Ventricular Septal Defect

Anatomy & Physiology

The flow through the defect is dependent upon the combined resistance to flow through the VSD, across pulmonary valve & lung vasculature.

The flow will be low if there is a very small hole, significant pulmonary stenosis (a common association with VSD) or raised pulmonary vascular resistance whilst it will be high in those with a large VSD and low pulmonary vascular resistance.

The pulmonary artery pressure will depend upon the size of the VSD and the presence or absence of pulmonary stenosis.

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The most common forms are in the muscular portion of the septum where they may lie posterior (1), apically (2) or anteriorly (3). The perimembranous (4) form is the next most common. It may extend posteriorly in the septum (inlet) or anteriorly towards the aortic valve (subaortic). More rarely (except in Asians) it is situated below both the aortic and pulmonary valves – doubly committed (5).

Presentation

Symptoms are generally proportional to size of shunt flow.

Small defects present with an asymptomatic murmur which is pansystolic in character and usually grade 3-4/6 in intensity.

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Large defects with a big shunt present with breathlessness and failing to thrive. There is tachycardia, an active precordium and a softer pansystolic murmur 1-2/6. There may also be a mitral diastolic flow murmur.

Large defects with small shunt are not breathless but may fail to thrive. If the shunt is small because of pulmonary stenosis then their will be an ejection systolic murmur at the upper left sternal edge. However if it is due to pulmonary vascular disease then murmurs, if present, will be quiet but the second sound will be loud.

Investigations

Electrocardiogram

Small defects have a normal ECG. Large defects with a big shunt have biventricular hypertrophy due to the pressure load on the RV and the volume load on the LV. If the shunt decreases due to either the development of pulmonary stenosis or vascular disease then the volume load decreases on the LV and the left ventricular hypertrophy resolves to leave right ventricular hypertrophy.

Chest X-ray

Small defects have a normal chest X-ray.

Large defects with a big shunt have cardiomegaly and pulmonary plethora.

Large defects with a small shunt have a normal heart size. If due to pulmonary vascular disease then there will also be large central pulmonary arteries and reduced peripheral pulmonary vascular markings.

Echocardiography

This shows size & position of VSD (arrow) and thus assists with the prognosis. It also allows identification of associated defects (ASD, pulmonary stenosis, aortic, mitral valve & arch lesions) when present. Colour Doppler is especially useful in identifying small defects.

The size of the shunt can be numerically estimated by Doppler flow techniques but the accuracy is poor and the method rarely used clinically. A reasonable subjective impression can however be made based on the LA and LV size which will be enlarged in a large shunt. This may stretch the mitral valve ring causes mitral regurgitation (LAVVR).

The pulmonary artery pressure can usually accurately be assessed using Doppler across the VSD. In the example the VSD velocity which using the Bernoulli equation (4V²) is equivalent to a pressure difference between the LV and RV of 64 mm predicating a normal PA pressure in most children.

Natural History

Small (& even some larger) lesions often close spontaneously either by muscular growth or plugging with tricuspid valve tissue. Larger lesions will either cause problems due to the size of the shunt (failure to thrive & recurrent chest infections) or cause irreversible pulmonary vascular disease. Life expectancy and exercise capacity will therefore be restricted.

Management

Small defects with normal pulmonary artery pressure and an insignificant shunt do not require treatment. The exception is doubly committed subarterial defects which, due to their proximity to the aortic root may cause aortic regurgitation and in most elective surgery is advised. Endocarditis prophylaxis on at risk occasions is necessary unless the defect closes spontaneously. Large lesions with a big shunt usually require medical management for heart failure with diuretics +/- ACE inhibitors. The calorie intake should also be maximised - usually with supplements. If the heart failure can be controlled then time may be allowed to pass to see if spontaneous reduction in size or closure will occur.

Otherwise surgical closure is required before vascular disease compromises the surgical outcome - usually within the first 6-12 months of life. Most require a Dacron patch but some may be closed by direct suture.

Transcatheter closure has been undertaken for muscular defects and a device has just become available for perimembranous defects and is under evaluation. The device is similar to the ASD device with a double disc made of nitinol metal which can be squashed into any shape and reforms into original shape on release. As the VSD is difficult to cross from the venous side the technique involves creating an arterial-venous loop. A catheter is passed from the femoral artery around the aorta into the left ventricle and across the VSD. A wire is then passed through the catheter into the pulmonary artery and snared by a wire passed from the femoral vein. The wire can then be pulled out of the femoral vein and the catheter removed.

VSD Plug Animation (file download time 15s)

Hover the mouse over the heart to see the animation

A sheath (large catheter) is then passed from the femoral vein across the VSD and the wire removed. The device is attached to a wire which is used to push it through the sheath. As it emerges from the sheath the first disc springs open. The catheter and device are then pulled back so the device is fitting snugly against the septum. The sheath is then withdrawn, the right ventricular disc springs out and the device clamps onto the septum sealing the defect. The wire is then unscrewed from the device and withdrawn.

Prognosis

This is excellent for most patients. The vast majority are able to live a normal and unrestricted life. Re-operations for residual VSDs are now uncommon.

This page was last edited 16/3/2004

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