Tuesday, September 7, 2010

Ventricular Septal Defect


Definition:

Ventricular Septal Defect (VSD) is defined as an anatomic defect in the ventricular septum.


The ventricular septum is mostly separating the right & left ventricles, and VSD usually creates a communication between the two ventricles.


Because the insertion of the septal tricuspid leaflet into the ventricular septum is a little lower (more apical) than that of the anterior mitral leaflet, it follows that the uppermost part of the septum is actually separating the left ventricle from the right atrium. A defect in that part creates a left ventricular-right atrial (LV-RA) communication.


LV-RA communication may also be created by VSD below the tricuspid valve, associated with a cleft in the tricuspid septal leaflet that carries the shunt to RA, rather than to RV.






LV-RA communication may occur either through the atrioventricular membranous septum (A), or more commonly through a defect in the interventricular septum and a defect in the septal tricuspid valve (B).
http://www.ctsnet.org/graphics/clincalcases/tatewaki/fig_7.jpg






Trans-thoracic echocardiography; Apical 4-chamber view; Insertion of the septal tricuspid leaflet (STL) into the ventricular septum is more apical than that of the anterior mitral leaflet (AML). The part of the septum between STL & AML actually separates the LV from the RA.
http://cardiophile.org/wp-content/uploads/2009/10/Apical-4C-mitral-partially-open.jpg


Embryology:

The inter-ventricular septum (IVS) consists of two parts:

  • Muscular septum, which comprises most of the inter-ventricular septum.
  • Membranous septum, which is only a small part of IVS.


The muscular septum develops as a muscular ridge from the floor of the primitive ventricle upwards, leaving a small inter-ventricular foramen high up, which is then closed by the membranous septum.

The membranous septum develops from:
  • Bulbar cushions ventrally.
  • Endocardial cushions dorsally.






Relations between the muscular ventricular septum, endocardial cushions (ECC), bulbar cushions and aortico-pulmonary (AP) septum.
http://sprojects.mmi.mcgill.ca/embryology/cvs/graphics/ivs_1.gif






Development of the membranous ventricular septum from the bulbar cushions and the endocardial cushions.
http://sprojects.mmi.mcgill.ca/embryology/cvs/graphics/ivs_2.gif


Anatomy:

The muscular ventricular septum consists of three parts:

1. Muscular outlet part: lies highest-up; separating the outflow tracts of the two ventricles. It is again divided by a muscular ridge called the Crista supraventricularis into two regions:
  • The supracristal region: above the Crista.
  • The infracristal region: below the Crista.
2. Muscular inlet part: lies posteriorly at the RV inlet directly related to the septal tricuspid leaflet (STL). It is to be noted that the STL is inserted posteriorly in the muscular inlet septum & anteriorly in the membranous septum. The part of the muscular inlet septum above the insertion of STL separates the LV from the RA and is thus called: the muscular atrioventricular septum; while the part below that insertion separates the LV from the RV and is an interventricular septum. Likewise; the membranous septum is divided by the STL into: the membranous atrioventricular and the membranous interventricular septum.






Membranous atrioventricular and membranous interventricular septum.
http://www.sahha.gov.mt/showdoc.aspx?id=567&filesource=4&file=fig02.jpg


3. Muscular trabecular part: the rest of the muscular septum, extending downwards from the outlet septum and downwards & anteriorly from the inlet septum, to reach the cardiac apex. This is the biggest part.


The membranous ventricular septum is a small part situated at the meeting of the three parts of the muscular septum.






Illustration of the 3 parts of the muscular ventricular septum as well as the membranous ventricular septum.
http://www.health.gov.mt/impaedcard/issue/issue3/2440/fig17.jpg






On the left side, the membranous septum lies just below the aortic valve, in the triangle between the right coronary & non-coronary leaflets.
http://www.sahha.gov.mt/showdoc.aspx?id=567&filesource=4&file=fig01.jpg


From the above discussion, we can conclude that below the level of the membranous septum; the posterior third of the mid-part of the interventricular septum is formed by the muscular inlet septum, while the anterior two thirds are formed by the muscular trabecular septum.


The whole lower third of the ventricular septum, on the other hand, is formed by the muscular trabecular septum, anteriorly and posteriorly.


Pathological types of VSD:

1. Peri-membranous VSD: defects in the membranous septum always involve the adjacent muscular septum, and thus called: perimembranous. According to the muscular part involved, the perimembranous VSD is classified into three subtypes: outlet, inlet & trabecular. Peri-membranous VSD may be so large to have multiple extensions into more than one muscular portion.

