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Ventricular Septal Defect

Ventricular Septal Defect

1. Definition

A. Defect in ventricular septum
B. Membranous
C. Inlet
D. Trabecular
E. Outlet
F. Most common congenital heart defect
G. 1/100 live births
H. 25% of all CHD

2. Morphologic Classification

A. Perimembranous (80%)
B. Borders tricuspid valve
C. Conduction system posterior rim
D. Muscular (5%)
E. Borders all muscle
F. Frequently multiple
G. Conduction system remote
H. Doubly committed subarterial (10%)
I. Borders both semi-lunar valves
J. Inlet (5%)
K. A-V canal type
L. Posterior position
M. Conduction system posterior rim

3. Morphologic Classification

A. Perimembranous with
B. Inlet extension
C. Anterior extension
D. Outlet extension
E. Muscular
F. Outlet (conal)
G. Trabecular
H. Inlet
I. Anterior
J. Apical
K. Doubly committed subarterial
L.Inlet (A-V canal)

4. Malalignment Type

A. Relates to the alignment of trabecular to conal septum
B. Embryologic looping of the heart
C. Aorta seems displaced relative to VSD
D. Types
E. Anterior = TET
F. Posterior = Interrupted arch or coarct-VSD
G. Rotational = Taussig-Bing

5. Associated Lesions

A. Almost 50% with associated anomalies
B. Patent ductus arteriosus = 6%
C. 25% in heart failure have PDA
D. Coarctation = 5-10%
E. Aortic stenosis = 2-3%
F. Subvalvular valvular

6. Pathophysiology

A. Shunting - Increased pulmonary flow
B. Greater flow through mitral valve = increased LV and RV work = LV hypertrophy ->C. and RV dilatation
D. Increased interstitial lung fluid
E. High pulmonary/low systemic flow = growth failure
F. Pulmonary vascular resistance increased
G. May develop Eisenmenger's syndrome and shunt reversal

7. Natural History

A. Spontaneous closure in majority
B. Pulmonary vascular resistance increases with age
C. Endocarditis rare - more in small or moderate VSD
D. 9% mortality at 1 year with large VSD if untreated
E. Late deaths: Eisenmenger's 20 years
F. AI develops during first decade = 5%
G. Infundibular pulmonary stenosis = 5%

8. Clinical Symptoms

A. Heart failure, poor feeding, growth failure, tachypnea
B. Precordial pansystolic murmur, hyperactive heart
C. Apical diastolic murmur - large flow across mitral
D. If PVR SVR - clinical cyanosis

9. Diagnosis

A. Chest x-ray: Pulmonary vascularity, cardiomegaly, CHF
B. EKG: RVH, LVH
C. Echo: Very accurate
D. Cardiac catheterization: R and L heart studies, cineangiograms

10. Indications for Surgery

A. Large VSD
B. < 3 months - CHF (Qp:Qs2:1)
C. Elective repair at 6 months (PVR < 8.0 units)
D. Small VSD (Qp:Qs<2:1)
E. Endocarditis
F. Cardiac Enlargement
G. Any Aortic Incompetence
H. Subarterial (supracristal) VSD - any size

11. Principles of Repair

A. PDA present - ligate prior to CPB
B. Avoid conduction bundles
C. Close defect with patch
D. RA approach whenever possible

12. Surgical Approach

A. Perimembranous VSD - RA approach
B. Subarterial VSD - Pulmonary outflow tract or R ventriculotomy, aorta
C. " Swiss cheese " septum - May need LV incision
D. PA banding - Palliation in multiple VSD's
E. Transvenous closure with umbrella device or direct vision (experimental)

13. Risk Factors

A. Major associated anomalies
B. PDA, coarctation do NOT increase risk
C. Multiple VSD's - less of a factor in current era
D. Young age - not a factor unless major associated anomalies

14. Results

A. Premature death < 2.5% if PVR low preoperatively
B. Normal weight gain within 1 year
C. Complete heart block = 1%
D. Normal cardiac function if corrected < 2 years of age
E. Residual shunts requiring reoperation < 1-2%
F. Pulmonary hypertension - depends on preoperative PVR
G. The younger the age at repair, the better the chance of normal PVR post-operatively

EXTENDED OUTLINE

1. Introduction

A. 1/1000 live births
B. Nearly 50% have additional major cardiovascular lesions (PDA, coarct, arch interruption)
C. First successful intracardiac closure - Lillehei, 1955, using cross-circulation

