Ventricular septum development and defect

Development of ventricular and outflow tract separation
Development of ventricular septum
Anatomical classification of Ventricular septal defect
Pathophysiology of ventricular septal defect (VSD)
What are the clinical features of ventricular septal defect (VSD)?
Heart sounds in ventricular septal defect
Murmur in Ventricular Septal Defect (VSD)

Development of ventricular and outflow tract separation

Ventricular Septation is done by 2 separate components - superior membranous and inferior muscular septum

Muscular Septum

It is a growth of inferior wall

It is produced due to the fusion of 3 components - right and left bulbar ridges and dorsal endocardial cushion.

Membranous Septum

This is situated above the muscular septum, fusion is continuous with septation of the outflow tract

Outflow Tract Septation

In early stages of development, outflow tract is a single tube called as bulbus cordis.

Bulbus cordis elongates to form proximal conus arteriosus and distal truncus arteriosus.

Two growths from wall in spiral pattern, inferior upwards - separate tract into 2 channels.

The mesenchyme and neural crest contribute to outflow septation process.

The fusion of outgrowths separate aortic and pulmonary outflow.

Anatomical classification of Ventricular septal defect

TypeI-Defect is in the MEMBRANOUS SEPTUM

Paramembranous / Perimembranous defect or Infracristal, Subaortic, conoventricular)

TypeII- Defect is seen in the MUSCULAR SEPTUM

Inlet,trabecular, central, apical, marginal or swiss-cheese type

TypeIII- Defect is seen in the OUTLET SEPTUM

Supracristal,subpulmonary,infundibular or conoseptal

Septal deficiency –AVseptal defect (AVcanal)

Read related topics

1. Development of ventricular and outflow tract separation
2. Heart sounds in ventricular septal defect
3. Murmur in Ventricular Septal Defect (VSD)
4. Development of ventricular septum
5. What are the clinical features of ventricular septal defect (VSD)?
6. Pathophysiology of ventricular septal defect (VSD)

Heart sounds in ventricular septal defect

P2 (pulmonary component of second heart sound)is usually soft in small – moderate and large VSD because the murmur mask P2. 
P2 is loud in VSD with PAH and Eisenmenger syndrome.
Split in VSD  1.Split is absent in small VSD
2.Wide mobile split is heard in moderate to large VSD due to the following

• Shortening of left ventricular systole 
• Prolonged right ventricular systole 

3.Single S2 is heard in Eisenmenger VSD
S2 is single in Eisenmenger syndrome because the left and right ventricle act as a common chamber and it eject blood into the great vessels at equal resistance.

Read related topics

1. Development of ventricular and outflow tract separation
2. Anatomical classification of Ventricular septal defect
3. Heart sounds in ventricular septal defect
4. Murmur in Ventricular Septal Defect (VSD)
5. Development of ventricular septum
6. What are the clinical features of ventricular septal defect (VSD)?
7. Pathophysiology of ventricular septal defect (VSD)

Murmur in Ventricular Septal Defect (VSD)

Murmur in VSD depends on the size of VSD. Depending on the size of VSD it may produce either pansystolic murmur or early systolic murmur.

• Murmur in trivial defct à produces – high pitched early  systolic decrescendo murmur at lower left sternal border.
• Small defect produce high pitched pansystolic murmur at the LLSB.
• Moderate defect produce high pitched pansystolic murmur at the LLSB.
• Large defect produce high pitched pansystolic murmur at the LLSB.
• VSD with PAH à high pitched early systolic decrescendo murmur.
• Eisenmenger VSD  high pitched early systolic decrescendo murmur.

So VSD with early systolic murmur is heard in

1. Trivial VSD
2. VSD with PAH
3. Eisenmenger VSD

What is the basis for pansystolic murmur with midsystolic accentuation in large VSD

Rapid ejection of large stroke volume into the dilated pulmonary artery produces pulmonary flow murmur. It is the cause for midsystolic accentuation.

Read related topics

1. Development of ventricular and outflow tract separation
2. Anatomical classification of Ventricular septal defect
3. Heart sounds in ventricular septal defect
4. Murmur in Ventricular Septal Defect (VSD)
5. Development of ventricular septum
6. What are the clinical features of ventricular septal defect (VSD)?
7. Pathophysiology of ventricular septal defect (VSD)

Development of ventricular septum

Interventricular septum has two components, Trabecular and membranous part of septum

Trabecular septum	Membranous septum
Develop from primitive interventricular septum	Develop from Proximal bulbar septum and proliferation from AV cushion

Embryology of ventricular septum and correlation with type of VSD.

