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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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