Rush Center for Congenital
and Structural Heart Disease

Contents

 

 

Introduction

Pediatric cardiology and cardiovascular morphogenesis

Congenital heart defects account for 20% of all congenital defects.  Five to 8 of every 1,000 live births suffer from congenital heart disease.  Many of these cardiac defects are lethal if left uncorrected.  Fortunately, advances in medical and surgical care made it possible for the overwhelming majority of these children to maintain normal lives into adulthood.  Understanding normal morphogenesis as well as uncovering etiological factors of congenital heart disease is essential when considering preventive measures to reduce or eliminate congenital heart disease.  A great deal of understanding normal cardiovascular development was achieved over the past few decades, yet it appears that what we lack in knowledge still far exceeds what we have been able to discern.  Structural changes through microscopic examination of animal models and sections of human embryos provided the initial comprehension of cardiac morphogenesis.  Later, molecular biology research enabled a greater depth of understanding of this process.  The discovery of etiological factors of congenital heart disease such as environmental and genetic syndromes provided an understanding, though limited, of the pathophysiological mechanisms of congenital heart disease.   On the other hand, this uncovered complexities of the process through which congenital heart disease develops due to inconsistency in the effect of identified etiological factors in producing heart defect.  Thus strengthening the notion that etiology is always multifactorial, much of which we continue to poorly understand their nature or mechanism of action.  These limitations coupled by the fact that the cardiovascular system completes its development in the first 2 months of gestation, much before any available diagnostic toll is capable of studying the cardiovascular system, makes it difficult to implement any realistic preventive measures.  However, this is bound to change as our understanding of heart development and etiological factors expands as along with advancement in the diagnostic and therapeutic tools we attain.

This website emphasizes the normal development of the cardiovascular system.  The goal is to provide a broad spectrum review of the various and at times conflicting theories of cardiovascular morphogenesis.  Many of the molecular biology aspects in this field were included, though this is not intended to be a reference to researchers in this field.  References provided in the “Experimental approaches to cardiac development” chapter by McQuinn and Takao from the second edition of "The Science and Practice of Pediatric Cardiology" are listed in the references section of this website to provide those interested in this field with a thorough resource for research in this field [1-360]. 

 

Cardiovascular morphogenesis in the human embryo

During the first 20 days of development, the human embryo is void of cardiovascular structures.  Over the next 40 days an amazing process transforms isolated angiogenic cell islets into a complex four chambered structure (table 1).  The various steps leading to the formation of the heart and great vessels may appear at times random and independent of each other, however, the interplay present between various developmental events become evident as failure of occurrence of a particular step in morphogenesis result in a spectrum of anomalies.

 

Table 1

Timetable of the development of various cardiovascular structures in human embryos

Weeks

Days

Somites

Length in mm

Cardiac Events

1-2

0-20

1

1.5

No heart or great vessels

3

20

2

1.5

Cardiogenic plate

3

21

5

1.5

Endocardial tubes

4

22

10

2

Fusion of endocardial tubes

4

23

12

2

Single median cardiac tube, first contraction ( ineffective)

4

25

17

2.5

Cardiogenic loop

4

26

20

3

Single atrium

5

29

25

4

Bi-lobed atrium

5

30

26

4

Beginning of circulation

5

31

28

4.8

Septum primum

5

35

 

7.5

A-V orifice, 3 chamber heart

6

36

 

8.5

Septum secundum

6

39

 

10

Complete inferior septum

6

40

 

10.5

Septation of bulbus and ventricle

6

42

 

13

Divided truncus arteriosus

7

49

 

20

4-chambered heart, Absorption of pulmonary veins