This is the commonest congenital heart disease after bicuspid aortic valve.

 

Prevalence

It is slightly more common in females (56%).

 

Pathology

Parts of septum-

  • Inlet septum extends from tricuspid annulus to tricuspid valve attachment.
  • Outlet septum extends from crista supraventricularis to pulmonary valve.
  • Membranous septum is divided into two by septal leaflet of tricuspid.
  • Trabecular septum.

Types of VSD-

  • Perimembranous – 80%.
  • Inlet – 5%.
  • Outlet – 5%.
  • Muscular – 10%.

Perimembranous VSD is also called infracristal while outlet VSD is also called supracristal.

Perimembranous VSD

  • is below the crista supraventricularis and behind the papillary muscle of the conus.
  • may be associated with malalignment of the infundibular septum.
  • if there is deficiency of the STL, there will be associated LV to RA shunting also. This is not to be confused with Gerbode defect, which is a defect of the atrioventricular septum.

Outlet VSDs are more common in the Far East.

Muscular VSD

  • is most commonly apical.
  • may be single or swiss cheese. Single ones may be central, apical or marginal.
  • Marginal VSD is also called anterior VSD.
  • is usually single on LV side and multiple on RV side.

Aortic cusp prolapse-

  • Can occur with outlet or PMVSD.
  • More common with outlet VSD.
  • Causes AR, which increases with age.
  • Can decrease shunting.
  • With outlet VSD, RCC prolapses. With PMVSD, usually RCC prolapses, less commonly NCC prolapses.
  • With outlet VSD, commissures are normal. With PMVSD, the RCC/NCC commissure is abnormal.
  • With PMVSD, infundibular PS may be associated.

Bundle of His is posteroinferior to PMVSD and anterosuperior to inlet VSD. Muscular and outlet VSDs are far removed.

 

Physiology

If the VSD is large, flow is dictated by relative resistances of pulmonary and systemic circulations. If it is not large, flow is dictated by the size of the defect.

In a normal baby, RV pressure falls to normal at the end of the first week. If this occurs in an infant with a large VSD, there will be severe shunting. However, this does not occur as pulmonary vascular resistance remains elevated (due to pulmonary vasoconstriction secondary to high LA pressure).

A VSD is called small when its size is less than one-third of the size of the aortic root (tiny-<2mm). It is also called Roger’s defect. Shunt may stop at the end of IVRT.

A VSD is called moderate sized when its size is about half that of the aortic root (one-third to two-third). The left to right pressure gradient is about 20 mm Hg. This means that RV pressure is not high, hence severe PAH would not occur. But the left to right shunt is considerable and hence left chambers become overloaded. There is transient right to left shunting during IVRT.

 

A VSD is called large if its size is about that of the aortic root. There is a large left to right shunt which can cause heart failure at 2 to 8 weeks. There is no gradient which means that RV pressure is high- this causes severe PAH to develop. There is bidirectional shunting.

 

History and physical examination

The VSD murmur can be heard from the first days of life.

With small VSDs, the only risk is that of IE, which is rare before 2 yrs of age. There is a grade 4 to 6 high pitched PSM which goes beyond A2. It is heard at the LPSB, but may be higher in outlet VSDs. Note the absence of murmur in diastole even though small amount of shunting is present. In muscular VSDs, midsystolic cutoff may occur. S2 may be widely split.

For moderate and large VSDs, shunting causes symptoms from 2 weeks of age. These include tachypnoea, sweating and “fatigue on feeding”. There is failure to gain weight, not height. Precordial bulge occurs at 6 months age. The PSM is harsh and extends throughout systole for a moderate sized defect, but ends after two-third of systole for a large sized defect. S2 is widely split with normal P2 intensity in a moderate sized defect, but is narrowly split with a loud P2 for a large defect. There will be an LV S3 and an MDM at the mitral area.

