CONGENITAL HEART DEFECTS

Question 1

What does cyanosis mean?

Answer 1

blue-purple discolouration of skin and mucous membranes caused by an elevated blood conc. of deoxygenated Hb.

Question 2

How does cyanosis occur in congenital heart disease?

Answer 2

cyanosis results from defects that allow poorly oxygenated blood from right side of heart to be shunted to the left side of the heart, bypassing the lungs

Question 3

What causes acyanosis?

Answer 3

defects that result in left to right shunting

Question 4

What is the result of large left to right shunts at atrial, septal or great vessel level?

Answer 4

Cause pulmonary artery volume and pressure to increase and can be associated with later development of pulmonary arteriolar hypertrophy and increased resistance to flow
Overtime the elevated pulmonary resistance may cause the shunt to reverse direction –> hypoxemia and cyanosis e.g. seen in Eisenmenger syndrome

Question 5

Give examples of congential heart diseases which are acyanotic.

Answer 5

ASD, VSD, PDA
Obstructive lesions: aortic stenosis (hypoplasia), pulmonary stenosis (valve, outflow branch), coarctation of the aorta, mitral stenosis

Question 6

give examples of cyanotic congenital HD

Answer 6

Tetralogy of Fallot
Transposition of great arteries
univentricular heart

Question 7

Discuss Atrial septal defects (ASD).

Answer 7

ASD is a persistent opening in the interatrial septum after birth.
ASDs relatively common (1 in 1500 live births)

Question 8

What is the most common site of an ASD?

Answer 8

region of the foramen ovale - known as ostium secundum ASD. Defect arises from inadequate formation of the septum secundum, excessive resorption of the septum primum or both

Question 9

What is a less common site for an ASD?

Answer 9

in the inferior portion of the interatrial septum - adjacent to AV valves
called the ostium primum defect. abnormality results from failure of septum primum to fuse with endocardial cushions

Question 10

What are the haemodynamic effects of an ASD?

Answer 10

increased pulmonary blood flow
RV volume overload
pulmonary hypertension is rare
eventual right heart failure

Question 11

What is a sinus venosus defect?

Answer 11

a type of atrial septal abnormality.
an ‘unroofing’ defect with absence of normal tissue between right pulmonary vein(s) and RA but often atrial septum is actually intact.
Sinus venosus defects often large and result in flow from right pulmonary veins and LA into right atrium –> similar pathophysiology of ASD

Question 12

What is PFO?

Answer 12

patent foramen ovale
found in around 20% of population
normally permanently seals by age of 6 months via fusion of atrial septa
PFP remains when fusion fails to occur

Question 13

Why is a PFO usually clinically silent?

Answer 13

because the one way valve, though not sealed remains functionally closed as LA pressure is greater than RA pressure
PFO takes significance if RA pressure becomes elevated e.g. in states of pulmonary hypertension or right heart failure, resulting in right to left intracardiac shunting
In this case deoxygenated blood passes directly into arterial circulation

Question 14

Why is the link between a PFO and a systemic embolism?

Answer 14

Patient suffering from a systemic embolism is likely to have a PFO
situation = paradoxical embolism
occurs when thrombus in systemic vein breaks loose, travels to RA, passes across PFO to LA (if right heart pressures are elevated, at least transiently e.g. a cough) –> systemic arterial circulation

Question 15

Discuss the pathophysiology of an uncomplicated ASD.

Answer 15

oxygenated blood from LA shunted to RA.
results in volume overload and enlargement of RA and RV
if RV compliance decreases over time due to excess load, the left to right shunt may lessen
if severe pulmonary vascular disease develops e.g. Eisenmenger syndrome, the shunt may reverse –> cyanosis

Question 16

What is a VSD?

Answer 16

Ventricular septal defect is an abnormal opening in the interventricular septum

Question 17

Where are VSDs located - give the most common location and others?

Answer 17

Most often located in membranous (70%) and muscular (20%) portions of septum
rare VSDs occur just below aortic valve or adjacent to AV valves

Question 18

Discuss the haemodynamic changes that accompany VSDs.

Answer 18

1. Left to right shunt
2. LV volume overload
3. pulmonary venous congestion
4. eventual pulmonary hypertension
   shunting from LV –> RV causes increased pressure and volume in pulmonary artery –> pulmonary circulation, LA and LV experience volume overload
   initially increased blood return to LV –> increased SV via Frank Starling mechanism
   eventually increased volume overload –> chamber dilatation, systolic dysfunction, and HF

Question 19

VSD leads to eventual pulmonary hypertension. What can this lead to?

Answer 19

augmented circulation through the pulmonary vasculature can cause pulmonary vascular disease as early as 2 years old.
As pulmonary vascular resistance increases –> intracardiac shunt may reverse its direction (Eisenmenger syndrome) –> cyanosis

Question 20

What are atrioventricular septal defects?

Answer 20

defects that arise from faulty development of embryonic endocardial tissues

Question 21

What is a PDA?

Answer 21

Patent ductus arteriosus
the ductus arteriosus is the vessel that connects the left pulmonary artery to the descending aorta during fetal life.
PDA results when ductus fails to close after birth –> persistent connection between the great vessels

Question 22

What causes the ductus arteriosus to constrict after birth?

Answer 22

smooth muscle of the ductus arteriosus usually constricts due to sudden rise in blood oxygen tension and a reduction in level of circulating PGs. Over next few weeks intimal prolif. and fibrosis –> permanent closure

Question 23

Discuss the pathophysiology of PDA.

Answer 23

As pulmonary resistance drops postnatally, the shunt reverse direction and blood flows from aorta into pulmonary circulation instead.
Due to Left to R shunt, the pulmonary circulation, LA and LV become volume overloaded
can lead to LV dilatation and left sided heart failure
Eisenmenger syndrome can develop causing reverse shunting

Question 24

What is congenital aortic stenosis and how is it caused?

Answer 24

most often caused by abnormal structural development of the valve leaflets
most common abnormality is coarctation of the aorta
The aortic valve in congenital AS usual have a bicuspid leaflet structure instead of a tricuspid leaflet config, causing an eccentric stenotic opening through which blood is ejected
bicuspid valves often become progressively stenotic over many years as the leaflets progressively fibrose and calcify –> common cause of AS in adults

Question 25

discuss the pathophysiology in congenital aortic stenosis

Answer 25

as the valvular orifice is significantly narrowed, LV systolic pressure must increase to pump blood across the valve into the aorta
in response to increased pressure load –> LV hypertrophies
the high velocity jet of blood that passes through the stenotic valve may impact the proximal aortic wall and contribute to dilatation of the vessel

Question 26

What is coarctation of the aorta?

Answer 26

consists of a discrete narrowing of the aortic lumen
most common associated cardiac abnormality is a bicuspid aortic valve
aortic coarctation often occurs in patients with Turner syndryme (45,XO)
majority of coarctations are next to the ductus arteriosus

Question 27

Discuss the pathophysiology of coarctation of the aorta.

Answer 27

due to aortic narrowing in coarctation, the LV faces an increased afterload
blood flow to head and upper extremities is preserved because the vessels supplying these areas usually branch off the aorta proximal to the obstruction but blow to descending aorta and lower extremities may be diminished

Question 28

What are possible compensatory alterations that can occur if aortic coarctation is not corrected?

Answer 28

1. development of LV hypertrophy
2. dilatation of collateral blood vessels from the intercostal arteries that bypass the coarctation and provide blood to more distal descending aorta
   eventually collateral vessels enlarge and can erode undersurface of ribs

Question 29

What are the two main categories of congenital heart lesions?

Answer 29

cyanotic and acyanotic