Cardiac Embryology

Adel Mohamad Alansary, MDAss. Prof. Anesthesiology and Critical Care

Ain Shams University

The beginning

Function of each Layer

Endocardium: Endothelial lining ,Connective tissue precursor (Valves and fibrous skeleton).

 Myocardium: Myocytes, Conduction system (Purkinje fibres),Myoendocrine cells (Atrial Natriuretic Factor production)

Epicardium Coronary vessel precursors, Visceral pericardial lining.

The beginning Two lateral extensions of

cardiac tissue become hollowed out to form a pair of endothelial tubes, which soon fuse to form the primitive cardiac tube.

Paired veins from the trunk (the cardinal system), liver, yolk sac and placenta enter the heart tube from below and a series of arterial arches emerge from the upper end.

HEART TUBE

the sinus venosus

the atrium

the ventricle

bulbus cordis

arterial trunk

Looping

Looping

Looping

• The fold of the loop is principally at the junction of bulbus cordis and ventricle. Note in panel C that the two end up side by side.

Formation of the Cardiac Loop

28 days

• Atrium grows dorsally to the left• Ventricle & bulbus cordis grows ventrally & to the right

30 days

At the end of the loop formation

normal d-loop l-loop

Abnormalities of Heart Position

Dextrocardia : cardiac loop to the left.= Heart in the right thorax associated with situs inversus (transposition of the viscera)

Ectopia cordis= Heart on the surface of chest caused by failure to close the midline

ENDOCARDIAL CUSION FUSION

Formation of Ventricular Septum1. Growth of Endocardial cushions

Septum Formation in A-V Canal

Valve formation

Valve Atresia

Tricuspid Atresia

ATRIAL SEPTUM

Interatrial Septum

Interatrial Septum

ASD

Secundum type defects are observed in 80% of cases. These are characterized by defects involving the foramen ovale and (usually) a defect in the septum primum.

Sinus venosus defects are usually positioned near the entrance of the superior vena cava. These are generally associated with anomalous entry of the right superior pulmonary vein.

ASD

Ostium primum defects are very similar to defects caused by failure of endocardial cushion fusion.

Rarely, complete agenesis of the septum occurs, giving a common atrium.

VENTRICULAR SEPTUM

Interventricular Septum

VSD

Type I defects are positioned in the infundibulum of the right ventricle, caudal to the pulmonary valve. These arise from defects in the formation of the bulbus cordis and truncus arteriosus. These are also referred to as supracristal, conal or infundibular VSD.

VSD

Type II defects occur in the membranous portion of the septum, and are the most commonly observed defects. These are also referred to as paramembranous VSD.

VSD

Type III defects are found in close proximity to the tricuspid valve, within the inlet of the right ventricle. These are thought to arise from defects in the partitioning of the AV canal by the endocardial cushions. Also identified as atrioventricular canal defects or inlet defects.

VSD

Type IV defects are present in the muscular portion of the interventricular septum. These can be single or multiple, showing extremely irregular borders (variable in many planes). Type IV defects are not easily visualized or repaired.

GREAT ARTERIES

Arterial Trunk This structure does truly septate,but

embryologically it is a simple coronal division in its embryonic straight position.

The septation extends upwards from the valves to end just beyond the origin of the paired sixth aortic arches, where it seals off against the posterior truncal wall.

As the sixth arch vessels are destined to be the branch pulmonary arteries, the posterior channel is now the main pulmonary artery. The anterior channel is the aorta.

RPA = right pulmonary arteryLPA = left pulmonary arteryAPS = aortopulmonary (truncal) septumRVO = RV outflowLVO = LV outflow

And so now you can compare the flow scheme on the left with the more lifelike imageon the right

Fate of Truncus Arteriosus & Aortic Sac

FateStructureLef t Right

TruncusArteriosus

Root ofPulmonary Trunk(proximal)

Root of Aorta(proximal)

Aortic sac Brachiocephalicartery

Arch of Aorta(proximal)

Fate of Aortic ArchesFateStructure

Right Left

1st Aortic arches Maxillary a. Maxillary a.

2nd Aortic arches Hyoid a. &Stapedial a.

Hyoid a. &Stapedial a.

3rd Aortic arches 1. Common carotida.

2. I nternal carotida. (proximal)

3. External carotida.

1. Common carotida.

2. I nternal carotida. (proximal)

3. External carotida.

FateStructure

Right Left

4th Aortic arches Subclavian a. Arch of Aorta &Subclavian a.

5th Aortic arches - -

6th Aortic arches Right Pulmonarya.

Ductusarteriosus & LeftPulmonary a.

Fate of Aortic Arches

Tetralogy of Fallot

Patent Ductus Arteriosus

Questions

the truncal septum fails to fuse with the septal crest?

- perimembraneous VSD the truncal septum is deviated to the PA side? - tetralogy of Fallot the truncal septum fails to develop? - truncus arteriosus the ventricular septum fails to reach the AV valve? - AV septal defects

Questions

the arterial trunk stays over the RV but does divide?

- double outlet RV the aortic valve pushes up and right instead of

the pulmonary? - transposition of the great vessels the ventricles fail to centralise over the AV valve - double inlet left ventricle (commonest

form of single ventricle.