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Tetralogy of fallot

Introduction:

Tetralogy of Fallot (TOF) is one of the most common congenital heart

disorders (CHDs). This condition is classified as a cyanotic heart disorder,

because tetralogy of Fallot results in an inadequate flow of blood to the lungs

for oxygenation (right-to-left shunt) (see the following image). Patients with

tetralogy of Fallot initially present with cyanosis shortly after birth, thereby

attracting early medical attention.

Normal heart Tetralogy of Fallot

Louis Arthur Fallot, after whom the name tetralogy of Fallot is derived,

was not the first person to recognize the condition. Stensen first described it in

1672; however, it was Fallot who first accurately described the clinical and

complete pathologic features of the defects.

Definitions:

Tetralogy of Fallot (TOF) is a congenital heart defect which is classically

understood to involve four anatomical abnormalities (although only three of

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them are always present). It is the most common cyanotic heart defect, and the

most common cause of blue baby syndrome

Etiology and Pathophysiology:

The cause(s) of most congenital heart diseases (CHDs) are unknown,

although genetic studies suggest a multifactorial etiology. A study from

Portugal reported that methylene tetrahydrofolate reductase (MTHFR)

gene polymorphism can be considered a susceptibility gene for tetralogy

of Fallot.

Prenatal factors associated with a higher incidence of tetralogy of Fallot

(TOF) include maternal rubella (or other viral illnesses) during

pregnancy, poor prenatal nutrition, maternal alcohol use, maternal age

older than 40 years, maternal phenylketonuria (PKU) birth defects, and

diabetes. Children with Down syndrome also have a higher incidence of

tetralogy of Fallot, as do infants with fetal hydantoin syndrome or fetal

carbamazepine syndrome.

As one of the conotruncal malformations, tetralogy of Fallot can be

associated with a spectrum of lesions known as CATCH 22 (cardiac

defects, abnormal facies, thymic hypoplasia, cleft palate, hypocalcemia).

Cytogenetic analysis may demonstrate deletions of a segment of

chromosome band 22q11 (DiGeorge critical region). Ablation of cells of

the neural crest has been shown to reproduce conotruncal malformations.

These abnormalities are associated with the DiGeorge syndrome and

branchial arch abnormalities.

The hemodynamics of tetralogy of Fallot depend on the degree of right

ventricular (RV) outflow tract obstruction (RVOTO). The ventricular

septal defect (VSD) is usually nonrestrictive, and the RV and left

ventricular (LV) pressures are equalized. If the obstruction is severe, the

intracardiac shunt is from right to left, and pulmonary blood flow may be

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markedly diminished. In this instance, blood flow may depend on the

patent ductus arteriosus (PDA) or bronchial collaterals.

Epidemiology

Tetralogy of Fallot (TOF) represents approximately 10% of cases of

congenital heart disease (CHD), occurs in 3-6 infants for every 10,000

births, and is the most common cause of cyanotic CHD. This disorder

accounts for one third of all CHD in patients younger than 15 years.

In most cases, tetralogy of Fallot is sporadic and nonfamilial. The

incidence in siblings of affected parents is 1-5%, and it occurs more

commonly in males than in females. The disorder is associated with

extracardiac anomalies such as cleft lip and palate, hypospadias, and

skeletal and craniofacial abnormalities. Genetic studies indicate that in

some patients with tetralogy of Fallot, there may be 22q11.2 deletion and

other submicroscopic copy number alterations.[4]

Tetralogy of Fallot is also observed in other mammals, including horses

and rats.

Diagnosis of Tetralogy of Fallot:

History:

The clinical features of tetralogy of Fallot (TOF) are directly related to

the severity of the anatomic defects. Most infants with tetralogy of Fallot have

difficulty with feeding, and failure to thrive (FTT) is commonly observed.

Infants with pulmonary atresia may become profoundly cyanotic as the ductus

arteriosus closes unless bronchopulmonary collaterals are present. Occasionally,

some children have just enough pulmonary blood flow and do not appear

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cyanotic; these individuals remain asymptomatic, until they outgrow their

pulmonary blood supply.

