Development of the Heart By Dr Manah Chandra Changmai MBBS MS
Appears in the middle of third week. Mesenchymal cells in the splanchnic mesoderm proliferate and form isolated cell clusters known as angiogenic clusters. Angiogenic clusters at first located in the lateral end but rapidly spread to cephalic end. Angiogenic clusters .
The angiogenic clusters acquire lumen. They unite to form a horseshoe-shaped plexus of small blood vessels. The anterior portion of the plexus is called cardiogenic area. The intraembryonic coleomic cavity located over the plexus later form pericardial cavity. Formation of endocardial heart tubes
After formation of neural tube and brain vesicles CNS grows rapidly in cephalic direction. It finally extends over the cardiogenic area and future pericardial cavity. Finally,the procordal plate and the cardiogenic plate are pulled forward. The cardiogenic plate and pericardial cavity become located ventrally and caudally.
The embryo folds in cephalocaudal and transversely bringing the two heart tubes closer. The two endocardial heart tube fuse in cephalo-caudal direction. The tube is attached to the dorsal side of the pericardial cavity by dorsal mesocardium.
The mesoderm adjacent to the endocardial tube form epimyocardial mantle. The epimyocardial mantle seperated from endocardial tube by cardiac jelly. Tube consists of endocardium,myocardium and epicardium.
Formation of cardiac loop Heart tube elongates and bends. The cepalic portion: bends in ventral and caudal direction to the right. The caudal portion: shifts in a dorsocranial direction and to the left.The bendings creates a cardiac loop.
Local expansion become visible after cardiac loop is formed. The atrial portion lie outside the pericardial cavity, later incorporated inside the cavity. The atrioventricular junction remains narrow and form atrioventricular canal. The bulbus cordis is narrow except its proximal third which later forms trabeculated part of right ventricle. The distal part of bulbus called the truncus arteriosus. The conus cordis forms the outflow tract of both ventricles.
The atrial portion of bulbus remain temporarily smooth walled. The proximal portion of the bulbus form the primitive right ventricle. The primitive ventricle becomes trabeculated and form the primitive left ventricle.
The left common cardinal vein disappear at 10 th week.
The remaining part in the left horn of sinus venosus is
The oblique vein of left atrium.
The coronary sinus.
Due to left to right shunt the right sinus horn and veins
The right horn is the only communication between sinus
venosus and the atrium.
The right horn is incoperated into right atrium to form
the smooth part of right atrium.
Development of sinus venosus
The entrance the sinoatrial orifice is flanked On each side by right and left venous valves. The superior portion of right venous valve disappear . The inferior part form two parts: a.The valve of inferior vena cava. b. The valve of coronary sinus. The crista terminalis originates from right sinus horn.
Endocardial cushions • Dorsal & ventral swellings • Fuse, dividing the single AV canal into paired canals • Involved in formation of interatrial & interventricular septa • Derived from neural crest • Involved in many CHDs Partitioning
• Septum primum grows from atrial roof toward endocardial cushions • Foramen primum: shunt that closes Atrial Partitioning I
• Foramen secundum: perforates septum primum, allowing shunt. • Septum secundum grows down,overlapping foramen secundum. Atrial Partitioning I
• Septum secundum grows down,overlapping foramen secundum • Foramen ovale : between septum primum & septum secundum Atrial Partitioning II
• Remaining portion of septum primum forms valve of foramen ovale. Atrial Partitioning II
Fetus • right side high pressure (high pulmonary resistance, etc.) • well oxygenated blood streams through foramen ovale. • valve of foramen ovale closes with left atrial contraction. After birth • right side low pressure (low pulmonary resistance). • valve remains closed (physiological closure). • valve eventually fuses (anatomical closure): fossa ovalis. Atrial Partitioning III
• Closes in week 7: not part of fetal circulation. • Muscular IV septum grows from floor. Ventricular Partitioning
• Membranous IV septum forms from endocardial cushions and bulbar ridges • Closure of membranous IV is associated with partitioning of truncus arteriosus Ventricular Partitioning
• Continuous set of ridges in bulbus cordis(bulbar ridges) and truncus arteriosus (truncal ridges). • Grow toward each other, spiraling 180º. Partitioning of Truncus Arteriosus
• Fuse to form spiraling aorticopulmonaryseptum, dividing aorta & pulmonary trunk • Bulbar ridges involved in formation of IV septum • Bulbar & truncal ridges derived from neural crest cells—clinical implications Partitioning of Truncus Arteriosus
• Membranous (= perimembranous, conoventricular) VSD. • Most common CHD (males>females) • Endocardial cushions & bulbar ridges fail to fuse with musc. septum • Muscular VSD • In muscular IV septum • “ Swiss cheese” VSD • Supracristal VSD • Least common Ventricular Septal Defects (VSD)
• (Ostium) Secundum ASDs • Most common ASD (females>males) • Usually due to problems with septum primum (perforated or too short), but sometimes septum secundum or both septa • AV septal defect (AV canal) • Endocardial cushion problems so that septum primum never fuses with cushion tissue • Patent foramen (ostium) primum • Valve defects • Sometimes no fusion of endocardial cushions: AV septal defect • 20% of Downs patients • Sinus venosus ASDs: very rare Atrial Septal Defects (ASD)
• 5-7% of all CHDs Four co-occurring heart defects • Pulmonary stenosis • Ventricular septal defect • Overriding aorta (dextroposition) • Right ventricular hypertrophy • Asymmetrical fusion of bulbar & truncal ridges Tetralogy of Fallot