av canal defect
TRANSCRIPT
Atrioventricular Canal Defect
Dr. Md. Rezwanul HoqueMBBS, MS, FCPS, FRCSG, FRCSEd
Associate ProfessorDepartment of Cardiac surgeryBSMMU, Dhaka, Bangladesh
Atrioventricular Septal Defect
Definition
A deficiency or absence of septal tissue immediately above & below the normal level of the AV valves including the region normally occupied by the AV septum in heart with two ventricle and the AV valves are abnormal to a varying degree.
Aortic valve is elevated, deviated anteriorly due to absence of usual wedged position of aortic valve above the AV valve.
It is caused by an abnormal or inadequate fusion of the superior and inferior endocardial cushion with the mid portion of the atrial septum and the muscular portion of the ventricular septum.
Synonyms: AV septal defect, AV canal defect, AV defect, ECD (Endocardial cushion defects), Ostium primum atrial septal defects, Common AV orifice
Atrioventricular Septal Defect Historical note
Rogers, Edwards : Recognized morphology of ostium primum ASD in 1948 Wakai, Edwards : Term of partial and complete AV canal defect in 1956 Bharati & Lev : Term of intermediate & transitional in 1980 Ugarte : Term of leaflet bridging ventricular septum in 1976 Rastelli : Described the morphology of common anterior leaflet in 1966 Lillehei : 1st repair of complete AV canal defect using cross circulation in 1954 Kirklin, Watkins, Gross : Open repair using oxygenator
Types of AV septal defect• Spectrum of disease, arbitrarily divided into- Partial, Transitional &
Complete AV canal defect.
• Partial AV canal defects -Large ostium primum ASD, cleft mitral valve between the
left superior and inferior leaflets, no interventricular communication, two distinct AV
valve orifices.• Transitional AV canal defect -An intermediate form of AVSD having two distinct left
AV valve and right AV valve orifices but also has both an ASD just above and a
ventricular septal defect (VSD) just below the AV valves. The VSD in this intermediate
form of AVSD is often restrictive. Although these AV valves in the intermediate form
do form two separate orifices, they remain abnormal valves..• Complete AV canal defects -have both defects in the atrial septum just above the AV
valves and defects in the ventricular septum (non- restrictive inlet VSD)just below the
AV valves. In complete AVSD, the AV valve is one valve that bridges both the right
and left sides of the heart, creating superior and inferior bridging leaflets.
Sellke: Sabiston & Spencer Surgery of the Chest, 7th ed., Copyright © 2005 Saunders, An Imprint of Elsevier
Sellke: Sabiston & Spencer Surgery of the Chest, 7th ed., Copyright © 2005 Saunders, An Imprint of Elsevier
Morphology
• AV valve apparatus- 5-6 leaflets• Left superior(LSL), left inferior(LIL), left lateral(LLL), the former two represents
anterior mitral leaflet.• Right superior(RSL), right inferior(RIL), right lateral(RLL) leaflet.• In partial AVSD, leaflets fuse on either side of ventricular crest, VSD may or may
not be present• In complete AVSD, LSL+RSL forms anterior bridging leaflet, LIL+RIL fuse to
form posterior bridging leaflet, VSD always present.• The degree of bridging and attachment of this bridging leaflet to underlying
misplaced papillary muscle determines Rastelli’s classification(1966).• The AV node and the conduction bundle is displaced inferiorly.(Lev)
Complete AVSD
In complete atrioventricular septal defect, a single atrioventricular valve annulus, a
common atrioventricular valve, and a
defect of the inlet ventricular septum are observed.
The common AV valve consists of at
least 4 leaflets. These include the
anterior and posterior bridging leaflets
and 2 lateral leaflets.
The anterior leaflet may be further
subdivided to produce a total of 5 leaflets. The classification system initially
described by Rastelli et al is used to
describe the morphology of the
atrioventricular valve.
The Rastelli classification for
complete AV canal defects.
A, In the Rastelli type A defect the
superior bridging leaflet is divided into
two leaflets at the crest of the
interventricular septum, corresponding to the right superior leaflet (RSL) and
the left superior leaflet (LSL).
B, In the Rastelli type B defect the LSL bridges across the septum and
attaches to a papillary muscle within
the right ventricle.
C, In the Rastelli type C defect
there is marked bridging of the
superior bridging leaflet, making it free floating and unattached to the
underlying interventricular septum.
Rastelli type A valve (a)
The anterior leaflet is divided into 2
portions of approximately equal size.
The lateral portions of this leaflet
attach to the anterior papillary
muscles in each ventricle.