At birth, some infants with tetralogy of Fallot do not show signs of

cyanosis, but they may later develop episodes of bluish pale skin during crying

or feeding (ie, "Tet" spells). Hypoxic tet spells are potentially lethal,

unpredictable episodes that occur even in noncyanotic patients with tetralogy of

Fallot. The mechanism is thought to include spasm of the infundibular septum,

which acutely worsens the right ventricular (RV) outflow tract obstruction

(RVOTO). These spells can be aborted with relatively simple procedures.

A characteristic fashion in which older children with tetralogy of Fallot

increase pulmonary blood flow is to squat. Squatting is a compensatory

mechanism, of diagnostic significance, and highly typical of infants with

tetralogy of Fallot. Squatting increases peripheral vascular resistance (PVR) and

thus decreases the magnitude of the right-to-left shunt across the ventricular

septal defect (VSD). Exertional dyspnea usually worsens with age.

Occasionally, hemoptysis due to rupture of the bronchial collaterals may result

in the older child.

The rare patient may remain marginally and imperceptibly cyanotic, or

acyanotic and asymptomatic, into adult life.

Cyanosis generally progresses with age and outgrowth of pulmonary

vasculature and demands surgical repair. The following factors can worsen

cyanosis in infants with tetralogy of Fallot:

Acidosis

Stress

Infection

Posture

Exercise

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Beta-adrenergic agonists

Dehydration

Closure of the ductus arteriosus

The predominant shunt is from right to left with flow across the VSD into the

left ventricle (LV), which produces cyanosis and an elevated hematocrit value.

When the pulmonary stenosis is mild, bidirectional shunting may occur. In

some patients, the infundibular stenosis is minimal, and the predominant shunt

is from left to right, producing what is called a pink tetralogy. Although such

patients may not appear cyanotic, they often have oxygen desaturation in the

systemic circulation.

Symptoms generally progress secondary to hypertrophy of the infundibular

septum. Worsening of the RVOTO leads to RV hypertrophy, increased right-to-

left shunting, and systemic hypoxemia.

Physical Examination

Most infants with tetralogy of Fallot (TOF) are smaller than expected for age.

Cyanosis of the lips and nail bed is usually pronounced at birth; after age 3-6

months, the fingers and toes show clubbing.

A systolic thrill is usually present anteriorly along the left sternal border. A

harsh systolic ejection murmur (SEM) is heard over the pulmonic area and left

sternal border. When the right ventricular (RV) outflow tract obstruction

(RVOTO) (eg, from pulmonary atresia) is moderate, the murmur may be

inaudible (more cyanotic patients have greater obstruction and a softer

murmur). The S2 is usually single (the pulmonic valve closure is not heard).

During cyanotic episodes, murmurs may disappear, which is suggestive of

lessened RV outflow to the pulmonary arteries. In individuals with

aortopulmonary collaterals, continuous murmurs may be auscultated. Thus, an

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acyanotic patient with tetralogy of Fallot (pink tet) has a long, loud, systolic

murmur with a thrill along the RVOT

The following may also be noted:

RV predominance on palpation

May have a bulging left hemithorax

Aortic ejection click

Squatting position (compensatory mechanism)

Scoliosis (common)

Retinal engorgement

Hemoptysis

Hematologic Studies

Hemoglobin and hematocrit values are usually elevated in proportion to the

degree of cyanosis. Prolonged cyanosis causes reactive polycythemia that

increases the oxygen-carrying capacity. The oxygen saturation in systemic

arterial blood typically varies from 65-70%. All patients with tetralogy of Fallot

who experience significant cyanosis have a tendency to bleed because of

decreased clotting factors and low platelet count. Hyperviscosity and

coagulopathy often ensue and are particularly deleterious in patients with a

right-to-left intracardiac shunt. The usual findings are diminished coagulation

factors, and diminished total fibrinogen, which are associated with prolonged

prothrombin and coagulation times.

ABG and Oximetry

Arterial blood gas (ABG) results show varying oxygen saturation, but pH and

partial pressure of carbon dioxide (pCO2) are normal, unless the patient is in

extremis, such as during a tet spell.

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Oximetry is particularly useful in a dark-skinned patient or an anemic patient

whose level of cyanosis is not apparent. Generally, cyanosis is not evident until

3-5 g/dL of reduced hemoglobin is present.

