11) PATHOPHYSIOLOGY OF DUCTAL DEPENDANT FOR

PULMONARY CIRCULATION CHD

Anatomy of Ductus Arteriosus

Connects the mainpulmonary artery todescending aorta.

Physiology of Ductus Arteriosus• Carries 60% of combinedvent. Output

• Diverts blood from highresistance pulmonarycirculation to low resistancedescending aorta andplacental circulation.

• PGE1 and PGI2 formedintramurally and in placentamaintain ductal patencyin fetal life

Post Natal Closure of PDA

• Functional closureIn 12 hr., contraction ofmedial smooth musclesdue to ↑ PO2 & ↓ PGE1.

• Anatomical closureIn 3 wk., replacement ofmuscle fibres with fibrosiscreating ligamentum arteriosus.

• If ductal closure causes significant decrease insystemic circulation, the condition is calledductus dependent systemic blood flow

• If ductal closure causes significant decrease inpulmonary circulation, the condition is calledductus dependent pulmonary blood flow

BEFORE BIRTH

AFTER BIRTH

DUCTUS ARTERIOSUS DEPENDENT

SYSTEMIC BLOOD FLOW

PULMONARY BLOOD FLOW

Lesions characterized by the entire or part ofthe systemic blood flow depends solely onthe patency of the ductus arteriosus.

– Coarctation of Aorta (severe)– Interrupted Aortic Arch– Hypoplastic Left Heart

Hypoxic lesions characterized by the pulmonary blood flow depends solely onthe patency of the ductus arteriosus.

– Pulmonary atresia– Severe pulmonary stenosis– TOF with severe pulmonary stenosis

DUCTUS ARTERIOSUS DEPENDENT

PULMONARY BLOOD FLOW

I) PULMONARY ATRESIA

• Congenital malformation of the pulmonary valve in which the valve orifice fails to develop.

• The valve is completely closed thereby obstructing the outflow of blood from the heart to the lungs

II) SEVERE PULMONARY STENOSIS

• Is a dynamic or fixed obstruction of flow from the right ventricle of the heart to the pulmonary artery.

• Usually due to isolated valvular obstruction (Pulmonary valve stenosis), but may be due to subvalvular or supravalvular obstruction.

III)TOF WITH SEVERE PULMONARY STENOSIS

• Large VSD• Overriding of the

aorta• **Pulmonary stenosis• RVH

***OBSTRUCTION OF PULMONARY FLOW

RVH

RIGHT ATRIAL PRESSURE ↑

SYSTEMIC CYANOSIS

PERSISTENT OPENING FORAMEN OVALE

Resistance Blood Flow

Fails

Shunting of unoxygenated blood from the right atrium into the left atrium

PDA

LEFT VENTRICLE

AORTA

PULMONARY ARTERY