Chordae tendineae attach the medial portion of this leaflet to the crest of the ventricular
septum or slightly to the right ventricular
side.
Interventricular communication may occur
between the anterior and posterior bridging
leaflets and underneath the anterior leaflet
in the interchordal spaces.
Rastelli type B valves
The rarest type, the anterior bridging leaflet is divided but overhangs the ventricular septum more so than in type A valves.
The chordae from the medial portion of the divided anterior leaflet have no direct insertion to the ventricular septum but rather insert onto an anomalous papillary muscle positioned in the right ventricle near the ventricular septum.
Because of the lack of chordal insertions to the septum, free interventricular communication occurs beneath the anterior leaflet.
Rastelli type C valve
The anterior bridging leaflet is larger and overhangs the septum more so
than with a type A and type B valves.
It is not attached in its mid portion to the ventricular septum or elsewhere and is referred to as being “freefloating.“
Free interventricular communication also occurs underneath this valve
leaflet.
The superior cushion–derived leaflet bridges the ventricular septum and attaches to thePapillary muscle of the conus atIts rightmost extent. A right superior leaflet (RSL)Typically attaches to the papillary muscle of the conus and to the anterior papillary muscle of the right ventricle (RV), and a right lateral leaflet (RLL) attaches to the anterior papillary muscle of the RV and to the posterior papillary muscle of the RV. The inferior cushion–derived bridging leaflet is usually cleft, giving theappearance of a right inferior Leaflet ( RIL) and a left inferior leaflet (LIL)
Position of conduction tissueThe location of the atrioventricular
(AV) node and the conduction tissue.
A, Normal heart. Note the location of
the AV node at the tip of the triangle
of Koch.
B, AV canal heart: The AV
node is now located within the nodal
triangle, not at the tip of the triangle
of Koch. The coronary sinus, AV
node, and bundle of His are displaced inferiorly compared with the normal
heart. RA, Right atrium; RBB, right
bundle branch; RV, right ventricle.
Kertesz NJ: The conduction system
and arrhythmias in common
atrioventricular canal. Prog Pediatr Cardiol 10:153–159, 1999.)
Anatomical variability:▪ Shortened dimension of the inlet
septum-to-ventricular apex, giving the
interventricular septum a “scooped-out”
appearance. This deficiency in the inlet
septum is typically deeper in complete
AV canal defects than in partial AV
canal defects.
▪ Lengthened dimension of the outlet
septum-to-ventricular apex, resulting in a
“goose-neck” appearance and anterior
displacement of the left ventricular (LV)
outflow tract. Although the LV outflow
tract is narrowed, true LV outflow tract
obstruction (LVOTO) is rare. In the
normal heart, the inlet septum-to-
ventricular apex length and the outlet
septum-to-ventricular apex length are
equal.
1. Normal 2. AVSD 3. After repair
▪ Absence of the usual wedged position of the aortic valve between the AV valves, caused by maldevelopment of the endocardial cushions. This results in elevation and anterior deviation of the aortic valve. ▪ Apical displacement of the attachments of the AV valves to the crest of the interventricular septum, caused by the deficiency in the inlet septum.
Atrioventricular septum• That portion of cardiac septum
which lies between the right atrium and the left ventricle.
• It consists of a superior membra-
nous portion and an inferior muscu-lar portion.
• The atrioventricular septum is ap-parent because the septal attach-ment of tricuspid valve is more api-cal than the mitral valve.
• The AV node lies in the atrial sep-tum adjacent to the junction be-tween the membranous and muscu-lar portions of atrioventricular sep-tum, and His bundle passes toward the right trigone between these two components
Embryology
Faulty development of the endocardial cushions, which represent the
primordia of the atrioventricular
Septum and atrioventricular valves,
plays a central role in the development of atrioventricular septal defects.
Complete failure of fusion of the
endocardial cushions results in
deficiency of the inlet portion of the
interventricular septum,
a common atrioventricular valve
annulus and common AV valve,
as well as deficiency of the inferior
(primum) portion of the atrial septum.
