Dr. Sandip GuptaPGT – Pediatrics

BSMCH

Development of Heart &

Congenital Malformations

Development of the heartDevelops from splachnopleuric mesoderm lying immediately cranial to the pro-chordal plate. This medoderm constitutes cardiogenic area

Cells of the area migrate between mesoderm and endoderm and arrange as to longitudinal cellular strands called cardiogenic cordscords become canalized to form two thin-walled endothelial tubes - called endocardial heart tubes

Formation of Single heart tube & pericardial cavity

As the lateral folds develop, the endocardial heart tubes gradually approach each other and fuse from the cephalocaudal direction to form a single unpaired heart tube

Fusion of endocardial heart tubes into one single is followed by a fusion of paired pericardial cavities so that finallysingle (common) pericardial cavity arises

• If the fusion is completed, theheart tube lies within the pericardial cavity and is attached to its dorsalside by a fold of mesodermal tissue -the dorsal mesocardium

• The dorsal mesocardium is transitorystructure that soon degenerates

• After disappearing of the mesocardium, the heart tube is freely housed in thepericardial cavity, being firmly fixed onlyat two sites:at arterial (cranial) and venous (caudal) ends

the single heart tube stage is achieved during the 23 -24 day when the heart begins regularly to beat

Formation of the heart wall

as the heart tubes fuse, the mesenchyme around them proliferates and forms a thick layer of cells - myoepicardial mantle

from the endothelium of the heart tube the myoepicardial mantle is separated by cardiac jelly - a gelatinous connective tissue

cells of the myoepicardial mantle differentiate into:- mesothelial cells - outermost layer called epicardium (visceral pericardium)- myoblasts - cardiomyocytes of myocardium

cells of cardiac jelly give rise to subendocardial layer of endocardium(PURKINJE FIBERS)

the mentioned processes result in three-layered composition of the heart wall known from microscopic anatomy:the inner endocardium, the middle myocardium, and the outer epicardium

• Development of the heart tube then continues by its uneven growth in the width and Length, • As a result it distinguishes in several portions in caudocranial axis there

are as follows :

sinus venosus - venous end, receiving blood from the umbilical, vitelline and common cardial veins on each side

primitive atrium - separated from the sinus by a terminal sulcus,

primitive ventricle - separated from the atrium by the AV sulcus,both portions are connected each other with an AV foramen.

bulbus cordis - is continuous with ventricle through the primary interventricular foramen;

--this portion will give rise to part the definitive right ventricle

truncus arteriosus - arterial end of the tube, which divides into paired ventral aortae

Formation of the Cardiac Loop

• The heart tube continues to elongate and bend on day 23. The cephalic portion of the tube bends ventrally, caudally, and to the right. And the atrial (caudal) portion shifts dorsocranially and to the left.

• This bending, which may be due to cell shape changes, creates the cardiac loop. Completed by day 28.

Septation of the heart

The septation process = division of the heart into two halves down midlinethe process begins in the 5th week and ends in a week later 3 septae take part in division of the heart in the right and left chamberthere are as follows:

interatrial septuminterventricular septum aorticopulmonary septum

Ventral endocardiac

cushion

Dorsal endocardiac

cushion

Atrioventricular tube

Left atrioventricular

tube

Right atrioventricular

tube

Compartmentation of heart 27 - 37th day

Compartmentation of primitive atrium ( 4th to 5th week)

Anomalies of atrial septum formation

Compartmentation of primitive ventricle(4th -8th wk)

The medial walls of the expanding ventricles become apposed and graduallymerge, forming the muscular IVS.The IV foramen, above the muscular portion of the IVS, shrinks on completion of the conus septum. outgrowth of tissue from the inferior endocardial cushion along the top of the muscular interventricular septum closes the foramen This tissue fuses with the abutting parts of the conus septum. Complete closure of the interventricular foramen forms the membranous part of the IVS.

Anomaly of ventricular septum development

Septum Formation In The Atrioventricular Canal

• At the end of the fourth week, two mesenchymal cushions, the AV endocardial cushions, appear at the superior and inferior borders of the AV canal.

• In addition to the superior and inferior endocardial cushions, the two lateral atrioventricular cushions appear on the right and left borders of the canal

Compartmentation of truncus arteriosus

and bulbus cordis

Malformation of cono-truncal region

• No septum formation : failure of conutruncal ridges to fuse -Truncus Arteriosus.

• when the conotruncal septum fails to follow its normal spiral course and runs straight down - TGA

• Unequal compartmentation : - TOF, PS

PTA

TGA

TOF

PDA - Patent Ductus Arteriosus

• 1st aortic arch – disappears

• 2nd aortic arch – disappears

• 3rd aortic arch - has the same development on the right and left side it gives rise to the common carotid artery & initial portion of the internal carotid artery.

•4th aortic arch - has ultimate fate different on the right and left side on the left - it forms a part of the arch of the aorta between left common carotid and left subclavian artery on the right - it forms the proximal segment of the right subclavian artery

•5th aortic arch - is transient and soon obliterates

•the 6th aortic arch - pulmonary arch

ABNORMALITIES OF AORTA

• Coarctation of Aorta: narrowing below subclavian artery.

• Double Aortic Arch:Rt dorsal Aorta persists betwn the origin of 7th intersegmental artery & its junction with Lt dorsal Aorta

• Right aortic Arch: Lt 4th arch& Dorsal aorta are obliterated & replaced by counterparts on Rtside

• Interrupted Aortic Arch: obliteration of the 4th Aortic Arch on Lt side.

THANK YOU