Cardiac Embryology Quick Facts

• The heart develops while it is functioning.
• Development begins at 3 weeks and is complete by 7 weeks.
• The heart is the first organ to complete its development during fetal growth.
• Most defects occur during the 4th and 5th week. 

0-20 Days

•  No heart or great vessels.

20th Day

• Vascular tube: 3 parts.
• Sinus venosus.

• Cardiac loop.

• Aortic Arches

Sinus Venosus

• Forms IVC/SVC, Pulmonary veins, CS, and posterior parts of the right atrium and left atrium.

Cardiac Loop

• Forms primitive atrium, ventricles and bulbus cordis.

Aortic Arches

• Forms great vessels, carotid arteries, pulmonary arteries, ductus arteriosus.
• There are 6 arches present.
• The 3rd, 4th and 6th arches persist.
• 3rd becomes carotid.
• 4th becomes left subclavian and Ao arc.
• 6th becomes right and left pulmonary arteries. 

23rd Day

• First (ineffective) contractions.

24th Day

• Bulboventricular loop.

D-Looped

• When the heart loops anterior and to the right…..this is NORMAL.

L-Looped

• Heart folds to the left…resulting in corrected transposition or L-transposition. The ventricles and the great vessels are transposed.  RA-LV-PA and LA-RV-AO.

27th Day

• Muscular septum/cushions appear.
• Failure of Atrial or Ventricular septation results in ASDs or VSDs.

   

31st Day

• Fusion of truncus swellings.
• Forms the AV, PV, AO and PA.

• Failure of truncus to spiral results in transposition of the great arteries. D-transposition. RA-RV-AO and LA-LV-PA.

• Persistent truncus arteriosus. 

   

   

   

34th Day

• Septation: fusion of conus and endocardial cushions.
• AV canal defects (partial or complete).

40th Day

• Final cushion formation, A-V valve cusps.

   

   

43rd Day

• Complete heart.

Concordance

• Chambers and valves that are properly aligned or a normally aligned heart.

Discordance

• Refers to chambers or valves that are malaligned.

   

   

3 Points of Reference for Transposition

• The position of the arterial trunks.
• The emergence of the arterial trunks from the ventricular chambers.
• The relationship of the ventricles to the atrioventricular valves. 

Important Pediatric Echo Rule

• The A-V valves (TV/MV) almost always attach to their appropriate ventricles (MV-LV, TV-RV) and the cono-truncal valves (AV/PV) attach to their appropriate arteries (AV-AO, PV-PA).