2. Muscular outlet VSD, in the muscular outlet septum, and is classified into two subtypes:
  • Muscular supracristal (also called: infundibular, doubly-committed or sub-arterial),
  • Muscular infracristal (also called: muscular outlet).

3. Muscular inlet VSD, in the muscular inlet septum.

4. Muscular trabecular VSD: usually multiple.


If a peri-membranous inlet VSD or a muscular inlet VSD lies immediately below the atrioventricular (AV) ring, without septal tissue separating the defect from the AV ring, it is called: AV canal-type VSD.






A: Image shows a ventricular septum viewed from the right side. It has the following 4 components: inlet septum from the tricuspid annulus to the attachments of the tricuspid valve (I); trabecular septum from inlet to apex and up to the smooth-walled outlet (T); outlet septum, which extends to the pulmonary valve (O); and membranous septum. B: Anatomic positions of the defects are as follows: outlet defect (a); papillary muscle of the conus (b); perimembranous defect (c); marginal muscular defects (d); central muscular defects (e); inlet defect (f); and apical muscular defects (g).
http://img.medscape.com/pi/emed/ckb/pediatrics_cardiac/1331339-1331342-892980-893111.jpg







Pathological types of VSD: A: Infundibular, B: Perimembranous, C: AV-canal type, D: Muscular trabecular.
http://img.medscape.com/pi/emed/ckb/pediatrics_cardiac/1331339-1331342-892980-893112.jpg








Pathological types of VSD
http://upload.wikimedia.org/wikipedia/commons/8/81/Heart_right_vsd.jpg



Secondary cardiac changes:

With small defects:

  • Cardiac chambers may be normal-sized.
  • Jet lesions (focal fibrous deposits) will form on the RV free wall which is hit by the jet of blood shunted from LV to RV.


With large defects:

  • LA & LV enlargement & thickening.
  • RV thickening; it may become as thick as LV.
  • PA widening; it may become wider than AO.
  • Absent jet lesions: because the blood is flowing almost smoothly through the big defect.


Complications of VSD:

  • Infective endocarditis.
  • Recurrent respiratory tract infections.
  • Left ventricular failure (LVF), due to volume overload.
  • Aortic regurgitation (AR), may occur if the defect is lying immediately below the aortic valve (as occurs in some perimembranous and some infundibular VSD’s).


Associated conditions:

The following conditions may be associated with VSD:

  • Additional defects: atrial septal defect (ASD), patent ductus arteriosus (PDA).
  • Coarctation of the aorta.
  • Valvular anomalies.
  • Double-inlet left ventricle.


Pathophysiology:

Pathophysiology of VSD depends on: Area & size of VSD and reaction of the pulmonary vasculature.


With small VSD: there is small left-to-right (L-R) shunt in the filling phases of the cardiac cycle, which increases in atrial systole, increases more in isometric contraction and reaches its maximum in ejection phases. In isometric relaxation phase it may stop transiently.


With moderate VSD: the same occurs until isometric relaxation phase when the shunt is reversed & becomes right-to-left (R-L).


In large VSD with mild increase in pulmonary vascular resistance (Rp): the same occurs until ejection phases when the shunt decreases then reverses & continues to be reversed in isometric relaxation.


In large VSD with markedly increased Rp: the shunt is minimized again in isometric contraction and is reversed in ejection phases & isometric relaxation.






L-R: left-to-right, R-L: right-to-left, +: small, ++: larger, +++: larger, ++++: maximum, +: stops transiently.


Reaction of the pulmonary vasculature:

The larger the shunt, the more aggressive the reaction of the pulmonary vasculature; with vasoconstriction & other pathological changes; ending in pulmonary vascular obstructive disease (PVOD).


On progression of PVOD; the shunt gradually decreases, and finally permanently reverses to become right-to-left (Eisenmenger’s syndrome).


Some patients with moderate or large VSD may develop RV infundibular stenosis, reducing the shunt & protecting the pulmonary circulation.


Left ventricular function in VSD:

LV function depends on:

  • Pulmonary vascular resistance: drop of Rp increases the shunt, with more volume overload & more chance of LVF.
  • Maturity of the infant, the myocardium & the cardiac nerves: the less mature the more the chance of LVF.
  • Time available for the compensatory mechanisms (concentric & eccentric hypertrophy) to operate; the shorter the time the more the chance of LVF.
  • Coronary blood flow: reduced flow increases the chance of LVF.
  • Foramen ovale: an open foramen ovale shunts the blood to RA protecting LV and reducing the chance of LVF.


