Ventricular Septal Defect

Aetiology
VSD may occur in various areas along the septum

• membranous septum- most common (70-80%)
• muscular septum (5-20%) may be multiple
• atrioventricular canal or inlet (<10%) - large & exist beneath the Av valves, associated with Down Syndrome
• Outlet (supracistal/infundibular/subarterial)- associated with aortic regurgitation

Often associated with other congenital heart defects: ASD, PDA

Pathophysiology

After birth, pulmonary vascular resistance (PVR) decreases as fetal circulation transitions to postnatal circulation

in patients with a VSD, left-to-right shunting develops across VSD as pulmonary resitance decreases

Pulmonary overcirculation associated with pulmonary hypertension may lead to the development of elevated pulmonary vascular resistance, which over time can become permanent (causing right-to-left shuning- Eisenmonger Syndrome)

Presentation

• harsh systolic murmur
• heard best at the lower left sternal border
• Radiates to the right lower sternal border
• Intensity varies based on the size of the VSD and the pulmonary vascular resistance (smaller defects cause louder murmurs)
• Very small defects , particularly in the muscular septum, are often audible in the newborn period
• Large defects- may not be audible until PVR decreases and shunting increases
• Small defects may be asymptomatic
• Large defects may result in dyspnoea, poor feeding and growth, profuse perspiration , recurrent respiratory infections
• Exam may reveal a palpable precordial thrill.

DDx

• Right ventricular outflow tract obstruction -eg Fallot Tetralogy
• Left ventricular outflow tract obstruction- eg aortic stenosis
• Mitral/Tricuspid regurgitation
• Primary pulmonary hypertension
• Vasculitis
• Left ventricular failure

Investigation
ECG- intraventricular conductiondelay or right bundle branch block, right axis deviation, right atrial abnormalities, RVH. In many cases, especially with small VSD, ECG is normal

Echo + Doppler > 90& sensitive & is usually diagnostic

• most sensitive for for VSD >6mm, less sensitive for muscular defects
• can calculate the degree of intracardiac shunting (pulmonary-to-systemic flow ratio, or QP:QS)
• also evaluates for other congenital abnormalities

VSDs are classified as restrictive (QP:QS<1.5), moderately restrictive (QP:QS 1.5-2.5) or non-restrictive (large defects)

• Shunts with QP:QS<1.5 - haemodynamically insignificant
• Shunts with QP:QS 1.5-2.0 - haemodynamically significant & can result in volume overload & arrhythmias

Cardiac catheterisation - useful if elevated PVR or associated defects are suspected but not confirmed by Echo

CXR - cardiomegaly + increased pulmonary vascular markings

Annual cardiac evaluation is indicated for adults with large uncorrected defects, late repairs, & Eisenmonger syndrome

Management

Wait for spontaneous closure or reduction in size od the defect-

50% close spontaneously during the first year of life

Surgical closure 

• at 6-12months if CHF or cardiomegaly present,
• earlier in infancy if CHF is not easily controlled
• indicated if QP:QS> 1.5, pulmonary artery systolic pressure> 50mmHg, left ventricular dysfunction, in membranous or outlet VSDs with more than mild aortic regurg, and if >2 episodes of endocarditis
• Small VSD closed by a purse-string procedure, larger one with a patch

CHF treated with digoxin, diuretics, and careful attention to nutrition

Prognosis

30-50% spontaneously close in 1st year of life

Large untreated defect may cause CHF within 6-8wk

Majority do well after closure

Post-op may have residual VSD or arrhtymias

Rare complications: right ventricular outflow obstruction or aortic insufficiency (treated surgically)