CHD

Question 1

Define congenital heart disease (CHD). At what stage of embryonic development do most defects arise?

Answer 1

CHD is a structural abnormality of the heart or great vessels present at birth, due to faulty embryogenesis. Most defects originate during weeks 3–8 of gestation.

Question 2

How common are congenital heart diseases in live births, and what is their contribution to infant mortality?

Answer 2

They occur in about 1% of live births and are the most common type of congenital anomaly, a leading cause of infant mortality in the first year.

Question 3

What is the difference between a left-to-right shunt and a right-to-left shunt in congenital heart disease?

Answer 3

L→R shunts (ASD, VSD, PDA) increase pulmonary blood flow, are acyanotic initially but can progress to Eisenmenger. R→L shunts (TOF, TGA, truncus) cause early cyanosis from systemic desaturation.

Question 4

Explain the development of cyanosis in right-to-left shunts and why clubbing/polycythemia occur.

Answer 4

Deoxygenated blood bypasses lungs into systemic circulation. Chronic hypoxemia stimulates erythropoietin → polycythemia. Hypoxia drives clubbing via distal growth factor signaling.

Question 5

Define Eisenmenger syndrome. What histopathological changes in pulmonary vasculature make this reversal irreversible?

Answer 5

Reversal of L→R shunt to R→L due to pulmonary hypertension. Pulmonary vessels develop medial hypertrophy, intimal proliferation, and obliterative sclerosis, making reversal irreversible.

Question 6

What are the systemic complications of long-standing cyanosis in CHD?

Answer 6

Polycythemia, clubbing, paradoxical emboli, brain abscesses, hyperviscosity, delayed growth and development.

Question 7

Why do some congenital heart diseases predispose to paradoxical embolism?

Answer 7

Because shunts (ASD, VSD, PDA with reversal) permit venous emboli to bypass pulmonary filter and reach systemic arteries → stroke, infarcts.

Question 8

List the environmental and genetic risk factors associated with congenital heart defects.

Answer 8

Genetic: Down (ASD, AVSD), DiGeorge (truncus, interrupted arch), Turner (coarctation). Environmental: maternal rubella (PDA), diabetes (TGA), alcohol (septal defects), teratogens (lithium, retinoic acid).

Question 9

How does maternal rubella infection specifically lead to PDA?

Answer 9

Rubella virus damages endothelium and alters prostaglandin signaling, preventing closure of ductus arteriosus after birth.

Question 10

Why does maternal diabetes predispose to transposition of the great arteries?

Answer 10

Hyperglycemia disrupts cardiac looping and outflow tract development, predisposing to malposition such as TGA.

Question 11

What are the three main types of atrial septal defects (ASD) and their embryological origins?

Answer 11

Secundum (foramen ovale region, most common), Primum (endocardial cushion defect, often with AV valve abnormalities), Sinus venosus (near SVC, with anomalous pulmonary venous return).

Question 12

Which ASD is most commonly associated with Down syndrome?

Answer 12

Primum ASD, often part of atrioventricular septal defects.

Question 13

Why are ASDs usually asymptomatic until adulthood?

Answer 13

Because atrial pressures are low, the L→R shunt is small and well tolerated for years until chronic volume overload develops.

Question 14

What auscultatory finding is classically associated with ASDs, and what is its pathophysiological basis?

Answer 14

Fixed, wide splitting of S2 due to prolonged RV systole from chronic volume overload and delayed pulmonic closure regardless of respiration.

Question 15

Why is paradoxical embolism a potential complication of ASDs?

Answer 15

Because transient rises in right atrial pressure can direct venous emboli across the defect into systemic circulation.

Question 16

Contrast the shunt magnitude in ASD versus VSD in early life.

Answer 16

VSDs create larger shunts due to higher LV–RV pressure gradient; ASDs generally produce smaller shunts.

Question 17

Which type of VSD (membranous vs muscular) is more common, and why?

Answer 17

Membranous VSD is most common (~90%) due to failure of membranous septum closure.

Question 18

Describe the hemodynamic consequences of a small restrictive VSD versus a large nonrestrictive VSD.

Answer 18

Small: loud murmur, minimal hemodynamic effect. Large: significant L→R shunt, pulmonary hypertension, RV hypertrophy, Eisenmenger risk.

Question 19

What pulmonary vascular changes occur in long-standing untreated large VSDs?

Answer 19

Medial hypertrophy, intimal thickening, and plexiform lesions of pulmonary arterioles → irreversible pulmonary hypertension.

Question 20

Why are VSDs more likely than ASDs to close spontaneously?

Answer 20

Because many are muscular and can close as myocardium grows and contracts.

Question 21

How does a VSD predispose to infective endocarditis, and which site is most commonly affected?

Answer 21

Turbulent jets injure endocardium, seeding bacteria; lesions usually form in RV outflow tract on low-pressure side of the defect.

Question 22

In autopsy, what changes would you see in the lungs of a patient with long-standing large VSD?

Answer 22

Severe pulmonary hypertension, vascular sclerosis, and advanced plexiform pulmonary arteriopathy.

Question 23

Describe the normal embryologic role of the ductus arteriosus and the physiological mechanism of its closure after birth.

Answer 23

Ductus diverts blood from PA to aorta in fetus. Closure occurs postnatally via increased PaO2 and decreased prostaglandins (functional then anatomic closure).

Question 24

Which maternal infection is strongly associated with PDA, and what is the proposed mechanism?

Answer 24

Congenital rubella, which interferes with ductal closure by endothelial and prostaglandin disruption.

Question 25

Explain why a PDA produces a continuous 'machinery-like' murmur on auscultation.

Answer 25

Because the aortic–pulmonary pressure gradient persists in both systole and diastole, producing continuous flow.

Question 26

How can a PDA initially cause volume overload in the left atrium and ventricle?

Answer 26

L→R shunt increases pulmonary venous return → LA dilation and LV volume overload.

Question 27

Why can a PDA become a right-to-left shunt in Eisenmenger physiology, and what clinical sign confirms this switch?

Answer 27

Pulmonary vascular resistance > systemic → reversed flow from PA to aorta, causing lower-extremity cyanosis (differential cyanosis).

Question 28

Explain the pharmacological use of indomethacin in PDA closure.

Answer 28

Indomethacin inhibits prostaglandin synthesis, promoting ductal closure.

Question 29

When is prostaglandin E1 infusion used in relation to PDA?

Answer 29

To maintain ductal patency in duct-dependent lesions (e.g., TGA, coarctation) until surgical repair.

Question 30

What are the four cardinal features of Tetralogy of Fallot (TOF)?

Answer 30

VSD, RV outflow obstruction (subpulmonic stenosis), overriding aorta, RV hypertrophy.

Question 31

What embryologic abnormality causes TOF?

Answer 31

Anterior and cephalad displacement of the infundibular septum.

Question 32

How does severity of RV outflow obstruction influence cyanosis in TOF?

Answer 32

Mild obstruction → L→R shunt, acyanotic. Severe obstruction → R→L shunt with cyanosis.

Question 33

Why do children with TOF squat during 'tet spells'?

Answer 33

Squatting increases systemic vascular resistance, reducing R→L shunt and improving oxygenation.