Archive for the ‘cardiology -congenital heart disease’ Category

What are the mechanisms of cyanosis in  cyanotic heart disease ?

Most of my fellows have difficulty in answering this question. (It is not the lack of knowledge though !)  In my view ,cyanosis can occur , by six  different  modes

  1. Reduced pulmonary blood flow  with some form of anatomical obstruction in RVOT with a communication between ventricles  (TOF physiology  ) , atria or both
  2. Reduced pulmonary flow with obstructive pulmonary vasculature (Eisenmenger physiology )
  3. Wrong way origin ( RV to Aorta/LV to Pulmonary artery ) : Transposition physiology
  4. Simple mixing of arterial  and venous  blood channels within the atria  ,ventricle or great vessel  without RVOT obstruction .This, in fact can causes increased  pulmonary blood flow (Technically left to right shunt ) and still there is cyanosis (These are called as Admixture lesions ) It is  also to be noted some of the admixture lesions  (Truncus, DORV,etc ) the mixing takes place only during systole  , while TAPVC,Common atrium, Tricuspid atresia*  admixture is more complete as it happens during  entire cardiac cycle.
  5. Isolated Right to left  shunt are  very rare ( Pulmonary AV fistula , SVC to LA )
  6. Complex combination of first 4 (Like bi-directional shunting , TGA combines ,  AV canal defect , with varying degree of pulmonary obstructive disease) Note : TOF and Eisenmenger are physiologically mimic each other , the  only difference is site of resistance to pulmonary flow. RVOT vs Lung vasculature )

* Essentially Atrial admixture is more complete than when it happens at ventricular or great vessel level

For advanced readers only

Now, is it possible for “Net” left to right shunt to  result in cyanosis ?

Yes*.Very much possible. The bulk of this group is referred to as admixture lesions with certain caveats.There should be an obligatory mixing without contribution from RVOT obstruction or raised PVR( *Please note theoretically  admixture can either be right to left  or  left to right shunt )

All pure admixture lesions are in fact net left to right shunts. (TAPVC, Single ventricle , Common atrium , Common AV canal ,Truncus, ) This is the group we have been traditionally calling cyanosis with increased pulmonary flow.

Its may also to be noted with  surprise some admixture lesions often  has less intense cyanosis than other forms as long as pulmonary blood flow is normal and the lung does its job perfectly .

*Please note Isolated classical left to right shunts , ASD, VSD, PDA can never cause significant cyanosis unless there is reversal of flow .However ,many Eisenmenger physiology  show net Left to right shunting only ( 1.2-1.5 : 1 or so ) but with a definite right to left component .What we call as typically bi-directional shunt .

How can cyanosis be minimal even in some cases of single ventricle ?

  • Even though there is single ventricle , there can be preferential (favorable)  streaming of right heart blood flow without gross mixing .
  • As discussed before good uninterrupted pulmonary blood flow will make the cyanosis less intense .

Is single ventricle with PS  admixture lesion or TOF physiology ?

Though single ventricle in isolation is an admixture lesion, when it has associated RVOT obstruction it ceases  to be admixture by definition  as mixing is augmented by the obstruction rather than by simple mixing.The complexity could be understood in certain situations  where admixture lesions  like common AV canal  go for raised PVR .Here the various quantum of contribution to cyanosis is mind boggling. (Original admixture, augmented by RVOT resistance, differential mixing at atrial and ventricular level  , hypoxia  at lung level due micro pulmonary AV fistulas in grade 4 heath Edwards etc )

Role of streaming in Admixture lesions

Streaming is selective flow of  venous blood into PA and arterial blood into Aorta even in the presence of  large septal defects. Favorable streaming implies good systemic saturation. Unfavorable streaming would mean PA saturation more than aorta.(It should be noted streaming and good admixture don’t go together. If good admixture has happened there can’t be any streaming and vice versa)

Streaming is common in which situations?

Inspite of absence of IVS, streaming has been noted in some cases of single ventricle with minimal cyanosis with good saturation in Aorta.

Streaming in TAPVC has some unique features.

Fetal circulation has certain preformed pathways. IVC blood deflects to LA through ASD/PFO .SVC blood preferentially enter RV-PA. In Infradiaphragmatic TAPVC where it  drains into IVC  highly saturated PV blood may stream  into LA  thorough ASD and reach LV nd result in  higher Aortic saturation.(This is in contrast the  classical type of TAPVC draining into RA  with little favorable streaming and hence  O2 saturation equilibrates between PA/Aorta.)

In Supra cardiac TAPVC that drains into SVC or coronary sinus  the streaming is unfavorable as it may preferentially cross tricuspid valve and enter PA making the saturation  higher than Aorta.

Streaming is less common in which lesions ?

