Fetal Heart Development

• The heart is mesoderm, the first organ to functionally develop.
• Endocardial cushions separate the upper, lower, left, and right chambers of the heart
• These cushions grow to divide into left and right atrioventricular canals and thin to create valves.
• The heart appears between 18-20 days.
• Two separate heart tubes are present at 20 days
• Fused heart tubes form at 21 days
• Fused heart tubes with primitive atrium and ventricles develop at 22 days.
• The heartbeat starts between 22-23 days.
• Cardiac looping, done to the right out counterclockwise, occurs from 23-28 days.
• Blood circulation begins at 28 days (4th week).
• Atrial and ventricular septation happens during week 4.
• Truncus swelling occurs during week 5.
• The umbilical cord forms during week 5.
• The umbilical cord includes two umbilical arteries that take depleted blood from the fetus to the mother.
• It also includes one umbilical vein that takes oxygenated blood from the mother to the fetus, within Wharton's jelly.
• A fully functioning final formed heart is developed by week 8.

Shunts

• The foramen ovale allows blood to flow from the right atrium to the left atrium, bypassing the right ventricle.
• The ductus arteriosus allows blood to flow from the pulmonary artery to the aorta.
• Failure of the Ductus arteriosus to close is common in premature infants.
• The Ductus venosus shunts blood from the umbilical vein to the inferior vena cava (IVC) and right atrium.
• Typically there are one or two veins in the liver.

Endocardial Cushion/Septal Defects

• Atrial Septal Defect (ASD)
• Ventricular Septal Defect (VSD)
• Tetralogy of Fallot (TOF)
• Transposition of great vessels

Circulatory System Defects

• A single umbilical artery is associated with chromosomal abnormalities and congenital defects.
• Arterial defects include: Patent Ductus Arteriosus (PDA), Coarctation of the aorta, and Double aortic arch.
• Venous defects include double or absent IVC or Superior Vena Cava (SVC).
• Patent Foramen Ovale (PFO) is also a defect.

Heart Sounds

• S1: Closure of mitral/tricuspid valves which is heard at the lower left sternal border or apex.
• S2: Closure of semilunar valves.
• Clicks are associated with valvular disease.

Shunting

• Right-to-left shunting causes cyanosis because blood bypasses the lungs and returns to the body.
• Left-to-right shunting involves a back leak of blood from the systemic to the pulmonary circulation, leading to pulmonary hypertension (HTN).

Murmurs

• Murmurs are whooshing or swishing sounds due to increased, obstructed, regurgitant or turbulent blood flow.

Seven S's

• Sensitive
• Short duration
• Soft
• Single
• Small
• Sweet
• Systolic

Cyanotic Diseases

• Truncus arteriosus: One vessel leaves the heart instead of two.
• TGA (Transposition of the Great Arteries): The great vessels are transposed.
• Tricuspid atresia: The tricuspid valve fails to form.
• TOF (Tetralogy of Fallot): Involves four defects.
• TAPVR (Total Anomalous Pulmonary Venous Return): There is no pulmonary artery.

Murmurs Details

• Still's murmur: Typically occurs in children aged 2-8 years, is a grade 1-3 murmur, and is loud in the supine position, going away when bearing down; it is the most common murmur.
• Venous hum: Common in children aged 2-5 years, is a grade 1-3 murmur, is soft and continuous and is heard while sitting down.
• Peripheral pulmonic stenosis: Occurs in newborns to 6-month-olds, is a grade 1-3 murmur, disappears in the supine position or with neck extension, radiates to the axilla and back, and is characterized by turbulent flow across pulmonary arteries.
• Pulmonary and aortic flow murmur: Can occur at any age, is a grade 1-2 murmur, can be caused by fever, dehydration, or anemia and occurs after illness symptoms.