Large VSD going into severe PAH with right to left shunting is called Eisenmenger’s complex. This usually occurs in adolescence. It usually develops after the initial period of high left to right shunting, although some patients can directly go to this stage from birth as their PVR is never allowed to fall. In this stage, there is no PSM. S2 is single and loud. LPH is present.

Causes of cyanosis in VSD are PAH and infundibular PS.

 

ECG

In moderate sized VSDs and in large VSDs before PAH stage, LA enlargement and LV volume overload are present. The only evidence of LVH in an infant may be a counterclockwise frontal QRS vector loop. In large VSDs in PAH, rsR’ or rR’ in v1 occurs in the stage of biventricular hypertrophy while QRS in v1 with slurring of upstroke of R and deep S in v6 occur in the stage of RVH. (rR’ refers to a prominent negative deflection on the R upstroke.)

 

Chest X-ray

In moderate and large VSDs, LA enlargement and LV enlargement are seen along with increased pulmonary vascular markings. In Eisenmenger’s complex, normal sized heart with prominent MPA and decreased pulmonary markings in the outer third of lung are seen.  

 

Echo

In PLAX, defect near the aorta is perimembranous VSD or subaortic VSD. More distal defects are central muscular VSDs. Clockwise rotation can reveal subpulmonic VSDs.

In PSAX, perimembranous VSD is at 10 to 11, subaortic VSD is at 11 to 12 and subpulmonary VSD is at 1.

In PSAX at mitral leaflet tips, anterior VSD is at 12 to 1, central is at 9 to 12 and inlet is at 7 to 9.

In apical 4 chamber view, defects from transducer out are apical, central and inlet.

In apical 5 chamber view, defects from transducer out are apical, central and subaortic/perimembranous.

Since RV pressure peaks after LV, the RV pressure obtained from gradient across the VSD may be an underestimation. If the VSD jet is not aligned towards the transducer, the RV pressure is overesimated. Because of these problems, always RV pressure should also be noted from TR jet, if one is present.

PMVSDs close by a pouch called an IVS aneurysm which is supposed to come from STL. Muscular defects close by muscle growth on RV side.

In severe PAH or severe RVOT obstruction, even during systole, there is right to left shunt.

 

Cardiac catheterization-

This is needed when echo results are ambiguous like when a moderate sized defect is found to caused PAH.

Long axis oblique view is used to find VSDs. To find VSDs in the posterior septum, four-chamber or hepatoclavicular view is used.

If PVR decreases to at least 8 units/m2 with 100% oxygen or NO, the case is operable.

 

Differential diagnosis

In atrioventricular septal defects, angiogram in AP view shows goose neck deformity.

In LV to RA shunt, murmur radiates to right middle and right upper sternal border. There is a tricuspid MDM also. There is oxygen step up at RA level in the absence of ASD (same can occur in VSD + TR also).

In VSD + AR, the AR murmur will not be audible before 2 years of age.

 

Medical treatment

Small VSD- no treatment other than IE prophylaxis is needed.

Moderate sized VSD and large VSD before PAH- In both these situations, there is significant left to right shunt. This causes volume overload of left ventricle. If left ventricle is not able to cope up with this increased load, it fails. Treatments of LV failure are-

  • furosemide- 1 to 3 mg/kg/day
  • enalapril- 0.1 mg/kg/day titrated up to 0.5 mg/kg/day
  • increasing caloric density of feeds
  • digoxin- 10 ug/kg/day.
  • Note- Furosemide can cause hypercalcemia and hypokalemia. Latter can be avoided by giving spironolactone alongside. Digoxin is added only if furosemide + enalapril fails and its utility is debated.

If symptoms do not respond to medical therapy, surgical correction is to be done.

If symptoms do respond to medical therapy, do serial echoes to see whether this is due to decrease in the shunt, which may be due to

  • decrease in VSD size
  • development of PAH or
  • development of RVOT obstruction.

Note that heart failure occurs only during infancy.

Severe PAH- If inoperable, red cell reduction be partial exchange transfusion taking care to avoid iron deficiency state, avoidance of high altitude and of air travel and heart lung transplantation are the options.