A decrease in systemic vascular resistance (SVR) during exercise, bathing, or

fever potentiates a right-to-left shunt and precipitates hypoxemia.

Radiologic Studies

Imaging studies used in the evaluation of tetralogy of Fallot (TOF) include

echocardiography, chest radiographs, and magnetic resonance imaging (MRI).

Echocardiography

Ductus arteriosus, muscular ventricular septal defect (VSD), or atrial septal

defect (ASD) is accurately diagnosed with color-flow Doppler

echocardiography. The coronary anatomy can be revealed with some degree of

accuracy, and valvar alterations can be detected with ease. In many institutions,

echocardiography is the only diagnostic study used before surgery.

Echocardiograms will usually reveal a large VSD with an overriding aorta and

variable degrees of right ventricular (RV) outflow tract obstruction (RVOTO).

Radiography

Initially, chest radiographs may not reveal any abnormality; however,

diminished vascularity in the lungs and diminished prominence of the

pulmonary arteries gradually become apparent.

The hallmark of tetralogy of Fallot is the classic boot-shaped heart (coeur en

sabot) (see the following image).

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Uplifted apex and absence of pulmonary artery segment typifies the "coeur en

sabot" (ie, boot-shaped heart) of tetralogy of Fallot.

Magnetic resonance imaging

MRI provides good delineation of the aorta, RVOT, VSDs, RV hypertrophy,

and the pulmonary artery and its branches.[9] MRI can also be used to measure

intracardiac pressures, gradients, and blood flows.

Drawbacks to MRI include the need for prolonged imaging times and the

requirement for sedation in small children to prevent motion artifacts.

Additionally, sick infants cannot be observed when enclosed in an MRI tunnel.

Electrocardiography

The use of electrocardiography (ECG) may be limited if multiple ventricular

septal defects (VSDs) or coronary artery anomalies are present or if the distal

pulmonary artery cannot be visualized adequately.

Right axis deviation (+120° to +150°) with right ventricular (RV) enlargement

may be seen.[10] Combined ventricular hypertrophy and right atrial hypertrophy

may be present.

If RV hypertrophy is absent on ECG, the diagnosis of tetralogy of Fallot should

be in doubt.

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A typical preoperative ECG is shown below.

Typical preoperative electrocardiogram (ECG) for tetralogy of Fallot.

Partial or complete right bundle branch block may be present; this is especially

true of patients after surgical repair (see the following image).

Typical findings on postoperative electrocardiogram (ECG) for tetralogy of

Fallot.

Cardiac Catheterization and Angiography

Cardiac catheterization provides angiographic visualization of ventricular and

pulmonary artery size. Catheterization also helps obtain pressure and oxygen

saturation measurements in different chambers and identifies any possible

shunts. In the presence of preexisting shunts, angiograms should be obtained

before complete surgical repair.

Cardiac catheterization findings include the following:

Assessment of the pulmonary annulus size and pulmonary arteries

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Assessment of the severity of right ventricular (RV) outflow tract

obstruction (RVOTO)

Location of the position and size of the ventricular septal defect (VSD)

Eliminating/ruling out possible coronary artery anomalies

Automatic internal cardiac defibrillator (AICD) placement is recommended in

patients with sustained ventricular tachycardia and those resuscitated after a

sudden death event.[11, 12]

Angiograms help identify coronary artery anomalies (see the image below);

however, catheterization is not mandatory in all patients. Cardiac catheterization

is extremely useful if the anatomy cannot be completely defined by

echocardiography, if disease in the pulmonary arteries is a concern, or if

pulmonary vascular hypertension is possible.

This angiogram shows a catheter in the right ventricle—severe infundibular

stenosis.

Diagnostic Considerations

Wide variation in the basic anatomic morphology, pathophysiology, clinical

signs and symptoms, and surgical methods of therapy is noted for tetralogy of

Fallot (TOF). Pathophysiology primarily depends on the severity of the right

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ventricular (RV) outflow tract (RVOT) obstruction. RVOT obstruction

determines the severity of right-to-left shunting, which is typical.

