Tetralogy of fallot (TOF)

By : - Dr. Sanjeev

Tetralogy of fallot

Commonest cyanotic congenital heartdisease in children above the age of twoyears constituting almost 75 % of all bluepatients.

Four constituents of tetra logy as describedoriginally by Fallot consist of :-

1. Ventricular septal defect (VSD)

2. Pulmonic stenosis

3. overriding or dextroposed aorta, and

4. Right ventricular hypertrophy

Pathophysiology :-

Physiologically the pulmonic stenosis causesconcentric right ventricular hypertrophywithout cardiac enlargement and an increase inright ventricular pressure -- when the rightventricular pressure is as high as the leftventricular or the aortic pressure, a right to leftshunt appears to decompress the right ventricle-- once the right and left ventricular becomeidentical, increasing severity of pulmonicstenosis reduces the flow of blood into thepulmonary artery and increases the right to leftshunt -- as the systolic pressures betweentwo ventricle are identical there is little or noleft to right shunt and the VSD is silent ------------

Cont…

The right to left shunt is also silent since itoccurs at insignificant difference in pressurebetween the right ventricle and the aorta -- the flow from the right ventricle into thepulmonary artery occurs across thepulmonic stenosis producing an ejectionsystolic murmur -- more severe thepulmonic stenosis, the less the flow into thepulmonary artery and the bigger the rightto left shunt -- more severe the pulmonicstenosis, the shorter the ejection systolicmurmur and the more the cyanosis ---

Cont…

 thus the severity of cyanosis is directlyproportional to the severity of pulmonicstenosis, but the intensity of the systolicmurmur is inversely related to the severityof pulmonic stenosis

The VSD of TOF is always large enough toallow free exit to the right to left shunt --- since the right ventricle is effectivelydecompressed by the VSD --- congestivefailure never occurs in TOF.

Cont…

 the right ventricular outflow obstructionresults in the delay in the P2 -- sincethe pulmonary artery pressure is reduced,the P2 is also reduced in intensity -- thelate and soft P2 is generally inaudible inTOF -- the S2 is , therefore, single andthe audible sound is A2 -- since the aortais somewhat anteriorly displaced, theaudible single A2 is quite loud --- theascending aorta in TOF is large and mayresult in an aortic ejection click

Cont…

Right ventricular hypertrophy reduced thedistensibility of the right ventricle duringdiastole ---- the right atrial contraction atthe end of diastole causes a relatively large`a ` wave (prominent in the jugular venouspulse).

Clinical features : -

Become symptomatic any time after birth

Paroxysmal attack of dyspnea

Cyanosis may be present from birth or makeits appearance some years after birth

Commonest symptoms are dyspnea onexertion and exercise intolerance

Patients assume a sitting posture – squatting– as soon as they get dyspneic. Althoughsquatting is not specific for TOF, it is thecommonest congenital lesion in whichsquatting is noted

Anoxic spells occur predominantly afterwaking up or following exertion.

Normal growth and development depend on anormal workload for the heart and normal flow ofoxygen-rich blood to all parts of the body. Babieswho have tetralogy of Fallot may not gain weightor grow as quickly as children who have healthyhearts because they tire easily while feeding.

 Squatting (a compensatory mechanism) isuniquely characteristic of a right-to-left shunt thatpresents in the exercising child. Squattingincreases the peripheral vascular resistance,which diminishes the right-to-left shunt andincreases pulmonary blood flow.

–Child becomes more cyanosed while crying, theseare called ‘cyanotic spells’or Fallot’s spells.

What causes a spell ?

Due to "spasm" or contraction of a band ofmuscle in the right ventricle just under thepulmonary valve. When this musclecontracts, it further narrows the channel forblood flow into the lungs. As a result,oxygen delivery becomes further reduced.This causes a spell

On physical examination : -

Cyanosis , clubbing, slightly prominent `a ‘wave in the jugular venous pulse, normalsized heart with parasternal impulse, asystolic thrill in less than 30 % patients.

Normal first sound,

Single second sound and

An ejection systolic murmur.

Investigations : -

ECG : right axis deviation with rightventricular hypertrophy

Echocardiography : identify the largeoverriding aorta, right ventricularhypertrophy and outflow obstruction.

Chest X – ray :

Boot shaped heart (itmeans apex is lifted up& there is a concavityin the region ofpulmonary artery)Boot shaped heart (itmeans apex is lifted up& there is a concavityin the region ofpulmonary artery)

Oligaemic lung fieldsOligaemic lung fields

Hilar vessels are few,lung vessels also few,large rt. Venricle.Hilar vessels are few,lung vessels also few,large rt. Venricle.

Treatment :

Management of complications and correctionof anemia

Treatment of Anoxic spells :

Knee chest position to increase aorticresistance. The increased aortic and leftventricular pressure reduces the rush ofblood through the septal hole from the rightventricle and improves blood circulation tothe lungs, decreasing the right to left shuntthus decreasing the amount of deoxygenatedblood entering the systemic circulation.

Oxygen through a face mask to increase theamount of oxygen in the blood.

