Development of the Heart and Congenital Heart diseases

SESSION 6

Development of the heart• Week 3• Cardiogenic region appears

– Overlying mesoderm differentiate into myoblasts and blood islands

– Horseshoe region at cephalic end

• Lateral Folding:– Brings the two endocardial tubes together in the

midline– Primitive heart tube

• Cephalocaudal folding: – Brings tube into the thoracic region

Primitive heart tube

Looping• Day 23 – day 28

• Cephalic portion• Ventrally• Caudally• Right

• Caudal portion

• Dorsally• Cranially• Left

What does looping achieve?

• Primordium of RV closest to outflow tract • Primordium of LV closest to inflow tract • Inflow is dorsal to outflow

• Forms transverse pericardial sinus

Atrial Septation• Two septums grow down

towards the endocardial cushions

• The first is the septum primum• Ostium primum (temporary

gap between septum and endocardial cushion)

• Ostium secundum (hole in the septum primum)

• The second is the septum secundum• Foramen ovale (hole in

septum secundum)

Ventricular septation• 2 components:

• Muscular portion• Membranous portion

• Muscular portion• Forms most of the septum• Grows upwards

• Membranous portion• Connective tissue • Grows down from endocardial

cushions

• They meet and fuse

• Defects usually occurs in the membranous parts.

Septation of the outflow tracts• Endocardial cushions appear in

Truncus arteriosus– Requires neurocrest cells migrating into

the heart

• Staggered appearance • They twist around each other

as they grow• Forming a spiral septum

Arches of the aorta

• Arterial systems develop from bilaterally symmetrical systems of arched vessels • 5 arches – 1,2,3,4,6 • 5th one regresses

• 4th Arch• RIGHT arch right subclavian artery• LEFT arch arch of the aorta

• 6th Arch • RIGHT arch pulmonary artery• LEFT arch pulmonary artery & ductus arteriosus

Recurrent Laryngeal Nerve • Each arch of the aorta has a corresponding nerve

• 6th arch recurrent laryngeal nerve

• Laryngeal nerve shifts caudally into thorax • Left larygneal nerve descends to T5- hooks around ductus

arteriosus • Right laryngeal nerve descends to T1/T2

• Laryngeal nerves both loop back up to innervate the larynx

Fetal Circulation

Fetus v. Baby Fetus Baby

Foramen ovale Fossa ovalis

Ductus arteriosus Ligamentum arteriosum

Ductus venosus Ligamentum venosum

Umbilical vein Ligamentum teres

Congenital Heart Diseases

Pressures in the heart

0-8mmHg

1-10mmHg

Diastole: 1-10mmHgSystole: 100-140mmHg

Diastole: 0-8mmHgSystole: 15-30mmHg

Pulmonary ArteryDiastole: 4-12mmHgSystole: 15-30mmHg

AortaDiastole: 60-90mmHgSystole: 100-140mmHg

Congenital Heart Diseases

• Atrial Septal Defects

• Ventricular Septal Defects

• Coarctation of the aorta

• Tetralogy of Fallot

• Transposition of the great vessels

Left to right shunt• Blood in left heart enters the right heart

• Requires a hole between right and left heart• The right heart is at lower pressure than left • If there is an opening blood flows from left to right

• Acyanotic

• Examples• Atrial Septal Defect• Ventricular Septal Defect• Patent Ductus Arteriosus

Atrial Septal Defect • Left to right shunt

• Hole atrial septum • Blood move from the left atria to the right atria

• Caused by failure of closure of:• foramen ovale• Ostium secundum• Ostium primum

• Leads to:• Pulmonary hypertension • Right ventricle overload • RIGHT HEART FAILURE

Ventricular Septal Defect• Left to right shunt

– Hole in intraventricular septum – Blood moves from left ventricle into

the right ventricle

• Caused by: failure of the membranous part of the ventricular septum to develop

• Leads to:– Pulmonary hypertension– Right ventricular hypertrophy– Pulmonary venous congestion– Dyspnoea – LEFT HEART FAILURE

Coarctation of the aorta

• Narrowing of the aorta usually occurring near the attachment of the ductus arteriosus

• Leads to:– volume overload in the heart – congestive heart failure

• Signs and symptoms:– Tachypnoea– Dyspnoea– RADIAL- RADIAL DELAY

Right to left shunt • Blood bypassing the lungs• This requires a Hole and a Distal Obstruction.

– The right heart is usually at a lower pressure than the left– However a distal obstruction in the right heart pressure in right heart

> left heart – Leading to blood flowing from the left to the right

• Cyanosis- Blue discolouration arising due to the presence of deoxygenated

blood in the arteries

• Examples– Tetralogy of Fallot

Tetralogy of fallot1. Overriding aorta

2. Ventricular septal defect (HOLE)

3. Pulmonary stenosis (DISTAL OBSTRUCTION)

4. Right ventricular hypertrophy

Transposition of the great vessels• The aorta and pulmonary artery

are reversed– RVaorta– LV pulmonary artery

• Not viable unless the 2 circuits communicate via: – patent ductus arteriosus– patent foramen ovale– VSD or ASD.

• Allows adequate mixing of blood to:– deliver enough oxygenated blood

to the body

• Treat– Englarging the septal defect and

increasing the mixing of blood