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Posts Tagged ‘pfo vsa asd pda in tgv dtgv’

TGV is the most common cyanotic heart disease to present at birth.The outcome is dismal unless it is intervened at the earliest .It becomes a real  emergency if the dTGA is associated with intact IVS and IAS. (Though foramen ovale /ductus  may help for a while prolonging the survival . Often times , it is restrictive and demands immediate septostomy if primary arterial switch correction is not attempted )

Presence of VSD provides vital time interval to plan  surgery in a less emergent fashion. Otherwise , arterial switch if  contemplated one has to do it before 2-3 weeks (Rarely up to a month ) .The principle is to reverse the circulation before the  systemic left ventricle regress its myocyte function as it is exposed to low pressure pulmonary circuit .

Hemodynamics

We know , dTGA  has two parallel circuits in a bizzare hemodynamic disconnect .The right sided  pulmonary circuit sustains  the systemic blood flow with deoxygenated blood.The left sided systemic circuit recirculates oxygenated blood into pulmonary circulation again and again.

Survival depends upon , the anatomical communication between two circuits and the effective quantum (Deoxygenated)  of blood flow to the lungs .

Which communication is best for survival d TGA ?

The key is to understand   what we mean by “mixing  vs  shunting”  and the effective pulmonary blood flow (ie quantum of truly deoxygenated blood reaching lungs  vs oxygenated blood recirculating  the lungs in a hemodyamically wasted loop

It appears both atrial  ventricular level  mixing is good for maintaining adequate O2 saturation than PDA .

What does PDA do ?

Ductus is expected to persist in  dTGA  when  IVS and IAS are intact  . It is not clear  what determines the persistence of duct  in dTGA with intact IVS. Principles of natural  hemodynamic adoption would argue , all patients with dTGA should never close their ductus and foramen ovale. While , In reality it may be true for PFO to persist, ductus often gets closed on schedule* , aggravating  the hypoxia .(Both flow mediated myogenic resposne, O2 content of ductal blood and size are the determinants of ductal closure)

The ductal circulation in dTGA can be complex . It initially  acts as a channel to mix both arterial and venous blood flow .It can become a liablity  if its large , as the pulmonary vascular resistance falls,  blood is shunted from aorta to pulmonary circulation and potentially precipitate failure .Please note,  this shunting  also can  improve  the saturation as it diverts aortic blood into lungs ,still the ultimate usefulness will depend upon intermixing  at some other level  other than ducuts , ie either atria  or ventricle .One should  realise  ductus can never bring  good admixture as it happens outside the heart .It is obvious intra cardiac  mixing  with ASD and VSD  is always better and devoid of providing differentially saturated blood  to the extremities  , which is an inherent feature  PDA mediated  mixing .If ductus  is the only means of mixing and shunting  the lower half of the body has  an advantage as it is perfused continuously by oxygenated blood .This  may manifest as  reversed differential cyanosis in few combinations of TGA physiology. (Relatively pink  lower limbs and cyanosed upper extremity )

Summary

Ductus can be a double edged friend or single edged foe  in dTGV . It depends upon the size , quantum of shunt and associated  channels of mixing like ASD and VSD . If it occurs with  intact IAS and IVS it plays a role of  life sustainer.

Presence of ductus is definitely useful  initially.It can either help by mixing, intermittent bi-drectional shunting  or committed left to right shunting .This is why we attempt to  preserve its patency or even recannalise it by stenting  in such situations .The later can be used to buy time and train the regressing LV .However ,large ductus can be counter productive  if additional shunts are also present where one should even contemplate closing it .

Reference

1.

pda in dtga ductus ductal flow in tga2.Transposition of the great arteries with intact ventricular septum and patent ductus arteriosus. Waldman JD, Paul MH, Newfeld EA, Muster AJ, Idriss FS.Am J Cardiol. 1977 Feb;39(2):232-8.

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