Cont …

beta-blockers such as propranolol

acute episodes may require rapidintervention with morphine to reduceventilatory drive and a vasopressorsuch as epinephrine, phenylephrine,or norepinephrine to increase bloodpressure.

Correction of anemia

Consider operation

Surgery : -

Blalock-Taussig operation : connectionbetween the right subclavian artery, andthe right pulmonary artery, which increasesthe amount of red oxygenated bloodreaching the lungs, relieving cyanosis.

Pott`s shunt : descending aorta isanastomosed to the pulmonary artery

Waterstont`s shunt : ascending aortaright pulmonary artery anastomosis

Cont….

Total correction: The hole in theventricular septum is closed with a patchand the obstruction to right ventricularoutflow, pulmonic stenosis, is opened.

These corrections allow blood flow to thelungs for oxygenation before being pumpedout into the body.

Coarctation of the aorta

There is localised narrowing ofthe aortic arch, just distal orproximal to the ductus orligamentum arteriosus and alsothe left subclavian artery.

40 – 80 % patients have abicuspid aortic valve.

There are three types :

A. Ductal coarctation

B. Preductal coarctation

C. Postductal coarctation (mostcommon)

Cont …

Pathophysiology :-

Physiologically the difference between thepreductal and postductal coarctation dependson the absence or presence of collateralanastomosing vessels -- in the fetal life, theright ventricular output passes down thedescending aorta through a wide ductusarteriosus and left ventricular output into theleft carotid and left subclavian arteries ---very little of the left ventricular output reachesthe descending aorta --- the portion of theaorta distal to the left subclavian and before theportion where the ductus arteriosus joins calledthe isthmus -------

Cont …

At birth, normally the isthmus is the mostnarrow part of the aorta -- if the fetushas a preductal coarctation it does notinterfere with his normal hemodynamic andcollaterals are not formed --- on the otherhand if a postductal coarctation is present itis operative in the fetal life as it interferewith right ventricular output reaching thedescending aorta --- this stimulates theformation of collaterals even in the fetal life-------------

Cont….

 after birth when the right ventricular outputis directed into the pulmonary arteries andthere is no flow from the pulmonary into theaorta, the descending aorta must receive itstotal supply from the left ventricle via theascending aorta -- since in preductalcoarctation there are no collaterals, theneonate becomes symptomatic immediately –hypertension resulting in LVF -- neonateswho have a postductal coarctation alreadyhave some collaterals and are spared fromdeveloping severe hypertension andcongestive cardiac failure ---------

Cont…

 the exact mechanism for theproduction of systemic hypertensionin coarctation is not known --- thenarrowed pulse pressure in thedescending aorta distal to thecoarctation has been implicated in therenal mechanism for the causation ofhypertension in coarctation.

Cont…

resting blood pressure the obstruction stimulates growth ofcollateral vessels between the proximal anddistal segments --- the intercostal vesselsalso participate in decompressing thehypertension upper segment --- theyenlarge and become palpable at the lowerborders of the ribs --- palpable collateralsare also felt at the medial and inferior angleor scapula --- because of thedecompression of the upper segment by thecollaterals, the resting blood pressure inthe upper extremities may be even normal(on exercise, systolic pressure getsaccentuated).

Clinical features : -

Uncomplicated coarctation :

Intermittent claudication (due to a temporaryinadequate supply of oxygen to the muscles of theleg)

Pain and weakness of legs and

Dyspnea on running

Physcial examination shows delayed and weakor impalpable femorals compared to strongbrachial arteries.

Dorsalis pedis palpable (because distal pulsepressure is wider)

Diagnosis can be excluded if femoral pulse iswell felt.

Cont…

Rarely it is possible for the patient to continue tohave pulmonary arterial hypertension ---- apatent ductus arteriosus may support the distalsegment of the aorta -- in such a situationgood femoral pulsations may be present in spiteof coarctation which would be preductal inlocation and cyanosis in toes --- it isimportant to remember that the site ofcoarctation does not determine whether the flowthrough the PDA is from left to right or from rightto left --------

Cont….

 whether the coarctation is preductal orpostductal, the flow is from left to right sincethe distal segment of the aorta in coarctationalmost never has a mean pressure below 50mm of Hg. ----- if the flow through the PDAis from right to left, it indicates that there issevere pulmonary arterial hypertension.

Heart size remains normal

Systolic thrill may be palpable in thesuprasternal notch

Prominent arterial pulsation in thesuprasternal notch and the carotid vessels

Cont…

Second sound is normally split with a loudaortic component

Late systolic murmur and/or early diastolicmurmur

Investigations :-

Electrocardiography : may show leftventricular hypertrophy

MRI : ideal

Chest X – ray :

X ray features : -X ray features : -

Heart is enlarged intransverse diameter dueto left VentricularenlargementHeart is enlarged intransverse diameter dueto left Ventricularenlargement

3 figures

Rib notching ( mostly 4th– 8th ) due to theirerosion by enlargedcollateral intercostalarteriesRib notching ( mostly 4th– 8th ) due to theirerosion by enlargedcollateral intercostalarteries