Segmental Approach to CHD

• First need to determine cardiac location and situs

• Second determine cardiac position and orientation

   

   

   

   

   

Situs

• Situs=sidedness
• Refers to the position of the atria and viscera relative to midline (the spine)
• Situs view of protocol determines location of aorta and IVC relative to spine
• Sweeping from situs to IVC helps show that the IVC is entering the RA which is to the patient’s right
• Children with situs abnormalities will have an increased occurrence of CHD 

Situs Focus

• Abdominal viscera (internal organs within the abdominal cavity): Stomach, intestine, liver and biliary system, pancreas, spleen, kidneys, ureters, and suprarenal glands
•  Atria

Situs Solitus

• Normal position of thoracic and abdominal organs
• Heart on he left with the RA on right and LA on left with apex
• Right side: Right atrium, Tri-lobed lung, liver, gallbladder, IVC
• Left side: Left atrium, Bi-lobed lung, stomach, single spleen, aorta, cardiac apex points to the left. 

Situs Inversus

• Complete reversal of all organs
• 80% chance of right aortic arch
• Most common defect is atrioventricular discordance and transposition of great arteries

Dextrocardia

• Only the heart is reversed and all other abdominal viscera is normal
• Do not confuse with Dextroposition

Situs Ambiguos (Heterotaxi)

• Reversal of some organs but not all
• Disordered arrangement in chest and/or abdomen
• Can have several different combinations of malformations
• Incidence of CHD is 80-100% 

Heterotaxi-Bilateral Left Sidedness (Polysplenia)

•  Also known as Left Isomerism
• Bilateral Left Sidedness: both sides of the body look the way the left side looks
• organs develop more symmetrically in mirror image; two spleens(or more) -one on each side
• 2 or more spleens
• Having two spleens increase the odds of rupturing during an accident or trauma causing internal bleeding
• Both lungs have 2 lobes
• Abd Ao and IVC seen on opposite sides of midline
• More common in females
• Bilateral left atrium
• Midline liver
• Stomach in variable locations
• Interrupted IVC with azygous continuation
• Azygous vein will be seen posterior to aorta in SBC imaging as it runs along the spine. It will be seen entering in the SVC (mostly from SSN)
• 60% of cases death occurs in first year
• CHD is less common but can include: PAPVR, ASD & AVSD.　

Heterotaxi-Bilateral Right Sidedness (Asplenia)

• Also known as Right Isomerism
• Bilateral Right Sidedness
• Both lungs have 3 lobes
• No spleen: Having no spleen can increase the risk of infection (Functional Asplenia)
• Bilateral right atrium: both atria resemble right atrium
• Some hepatic veins may connect directly into RA instead of entering IVC first
• Midline Liver
• Variable stomach locations
•  Most of the time abd Ao and IVC are on the same side of spine
• More frequent in males
• Common cardiac malformations
• AV canal
• Univentricular Heart
• Transposition of great arteries
• Common atrium
• PAPVR/TAPVR

Cardiac Position

• Defining the side of the thorax that contains the most of the heart
• Levo-position to the left
• Meso-position in the middle
• Dextro-position to the right

Cardiac Orientation

• Levocardia- to the left
• Mesocardia- middle
• Dextrocardia- to the right

Types of Dextrocardia

• Mirror image dextrocardia: Apex to the right, RV anterior
• Dextrorotation dextrocardia: Apex to the right, RV Posterior
• Dextroposition dextocardia: Apex to the left, RV anterior

Atrial Situs-RA

• Thicker limbus of the foramen ovale on RA side
• Appendage is broad, triangular shaped and larger than LA appendage
• Coarse and muscular appearing due to pectinate muscle
• Coronary sinus 

Atrial Situs-LA

• Thin valve of foramen ovale on left atrium side
• Smaller and more finger-like appendage
• Smoother walls  
• No coronary sinus

Atrial Situs Solitus

• Morphologically right atrium is located anterior and to the right of the morphological left atrium

Atrial Situs Inversus

• Right atrium is on the left, still anterior to the atrium

Ventricular Situs-RV

• Thinner and not as muscular
• Tricuspid valve always follow the right ventricle
• Moderator band
• Trabeculated
• Tricuspid valve is more apically displaced than the mitral valve 

Ventricular Situs-LV

• Thick muscular wall
• Mitral valve will follow the right ventricle
• May see false tendons
• Smoother wall