Transposition of Great Arteries!

Hello!

So I have divided the post into two parts - A short summary for those who don't have the time to read everything (#TLDR) and a nice long explanation for those who want to read everything :)

Let's start with TLDR.

#TLDR: In TGA, oxygen-poor blood from the body enters the right side of the heart. But, instead of going to the lungs, the blood is pumped directly back out to the rest of the body through the aorta.

Oxygen-rich blood from the lungs entering the heart is pumped straight back to the lungs through the main pulmonary artery. Survival is impossible without shunts like VSD, ASD and PDA. (PGE1 to maintain PDA is treatment!)

Risk factors:

Infants  of  diabetic  mothers

DiGeorge  syndrome

It is more common in males

Physical  findings:

Cyanosis at birth, Parasternal  heave, Loud S2

CXR - Egg-shaped  heart, increased  pulmonary  blood  flow 

Echocardiography is diagnostic

That's it!

Let's learn about the transposition of great arteries in detail...

So...What is-Transposition of the Great Arteries?

 It is a birth defect of the heart in where the two main arteries carrying blood out of the heart – the pulmonary artery and the aorta – are switched in position, or “transposed.”

Physiologically the aorta is behind the pulmonary artery but here it is in front of it.... In addition to that..

Depending on the position of the aorta it is classified as

1) D(dextro)-tga : the aorta is to the right of the pulmonary artery.)

 2)L(levo)-tga :the aorta is  to the left of the pulmonary artery.( This is a rarer defect.)

Pathophysiology:

In TGA, oxygen-poor blood from the body enters the right side of the heart. But, instead of going to the lungs, the blood is pumped directly back out to the rest of the body through the aorta.

Oxygen-rich blood from the lungs entering the heart is pumped straight back to the lungs through the main pulmonary artery.

So there are to independent circuits functioning here.

Survival is impossible without few other cardiac defects in the form of shunts.... like

1) Ventricular septal defect2

2)Arial septal defect

3)patent ductus arteriosus.

These shunts will allow mixing of the blood to help increase the oxygen saturation of the systemic circulation.

RISK FACTORS:

Infants  of  diabetic  mothers and  in  males  (3 : 1).  d-TGA, especially  when  accompanied  by  other cardiac  defects like pulmonic  stenosis  or  right  aortic  arch,  can  be associated  with  deletion  of  chromosome  22q11.2  (DiGeorge  syndrome).

CLINICAL  MANIFESTATIONS :

This  condition  is  a  medical emergency,  

Cyanosis  and  tachypnea  recognized  within  the  1st  hr or  days  of  life.

Hypoxemia  is  usually  moderate  to  severe.

 Physical  findings,  other  than  cyanosis,  may  be  remarkably  nonspecific.

Parasternal  heave  may  be  present. 

2nd  heart  sound  is  usually single  and  loud,  although  it  may  be  split.  

Murmurs  may  be  absent,  or  a  soft  systolic  ejection  murmur  may  be  noted  at  the  midleft  sternal border.

 DIAGNOSIS :

Electrocardiogram  is  usually  normal,  showing  the  expected  neonatal  right-sided  dominant  pattern.

Chest  x-rays  may  show  mild  cardiomegaly,  a  narrow  mediastinum  (the  classic  “egg-shaped  heart”),  and normal  to  increased  pulmonary  blood  flow.  In  the  early  newborn period,  the  chest x-ray  is  generally  normal.   

Echocardiography  is  diagnostic  and  confirmatory.

TREATMENT

On suspection,  an  infusion  of  prostaglandin  E1 is  initiated  immediately  to  maintain  patency  of  the  ductus arteriosus  and  improve  oxygenation  (dosage:  0.01-0.20  µg/kg/min). 

Because  of  the  risk  of  apnea  associated  with  prostaglandin  infusion, neonatal  endotracheal  intubation  should  be  available.

Hypothermia  intensifies  the  metabolic  acidosis  resulting  from hypoxemia, and thus the patient should be kept warm.

Infants  who  remain  severely  hypoxic  or  acidotic  despite  prostaglandin  infusion  should  undergo  Rashkind  balloon  atrial  septostomy.  also  usually  performed in  all  patients  in  whom  any  significant  delay  in  surgery  is  necessary. 

Some  patients  with  TGA  and  VSD may  require  balloon  atrial  septostomy  because  of  poor  mixing, even  though  the  VSD  is  large. 

Others  may  benefit  from  decompression of  the  left  atrium  to  alleviate  the  symptoms  of  increased  pulmonary blood  flow  and  left-sided  heart  failure.

The  arterial  switch  (Jatene)  procedure  is  the  surgical  treatment  of choice  for  neonates  with  d-TGA  and  an  intact  ventricular  septum  and is  usually  performed  within  the  1st  2  wk  of  life.  

The  reason  for  this time  frame  is ... pulmonary  vascular  resistance  declines  after  birth ,pressure  in  the  left  ventricle  (connected  to  the  pulmonary  vascular  bed) also  declines.  

This  drop  in  pressure  results  in  a  decrease  in  left  ventricular  mass  over  the  1st  few  wk  of  life.  If  the  arterial  switch  operation is  attempted  after  left  ventricular  pressure  (and  mass)  has  declined  too far,  the  left  ventricle  will  be  unable  to  generate  adequate  pressure  to pump  blood  to  the  high  pressure  systemic  circulation. 

The  arterial switch  operation  involves  dividing  the  aorta  and  pulmonary  artery  just above  the  sinuses  and  reanastomosing  them  in  their  correct  anatomic positions. 

 The  coronary  arteries  are  removed  from  the  old  aortic  root along  with  a  button  of  aortic  wall  and  reimplanted  in  the  old  pulmonary root  (the  “neoaorta”).  

By  using  a  button  of  great  vessel  tissue,  the surgeon  avoids  having  to  suture  directly  onto  the  coronary  artery   The procedure  has  a  survival  rate  of  >95%  for  uncomplicated  d-TGA.  It  restores  the  normal  physiologic  relationships  

Atrial  switch  procedures  reverse  blood  flow  at  the atrial  level  by  the  creation  of  an  interatrial  baffle  that  directs  systemic venous  blood  returning  from  the  vena  cavae  to  the  left  atrium,  where it  will  enter  the  left  ventricle  and  then,  via  the  pulmonary  artery,  the lungs.  The  same  baffle  also  permits  oxygenated  pulmonary  venous blood  to  cross  over  to  the  right  atrium,  right  ventricle,  and  aorta.  It is not recommend as it has a lot of complications of rhythm also leaves  the  right  ventricle  as  the  pumping  chamber  and  these “systemic”  right  ventricles  often  begin  to  fail  in  young  adulthood.

Well that was extensive...🤓But I hope it wasn't boring!😌

Stay Awesomesauce!

Medha 😊