Spontaneous VSD closure:

Spontaneous complete closure occurs in 45 % of all cases by age 3 years.
Spontaneous closure, however, may be delayed to age 10 years.
Large VSD with CHF in infancy will close spontaneously in only 7 % of these cases.
Infundibular VSD, and AV canal type VSD do not close spontaneously.


Mechanisms of spontaneous closure:

Spontaneous closure of VSD may occur by one of the following mechanisms:

  • Adherence of tricuspid valve leaflet to VSD closing the defect.
  • Hypertrophy of septal muscle around the defect until complete closure.
  • Growth of fibrous tissue, closing the defect.
  • Rarely: adherence of aortic valve leaflet to VSD.

Clinical picture:

Female/male ratio: 1/1.


Symptoms of VSD:

Small VSD with small shunt is usually asymptomatic.


If the VSD & the shunt are large enough, the following symptoms may occur:
  • Symptoms of congestive heart failure (CHF).
  • Repeated respiratory infections.
  • Slow weight gain.


Signs of VSD:

1. Palpation may reveal:

  • Hyper dynamic LV & RV impulse.
  • Systolic thrill, maximum at the left 3rd & 4th intercostal spaces (ICS).


2. Auscultation may reveal:

  • Loud first heart sound (S1).
  • Loud pulmonary component of the second heart sound (P2) with narrow splitting.
  • Pan systolic murmur allover the precordium, maximum at the left 3rd & 4th ICS. The murmur, however, is short and does not reach S2 in patients with small muscular VSD.
  • Mitral flow murmur (mid-diastolic rumble).

3. Clinical manifestations of CHF may be present.


Clinical improvement may occur over time due to:

  • Narrowing of VSD,
  • Infundibular PS, or
  • Pulmonary hypertension (PHT).




How to differentiate?


With VSD narrowing:  
Pan systolic murmur becomes: softer, more localized, and may become Shorter.


With infundibular PS:
  • VSD murmur becomes softer & shorter.
  • P2 intensity: diminished.
  • S2 splitting: wider.


With PHT:
  • Pan systolic murmur: softer & shorter.
  • P2 intensity: accentuated.
  • S2 splitting: narrower.
  • PHT & pulmonary regurgitation (PR) murmurs may develop.
  • Eisenmenger's syndrome will be the end result with right-to-left shunt and cyanosis.



The signs of associated lesions should also be kept in mind:






Natural history:

The majority of VSD’ s are small and do not present a serious problem.


Large defects can lead to

  • CHF.
  • High morbidity and frequent hospitalizations.
  • High mortality.

Significant infundibular PS develops in 3 % of cases, and may precipitate cyanotic spills.


Pulmonary vascular obstructive disease (PVOD) is rarely severe in the 1st year; However, Nearly all deaths beyond infancy in medically-managed patients are due to PVOD.


The average age of death in Eisenmenger’s syndrome is 33 years.


Death occurs suddenly in the majority.


Aortic regurgitation (AR) is rare and usually occurs with perimembranous or infundibular VSD’s. It usually progresses rapidly and predisposes to infective endocarditis.


Overall survival of patients with VSD is good.


Survival in patients without surgery is much better in the absence of cardiomegaly, and when the pulmonary artery systolic pressure is < 50 mmHg, indicating a milder form of PVOD. 

Electrocardiography: 

With small defects: ECG is usually normal for age. 

With large defects: 
  • RV forces do not regress, and LV forces progress, resulting into a pattern of bi-ventricular enlargement within few weeks of life. 
  • LA enlargement and frequently RA enlargement occur. 

With PHT or PS: 
  • QRS axis becomes deviated further to the right. 
  • LA enlargement (LAE) & LV hypertrophy (LVH) regress, while pure RV hypertrophy (RVH) remains. 

Chest x-ray: 

With small defects: Chest x-ray (CXR) is usually normal. 

With large defects: 
  • Cardiomegaly due to multi-chamber enlargement. 
  • Central PA dilatation. 
  • Pulmonary plethora. 
  • Left lower lobe (LLL) lung collapse may occur. 

With PHT: 
  • Heart size regresses towards normal. 
  • Central PA become more dilated. 
  • Pulmonary plethora regresses and finally oligemia results. 

