Posts Tagged ‘tetrology of fallot’

The right to left shunt  in TOF  occurs by  which of the the following route ?

  1. RV- VSD- LV -Aorta

  2. RV-  Aorta

  3. RV – VSD- Aorta

  4. All of the above can occur

    Answer : 2   Most shunting occur by direct streaming of RV blood into Aorta . If the aortic  override  is near 50 %  it need not even cross the VSD in it’s  circuit. (Although theoretically all of the above can occur)


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Second heart sound in TOF is often single and loud . It is often  best heard in left 2nd intercostal space as well as on right 2nd  space.

This is primarily due

  1. Presence of  pulmonary stenosis  and  resultant reduced pulmonary blood flow makes P2 soft or absent .Hence  A2 becomes loud by default.
  2. In tune with any  cono -truncal anomaly  , aortic root  is  anteriorly  malposed  in TOF. This brings the aorta  closer to chest wall  (Nullifying the  aquastic insulation  of main  pulmonary trunk  ) and results in a  booming aortic  second heart sound.
  3. Increased flow across  aortic valve . In cyanotic heart disease with reduced pulmonary blood flow aortic flow is augmented and may even result in dilatation of aorta . A large aorta with increased flow is perfect setting  for  generating a loud A2  . It  is common to hear a  aortic ejection click as well in these situations .

When you hear a single  second heart sound at  the base  of heart  , how do you recognise it to be   A2  or P2 ?

Will be answered shortly.

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It is a combination of biochemical and  pulmonary receptor mediated dyspnea.

1. Hypoxia gets accentuated on exertion and it stimulates  chemoreceptors  located  in brainstem  as well as  aortic arch and its branches.

2. Equally important is the ventilation /perfusion mismatch that occur during exertion as the pulmonary blood flow significantly drops while the lung will continue with normal ventilation .This  increases the  Vp/Vq   (> 1) and  worsen the hypoxia  and   can independently trigger the sensation of dyspnea due to stretching of airway mechanoreceptors..

(It is  prudent to recall ,the later mechanism (Vp/Vq mismatch ) is  explicitly involved in  isolated  valvular pulmonary stenosis .Here , there is no admixture  mediated hypoxia , still the patient experience significant dyspnea  due  to meager  reduction  in pulmonary blood flow.)

3. Further ,  there are some morphological changes that occur in pulmonary vasculature in patients with TOF.This is due to chronic hypoxia as well as  “chronic low flow” mediated vascular reactivity. Micro vascular dysfunction in the alveolar capillary bed  is  possible in TOF. There  is  some evidence to suggest pulmonary gaseous exchange is impaired when compared to normal lungs.This can also contribute to the dyspnea in TOF.


The following article excellently describes the pulmonary dysfunction  that occurs in patients with TOF .It is prudent to note  ,the abnormal  lung function fails to get corrected even after total surgical correction in many.


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Heart is the first organ to differentiate in the fetus.The first heart beat begins on the 22nd day of fetal life ! . From that day , it’s function is linearly determine the   fetal growth  .It continues in the new-born,  infancy and  up to late child hood.

It is no surprise  then, to detect growth retardation in congenital heart disease. A proper evaluation begins right from fetal mass / birth weight estimation  .Motor and cognitive milestones should be assessed meticulously .

The pattern of growth affliction is  complex  and poorly understood.Few  working rules are  often taught in cardiology classrooms.

Caution : This is a too simplified version. Discerned readers should consult all sources cited here.

Acyanotic heart disease

ASD, VSD, PDA  tend to affect weight gain  more but generally do not affect height  much  . But, the onset of pulmonary  hypertension early in the course will severely  affect height as well.

Co arctation of  Aorta and other Aortic interruptive   diseases  can have a differential  affection of growth . (Upper part of body > Lower part)

Cyanotic heart disease

CHD  affects both height and weight proportionately. Cyanotic  heart disease with increased pulmonary blood flow  the overall survival is less ,  recurrent failure is common  and hence growth and development is more affected.

The mechanism of stunted  growth.

The often used terminology  ‘failure to thrive” , may not be attributed to heart disease per-se. It has to be multi factorial and  is related to  social well-being  ,  feeding habits , and mother’s effort  , interruptions due to co existing illness , effects of surgery  etc. Obviously these factors operate  more  in infants with increased pulmonary blood flow.

Effect  on cognitive function

Contrary  to the expectations  even chronic hypoxia and cyanosis has no compelling effects  on the child’s intelligence . Unless there is co existing  neurological defects severe compromise of cognition  is  uncommon.

However now we realise , brain development do  suffer   in hypoxic environment.In fact, the damage  to cognition could start right from the fetus .

New evidence is coming  up.

*Recurrent hypoxia spells and convulsions in TOF  can lead to reduced cognition

Is the normal  growth  and development   restored after complete correction of the disease by  cardiac surgery ?

The expected benefit is usually achieved  . The catch up occurs . But it is not guaranteed,   especially in  cyanotic heart disease. As , many times the  destined growth of a child   is  reprogrammed and  predetermined  in the fetus itself.

Link to a rare review article on the topic

References  on Growth impairment in congenital heart disease


R. L. Naeye, “Anatomic features of growth failure in congenital heart disease,” Pediatrics, vol. 39, no. 3, pp. 433–440, 1967.