Other conditions to consider when evaluating a patient with suspected Tetralogy

of Fallot with pulmonary stenosis include acute anemia, asthma and reactive

airway disease, bacteremia and sepsis, cardiogenic shock, Ebstein malformation

of the tricuspid valve, pseudotruncus arteriosus, pulmonary atresia, septic

shock, and ventricular septal defect (VSD).

Differential Diagnoses

Aortic Stenosis

Pediatric Acute Respiratory Distress Syndrome

Pediatric Apnea

Pediatric Bronchiolitis

Pediatric Foreign Body Ingestion

Pediatric Patent Ductus Arteriosus Surgery

Pediatric Pneumonia

Pneumothorax

Pulmonic Valvular Stenosis

Sickle Cell Anemia

Prehospital Management

Infants with cyanosis and/or respiratory distress, including those with tetralogy

of Fallot (TOF), require oxygen. Blow-by O2 (BBO2) is the least objectionable.

Use the open-end of a cannula or tube.

Permit the baby to remain with the mother or father. Do not provoke the infant

by attempting to start an intravenous (IV) line, especially if one is not skilled in

pediatric IV placement. However, an intraosseous (IO) insertion could be an

immediate life-saving tool in emergent situations

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Emergency Department Management

The emergency physician should be able to recognize and treat a hypercyanotic

episode (tet spell) as one of the very few pediatric cardiology emergencies that

may present to the emergency department (ED).

Hypercyanotic episodes are characterized by paroxysms of hyperpnea,

prolonged crying, intense cyanosis, and decreased intensity of the murmur of

pulmonic stenosis. The mechanism is secondary to infundibular spasm and/or

decreased systemic vascular resistance (SVR) with increased right-to-left

shunting at the ventricular septal defect (VSD), resulting in diminished

pulmonary blood flow. If left untreated, it may result in syncope, seizure,

stroke, or death.

Treatment for the acute setting of hypercyanosis

Place the baby on the mother's shoulder with the infant's knees tucked up

underneath. This provides a calming effect, reduces systemic venous return, and

increases SVR.

Oxygen is of limited value, as the primary abnormality is reduced pulmonary

blood flow.

Morphine sulfate, 0.1-0.2 mg/kg intramuscularly (IM) or subcutaneously (SC),

may reduce the ventilatory drive and decrease systemic venous return.

Phenylephrine, 0.02 mg/kg IV, is used to increase SVR.

Case reports in the literature describe using a dexmedetomidine infusion to

ameliorate symptoms in hypercyanotic neonates.[13] Caution is warranted and the

drug must be carefully titrated by initiating at a very low dose of 0.1-0.125

mcg/kg/hour (without a bolus).[14] A case report of a 3-year old child with

history of tetralogy of Fallot repair at age 9 months describes atrial standstill

following mitral valve replacement.[15]

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Treating acidosis with sodium bicarbonate may reduce the respiratory center

stimulating effect of acidosis.

As a last resort, use general anesthesia.

Medical Treatment

Asymptomatic infants need no special medical treatment.

Surgery is the definitive treatment for the cyanotic patient with tetralogy of

Fallot (TOF).

The primary role of medical therapy is in preparation for surgery. Most infants

have adequate saturations and usually undergo elective repair. In infants with

acute cyanotic episodes, placing them in a knee-chest position may prove

helpful in addition to administering oxygen and intravenous (IV) morphine.

In severe episodes, IV propranolol (Inderal) may be administered, which relaxes

the infundibular muscle spasm causing right ventricular (RV) outflow tract

obstruction (RVOTO). Progressive hypoxemia and the occurrence of cyanotic

spells are indications for early surgery.

Consult a pediatric cardiologist and pediatric surgeon.

Surgical Considerations

Because tetralogy of Fallot (TOF) is a progressive disorder, most infants require

some type of surgical procedure. The timing of complete surgical repair is

dependent on numerous variables, including symptoms and any associated

lesions (eg, multiple ventricular septal defect [VSD], pulmonary atresia).

Currently, the trend is to perform a complete surgical procedure (often

electively) before the age of 1 year and preferably by the age of 2 years. Studies

have shown, however, that surgery is preferably done at or about 12 months of

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age. The majority of patients born with tetralogy of Fallot now thrive well into

their adult years.

