Card Embryo

Question 1

When does the heart begin to develop?

Answer 1

18-19 days after conception

Question 2

What does the heart develop from?

Answer 2

The embryologic mesoderm

Question 3

What is the Carnegie Stage System?

Answer 3

Carnegie stages are a system used by embryologists to describe the maturity of an embryo across species

Question 4

What Carnegie Stage does cardiac development occur?

Answer 4

Between Carnegie Stage 8 and 23 (human days post-conception 17-19 and 56-60)

Question 5

What is the cardiogenic plate?

Answer 5

Develops from the mesodermal germ layer at the cranial pole of the embryo and develops into the myocardium and endocardium

Question 6

What is the cardiogenic cord?

Answer 6

Develops from the cardiogenic plate; the 2 cardiogenic cords develop into an internal lumen (endocardial tube)

Question 7

What is the endocardial tube?

Answer 7

Forms from the cardiogenic cords; they fuse to form the primitive heart tube

Question 8

When does the primitive heart tube demonstrate regionalization?

Answer 8

DPC 22-23 (dates post conception)

Question 9

Describe the primitive heart tube from venous to arterial pole

Answer 9

Sinus venosus (posterior RA, sinus node, coronary sinus) –> Primitive atrium (anterior RA and LA and auricles) –> Primitive ventricle (LV) –> Bulbus Cordis (RV) –> Truncus Arteriosus (ascending aorta and pulmonary trunk)

Question 10

What is heart folding?

Answer 10

Morphogenesis of the primitive heart tube on DPC 23-28 resulting in the S-shaped, asymmetric heart

Question 11

What happens if heart folding is disrupted?

Answer 11

May lead to abnormal atrial situs, dextrocardia, and ventricular inversion

Question 12

Where does the primitive sinus venosus develop during heart folding?

Answer 12

Develops cranially and posteriorly/superiorly

Question 13

Where does the primitive atria develop during heart folding?

Answer 13

Develops dorsally and caudally

Question 14

Where does the primitive ventricle develop during heart folding?

Answer 14

Develops ventrally and cranially

Question 15

What does the intervening transitional zones between the primitive atria and ventricle become during heart folding?

Answer 15

Cardiac septa, valves, conduction system, and fibrinous skeleton of the heart

Question 16

What do the endocardial cushions become?

Answer 16

The AV valves, septation of the heart chambers, and outflow tracts

Question 17

What does the ventricular inflow septum arise from?

Answer 17

The primary ring

Question 18

What does the ventricular inflow septum develop into?

Answer 18

Superior and inferior atrioventricular cushions

Question 19

What happens if there is disruption of the ventricular inflow septum formation?

Answer 19

Tricuspid valve abnormalities or atresia

Question 20

What does the ventricular outflow septum arise from?

Answer 20

The transitional zone on the arterial pole of the folded heart

Question 21

What happens if there is disruption of the ventricular outflow septum formation?

Answer 21

A spectrum of outflow tract malformations and subaortic VSDs

Question 22

What makes up the interatrial septum?

Answer 22

Septum primum, septum secundum, and AV canal septum

Question 23

Describe the formation of the interatrial septum

Answer 23

At ~ DPC 28, the septum primum grows from the atrial roof down towards the AV endocardial cushions (does not touch so you get an ostium primum/foramen primum) –> The septum secundum then forms as an infolding of the atrial roof on the RA border of the septum primum –> as it grows, it closes the ostium primum and fuses with the septum primum by second month of gestation except for at the ostium secundum (anterior and superior border)

Question 24

What is the fossa ovalis?

Answer 24

Closure of the foramen ovale (fusion of the septum primum and secundum); remnant of the foramen ovale

Question 25

What does the leading edge of the septum secundum become?

Answer 25

The superior limbic band (seen in the RA)

Question 26

What does the atrioventricular endocardial cushion develop into?

Answer 26

The AV valves, interatrial septum and interventricular septum

Question 27

What is an ostium primum ASD?

Answer 27

Failure of the septum secundum to fuse with the endocardial cushion

Question 28

What is a partial versus transitional vs complete AV canal defects?

Answer 28

Partial = isolated primum defect; Transitional = concurrent inlet VSD below the AV plane with a primum defect that is restrictive; Complete = transitional AV canal defect that is non-restrictive

Question 29

What is commonly seen with transitional and complete AV canal defects?

Answer 29

They present with abnormalities of both AV valves + a common annulus, bridging leaflets, and a “cleft” left AV valve

Question 30

What determines cardiac situs?

Answer 30

The position of the morphologic RA, NOT where the heart sits in the chest or where the apex is located

Question 31

What are morphologic features of the RA?

Answer 31

Pectinate muscles outside of the appendage + larger, broader atrial appendage + eustachian valve + limbus of the fossa ovalis + IVC and coronary sinus drainage (except in certain heterotaxy syndromes)

Question 32

Levocardia vs Dextrocardia vs Mesocardia

Answer 32

Based on where the apex is directed (levo = apex directed to the left, dextro = apex to the right, meso = midline)

Question 33

Levoposition vs Dextroposition vs Mesoposition

Answer 33

Based on the heart’s position within the chest (levo = normal anatomy, dextro = heart in the right chest, meso = heart in the middle of the chest)