Morphology of A-V Septal Defect (I)
1. Interatrial communication 1) Ostium primum ASD 2) Common atrium entire limbus & fossa ovalis are absent
3) Absence of interatrial shunt rarely, due to complete attachment of AV valve tissue to atrial septum
2. Interventricular communication 1) Partial form 2) Complete form 3. AV valves 1) Two AV valve orifice 2) Common AV valve orifice
3) Unusual AV valve
combination
4) Accessory orifice ; 5 %
5) Single papillary m ; 5 %
4. Ventricle; hypoplasia in 7%
5. Septal malalignment
6. LVOT or inflow obst.
7. Conduction system; LAD
Seoul National University HospitalDepartment of Thoracic & Cardiovascular Surgery
Morphology of AV Septal Defect (II)1. Major associated cardiac anomalies 1) PDA(10%) 2) TOF(10%) 3) DORV(3%) 4) TGA(rarely) 5) Unroofed coronary sinus with Lt. SVC (6%, frequent in common atrium)2. Minor associated cardiac anomalies 1) ASD 2) Unroofed coronary sinus without Lt. SVC 3) Partially unroofed coronary sinus 4) Azygos extension of IVC3. Pulmonary vascular disease ; earlier onset than VSD4. Down syndrome 1) Rare in partial form & common in complete form (75%) 2) Lt-sided obstruction & associated anomalies less common 3) Frequent advanced pulmonary disease
Seoul National University HospitalDepartment of Thoracic & Cardiovascular Surgery
Atrioventricular Septal Defect
LV Outflow & Inflow Obstruction• Incidence 1% in unoperated cases Higher incidence after operation• Etiology 1. Elongation & narrowing due to more extensive area of direct fibrous continuity aortic valve & LSL 2. Short, thick chordae that anchor to the crest of ventricular septum 3. Bulging of anterolateral muscle bundle(m. of Moulart) 4. Morphologically discrete subaortic membrane or excrescences of aortic valve orifice 5. Abnormally positioned papillary muscle
Seoul National University HospitalDepartment of Thoracic & Cardiovascular Surgery
Causes
Trisomy 21 (Down syndrome) is the most frequent, others - Trisomy 13 and Trisomy 18, Interstitial deletion on chromosome 16. * In children with Down syndrome, AV canal defects are seen in 20–25% or a 1000-fold increased risk when compared with the incidence in the general population.
• Sellke: Sabiston & Spencer Surgery of the Chest, 7th ed., Copyright © 2005 Saunders, An Imprint of Elsevier
May be a component part of-Dandy-Walker malformation, Heterotaxy syndromes (asplenia and occasionally with polysplenia).
Associated condition-TAPVCEbstein anomaly. DiGeorge syndrome
Frequency
Atrioventricular septal defects account for 2-9% of congenital heart dis-ease in various series. Most investigators report a prevalence rate in the range of 3-5%.
The male-to-female distribution of atrioventricular septal defect is approximately equal.
The incidence of atrioventricular septal defect is higher among stillborn infants, likely due to the higher number of chromosomal and other genetic anomalies in this group. The pooled frequency of atrioventricular septaldefects from several series of congenital heart disease in stillborn infants was about 7%.
Atrioventricular Septal Defect
• Pathophysiology• Partial AV canal defects result from the failure of the endocardial cushions
to meet the septum primum producing a low-lying (ostium primum) defect in the atrial septum ; a cleft mitral valve is also usually present.
• Complete AV canal defects result from maldevelopment of the endocardial cushions, producing a single, common AV valve & VSD in addition to an ostium primum ASD.
• The degree of left-to-right shunting through the atrial defect is determined by the size of the communication and the relative compliance of the 2 atria and ventricles. Ventricular compliance is affected by the level of
pulmonary vascular resistance (PVR).• Pathophysiology results from left-to-right shunting at the atrial and/or ven-
tricular level as well as AV valve insufficiency, producing pulmonary over-circulation and congestive heart failure, particularly during early infancy.
• http://emedicine.medscape.com/article/894813-overview
Pathophysiology( cont.)
Patients with little atrioventricular valve regurgitation and high pulmonary vascular resistance (PVR) are asymptomatic early in life, and their condition may be difficult to diagnose.
These patients occasionally remain relatively asymptomatic until their second or third decade, when they develop increasing cyanosis from advanced pulmonary vascular disease.
In most cases, the PVR decreases normally over the first 6 weeks of life,and the patient develops a large left-to-right shunt through both the atrial and ventricular defects, resulting in congestive heart failure (CHF).
Patients with clinically significant atrioventricular valve regurgitation may also have signs of CHF, such as tachypnea, excessive sweating, and failure to appropriately gain weight.
Mortality/Morbidity
Patients with complete atrioventricular septal defect typically develop tachypnea, respiratory tract infection and failure to thrive in the first few months of life. Patients may survive past the first few years of life without surgical intervention if the PVR remains elevated, although they may develop irreversible pulmonary vascular obstructive disease (PVOD) at a rapid rate.
In patients with a nonrestrictive VSD component, pulmonary vascular disease (Eisenmenger syndrome) eventually occurs unless the VSD component is surgically closed.
Cyanosis occurs when patients develop some degree of right-to-left shunt at either atrial or ventricular levels.