2. Anatomic classification

A. Divisions of interventricular septum
1) Membranous septum
2) Outlet or conal septum
3) Inlet septum or septum of atrioventricular (A-V) canal
4) Muscular or trabecular septum
B. Perimembranous (conoventricular, paramembranous, Type II)
1) 80% of all VSDs
2) May be seen w/malalignment of conal septum
a) Anterior in TOF (RVOTO)
b) Posterior in interrupted arch (LVOTO)
3) Relations
a) Between conal (outlet) and trabecular (muscular) septum
b) Posteroinferior edge can extend to TV in area of anteroseptal commisure
c) May extend to noncoronary cusp of AV, causing aortic regurgitation
4) Anterior leaflet of TV may bulge into defect during systole appearing as aneurysm of membranous septum (angiography)
5) LV to RA shunt if anteroseptal commisure becomes adherent to defect
C. Subarterial (outlet, conal, supracristal, subpulmonary, infundibular, Type I)
1) 5-10% of all VSDs
2) Superior edge in conjoined annuli of aortic and pulmonary valves
3) Right or non-coronary cusp of AV is relatively unsupported, may prolapse, cause AR
D. Atrioventricular canal type (inlet, Type II w/ extension into inlet septum)
1) <5% of surgically treated VSD
2) Relations
a) Posterior rim runs along septal leaflet of TV to central fibrous body to anterior leaflet MV
b) Superiorly, usually extends to membranous septum
c) No intervening muscle between defect and TV
d) Medial papillary muscle (Lancisi) attached to anterior margin of defect
3) Anterior leaflet of MV may be cleft
E. Muscular (Type IV)
1) Muscular tissue all the way around the defect
2) Frequently multiple
3) Location - surgical approach
a) Anterior - approached through RV-high transverse ventriculotomy
b) Inlet septum - separated from TV by muscle - approached through TV
c) Mid-muscular - approached through TV
d) Apical-LV apex (Glenn’s)-RA or low, vertical R ventriculotomy (Kirklin)
e) Outlet, muscular VSD’s similar to subarterial (physiologically) but have a rim of muscle between defect and semilunar valve annuli
4) Swiss cheese septum
a) True form (multiple openings on RV and LV sides of defect) is rare - may not be totally correctable
b) Septal band on RV side can give appearance of multiple openings

3. Atrioventricular conduction system

A. Anatomy
1) Triangle of Koch
a) Tendon of Todaro superiorly
b) Tricuspid annulus inferiorly
c) Coronary sinus orifice posteriorly
d) Apex is central fibrous body and atrial portion of membranous septum
e) Exact position of AV node in triangle may be variable
2) His bundle (direct continuation of A-V node
a) Passes through rightward part of right trigone of central fibrous body
(1) This is just inferior to the commisure between the septal and anterior leaflets of TV
b) Continues along posteroinferior margin of membranous septum and crest of muscular septum - gives off branches that form LBB
(1) This is just beneath the commisure between right and non-coronary cusps of aortic valve
c) Lies on left side of septum in 75-80%
B. Techniques to avoid injury
1) Suture along right ventricular side of septum to avoid His bundle on left side of muscular septum
2) When membranous septum is deficient
a) A-V node migrates posteriorly toward crux of heart (junction of AV and interventricular grooves)
b) His bundle passes along posteroinferior rim of defect
c) Avoid this by placing sutures a few millimeters from posteroinferior rim, and not penetrating the septum
d) Anterior to muscle of Lancisi - less danger of conduction injury
3) A-V canal type VSD - conduction tissue runs along posteroinferior border of defect
4) Inlet muscular VSD - conduction tissue is anterosuperior to defect

4. Pathophysiology

A. Qp/Qs = ratio of pulmonary to systemic flow
1) (aortic O2 sat - central venous O2 sat)/(pulm venous O2 sat - pulm art sat)
2) Can assume PV sat = aortic sat
B. Increased pulmonary flow
1) LA enlargement, LV overload
2) Pulm HTN is reversible in early stages
3) Intimal proliferation and medial hypertrophy will eventually lead to fixed, irreversible pulm HTN
4) Histologic severity of pulmonary hypertensive dz correlates directly with PVR and inversely with magnitude of shunting
5) Gradual increase in PVR decreases L?R shunting and decreases CHF as pulm vasc bed replaces LA pressure as determinant of flow resistance across lungs
6) Eisenmenger’s syndrome
a) Cyanosis and R heart failure due to reversal of shunt flow
b) PVR is greater than SVR
c) VSD closure in this setting associated with severe, acute R heart failure
C. Nonrestrictive: little resistance to flow, approximating at least the diameter of the aortic valve
1) RV systolic pressure equal to LV pressure
2) Large increase in pulmonary blood flow
a) Inversely proportional to pulmonary vascular resistance
3) Multiple small VSD’s may hemodynamically act like a large VSD
D. Small VSD
1) VSD presents resistance to flow, preventing increase in RV pressure
2) Qp/Qs rarely exceeds 1.5
E. Moderate VSD
1) Qp/Qs = 1.5 - 2.5
2) Less likely to cause fixed pulmonary hypertensive vascular disease

