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Common Congenital Heart Lesions

(pgs 349-370 from readings on Thursday 16th and Monday 20th) Chapter 16: Congenital Heart Disease

Embrology:

  • Two angioblastic cords form from the embryonic disc, cords canalize

and

fuse

to form the endocardial heart tube

  • Heart tube has five sections:

(continuous with aortic

arch)

Heart

tube

segment

(top

to

bottom)

Future Structures

Truncus Arteriosus Bulbus Cordis Primitive Ventricle Primitive Atrium Sinus Venosus

Aorta, Pulmonary Artery Outlet of ventricles Inlet of ventricles Right and left atria Part of right atrium

  • Atrioventricular canal: separates the primitive ventricle and primitive atria, forms the mitral and tricuspid valves.

  • Septation of the atria:

      • o

        septum primum grows down from roof of common atrium

        • o

          septum fuses with endocardial cushion at the sides, forming ostium primum

        • o

          center of septum primum degenerates, forming ostium seuondum

        • o

          ostium primum eliminated

        • o

          septum secundum forms to right of septum primum and grows down

        • o

          septum secundum overlaps ostium secundum

        • o

          septum secundum fuses with EC cushion and forms foramen ovale

        • o

          foramen ovale allows blood to pass from RA to LA in fetus

  • Septation of AV canal: EC cushions swell and fuse to form the AV valves

  • Septation of the ventricles and outflow tracts

        • o

          4th week: common ventricle grows leaving a medial muscular ridge which forms the muscular part of the IV septum; does NOT fuse with EC cushions

        • o

          5th week: bulbus cordis and truncus arteriosus form bulbar ridges, which fuse and spiral 180°Æ aorticopulmonary septum

        • o

          7th week: EC cushions fuse with right and left bulbar ridges, forming membranous part of IV septum

    • Development of valves: proliferation of mesenchymal tissue, blood flow and cell death shapes valves, AV valves leave behind fine muscular strands connecting valve to wall of ventricleÆ chordae tendineae

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