Most surgeons today recommend the primary corrective procedure, and current

results are excellent. Infants with cyanosis are stabilized by administering

prostaglandins (to maintain the ductus in an open state). The use of

prostaglandins has significantly decreased the need to perform urgent surgery.

Instead of performing systemic-to-pulmonary artery shunts on critically ill

cyanotic-hypoxic infants, surgeons now have the luxury of having extra time to

assess the patient's anatomy and to perform the primary procedure on an

elective basis.

Primary repair avoids prolonged right ventricular (RV) outflow obstruction and

the subsequent right ventricular hypertrophy (RVH), prolonged cyanosis, and

postnatal angiogenesis.

Factors that increase risk for early repair of tetralogy of Fallot (TOF) include

the following :

Low birth weight

Pulmonary artery atresia

Major associated anomalies

Multiple previous surgeries

Absent pulmonary valve syndrome

Young or old age

Severe annular hypoplasia

Small pulmonary arteries

High peak RV–to–left ventricular pressure ratio

Multiple VSDs

Coexisting cardiac anomalies

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Contraindications

Contraindications to primary repair in tetralogy of Fallot include the following:

The presence of an anomalous coronary artery

Very low birth weight

Small pulmonary arteries

Multiple VSDs

Multiple coexisting intracardiac malformations

Palliative Procedures

The goals of palliation for tetralogy of Fallot (TOF) are to increase pulmonary

blood flow independent of ductal patency and to allow pulmonary artery growth

and even total correction. Occasionally, an infant with pulmonary atresia or an

anomalous left anterior descending (LAD) coronary artery that crosses the right

ventricular (RV) outflow tract (RVOT) may not be a surgical candidate for

establishing transannular RV–to–pulmonary artery continuity and may require

placement of a conduit.

Although artificial conduits can be used, infants with extremely small

pulmonary arteries may not tolerate total correction in infancy. These infants

may require palliation instead of corrective surgery. Various types of palliative

procedures have been developed, but the current procedure of choice is the

Blalock-Taussig shunt.

The Potts shunt has been abandoned because of a tendency toward increased

pulmonary blood flow and increasing difficulty with takedown at the time of

corrective surgery. The Waterston shunt is sometimes used, but it also increases

pulmonary artery blood flow. This shunt is more related to pulmonary artery

stenosis, which generally requires reconstruction. The Glenn shunt is no longer

used because of difficulty in performing a subsequent definitive repair.

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Blalock-Taussig shunt

Given the problems associated with the aforementioned shunts, placement of

the modified Blalock-Taussig shunt (using a Gore-Tex graft between the

subclavian artery and pulmonary artery) is the procedure of choice (see the

following images). Advantages of the modified Blalock-Taussig shunt include:

(1) preservation of the subclavian artery, (2) suitability for use on either side,

(3) good relief of cyanosis, (4) easier control and closure at time of primary

repair, (5) excellent patency rate, and (6) decreased incidence of iatrogenic

pulmonary/systemic artery trauma.

This image shows completed blocking with a Taussig shunt

This image shows a closed ventricular septal defect and closure of right

ventriculotomy with Gore-Tex.

The mortality rate is reportedly less than 1% when placing this shunt. However,

the Blalock-Taussig shunt elicits a few complications, including hypoplasia of

the arm, digital gangrene, phrenic nerve injury, and pulmonary artery stenosis.

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The longevity of palliation after shunt placement varies according to the

patient's age at the time of surgery and the type of shunt.

Other palliation procedures

Other forms of palliation that are rarely used today include patching of the

RVTO without cardiopulmonary bypass (CPB). This procedure can cause

destruction of the pulmonary valve and significant intrapericardial adhesions,

and the increased pulmonary artery blood flow can result in congestive heart

failure (CHF); therefore, its role is limited to treatment of infants with tetralogy

of Fallot complicated by pulmonary atresia and/or hypoplasia of the pulmonary

artery.

