Posts Tagged ‘pulmonary arterial hypertension’

When I asked this seemingly simple  question to my cardiology fellows , I found they struggled  to come out with a proper  answer .I hope this will  make the  issue simpler .

Why the onset of PAH in VSD is early and late in ASD ?

Though number of factors are involved in the genesis of PAH , the single important reason  is  behavior of pulmonary circulation  especially the pulmonary arteriolar muscle .

Normal pulmonary vasculature losses it’s muscle rapidly after  birth and the pulmonary vascular resistance (PVR) falls to the adult level by 6 months .(Bulk of the fall occur in first 60 days) This is the same time the RV dominance is lost and RVH regresses . This also coincides with peaking of  left to right  shunting peaks and may result in cardiac failure .

Though  both ASD and VSD shunts are  highly dependent on PVR ,   VSD  shunting has more muscle power namely the LV contractility  , hence  VSD shunt is established  much earlier   than ASD . This can be ascertained in bedside as  VSD murmurs are heard even within 30 days while ASD is silent for many moths or even years . (Does not apply for Primum defects)

ASD  shunt rarely  meddles   lung  maturation process .(Maturation here means loss of  pulmonary arterioloar smooth  muscle -also  called as Involution  )  This vital  initial period lasts up to 6 months of life .VSD  interferes with this  involution of pulmonary arteriolar smooth muscle .( Please note near complete  involution still can occur in small VSDs with very little shunting )

In large VSD the PVR  will never ,  ever fall to normal levels  and   making it easier for  progressive vascular changes  that occur in  untreated large VSDs that  lead to Eisenmenger syndrome

*Please note  ASD can also reach that stage but it takes many years as the pulmonary vascular resistance has to raise from  very low levels which was made possible by complete involution of pulmonary vasculature .

It is obvious   AP window , PDA  express more  powerful left to right shunts which are associated with very high PVRs .

Final message

A simplified version of answer

Version 1

In VSD  the onset  of left to right  shunt occurs early even within 3 months of life  since VSD shunt is augmented by LV contraction . This is the crucial time of lung  vascular maturation   which gets interfered with  .ASD shunt is  established only after the pulmonary vasculature  involutes .This explains early onset of PAH in VSD  and late in ASD .

Version 2

ASD shunting is primarily depend on RV compliance which is high in early infancy so it takes time to establish the shunt .while VSD shunting does not  depend upon this RV regression.

* Please note  regression of  RV  dominance and compliance is directly dependent on maturation of lung.

** Note these  explanations are not absolute .Some of the complex forms of ASD and intrinsic vascular injury of pulmonary circulation (Various  fetal distress )  can progress into accelerated pulmonary arterial hypertension


  1. Excellent discusions are available in old edition of Moss and Adams
  2. Rabinovitch has done pioneering work on this topic .
  3. Robert Roberts text book of Adult congenital heart disease also explains it succinctly

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Interventions in Eisenmenger  syndrome  or severe PAH in  left to right shunt continues to be a major diagnostic issue.The challenge lies   not only in  assessing whether the progression of PAH can be prevented by  blocking the left  to right shunt , but also  to assess  it’s impact  on  survival.

The factors  involved are

  1. Pulmonary artery pressures
  2. Pulmonary blood flow
  3. Pulmonary vascular  resistance
  4. RV function
  5. Co-morbid /general condition of the patient

While cardiologists worry more about LV , surgeons have different issue .  In left to right  shunts with PAH  RV function bothers them more , as the high pulmonary artery pressure may never allow the surgeons to come off the pump , once the decompression provided by ASD/ VSD  is removed

How relevant is Ohm’s Law in complex shunt with leaky valves and bidirectional shunting ?

The fundamental hemodynamic equation  is derived from  Ohm’s law .How relevant  is  Ohm’s law in Eisenmenger  is not clear.  For decades we have been using complicated calculations with many presumed  and assumed parameters.  The calculation of effective pulmonary blood flow in bidirectional shunt may be most complex equation in clinical  cardiology. One can only imagine how one error could amplifies the other.

The hemodynamic equivalent of  Ohm’s law states

R = Pressure / Flow .The current thinking is  If the PVR is between 6-8 it is operable .

Is it really that simple ?

We know pressures  can be measured with a fair degree of accuracy . Flow  and resistance are  subjected to change in a  moment  to moment basis  .They are  determined by a gamut of  neural and humoral factors.

Ironically , we are not yet clear , whether flow determines  the pressure or pressure determine  the flow .