There are three important types of VSD.

1. Inlet type of VSD
2. Outlet type of VSD
3. Trabecular type.

Inlet type of VSD is due to the malalignment between the inlet and trabecular septum.

Here the defect in ventricular septum originate from the AV cushions.

Outlet type of VSD : Occur due to malalignment between the outlet and trabecular septum.

The defect is derived from proximal bulbar septum.

Trabecular type of VSD : Defect occur in that part of septum derived from primitive ventricular septum.

Types of VSD are

Perimembranous

It is the most common defect also called as subaortic or infracristal

Inlet type

Subtricuspid / AV canal type

Outlet type

Subpulmonic supra critical or infundibulbar

Read related topics

1. Development of ventricular and outflow tract separation
2. Anatomical classification of Ventricular septal defect
3. Heart sounds in ventricular septal defect
4. Murmur in Ventricular Septal Defect (VSD)
5. What are the clinical features of ventricular septal defect (VSD)?
6. Pathophysiology of ventricular septal defect (VSD)

What are the clinical features of ventricular septal defect (VSD)?

Clinical features of VSD depends on the size of septal defect.

Small VSD is asymptomatic.

Moderate and large VSD may present as dyspnoea on exertion, palpitation or recurrent chest infections.

Following are the clinical signs in VSD

1. Pulse is hyperkinetic in moderate to large VSD due to the vigorous left ventricular ejection.
2. Apex is forceful with cardiomegaly.
3. JVP in moderate to large VSD is prominent with a-v waves.
4. But in VSD with Eisenmenger syndrome small a wave is seen.
5. Systolic thrill is felt at lowersternal border.
6. Wide split of S2.
7. Left ventricular S3 is present.
8. Pansystolic murmur is heard at the lowersternal border.
9. There  may be  middiastolic flow murmur at apex.

Read related topics

1. Development of ventricular and outflow tract separation
2. Anatomical classification of Ventricular septal defect
3. Heart sounds in ventricular septal defect
4. Murmur in Ventricular Septal Defect (VSD)
5. Development of ventricular septum
6. Pathophysiology of ventricular septal defect (VSD)

Pathophysiology of ventricular septal defect (VSD)

Pathophysiology in VSD depends on the size of VSD. There are two types of VSD based on the size of defect.

Restrictive VSD (Small / moderate sized )

Non restrictive VSD

Pathophysiology of restrictive VSD

In restrictive VSD there is resistance to left to right shunt at the site of defect. Here the right ventricular systolic pressure is less than left ventricular systolic pressure.

Small VSD

Right ventricular systolic pressure is normal and pulmonary vascular resistance is also normal. So there is predominant left to right shunting during systole. These type of VSD usually closes spontaneously .

Moderate VSD

Right ventricular systolic pressure is elevated but it is less than left ventricular systolic pressure. Pulmonary vascular resistance is low. There is left to right shunt during systole and diastole occurs. Here predominantly left ventricular volume overload is seen. These type of lesions may occasionally undergoes spontaneous closure. The incidence of Eisenmenger syndrome is rare. Left ventricular failure is the main complication.

Pathophysiology of non-restrictive VSD

In non-restrictive VSD the systolic pressure in left ventricle and right ventricle is equal so both act as a common chamber and shunt depends on pulmonary and systolic vascular resistance. Here the pulmonary vascular resistance is high. There is large left to right shunt and left ventricular volume overload is seen. Eisenmenger syndrome is common.

When the patient develops pulmonary hypertension in non-restrictive VSD the left ventricular volume overload decreases. Left to right shunt also decreases and right to left shunt increases. Right ventricular pressure overload develops

Read related topics

Development of ventricular and outflow tract separation
Anatomical classification of Ventricular septal defect
Heart sounds in ventricular septal defect
Murmur in Ventricular Septal Defect (VSD)
Development of ventricular septum
What are the clinical features of ventricular septal defect (VSD)?
Pathophysiology of ventricular septal defect (VSD)