Although patients' quality of life may be impaired at this point, their life expectancy may be
20-50 years.
Clinical HistoryTachypnea, repeated respiratory infections, poor feeding, and failure to thrive are frequent symptoms in patients with complete atrioventricular septal defect (AVSD) and large left-to-right shunts.
These symptoms are usually present by 6-8 weeks and due to blood flow through the large interventricular communication with or without incompetence of the common atrioventricular valve.
Pulmonary vascular disease results from damage caused by excessive pulmonary flow and elevated pulmonary artery pressure due to the large ventricular septal defect (VSD). Irre-versible pulmonary vascular disease may be present by age 2 years or, in rare cases, earlier.
Physical
General physical examination may show characteristics of Down syndrome, including flat fa-cial profile, upslanting palpebral fissures, prominent inner epicanthal folds, Brushfield spots, protuberant tongue, abnormal palmar creases, and fifth finger clinobrachydactyly. Inspection may reveal pallor or Harrison grooves (horizontal depression along lower border of chest at diaphragm insertion site due to chronic tachypnea).
Failure to thrive is common due to excessive metabolic cardiovascular requirements and poor caloric intake (due to tachypnea) is common.
Cardiac examination
The cardiac examination is remarkable for and overactive precordium. The volume and pressure overload on the right ventricle result in a prominent systolic heave along the left sternal border and subxiphoid regions.
The pulmonary component of the second heart sound may be palpable at the left second intercostal space.
Regurgitation of the atrioventricular valve may uncommonly result in a palpable apical thrill.The first heart sound is single and often accentuated. The second heart sound is narrowly split, with an accentuated pulmonary component.
A crescendo-decrescendo murmur may be audible at the upper left sternal border due to increased blood flow through a normal pulmonary valve.
A mid diastolic rumble may be audible at the lower left sternal border and apex due to the Increased flow across the common atrioventricular valve.
A holosystolic murmur is often appreciated at the apex due to atrioventricular valve insufficiency.
Because the VSD in complete atrioventricular septal defect is large and unrestrictive, it is not associated with a murmur.
Cardiac examination- cont.
When pulmonary vascular resistance (PVR) is elevated, the systolic murmur may not be prominent, and the diastolic rumble may disappear, reflecting less left-to-right shunt.
This finding can occur in the infant in whom PVR has never fallen or in the older child with developing pulmonary vascular obstructive disease (PVOD), for whom the improvement in congestive heart failure (CHF) symptoms is an ominous finding.
In patients with advanced PVOD, the left parasternal impulse is prominent, S2 may be palpable, and the systolic murmur may be soft and short.
A high-pitched decrescendo diastolic murmur of pulmonary insufficiency (Graham Steel murmur) may be detected at the left upper sternal border, reflecting severely elevated PVR.
Factors that can influence hemodynamics in Down syndrome include chronic nasopharyngeal obstruction, relative hypoventilation, carbon dioxide retention, and sleep apnea.
Nonspecific CHF signs that may be seen include hepatosplenomegaly, pulmonary rales, and tachypnea. Skull erosion and striations have been noted from venous distension and increased blood volume.
Techniques of Operation1. Direction
1) Closure of atrial communication
2) Closure of ventricular communication
3) Avoidance of damage to conduction
4) Creation of two competent valves
2. Technique
1) Repair of partial AV canal defect
2) Repair of complete AV canal defect
one - patch technique
two - patch technique
3) Repair of associated cardiac anomalies
Indications for Operation1. Partial AV canal defect Optimal age for operation is 1-2 years of age except when CHF or growth failure is evident earlier in life2. Complete AV canal defect Operation is indicated early in the 1st year of life when the infants general condition is good, repair can be delayed until 3-6 months of age.3. Coexisting cardiac anomalies Although certain major cardiac anomalies increase
risk of AVSD, their presence rarely alters the indication for operation.
AV Valve Repair in AVSD
• The most anterior point of LSL-LIL opposing edge should be found and sutured through it, and the ante-rior edges be sutured to the polyester patch
• The patch must be appropriate dimension & configu-ration and tailoring the waist of the patch is critical
• Remodeling leaflet closure by suturing portions of left superior leaflet and left inferior leaflet together in ar-eas of regurgitation.
• Annuloplasty at commissure and making the edge of the pericardial patch along it shorter than the com-bined length of the base of leaflet
Surgical techniqueTwo techniques are widely used, a 1-patch technique
and a 2-patch technique.
First elevate the common AV valve to its closed position by injecting cold isotonic NaCl solution into the ventricles to
assess valvular competence and structure.