Echocardiography: 

  • The three modes: two-dimensional, Doppler and color Doppler echocardiography are essential in all cases. – Some defects may not be seen by two-dimensional but only Doppler & color Doppler echocardiography can detect them. 
  • Even those seen by two dimensional echocardiography, need Doppler & color Doppler modes to identify their pathological types. 

Echocardiographic identification of the pathological types of VSD:

Multiple echocardiographic views are usually needed to detect and verify the types and subtypes of VSD; since the ventricular septum is a curved structure. 

In the Parasternal short-axis view at the level of the ventricular outflow tracts; the following types can be seen: 
  • Perimembranous (yellow) near to the tricuspid leaflet without separating septal tissue, 
  • muscular infracristal (blue) in the middle of the septum, 
  • and infundibular (red) near to the pulmonary leaflet without separating septal tissue. 

The subtype of the perimembranous defects is defined by the direction of the color Doppler signal: 

  • along the tricuspid leaflet in inlet subtype, 
  • towards the RV free wall in trabecular subtype, 
  • and towards the RV outflow tract in outlet subtype. 





Parasternal short-axis view: Perimembranous VSD. http://www.yorksandhumberhearts.nhs.uk/upload/ACHD%20files/VSD%20Slide3.JPG 

In the Parasternal short-axis view at the mid-ventricular level; the following types can be seen: 

  • Muscular inlet (green) in the posterior third,
  • and muscular trabacular (black) in the anterior two thirds of the septum. 


In the Parasternal long-axis view; the following types can be seen: 

  • Perimembranous (yellow) immediately below the aortic valve, 
  • and the muscular trabecular defects (black) in the rest of the septum. 
  • With lateral angulation to show the RV outflow tract, the infundibular VSD can be seen. 

The subtype of the perimembranous defects is defined by the direction of the color Doppler signal: 

  • along the ventricular septum in the inlet subtype, 
  • and towards the RV free wall in the trabecular subtype. 

The outlet subtype cannot usually be seen in this view. 




Parasternal long-axis view: Perimembranous VSD http://www.yorksandhumberhearts.nhs.uk/upload/ACHD%20files/VSD%20Slide4.JPG 

In the apical four-chamber view; the following types can be seen:

  • Perimembranous inlet subtype (red arrow) adjacent to the tricuspid leaflet, 
  • muscular inlet (green) in the basal third of the septum, 
  • and muscular trabecular (black) in the mid and apical thirds of the septum. 






Apical 4-chamber view: Muscular trabecular VSD with left-to-right shunt. 
http://upload.wikimedia.org/wikipedia/commons/7/79/Ventricular_Septal_Defect.jpg 

In the apical five-chamber view; the following types can be seen:

  • Infundibular (red) in the basal part of the septum, 
  • and muscular trabecular (black) in the mid and apical thirds of the septum. 
  • The perimembranous defects may be also seen in this view with appropriate angulation of the transducer. 





Apical 5-chamber view: Perimembranous VSD. 
http://www.yorksandhumberhearts.nhs.uk/upload/ACHD%20files/VSD%20Slide2.JPG 




Apical 5-chamber view: Muscular trabecular VSD with left-to-right shunt. 
http://www.yorksandhumberhearts.nhs.uk/upload/ACHD%20files/VSD%20Slide1.JPG 

Echocardiography is also useful for: 
  • Calculation of the gradient across VSD; the larger the gradient the smaller the defect. 
  • Calculation of pulmonary blood flow (Qp) / systemic blood flow (Qs) ratio, which helps in the management decision making.

Continuous-wave Doppler across VSD. http://www.yorksandhumberhearts.nhs.uk/upload/ACHD%20files/VSD%20Slide5.JPG 


Cardiac catheterization: 

In most patients with VSD echocardiographic techniques can accurately diagnose and identify the types and subtypes of VSD and cardiac catheterization is not needed. 

Indications for cardiac catheterization in patients with VSD: 

  • When the non-invasive testing is non-conclusive and the hemodynamic significance of VSD is questionable. 
  • When the assessment of pulmonary artery pressure and pulmonary vascular resistance is essential. 
  • Therapeutic catheterization; for VSD device closure. 

Cardiac catheterization findings: 

Oximetry: 

  • O2 step-up is detected at RV level, in most cases. 
  • It may be detected at RA level: In presence of an associated patent foramen ovale (PFO), or in the presence of LV- RA communication. 

