Saturday, October 16, 2010

Aortico-Pulmonary Septal Defect



Definition:


Aortico-Pulmonary Septal Defect (APSD), Aortico-pulmonary window, Aortico-pulmonary fenestration, or aortic septal defect, refers to a communication between the ascending aorta and the pulmonary trunk.


Embryology:


Structure of the bulbus cordis:


Bulbus cordis is formed of 3 parts:
  • Proximal part.
  • Middle part, called the Conus cordis.
  • Distal part, called: the Truncus arteriosus.







The bulbus cordis is the most cranial part of the heart tube.
http://www.luc.edu/faculty/wwasser/dev/heart4.jpg


Division of the bulbus cordis:


The major bulbar cushions (right & left) and the minor bulbar cushions (anterior & posterior) develop in the lumen of the truncus arteriosus and descend towards the ventricles in a spiral way, forming the Aortico-pulmonary septum, which divides the truncus arteriosus into:
The pulmonary trunk (the anterior half) connected with RV outflow tract.
The ascending aorta (the posterior half) connected with LV outflow tract.
The bulbar cushions also share (with the endocardial cushions) in the formation of the membranous ventricular septum, which lies immediately below the aortic valve.





Septation of the bulbus cordis.
http://isc.temple.edu/marino/embryology/Heart98/heart97b/img020.gif







http://pediatriccardiology.uchicago.edu/MP/CHD/TOF/Diagram-outflow%20tract.gif



Aortico-pulmonary septum.
http://www.coheadquarters.com/PennLibr/MyPhysiology/Mod21/figdev2.05.gif



Aortico-pulmonary septum.
http://www.ctsnet.org/graphic/3_6_1.jpg



http://upload.wikimedia.org/wikipedia/commons/b/b9/Gray470.png


Anatomy:


The ascending aorta slants anteriorly towards the sternum then emerges from the pericardium and turns backwards to continue as the aortic arch.
The pulmonary trunk curves infront of the ascending aorta from right to left and then backwards to emerge from the pericardium. It then divides into the right and left pulmonary arteries in the concavity of the aortic arch and infront of the left main bronchus.



http://www.heart-healthy.org/images/heartnice.jpg



http://www.wired.com/images/article/full/2007/09/pericardium_580x.jpg




Pathology:


APSD results from deficiency of the Aortico pulmonary septum.
APSD is usually a single wide opening between the left side of the ascending aorta and the right side of the pulmonary trunk, close to the origin of the right pulmonary artery.
The secondary cardiac pathological changes are similar to those occurring with a large PDA.

Associated anomalies include: 
  • PDA. 
  • VSD. 
  • Tetralogy of Fallot. 
  • Sub-valvular aortic stenosis.




http://t0.gstatic.com/images?q=tbn:0h945lQobwGQ0M:http://www.mdconsult.com/das/patient/body/0/0/10041/22711_en.jpg&t=1



http://ats.ctsnetjournals.org/content/vol77/issue2/images/medium/14570.484.gr1.gif




Pathophysiology:


Pathophysiology of APSD is similar to large PDA.


Clinical picture:


The clinical picture of APSD is usually similar to large PDA, but the murmur is a little lower along the left sternal border.

In rare cases the defect is small, where:
  • Patients are asymptomatic.
  • And an ejection click may be heard.


Chest x-ray:


Similar to PDA but:
  • AO knuckle is not enlarged.
  • A right aortic arch may be associated.


Electrocardiography:

  • Left ventricular hypertrophy (LVH) associated with right ventricular hypertrophy (RVH) in most cases.
  • Isolated RVH in:
    • Very young infants.
    • Older patients with PHT.


Echocardiography:


Will show the pathology.



Parasternal short axis view.
http://img.medscape.com/pi/emed/ckb/pediatrics_cardiac/889392-893798-127.jpg



Parasternal short axis view.
http://www.cmj.org/periodical/images/200812/2008121815446964.jpg



http://www.scielo.br/img/fbpe/abc/v73n1/a06fig03.gif



http://www.scielo.br/img/fbpe/abc/v73n1/a06fig04.gif





Indications of cardiac catheterization:

  • Patients suspected to have PDA with any atypical finding that suggests APSD.
  • Patients with PHT suspected to have PDA or APSD.
  • Associated VSD.


Natural history:


Some cases are diagnosed as PDA and only discovered at surgery.
CHF is common.
Infective endocarditis is also a risk.


Medical management:


Similar to large PDA


Surgical management:


Surgery is recommended in all cases of APSD, although surgical risk is high, since prognosis is poor otherwise.


Surgical techniques include:
  • Obliteration of the aortic end by Dacron patch from within the AO under cardio-pulmonary (CP) bypass.
  • Ligation without CP bypass may result in incomplete closure, recurrence, or hemorrhage.
  • Division under CP bypass with suture closure of the aortic and pulmonary ends may distort the great vessels.



The defect is approached directly through an incision made along the middle of the aortopulmonary window itself. Both aorta and pulmonary artery defects are closed under direct vision of adjacent structures.
http://ats.ctsnetjournals.org/content/vol77/issue2/images/medium/14570.484.gr2.gif



The aorta and pulmonary arteries are completely separated. A different pericardial patch is used to close the defect in each vessel.
http://ats.ctsnetjournals.org/content/vol77/issue2/images/medium/14570.484.gr3.gif

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