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 5 th one regresses 4 th Arch RIGHT arch  right subclavian artery LEFT arch  arch of the aorta 6 th Arch RIGHT arch  pulmonary artery LEFT arch  pulmonary artery & ductus arteriosus

Recurrent Laryngeal Nerve Each arch of the aorta has a corresponding nerve 6 th 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 FetusBaby Foramen ovaleFossa ovalis Ductus arteriosusLigamentum arteriosum Ductus venosusLigamentum venosum Umbilical veinLigamentum teres

Congenital Heart Diseases

Pressures in the heart 0-8mmHg 1-10mmHg Diastole: 1-10mmHg Systole: mmHg Diastole: 0-8mmHg Systole: 15-30mmHg Pulmonary Artery Diastole: 4-12mmHg Systole: 15-30mmHg Aorta Diastole: 60-90mmHg Systole: mmHg

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 fallot 1.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 – RV  aorta – 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