Pressures: 

Pressures in RV & PA and usually LA increase with increasing shunt. 

Angiography: 
  • Left ventriculography helps assess the LV size & function, as well as the VSD size, number & site, if echocardiography is non-conclusive. 
  • Aortography may be done for aortic valve assessment. 

Differential diagnosis: 

Isolated VSD should be differentiated from:
  • Sub-valvular pulmonary stenosis (PS). 
  • Sub-valvular aortic stenosis (AS). 
  • Atrio-ventricular septal defects (AVSD). 
  • Persistent truncus arteriosus (PTA). 
  • Transposition & mal-position complexes. 

Medical management: 
  • Prevention & treatment of infective endocarditis. 
  • Prevention & treatment of congestive heart failure (CHF). 
  • Prevention & treatment of respiratory tract infections. 
  • Prevention & treatment of anemia. 
  • Treatment of Arrhythmia. 
  • In Eisenmenger’s syndrome: 
    • Pregnancy is contraindicated since the mortality in these cases is very high (about 27%).
    • Contraceptive pills are also contraindicated; and contraception should be ensured with means other than the contraceptive pills. 

Indications for VSD device or surgical closure: 

  1. Symptomatic patients with CHF. 
  2. Significant VSD, as indicated by any of the following: 
    1. Qp/Qs >1.5.
    2. Pulmonary artery systolic pressure >50 mmHg.
    3. Increased LV and LA size.
    4. Deteriorating left ventricular function.
  3. Moderate or severe aortic regurgitation and a history of recurrent endocarditis; in patients with perimembranous or muscular outlet VSD.
  4. In patients with pulmonary hypertension; VSD closure is done only if PVOD is thought to be reversible as indicated by any of the following:
    1. Pulmonary arteriolar resistance < 7 Wood units.
    2. Left-to-right shunt with Qp/Qs of at least 1.5.
    3. Strong evidence of pulmonary reactivity when challenged with a pulmonary vasodilator (oxygen, nitric oxide).
    4. Lung biopsy evidence that pulmonary artery changes are reversible (rarely required).


Catheter closure:

Both perimembranous & muscular trabecular VSD’s can be closed by catheter devices, such as: Rshkind, Amplazer, and Cardioseal devices.


Ventricular septal defects that are situated very close to any of the cardiac valves are not amenable to trans-catheter closure.


Technically; VSD catheter closure is more difficult than ASD closure, especially the perimembranous types: Its success needs precise anatomic definition of the defect and its relation to other cardiac structures.


Congenital, post-infarction and traumatic VSD’ s were all successfully closed by catheter devices.


Concurrent closure of VSD & PDA was done, as well as VSD closure with pulmonary valvuloplasty, in the same patient in one sitting.


Some muscular VSD’ s, even multiple defects, not amenable for surgeons, could be closed by catheter devices; guided by either trans-thoracic or trans-esophageal echocardiography.


Complications of catheter closure:
  • Mal-positioning.
  • Tamponade.
  • Hemolysis.
  • Embolization into the PA.
  • Transient junctional rhythm.






A Nitinol implantable device for closing a muscular VSD (Ventricular Septal Defect). The centre is 4 mm across, and it's mounted on the delivery catheter. It is of the Amplazer type (AGA Medical Corporation, Plymouth MN, USA) Photograph by Kjetil Lenes, Norway.
http://upload.wikimedia.org/wikipedia/commons/thumb/b/ba/VSD_plug.jpg/800px-VSD_plug.jpg


Surgery in patients with VSD:

When surgery is indicated in childhood, elective surgery is usually performed between 3 and 9 months of age.


Surgical closure can be accomplished with sutures or using a patch.


Video: Echocardiography: Parasternal long-axis and apical 5-chamber view: Perimembranous trabecular VSD.
http://www.youtube.com/watch?v=p2WPALg2W7Q&NR=1





Video: Echocardiography: Apical 4-chamber view: an unusually large muscular trabecular VSD.
http://www.youtube.com/watch?v=1u2EK9S8q5s




Video: Echocardiography: Apical 4-chamber view: Multiple muscular trabecular VSD.
http://www.youtube.com/watch?v=u1JbsH3bY4c


Video: Echocardiography: Apical 5-chamber view: Subaortic membrane and VSD.
http://www.youtube.com/watch?v=rp5bLo3ZOD8




1 comment:

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