Congenital Heart Defects

When is the most sensitive period for CV development?

3-6 weeks

When does circulation begin?

By the end of the 4th week

When does septation begin?

33-37 days

What happens at 43 days?

The fetal heart is developed into complete complex structure

Discuss early forms of heart tubes

They are formed early in embryonic development

They lie parallel to each other and towards the head.

A single heart tube will consist of external myocardial mantle and an internal mantle.

Layers of the primitive heart tube

Endocardium-inner lining of tube

Cardiac jelly- gelatin like middle layer (helps cushion and shape)

myocardium- muscular outer layer that becomes heart muscle

When does the heart begin to beat?

22-23 days

Looping step-when and what occurs?

By day 23- tube is too long so it begins to bend to a “U” shape.

By day 28- the loop points to the right

Why is the looping step important?

It places the atria behind and above the ventricle. There are still no walls and no valves.

What is important about the atrioventricular canal in embryonic stage?

The atrium connects to the ventricle through 1 passage called the atrioventricular canal. Later this AV canal splits into 2 passages- one for the tricuspid valve, one for the mitral valve

Sinus venosus

Consists of 2 horns which will eventually contribute to formation of the SVC, IVS, CS and the posterior wall of the atria. Distal portion of left horn usually dissipates.

Primitive atrium

Develops into the right and left atrium

Primitive ventricle

Develops into left ventricle

Bulbus cordis

Develops into right ventricle

Truncus arteriosus

Develops into aorta and pulmonic arches

When does septation of the chambers occur?

During the 4th and 5th weeks of fetal development, the division of 4 chambers occurs

What are steps of septation of the atria?

1.Septum primum forms and grows downward leaving a hole called ostium primum.

2. Septum primum grows and closes ostium primum.small holes open higher up and these form a new opening called ostium secundum which keeps blood flowing between atria.

3. 2nd thicker wall called septum secundum grows down to 1st wall. Leaves an oval shaped hole, called foramen ovale.

4. Lower edge of septum primum now act like a flap. Important to fetal life bc allows blood to bypass the lungs which aren’t working yet.

What changes after birth in the heart?

The pressure in LA becomes higher than in the right bc lungs are working now. This pressure pushes the flap of septum primum against septum secundum closing the foremen ovale. Eventually this seals and becomes fossa ovalis.

Septation of atrioventricular canal?

1. Endocardial cushions form. Small swellings of soft tissue forms inside early AV canals

2. Cells move in and change- cells from endocardium move into these cushions and become stronger

3. Cushions grow and meet- top, bottom and side cushions grow and fuse together

4. Results in 2 canals- single canal is now 2 and will become tricuspid and mitral valves.

Septation of ventricles and outflow tracts

1. Starting point (end of week 4)- primitive ventricles grow and a muscular ridge grows (primitive IVS)

2. Interventricular foramen- muscular ridge doesn’t go all the way up and allows blood to move freely between ventricles.

3. Closing the gap- end of week 7, new tissues grow and fuse with muscular septum and close to separate the ventricles

Aortic arch formation?

At 4 weeks. 6 pairs of aortic arches not all the same time and their functions vary

Aortic arch formation and functions

3rd- becomes original of ICA

4th- becomes aortic arch

6th- becomes origin of pulmonary arteries

1st, 2nd, 5th- gets absorbed

When does Aorticopulmonary septation of the truncus arteriosus into aorta and pulmonary artery occur?

In the 5th week of development

How does the aorta and pulmonary artery form?

1. Special cells from neural crest to create 2 tissue ridges and fuse in the middle,

2. Spiral twist- as they fuse the ridges twist in 180’ spiral (aka aorticopulmonary septum)

3. Septum splits the single tube into 2 separate. Pulmonary artery connects to RV. Aorta connects to LV.

When do the semilunar valves form?

Just before aorticopulmonary septum is finished. Blood flow and programmed cell death sculpt these lumps into 3 thin cusps

When do atrioventricular valves form?

After the endocardial cushions split the AV canal into right and left sides, more tissues grow around each opening.

Fetal heart circulation- full blood flow

1. Umbilical vein- vein brings oxygenated blood to fetus. Arteries in fetus carry deoxygenated blood.

2. ductus venosus (1st fetal shunt)- avoiding flow through the liver

3. Ivc

4. Ra- Oxygen is increased- flow directed to foramen ovale by eustachian valve

5. Foramen ovale-(2nd fetal shunt)- right to left follows the MV to LV to aorta

end of 1st cardiac structure flow

6. TV- some IVC blood goes into RA and follow the regular path with SVC and CS through TV

7. RV

8. PA

9. MPA

10. Fetal lungs are collapsed. Only very little blood goes to pulmonary beds. Blood goes out LA-MV-LV-aorta. Most gets shunted out.

11. Ductus arteriosus-(3rd fetal shunt)- right to left bypass the lungs and goes into descending aorta

12. Umbilical arteries carry deoxygenated blood back to placenta to begin the process again

Quick version- fetal heart blood circulation

1. Umbilical vein- ducted venosus- IVC- RA- foramen ovale-( LA-MV-LV-aorta)

   some will go….

2. IVC,SVC and CS- RA-TV-RV-PV-MPA-ductus arteriosus- aorta

How does pressure changes in the heart change?

Blood from lungs increase pressure in LA. At the same time, cutting the cord lowers blood returning to the RA. Resulting in LA pressure becoming higher than the right arterial pressure and this pushes the foramen ovale shut.

Fetal shunt- foramen ovale becomes?

Fossa ovalis

Fetal shunt- ductus arteriosus becomes?

Ligamentum arteriosum. Forms the aorta and pulmonary artery

Fetal shunt- ductus venosus becomes?

Ligamentum venosum. After birth it constricts and blood entering the liver will pass through hepatics.

Congenital defects- describe atrial septal defects

1. Ostium primum- lower part of septum by AV valves

2. Ostium secundum- central part of septum

3. Sinus venosus- superior interarterial septum

Congentital heart defect- describe ventricular septal defects

1. Perimembraneous- most common, membranous part of IVS by AOV

2. Inlet- by TV

3. Subarterial- below AOV and PV

4. Muscular- can have many in muscular septum

Congentital heart defects- patent ductus arteriosus

Blood leaving the aorta is shunted back to the pulmonary artery traveling to the LA. Can cause left ventricular volume overload.

Congentital heart defect- Ebstein’s Anomaly

Tricuspid leaflets are displaced apocalyptic one or more leaflets.

RV becomes smaller. ARV- atrialized RV. FRV- functional RV.

Congenital defect- tetralogy of Fallot

Combination of 4 related heart defects that occur together:

VSD, overriding aorta, pulmonary stenosis, right ventricular hypertrophy

Congenital defect- Eisenmenger’s syndrome

Starts as a small ASD/VSD that’s undetected. Overtime shunt may cause volume increases in the right side. Increased right side pressure leads to pulmonary hypertension. This changes pressures from left to right-right to left so systemic circulation will have deoxygenated blood.

What does abnormal vasculature include?

Aortic stenosis

Pulmonic stenosis

Patent foramen ovale- left to right shunting; can cause right side enlargement

Abnormal vasculature coarction of aorta

Narrowing of the aorta; near origin of left subclavian artery; result of shelf like tissue fold (preductal or postductal)

Transposition of great arteries

The aorta originates from RV and the pulmonary artery originates from the LV.