In common atrium and TAPVC draining into  RA  streaming is less common.In tricuspid atresia streaming is almost impossible as TV is non existent and this ensures complete mixing in the atria and hence cyanosis is likely to be severe.

Can TOF behave  like an admixture lesions ?

Technically yes.If the RVOT obstruction is minimal ,(What was called then as pink Fallot ) We haven’t  understood this entity properly for so long. Atleast  I was baffled to read when J.K Perloff mentioned in his book  during my DM fellowship days, that TOF can manifest  with predominant left to right shunt with little or absent cyanosis.

The  aortic override in TOF facilitated by large malaligned VSD make it a sort of admixture  situation as  RVOT resistance is too little to offer any resistance, (rather it welcomes more blood from left side ! ) So , should we call it simple VSD physiology , admixture physiology or  just acyanotic forms of TOF ?)

Key points

Though admixure lesions are discussed separately , bulk of them  actually represent cyanosis with increased pulmonary blood flow situations.

The  net pulmonary blood flow is much more important than the quantum  of admixture in determining the degree cyanosis

Finally , one should appreciate  there can be combination admixture lesions with obstructive RVOT components . (Tricupid atresia+Pulmonary stenois )

Further reading

An excellent review article on this rare topic of  admixture physiology

  1. Jaganmohan A Tharakan Admixture lesions in congenital cyanotic heart disease Ann Pediatr Cardiol. 2011 Jan-Jun; 4(1): 53–59.


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Spontaneous closure of VSD is  a well recognised  phenomenon, than ASD  though both happen in equal frequency.The simple reason being VSD is a noisy disease , ironically the smaller the size of VSD  more noisy it is . Hence  it is rarely  missed  while ASD is largely silent in children. For this reason  it is  possible ASD may be the most common congenital disease .

Natural history of ASD(OS) closure

  • ASDs of size 3-4 mm 100 % will close by 3  years
  • Bulk of the ASD < 8  mm close spontaneously by 5 years.
  • ASD> 10mm is unlikely to close

Factors that determine spontaneous closure

  • Apart from size and location
  • Closure  is accelerated by remnant of flap of foramen  ovale
  • Fenestrations and  Septal  aneurysms also  favor spontaneous closure.
  • Margins  of the defect if rough  triggers fibrotic reactions

spontaneous closure of asd

Why SVC and primum defect do not close easily ?

Plane of ASD  secundum is single and  bridging of tissue is possible .

Sinus venous and  primum defects exhibit  holes which run in multiple planes hence approximation not possible . They also do not  have a valve mechanism.

Un-natural history of ASD

In the current era, one more  force interferes  with spontaneous closure of ASD . It  comes from the  hyper trained aggressive Interventional cardiologists who compete with the nature and easily prevail over it !


asd spontaneous closure

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Can we close an  ASD in a  25 year old women  severe  pulmonary hypertension ?
Volumes of literature has been written  on the subject.Dedicated cath studies  have been done with multiple parameters .
Still , there is a lingering doubt !
Here is  a  3 minute  practical solution  based on 5 easily available parameters. (* Also referred to as  unscientific  in medical parlance !)
1.  O2 saturation
2. Pulmonary artery diastolic and pulse pressure
3. RV function,
4 .Systemic pressure
5. Functional class
  • If O2 saturation is > 90 % consistently  there is likely to be significant  left to right shunt  .Closure is to strongly considered
  • If 02  saturation is near 95 % there is absolutely no contraindication at any level of PVR.
  • Systolic pulmonary artery pressure derived by TR jet is least useful index.Pulmonary artery diastolic pressure reflects true vascular  reactivity of the pulmonary  circulation.A wide swinging pulmonary arterial pulse indicates dynamism in circulation and hence operablity.
  • If pulmonary artery  pulse pressure is  wide (>50)  , or PA diastolic BP is < 30 one can safely presume irreversible damage to pulmonary vasculature has not occurred and these patients would  benefit  from surgical closure .
  • RV  function should be assessed carefully in every patient.This is as important as PVR .Significant RV dysfunction is an absolute contraindication.
  • Never close the shunt in patients who is in class 4  symptoms.
  • Never close a shunt if the systemic blood pressure is low( 90mmhg)
  • Some believe  PDA may be closed at any given PVR , while  worst outcomes occur with ASD as supra-systemic pulmonary pressure is possible.
Always monitor these patients meticulously especially  in the initial days following surgery  for deterioration .Most patients will do well if they cross the first 30 days. The RV  learns to adopts with  new  pulmonary hemodynamics !


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All left to right shunts are  acyanotic heart disease to begin with. Cyanosis appears if there is progressive PHT and reversal of shunt .We know this happens late in ASD.(third decade)

It is important to remember some of the  patients  with large ASD  can show significant desaturation without severe pulmonary HT.  This should not be mistaken for Eisenmenger reaction.

How ?