The right heart blood flow can get complicated by not only bi-directional shunt but also  by pulmonary  and tricuspid regurgitation ,

There is a huge perception problem here .  We are tuned  to think ,  reversibilty of PAH is  same as operability  of shunt lesion . Definitively not !  This is the reason why there is  a vast difference in  ultimate outcome  with  little correlation with PVR !

In  Eisenmenger   physiology  , critical decisions  regarding surgery  are made outside  the cath lab 

  • Good clinical  acumen,
  • A meticulous echocardiography
  • Hard parameters  like  pulmonary  artery diastolic pressure and pulse pressure
  • Above all a  harmonious  Cardiologist – Cardiac surgeon team is vital to plan  this  complex surgery

So, now it would seem  cath studies  are  primarily done for  academic pursuit ,  and  it  rarely helps  in genuine decision-making process.

The following table  synthesized in our hospital (Mainly with  clinical data ) can be a useful tool.

Reference: Learnt in the bedside from poor children of India

We had a situation like this   . A patient was  in class 3 or 4  and calculated PVR was less than 6 Wood units what will you do ?

Never give importance to numbers .  These  patients  will 99% of times won’t survive a shunt closure surgery.

Future development

With  the availability of modern drugs like Nitric oxide, prostocyclins, Sildenafil  analogues  medical management has a potential to improve upon surgical results. Unfortunately large studies are not possible in these population . In the surgical front, fenestrated  VSD closures peri-operative intensive nitric oxide   show some promise.

 Final message

I think  we are about to say a  final   good-bye* to oxymetry  ( or even cath study )  in  the  work up of  PAH  due to shunts.

*Still, pressures of  right heart chambers and pulmonary artery  is vital .Echo can not be expected to provide accurate measure of PA pressure .(Even though there some echo studies  available to calculate  qp/qs and PVR non invasive)


Pulmonary artery pulse pressure : A simple parameter to assess reversibility  of PAH

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Pulmonary hypertension (PH)is a very common clinical problem in cardiology.The classification of PH  has been little complex. Now we have a fairly clear scheme formulated in 2008 in a small beach side county of  California called Dana point .

I have tried to simplify it without affecting the core

Click on the image if  slide is not displaying

Category 1 is again divided into 5 categories

1.1 /1.2/1.3/1.4/1.5

Other categories( Category 2 to 5)

* Note there is a special category called 1 ‘ for pulmonary veno-occlusive disease .This should be distinguished from CTEPH


Remember  99 %  all  pulmonary hypertension will be constituted by the following  seven entities .

Idiopathic PAH  1.1

Familial PAH       1.2

Connective tissue disease 1.4.1

Congenital heart disease  1.4.4

Left sided valvular /Myocardial heart disease 2.3.3

Secondary to  COPD  3.1


In India  (probably worldwide ) the commonest  cause for  PH is  2.3.3

The updated pulmonary hypertension  classification is available here

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                                  Even as cardiology community is preoccupied with systemic hypertension & CAD  ,  pulmonary arterial hypertension(PAH) is a much neglected , still  an important clinical cardiac problem encountered . The irony is self evident , there are half a dozen methods to grade systemic hypertension not even a single stadardised grading available for pulmonary arterial hypertension. The WHO  working group defined pulmonary hypertension  few decades ago and was not clinically graded .The only grading available is based on  the pulmonary vascular biopsy changes (Heath Edwards) 

                                   Currently PAH management has gone through revolutionary changes. There is an urgent  need for grading  this entity .This will facilitate to  diagnose , manage and assess the efficacy of the currently available treatment.

                                Developing countries like ours have a great number of PAH due to rampant rheumatic heart disease.  A simple study was done in  100 patients with PAH .Bulk of the study population had RHD .Few had primary pulmonary  hypertension .Systolic , diastolic, and mean pressure was assessed by doppler echocardiographic analysis of tricuspid regurgitation (TR) and pulmonary regurgitaion(PR) jets. TR jet provided the systolic PA pressure , PR jet provided mean as well as diastolic PA pressure .TR jet was available in all patients. PR jet was available only in 60 patients .Hence the diastolic andmean PA pressure data has been extrapolated in some  and  was plotted in a scatter diagram. Five equal quintiles were divided. Patients in first  and 2nd quintiles were graded 1   and third  and 4th  quintile were  graded 2 ,  5 th  was graded 3 respectively. From this cut off points for  various grades of PAH were identified .The top 3% of patients  with highest PAP were graded as grade 4 and all of them had supra systemic PAH. 

The following grading is suggested for PAH* 

 *This is a preliminary  attempt to grade PAH. This could be applicable mainly in rheumatic heart disese and primary pulmonary hypertension .Further refining of methodology is  required.PAH grading may be little different in congenital left to right shunts.

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