In very ill neonates with multiple medical problems, balloon pulmonary

valvulotomy has been shown to increase oxygen saturation, thus obviating the

need for emergency palliative surgery. However, perforation of the pulmonary

artery is a risk with this procedure in neonates. A study by Park et al indicated

that shunting or primary repair of neonates with symptomatic tetralogy of Fallot

produced similar mortality and results.

A study by Robinson et al found that intraoperative balloon valvuloplasty is

associated with significant longitudinal annular growth, with normalization of

annular size over time. This technique may be most useful in patients with

moderate pulmonary stenosis and moderate pulmonary valve dysplasia.

Corrective Surgery

Primary correction is the ideal operation for treatment of tetralogy of Fallot

(TOF) and is usually performed under cardiopulmonary bypass (CPB). The

aims of the surgery are to close the ventricular septal defect (VSD), resect the

area of infundibular stenosis, and relieve the right ventricular (RV) outflow tract

obstruction (RVOTO).

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Before cardiopulmonary bypass is initiated, previously placed systemic-to-

pulmonary artery shunts are isolated and taken down. Patients then undergo

cardiopulmonary bypass. Associated anomalies, such as atrial septal defect

(ASD) or patent foramen ovale, are closed.

Postoperative Monitoring and Results

All infants undergoing open-heart procedures are sent to the pediatric intensive

care unit (PICU). Hemodynamic parameters must be followed postoperatively.

One study of children who underwent complex open heart surgery procedures

found short-term outcome may be predicted by the amount of inotropic and

pressor support received in the ICU. The greater the support, the worse the

outcome. All infants initially remain intubated on a ventilator until cardiac and

respiratory statuses stabilize. To maintain systemic peripheral perfusion,

adequate cardiac output and atrial pacing may be required. Patients should be

weighed daily to follow volume status. Patients with heart block should have

temporary atrioventricular (AV) pacing. If intrinsic conduction has not returned

in 5-6 days, the patient probably needs a permanent pacemaker.

Results

The outcome of surgical repair is excellent with minimal morbidity and

mortality. To date, no difference in operative mortality rates has been noted

between transventricular and transatrial approaches.[21]

The occasional patient may have an elevated right ventricle (RV)–to–left

ventricle (LV) pressure ratio. This may be due to a number of causes including

a residual ventricular septal defect (VSD), pulmonary artery stenosis, and

pulmonary artery and valve atresia. These patients tend to do poorly, and

echocardiography is warranted to find the cause. Surgical revision may be

required to correct the etiology of the high RV pressures. As in previous studies,

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it is now apparent that preservation of pulmonary annulus can decrease the rate

of reoperation.

With improved techniques, excellent results with early 1-stage repair in infants

have been reported. Overall, the mortality rate in most series is 1-5% when the

repair is performed primarily or after a systemic-to-pulmonary artery shunt.

Similarly, the mortality rate of infants undergoing palliative shunt placement is

low (0.5-3%). The survival rate at 20 years is approximately 90-95%.

Improved techniques of myocardial protection with hypothermia, cardioplegia,

and even total circulatory arrest are providing excellent results by enabling

more precise anatomic repairs in younger infants. Nevertheless, infants

receiving complete correction before age 1 year have an increased risk

compared with patients older than 1 year.

Revision/reoperation

The literature suggests that approximately 5% of individuals will need a

revision/reoperation at some point. Indications for early reoperation include a

residual VSD or a residual RV outflow tract obstruction (RVOTO). Residual

VSDs are poorly tolerated in patients with tetralogy of Fallot (TOF), because

these individuals cannot tolerate an acutely imposed volume overload. Small,

residual VSDs are common after surgical repair and are usually clinically

insignificant.

A residual VSD with a 2:1 shunt or an RVOTO of greater than 60 mm Hg is an

urgent indication for reoperation. Surgery can be performed with low risk and

can result in dramatic improvements. Occasionally, pulmonary valve

insufficiency may increase and may be associated with RV failure.

Once tetralogy of Fallot has been repaired in infancy or childhood, about 5% of

individuals require repair or replacement of the pulmonary valve. Because of

better results from surgery in the present era, long-term survivors are

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increasingly reported. In most of these individuals, pulmonary regurgitation is

the clinical presentation and can be treated with a prosthetic tissue valve. This

problem is generally treated with a pulmonary valve replacement. Porcine

valves are preferred over mechanical valves, because they have lesser tendency

to thrombose.