The central apposition of the SBL and IBL is the area
where the 2 leaflets meet at a point separating the left and
right AV valves.
Identify and mark these points with fine polypropylene
Sutures.
Surgical technique-cont.
• Fashion a patch of polytetrafluoroethylene (PTFE, Gore-Tex) into a crescent shape to match the
dimensions of the VSD.• Secure this patch along the ventricular septal crest
slightly on the rightward aspect, particularly
inferiorly, to avoid the conduction system. For the
1-patch technique, divide the SBL and IBL along a
line separating them into right and left components. • Tailor a single polyethylene terephthalate (Dacron)
or PTFE patch to close both the VSD and ASD
Surgical technique-cont.• Secure the patch to the crest of the ventricular
septum. • Then, resuspend the leaflets to the patch by passing
interrupted sutures through the cut edge of the left AV valve
leaflet, the patch, and the cut edge of the right AV valve, and
tie the sutures closure of the cleft is an important mechanism
in preventing postoperative left AV valve regurgitation • Significant AV valve regurgitation, severe dysplasia of the left
AV valve, and failure to close the cleft of the left AV valve as
important risk factors for repeat surgery. • Significant postoperative left AV valve regurgitation is also a
risk factor for surgical and long-term mortality.
A. Single patch repairB. Modified single patch repairC. Double patch repair
Septal Patch for AVSD Repair
Too wide patch, theoretically left ventricular outflow obstruction & long patch with high AV valve level, possible AV valve regurgitation
Surgical technique-cont.
• Closure of the cleft is an important mechanism in
preventing postoperative left AV valve regurgitation • Significant AV valve regurgitation, severe dysplasia
of the left AV valve, and failure to close the cleft of
the left AV valve as important risk factors for repeat
surgery. • Significant postoperative left AV valve regurgitation
is also a risk factor for surgical and long-term
mortality.
AVSD. Repair of Mitral Cleft
Partial Annular Plication
• Two furling stitches with 3 pledgets or three furling stitches with 4 pledgets are placed along the annulus of either or both sides for mitral valve regurgitation
AV Valve ReplacementAfter AVSD Repair
• Lengthening the mitral-aortic septum, thus the valve is
well away from the LVOT
Features of Postoperative Care
1. Vigilance must be exercised to detect any impor-tant imperfections in the repair
2. LAP is higher 6 mmHg than CVP : suggest mitral valve stenosis or insufficiency3. Prophylaxis against PA hypertensive crisis4. Evaluation on left AV valve regurgitation : predispose patient to death within 1 year5. Evaluation of left to right shunt6. Reoperation is indicated in severe regurgitation
and significant residual shunt
41
Postoperative details
Ventilator maneuvers include high FiO2, lowering of PCO2 (25-30 mm
Hg), avoidance of acidosis, and use of inhaled nitric oxide (5-80 ppm).
Some authors routinely use phenoxybenzamine (1 mg/kg) at the
initiation and conclusion of cardiopulmonary bypass, as well as every 8
-12 hours postoperatively (0.5 mg/kg) in high-risk patients.
Intravenous nitroglycerine, nitroprusside, aminophylline, and prostacy-clin all have been advocated for the management of pulmonary
hypertensive crises.
Generally, avoid high-dose dopamine and alpha-adrenergic agents if
possible.
Carefully evaluate low cardiac output with TEE and, if necessary,
cardiac catheterization.
42
Complications
Most repeat surgeries following repair of AVSD are because of left AV
valve regurgitation.
Significant postoperative AV valve regurgitation occurs in 10-15% of
patients, necessitating additional surgery for valve repair or replacement
in 7-12% of patients.
With improved understanding of the conduction system in AVSDs,
incidence of permanent complete heart block is approximately 1%, as
reported by Studer et al and Kadoba et al. Heart block encountered in the
immediate postoperative period may be transient and result from edema
of or trauma to the AV node or bundle of His.
However, according to Kadoba et al, right bundle branch block is
common (22%).
Results of Operation
1.Survival 1) early death 2) time related survival2. Mode of death 1) early : acute cardiac failure and pulmonary dysfunction 2) late : chronic or subacute cardiac failure3. Incremental risk factors for prema-
ture death 1) earlier date of operation 2) functional class 3) prerepair AV valve incompetence 4) interventricular communication
5) accessory valve orifice 6) major associated cardiac anomalies 7) young age ; not now 8) Down syndrome 9) need for reoperation 10) single papillary m. 11) hypoplasia of ventricle4. Heart block & arrhythmia5. Functional class6. AV valve function7. LVOT obstruction8. Residual pulmonary hyper-
tension