5. Natural history

A. Tendency for spontaneous closure vs. risk of hypertensive pulmonary vascular disease
B. Severity of symptoms depends on shunt volume across VSD
1) Qp/Qs increases as PVR decreases in first weeks of life
2) Symptoms = recurrent resp infections, SOB, failure to thrive
3) PA’s can exert extrinsic compression on airways and increased air trapping
4) Untreated symptomatic children have 10% 1-year mortality
C. Irreversible pulmonary HTN unusual in 1st year of life
D. Untreated children w/large VSDs will develop Eisengmenger’s complex
1) Hemoptysis, polycythemia, cerebral abscess/infarction, R heart failure
2) Preceded by resolution of CHF
3) Cyanosis by end of 1st decade of life
4) Premature death by age 35
E. Spontaneous closure
1) Perimembranous A-V canal and subarterial
2) Inversely related to pt age
a) 1 mo.: 80% will close (large VSD)
b) 6 mo.: 50%
c) 12 mo.: 25%
F. Infundibular PS or RVOTO in 5-10% w/nonrestrictive
1) Myocardial hypertrophy
2) R to L shunt when RVOTO severe
3) May protect pulmonary vascular bed
G. Bacterial endocarditis - 0.15-0.3% per year - more common in small & moderate VSDs
H. Aortic valve insufficiency
1) Subarterial perimembranous (percentage)
2) Right and/or non-coronary cusp
3) May be an indication for surgery (VSD closure)

6. Diagnosis

A. Clinical features
1) Harsh pansystolic murmur
a) Small are usually asymptomatic
2) Large (low PVR)
a) CHF
b) Tachypnea, hepatomegaly, failure to thrive, repeated pulmonary infections
c) Precordial pansystolic murmur
d) Prominent S3, diastolic murmur at apex (increased flow across MV)
3) Large (elevated PVR)
a) Shunt is bi-directional
b) Softer or absent systolic murmur
c) Absent diastolic murmur
d) Loud P2
e) Precordial thrill
B. ECG
1) Small defect - normal ECG
2) Large defect
a) LAE, LVH early
b) LVH, RVH as PVR rises
C. CXR
1) Small defect - normal CXR
2) Significant L to R shunting
a) Cardiomegaly due to LA dilatation
b) Increased pulmonary flow
D. Echocardiography
1) Size, location of defect; estimate RV pressure, magnitude of shunting
2) In neonates with symptomatic, isolated VSD, echo alone may suffice
E. Cardiac catheterization
1) Mandatory in older children to assess PVR and pulmonary HTN
2) Shunt volume, Qp/Qs , irreversible component of pulmonary HTN

7. Treatment

A. Dictated by symptoms, associated defects, age at presentation, PVR, location
B. Surgical indications
1) Early in life - intractable CHF
2) Failure to thrive - most common
3) Asymptomatic - delay to 12 mo of age (spontaneous closure)[Mavroudis = 6mo]
4) 6 mo. + pulm HTN = operate
5) Small defect, asymptomatic - watch (controversial after age 10)
6) A-V canal and subarterial - no tendency to close, operate early
7) PA banding
a) Swiss cheese type + symptomatic
b) VSD w/ straddling A-V valve
c) Contraindication to surgery
(1) Fixed pulmonary HTN (greater than 8 Wood units) [Wood units = mm Hg/L/min/m2]

8. Operative technique

A. Ligate ductus soon after institution of CPB
B. Most repaired through RA (except subarterial and outlet muscular)
1) Subarterial - via pulm valve
2) Muscular - depends upon location
a) Mid-muscular - RA
b) Right or left ventriculotomy may be needed for anterior muscular
c) AI - patch VSD closure may be enough (mod-severe may require repair)
d) Prosthetic patch (PTFE, dacron)
e) Avoid conduction tissue (posteroinferior rim of VSD)
f) Hypothermic (18C) circulatory arrest helps in small (<8kg) infants

9. Results

A. Early mortality approaches 0
B. Multiple VSD’s, associated anomalies = 7% mortality c) Arrhythmia
1) RBBB = 80% (R ventriculotomy)
2) RBBB = 34% (R atriotomy)
3) RBBB + L anterior hemi-block = 8-17%
4) CHB approaches 0
C. Residual VSD = 0.7-2%