Surgical Complications

Early postoperative complications following repair of tetralogy of Fallot (TOF)

include the creation of heart block and residual ventricular septal defects

(VSDs). Ventricular arrhythmias are more common and are reportedly the most

frequent cause of late postoperative death. Sudden death from ventricular

arrhythmias has been reported in 0.5% of individuals within 10 years of repair.

The arrhythmias are thought to occur in fewer than 1% of patients having an

early operation. As with most heart surgery, the risk of endocarditis is lifelong,

but the risk is much less than in a patient with an uncorrected tetralogy of Fallot.

Medication:

The goals of tetralogy of Fallot (TOF) therapy are to reduce the ventilatory

drive, increasing systemic venous return, and to increase peripheral vascular

resistance.

Analgesics

Analgesic agents reduce ventilatory drive. In addition, pain control ensures

patient comfort and promotes pulmonary toilet. Most analgesic agents have

sedating properties, which are beneficial for patients who are having

hypercyanotic episodes.

Morphine sulfate (Duramorph, Astramorph, MS Contin)

Morphine is the drug of choice (DOC) for narcotic analgesia because of its

reliable and predictable effects, safety profile, and ease of reversibility with

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naloxone.This agent is administered intravenously (IV), may be dosed in

number of ways, and is commonly titrated until the desired effect is obtained.

Alpha-adrenergic Agonists

Alpha-adrenergic agents improve hemodynamic status by improving

myocardial contractility and increasing heart rate, resulting in increased cardiac

output. Peripheral resistance is increased by vasoconstriction, increased cardiac

output, and elevated blood pressure.

Phenylephrine

Phenylephrine is a strong postsynaptic alpha-receptor stimulant with little beta-

adrenergic activity. This drug produces vasoconstriction of arterioles, thereby

increasing peripheral venous return.

Prognosis

Early surgery is not indicated for all infants with tetralogy of Fallot (TOF),

although, without surgery, the natural progression of the disorder indicates a

poor prognosis. The progression of the disorder depends on the severity of right

ventricular (RV) outflow tract obstruction (RVOTO). In the present era of

cardiac surgery, children with simple forms of tetralogy of Fallot enjoy good

long-term survival with an excellent quality of life. Late outcome data suggest

that most survivors are in New York Heart Association (NYHA) classification I,

although maximal exercise capability is reduced in some.

Sudden death from ventricular arrhythmias has been reported in 1-5% of

patients at a later stage in life, and the cause remains unknown. One study found

left ventricular longitudinal dysfunction to be associated with a greater risk of

developing life-threatening arrhythmias. Continued cardiac monitoring into

adult life is necessary. For some time, it has been suspected that certain children

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may have inherited a predispostion to developing long QT syndrome. A 2012

study by Chiu confirmed this suspicion.

If left untreated, patients with tetralogy of Fallot face additional risks that

include paradoxical emboli leading to stroke, pulmonary embolus, and subacute

bacterial endocarditis. In most of these children the causes of stroke have been

related to thromboemboli, prolonged hypotension/anoxix and polycythemia.

What is often forgotten is that residual shunts or a patent foramen ovale are also

known causes of strokes. The investigation of strokes in these children usually

begins with a CT scan of the brain followed by an ECHO.

Without surgery, mortality rates gradually increase, ranging from 30% at age 2

years to 50% by age 6 years. The mortality rate is highest in the first year and

then remains constant until the second decade. No more than 20% of patients

can be expected to reach the age of 10 years, and fewer than 5-10% of patients

are alive by the end of their second decade.

Most individuals who survive to age 30 years develop congestive heart failure

(CHF), although individuals whose shunts produce minimal hemodynamic

compromise have been noted, albeit rarely, and these individuals achieve a

normal life span. However, cases of survival of patients into their 80s have been

reported. Due to advanced surgical techniques, a 40% reduction in deaths

associated with tetralogy of Fallot was noted from 1979 to 2005. As might be

expected, individuals with tetralogy of Fallot and pulmonary atresia have the

worst prognoses, and only 50% survive to age 1 year and 8% to age 10 years.

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