Great vessels, foetal circulation, changes at birthDr Jane HollandCVR 2214/03/11

Conus cordis / truncus arteriosus – septum formationTruncus cushions (swellings)

Right superiorLeft inferior

Right superiorGrows distally & to left

Left inferiorGrows distally & to right

⇒ Cushions twist around each other

Cushions fuseForm septum

Aortic channelPulmonary channel

Similar cushions develop in the conus cordis also

Unite distally with the truncus septum

⇒ conotruncal septumOutflow tract of right ventricleOutflow tract of left ventricle

Animation –http://www.med.uc.edu/embryology/chapter7/animations/contents.htm

Transposition of the great vessels

Conotruncal septum fails to spiralNot compatible with life unless another shunt is presentCyanosis, usually systolic murmur

Unequal division of conus cordis(Septum too anterior)

Pulmonary stenosisNarrow right ventricular outflow

Large VSD Ventricular septal defect

Overriding aortaFrom directly above septal defect

Hypertrophy of the right ventricleRaised right interventricular pressure

Tetralogy of Fallot

Right to left shuntCyanosis

Palpable thrillSystolic murmur

Pulmonary & left sternal border

Patients characteristically squat to improve symptoms

Persistent truncus arteriosus

Single outflow tract remains

Conotruncal ridges fail to fuseNo dividing septum

Cyanosis, systolic murmur

Always associated with a VSDMembranous portion of septum fails to develop superiorly

Aortic arches – initial development

Caudally, dorsal aortae fuseRemain paired in region of pharyngeal arches (cranially)

Each arch receives an arteryAortic archRun from aortic sac to dorsal aorta

Not all present simultaneouslyDevelop 1st ⇒ 6th

Many obliterate

1st arch – disappears*2nd arch – disappears*3rd arch

Common carotidProximal internal carotidExternal carotid branches off 3rd arch

4th archLeft – arch of aortaRight – subclavian artery

5th arch – disappears6th arch

Pulmonary trunkLeft - Ductus arteriosus

* Small remnants remain – NS module!!

Dorsal aortae

CraniallyInternal carotid arteries

Between 3rd & 4th arches Obliterates

More caudallyRight

Forms part of subclavianObliterates

LeftDescending aorta

Course of recurrent laryngeal nerve (supplies larynx)

6th arch

4th arch

Vitelline arteriesNumber of paired vessels from dorsal aortaSupply yolk sac (& then gut)Fuse – coeliac / SMA / IMA

Umbilical arteriesOriginally from dorsal aortaThen develop secondary connection to iliacsMedial umbilical ligaments

Venous system – initial development

Vitelline veinsForm plexus around duodenumRun through septum transversum to reach sinus venosusLiver cords disrupt these veins

Hepatic sinusoids formed

Right vitelline vein persistsForms hepatocardiac IVCDistally – Portal vein & SMV

Left vitelline veinMostly obliterates

Umbilical veinsInitially pass to either side of developing liver

Then develop connections to hepatic sinusoids

Proximal right & left umbilical veins obliterate

Remainder of right umbilical vein obliterates

Left vein now carries all blood from placenta to liver

Develops direct connection to right hepatocardiac channelDuctus venosusBypasses sinusoids of liver

PostnatalLeft umbilical vein Ligamentum TeresDuctus venosus Ligamentum venosum

Anterior cardinal veinsCephalic part of embryo

Posterior cardinal veinsRest of embryo

(Initially symmetrical)

Additional veins then formSupracardinal veins

Body wallSubcardinal veins

KidneysSacrocardinal veins

Lower extremities

Cardinal veins

Anterior cardinal veinsDrain cephalad embryoRight-left anastomosis

Brachiocepalic vein

Right forms SVC

Posterior cardinal veinsInitially drain rest of embryoMostly obliterate

Supracardinal veinsAzygos system of veins

Drain body wall

Subcardinal veinsAnastomosis formsLeft renal vein

Left subcardinal veinMostly disappearsDistal part persists as the left gonadal vein

Right subcardinal veinDevelops into part of IVC

Renal segment

Sacrocardinal veinsAnastomosis formsLeft common iliac vein

Right sacrocardinal veinDevelops into part of IVC

Foetal circulation

Postnatal circulation

Patent ductus arteriosusIn foetus, blood flows right to leftClosure postnatally:

Mediated by bradykininMuscular contraction

Neonate with PDA – blood flows left to rightPulmonary hypertension“machine-like” murmur

Systole & diastole

To close PDAIndomethacin

To keep DA patent PGE

Coarctation of aortaNarrowing of aorta below origin of left subclavian5-8% of all congenital heart defects

Diagnosis can be delayedPre- or Postductal

Pre-ductalINfantile – IN close to the heartDuctus arteriosus usually persists

PostductalLigamentum arteriosum

Collateral circulationIntercostal arteriesInternal thoracic artery

From subclavianSo proximal to narrowing

AcyanoticLeft to right shunt

ASDVSDPDA

Tetralogy of FallotTransposition of great vesselsTruncus arteriosusTricuspid atresiaTAPVR

CyanoticRight to left shuntReduced flow to pulmonary circulation5 T’s

Uncorrected ASD, VSD or PDAAll initially acyanotic – left to right shunts

Pulmonary hypertension developsAs pulmonary vascular resistance increases, the shunt reverses

Was Left to RightNow Right to Left

Late cyanosis develops

Eisenmenger’s syndrome