Left-to-right Shunts

These shunts due to not cause cyanosis at birth, as the pressure in the left circulation is more than the right

– The increased pressure in the pulmonary circulation leads to remodeling and pulmonary hypertension

– This causes right ventricular hypertrophy and will eventually cause a reversal to a right-to-left shunt

– This is called Eisenmenger’s syndrome which occurs about 10-15 years

– This is a progressive condition which will lead to heart failure usually at the age of 40 if left untreated 

Atrial septal defect (ASD)

This is a defect which leads a residual hole between the two atria.

– A failure to close the flaps leaves a patent foramen ovale.  In the neonatal heart, pressure is higher in the LA than RA, so blood is shunted from left-to right atrium

The atrial septal defect exists in two main types:

i) Ostium primum – This is a defect at the bottom of the atrial septum

– Occurs when septum primum does not grow all the way down

ii) Ostium secundum – This is a defect in the centre of the atrial septum which is more common

– Occurs when the septum secundum does not grow enough during development

Symptoms:

– Most are asymptomatic and go undetected for many years

– Increases the risk of chest infections

– Gives fixed splitting of S2 ( due to a delay in the closing of the pulmonary valve)

– Can cause an ejection systolic murmur loudest at upper left sternal edge (due to increased flow across the P valve)

Complications:

– Paradoxical emboli –> Embolism from the venous system passes through foramen ovale to the left side of the heart entering the systemic circulation and causing a stroke

Diagnosis:

– Echocardiogram

– ECG –> this can show right bundle branch block with axis deviation

– CXR –> may show cardiomegaly and enlarged pulmonary arteries

Management:

– Small ASDs may close on their own so many only require monitoring

– ASDs large enough to cause symptoms or right ventricular dysfunction will require surgery or cardiac catherization

Ventricular septal defect (VSD)

This is a hole which connects the ventricles which is the most common congenital heart defect.

– VSD can also be acquired and is a complication of myocardial infarction

– During development, a muscular ridge of tissue grows upwards from the apex

– This fuses with a thinner membranous region coming down from the endocardial cushion

– If they don’t fuse properly, a gap remains leaving a defective ventricular septum

– In the neonatal heart, pressure is higher in the Left ventricle than the right ventricle

– Therefore, VSDs result in shunting of blood from the left to the right

Symptoms:

If small VSD:

– Most of these are symptomatic

– Pansystolic murmur at lower left sternal edge (loud murmur implies smaller defect) with a quiet P2

If large VSD:

– Gives symptoms of heart failure (breathless, poor growth)

– Predisposes to recurrent chest infections

– Gives either no murmur or soft pansystolic murmur with a loud P2

– The louder the murmur is, the narrower the hole and less severe the disease

– If left untreated will progress to Eisenmenger’s syndrome

Diagnosis:

Echocardiogram

Management:

Medical management of heart failure followed by surgery to close hole if large

Patent ductus arteriosus (PDA)

This is a condition which is defined as a failure of the duct to close by a few days after birth 1

– During embryological development, the ductus arteriosus allows blood to flow from pulmonary artery to aorta bypassing lungs.

– In term infants, in normally closes shortly after birth due to increased pulmonary flow (this enhances clearance of maternal prostaglandins which maintain duct patency)

– But a failure of the ductus arteriosus to close results in left-to-right shunt between the aorta and the pulmonary artery, as the pressure is higher in the aorta than pulmonary artery

– It is associated with prematurity and maternal rubella infection

Symptoms:

– Asymptomatic at birth with no cyanosis

– However, if left untreated can lead to Eisenmenger syndrome and heart failure later in life

– Continuous ‘machine-like’ murmur described as “rolling-thunder” with a left sub-clavicular thrill

– Wide pulse pressure

– Heaving apex beat

– Poor growth

Diagnosis:

Echocardiography

Management:

– Indomethacin –> inhibits prostaglandin E synthesis causing closure of the ductus arteriosus

– If very large or persistent, requires surgical repair