A. Mehrizi and A. Drash, “Birth weight of infants with cyanotic and acyanotic congenital malformations of the heart,” Journal of Pediatrics, vol. 59, no. 5, pp. 715–718, 1961.

R. J. Levy, A. Rosenthal, D. C. Fyler, and A. S. Nadas, “Birthweight of infants with congenital heart disease,” American Journal of Diseases of Children, vol. 132, no. 3, pp. 249–254, 1978.

H. H. Kramer, H. J. Trampisch, S. Rammos, and A. Giese, “Birth weight of children with congenital heart disease,” European Journal of Pediatrics, vol. 149, no. 11, pp. 752–757, 1990.

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Squatting is an excellent hemodynamic adaptation in patients with TOF. Children with TOF assume this posture   in  a natural and effortless manner . For years cardiologists are fascinated by this maneuver  and the mechanism by which it gives relief  to those patients with TOF.

Now , we have realised  this posture  has a new diagnostic role in echocardiography ! This paper was presented in the recently concluded  Annual scientific sessions of cardiological society of India held in Kolkatta December 2010

Download  the full   presentation in PDF  format  (  Squat Echo)

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Tetrology of Fallot is the commonest cyanotic heart disease . In 1973 , working at Portland,  Oregon , Bonchek  and colleagues created this classic with intense clinical acumen , that defined the way   how we understood TOF   in infancy  . Such studies  have  become extinct in this fast paced cardiology academia !

With due tributes , here is a slightly modified version of Bonchek classification of  TOF in infancy .

Every cardiologist must read every line of this article  which came 37 years ago  !

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It is a well known fact squatting is a simple compensatory posture adapted by children with cyanotic heart disease during exertion to get relief from breathlessness. The children with tetrology of Fallot and related conditions have baseline hypoxia due to right to left shunting .This gets aggravated during exertion. Squatting promptly relieves this exercise-induced worsening of dyspnea. The oxygen saturation improves immediately after assumption of squatting posture. The exact mechanism by which squatting relives the dyspnea is not clear.

Apart from squat induced po2 raise there is a fall in the concentration of pco2 and raise in blood Ph that pacify the sensitive respiratory centers,thereby bringing down the tachypnea

Hemodynamics of squatting has two phases

  • Immediately ( First 15 seconds) after squatting there is a sudden drop in venous return.
  • Sustained squatting for 1-2 minutes result in steady increase in venous return, raised systemic vascular resistance.

Both these effects help the children with TOF. The initial trapping of highly desaturated blood in the lower extremity gives a quick relief as soon as the child assumes this posture. In the next 15 seconds or so the systemic vascular resistance increases and bring the aortic after load sufficiently high to divert the blood into the pulmonary artery.

The net effect of squatting is there is a transient or sustained (as long as child squats) increase in pulmonary blood flow and this is made possible by the relative reduction of right to left shunt as the aortic and systemic resistance is raised by this posture.

Other explanations

There is one more possible effect of squatting. By, compressing abdomen (Knee chest) cause a mechanical push on the splanchnic blood pool into the aorta which has high o2 saturation. This is thought to provide immediate relief to brain hypoxia and avoid the vicious respiratory/ hemodynamic cycle

What is the clinical inference from squatting in cyanotic heart disease?

Squatting implies there should be a large VSD, associated with a delicate right to left shunting very much dependent on the degree of pulmonary stenosis or ( any RVOT obstruction) and the systemic vascular resistance.

How common is squatting history in pulmonary atresia with VSD ?

It can occur with collaterals are sparse.The mechanism of relief is slightly different.

The likely mechanism of relief with squatting in Pulmonary Atresia, VSD is two fold.

1. The Initial relief is due to trapping of deoxygenated venous blood in squat posture, which is similar to TOF

2.The sustained benefit is due to raised systemic vascular resistance which favors more flow across MAPCAs from Aorta.

The second one has no authentic reference , but its a hemodynamic plausiblity as there is zero RVOT flow in PA with VSD.

What are the other cyanotic heart diseases in which squatting is reported ?

  • Tricuspid atresia
  • Double outlet right ventricle with pulmonary stenosis
  • Any combination of large VSD and RVOT obstruction
  • Rarely in Eisenmenger syndrome*10%)

*Mechanism of squatting episodes in Eisenmenger is tough to explain. But, it does give relief. The most plausible mechanism is the raise in SVR with squatting tilts temporarily a favorable QP/QS as PVR -SVR ratio falls .(Venous return component doesn’t operate here as in squatting of TOF) It should be noted squatting is mainly reported only in VSD Eisenmenger.. ASD/PDA -Eisenmenger is extremely rare or doesn’t occur. This is understandable as Interventricular communication has to be present to shift in QP/QS with a response to a rise in SVR.

Squat equivalents

Assuming a squat position has cultural issues. Grown-up children may avoid these public places. Standing with legs crosse is a common posture. In fact, the mother holding a crying baby in a chest with knees folded promptly prevents a spell . This can be called “squatting by proxy”

*Though squat equivalents do give relief from dyspnea they are given less significance in terms of diagnostic value of TOF


1.Paul R. Lurie ,Postural effects in tetralogy of Fallot The American Journal of Medicine Volume 15, Issue 3, September 1953, Pages 297-306

2. Warren G. Guntheroth. M.D.Beverly C. Mortan. m.Venous return with knee-chest position and squatting in tetralogy of Fallot American Heart Journal Volume Volume 75, Issue 3, March 1968, Pages 313-318

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