation after Repair of partial Atrioventricular Septal Defects

Regurgitation or stenosis of the left atrioventricular valve [ 10% to 15%].

Subaortic stenosis. Residual recurrent ASD.

• late reoperation following repair of complete avsd occurs in approximately 17% of patients during the first 20 years after surgical repair.

• Lesions requiring reoperation include left and right atrioventricular valve regurgitation, left atrioventricular valve stenosis (native and prosthetic), and residual/recurrent ASDs or VSDs.

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