In  any large ASD ,

  • IVC blood can stream into LA by hitting preferentially the lower part of IAS.( It is the old fetal route that heart does not forget  and indulges whenever the  local hemo-dynamics permits !)
  • During straining , (Valsalva and equivalents)  right atrial pressure can exceed LA and small amount of shunts occur across RA.
  • ASD is often (15%) associated with systemic venous anomaly. The common one is persistent LSVC.  LSVC  is usually connected to coronary sinus . If it has a communication with LA (Un-roofed CS) , there can be significant cyanosis .
  • Further , a large ASD can act as a single atrium and considerable mixing happens and cyanosis results.

Finally ,two conditions should always be considered

  • ASD if associated with VPS auguments R-L shunt .
  • TAPVC can be mistaken for Eisenmengerisation of  ASD in bedside which presents as clinical signs of ASD + Cyanosis

* It is useful to recall ,even PFOs can shunt right to left at times of extreme RA pressures like during PEEP ventilation and orthostatic  deoxia in sick ICU patients are reported (If PFO can shunt R-L , why not huge ASD ?)

Final message

Cyanosis  in ASD is not always  an ominous sign .There are few important causes other than Eisenmenger. Though it  occurs intermittently , persistent mild desaturation is also possible.

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Congenital heart disease (CHD) still constitute an significant  subset in cardiology practice.The moment you ask how do you classify CHD  to any cardiologist , the answer  would come promptly as “cyanotic and acyanotic CHD “. Such is the power traditional clinical teaching .
There is a fundamental embryological and functional classification available put forth by Clark.It lifts  our understanding about congenital heart disease to a  different perspective. I wish,every cardiology fellow should know this.
 Link to embryological classification of congenital heart disease .
 A subset for cono-truncal anomalies is also available.
cono truncal anomalies embryology of heartReference
Clark EB. Mechanisms in the pathogenesis of congenital heart defects. In: Pierpont ME, Moller J, editors. The Genetics of Cardiovascular Disease. Boston, MA: Martinus-Nijoff; 1986. pp. 3–11.

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Inter atrial septal aneurysm is a benign disorder of IAS where the flap  of fossa ovalis bulges on either to right  or left atrium. It may be associated with fine fenestration or even a classical  ostium secundum  ASD.

atrial septal aneurysm 002

An unusual buckling motion of IAS aneurysm.

Though the pressure within the atria is one of the determinant of this  bulge.The morphology of the flap is such that it more often prolapse into LA than RA. Rarely it can be dynamic and  moves 180 degrees , buckling between RA and LA .This unusual  motion is real stress to IAS and can trigger atrial  ectopic beats. and atrial tachycardia .

Read  related article  IAS aneurysm 


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Dual LAD is an interesting coronary artery anomaly proposed  originaly  by Spindola in 1983 .He classified it into 4 types. In recent years the  dual LAD has increased from 4 to 6 types.

The essential criteria to diagnose  could be summarised.

  1. Two LADs should be identified.
  2. One would be  large and another small
  3. Both should give a  diagonal  branch .

* Ramus is virtually unknown  if there is dual LAD .

The origin  of second LAD can be from

  • LMCA
  • RCA
  • Direct from Right coronary sinus


  • Can be epicardial
  • Intra -myocardial
  • Or both


  • Diagonal
  • Septal
  • or Both

Drainage area

  • Highly variable

Implication for intervention

  1. Apart  from  the surprise element , the second LAD   has  little impact on the interventional protocol.
  2. However , it may confer a  ischemic protection  as the critical anterior wall has a twin blood supply.
  3. Whether  they are protected from primary  VT or VF is to be studied  because of better electrical stability
  4. Second LAD may act as an additional collateral channel.

Spindola’s  classification of Dual LAD (Types 1 to 4  was called sometimes A,B,C,D )

classification of dual LAD

Source : Lee et al. BMC Cardiovascular Disorders 2012, 12 :101

Spindola type 1 to 4 classification of dual LAD

An illustration of  first 4 types  of Dual LAD .Note  the type 4 originates from RCA. Image courtesy : Prachi P. Agarwal Ella A. Kazeroon . AJR:191, December 2008

Surgical issues ( This is  excellent data  from India . I convey  my   greetings to one  the authors Dr D.B Baruah,  my friend  from  CMC Vellore !)

dual lad classification Spindola-Franco H, Grose R, Solomon


Spindola-Franco H, Grose R, Solomon N. Dual left anterior descending coronary artery: angiographic description of important variants and surgical implications. Am Heart J 1983:105;445-55

Dual Left AnteriorDescending CoronaryArterySurgical Revascularization in 4 Patients Tex Heart Inst J 2000;27:292-6


Dual LAD  CT  Angiogram : http://www.ajronline.org/doi/pdf/10.2214/AJR.08.1193

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