INTRODUCTION — Tetralogy of Fallot (TOF) includes the following major features (figure 1):
●Right ventricular outflow tract (RVOT) obstruction
●Malalignment ventricular septal defect (VSD)
●Concentric RV hypertrophy
The pathophysiology, clinical features, and diagnosis of TOF will be reviewed here. Other related topics include:
EPIDEMIOLOGY — The prevalence of TOF in the United States is approximately 4 to 5 per 10,000 live births [1,2]. This defect accounts for approximately 7 to 10 percent of cases of congenital heart disease and is one of the most common congenital heart lesions requiring intervention in the first year of life . TOF occurs equally in males and females .
ANATOMY — The exact embryologic abnormality that accounts for TOF is unknown. What is recognized is that during development, there is anterior and cephalad deviation of the infundibular septum. This results in a malaligned ventricular septal defect (VSD), with the aortic root overriding the defect and leading to subsequent right ventricular outflow tract (RVOT) obstruction (figure 1). The ensuing RV hypertrophy is thought to be a response to the large VSD and RVOT obstruction, with resultant systemic RV systolic pressure.
Ventricular septal defect — The VSD in TOF is most commonly a single large, malaligned subaortic defect located in the perimembranous region of the septum (image 1). The VSD can extend into the muscular septum. There are rarely other muscular VSDs. (See "Isolated ventricular septal defects (VSDs) in infants and children: Anatomy, clinical features, and diagnosis".)
Right ventricular outflow tract obstruction — The RVOT obstruction is often at multiple levels (image 2):
●Anterior and cephalad deviation of the infundibular septum results in subvalvar obstruction
●Hypertrophy of muscular bands in this region can further accentuate subvalvar obstruction
●Pulmonary valve annulus is usually hypoplastic, although, in some instances, it is of normal size
●Pulmonary valve itself is frequently bicuspid and stenotic
In addition, it is not uncommon to identify an area of supravalvar narrowing in the main pulmonary artery at the sinotubular ridge. There may also be further obstruction at the branch pulmonary arteries. These may be diffusely hypoplastic or have focal areas of stenosis, most commonly at the proximal branch pulmonary arteries. The proximal left pulmonary artery near the site of ductal insertion is a frequent location for stenosis (image 3A-B).
Overriding aorta — Overriding aorta is a congenital anomaly in which the aorta is displaced to the right over the VSD rather than the left ventricle. This results in blood flow from both ventricles entering into the aorta.
The degree of aortic override of the VSD can vary widely and is one of the major factors used by some groups to differentiate between TOF and double-outlet RV. If one defines double-outlet RV as the absence of aortic/mitral valve fibrous continuity, then the degree of override is not relevant to diagnosis. If, however, one defines double-outlet RV as a condition with greater than 50 percent aortic override, then, by definition, the degree of aortic override in TOF is limited.
Associated cardiac features — There are a number of frequently associated anatomic features that are important to look for when evaluating a patient with TOF since they affect therapy. Associated cardiac anomalies occur in approximately 40 percent of patients with TOF :
●Approximately 25 percent of patients have a right aortic arch. This is particularly important to identify if one is contemplating a palliative shunt.
●Abnormalities of the coronary arteries, such as the left anterior descending arising from the right coronary artery, are seen in approximately 10 percent of patients [5,6]. These are important to identify prior to complete repair since the course of the artery may run directly across the RVOT; inadvertent transection could have catastrophic consequences.
●Occasionally, patients have significant aorticopulmonary collateral vessels that may require attention prior to or at the time of surgery.
●A patent ductus arteriosus, multiple ventricular defects, and complete atrioventricular septal defects may be present.
●Infrequently, aortic valve regurgitation is present due to aortic cusp prolapse.
GENETIC FACTORS — Although TOF may present as part of a known syndrome, this lesion typically occurs sporadically without other anomalies.
Surveys of patients with nonsyndromic TOF have reported the following genetic abnormalities:
●In one study of 114 patients with nonsyndromic TOF, 4 percent of patients had mutations in transcription factor NKX2-5, which appears to have a role in cardiac development .
●In genome-wide surveys of patients with nonsyndromic TOF and their parents, de novo copy number variants were estimated to be present in approximately 10 percent of sporadic cases of TOF, compared with less than 0.1 percent in controls, at several chromosomal locations . Several reports have associated TOF with mutations in TBX1, ZFPM2, and GATA5 [9-12].
●MTHFR polymorphism has also been associated with an increased risk of development of TOF .
Further investigation is required to determine the role of these mutations and polymorphisms in the evolution of TOF.
Approximately 15 percent of patients with TOF present with associated syndromes [9,14-20]:
●Down syndrome (trisomy 21). (See "Down syndrome: Clinical features and diagnosis".)
●Alagille syndrome (mutations in JAG1). TOF as the sole manifestation of JAG1 mutations without other evidence of Alagille syndrome has also been reported . (See "Inherited disorders associated with conjugated hyperbilirubinemia", section on 'Alagille syndrome'.)
●DiGeorge and velocardiofacial syndromes (deletion on chromosome 22q11). There may be susceptibility genes for TOF within the latter region of chromosome 22q11 in children without extracardiac anomalies [19,22,23], and 22q11.2 deletion syndrome is unrecognized in many adult patients with TOF . (See "DiGeorge (22q11.2 deletion) syndrome: Clinical features and diagnosis".)
PATHOPHYSIOLOGY — The physiologic consequences of TOF are largely dependent upon the degree of right ventricular (RV) outflow obstruction. Since the ventricular septal defect (VSD) is typically large and unrestrictive, the pressure in the RV reflects that of the left ventricle. As a result, the direction of blood flow across the VSD will be determined by the path of least resistance for blood flow, not by the size of the VSD. If the resistance to blood flow across the obstructed RV outflow tract (RVOT) is less than the resistance to flow out of the aorta into the systemic circulation, blood will naturally shunt from the left ventricle to the RV and into the pulmonary bed. In this situation, there is predominately a left-to-right shunt, and the patient will be acyanotic.
As the degree of RV outflow obstruction increases, the resistance to blood flow into the pulmonary bed also increases. If the RV obstruction exceeds systemic resistance, it becomes easier for blood to cross the VSD from the RV into the left ventricle and go out the aorta. This right-to-left shunt across the VSD results in a large volume of desaturated blood entering the systemic circulation, causing cyanosis (figure 1). In patients with unrepaired TOF, chronic cyanosis can result in erythrocythemia.
One of the physiologic characteristics of TOF is that the RVOT obstruction can fluctuate. An individual with minimal cyanosis can develop a dynamic increase in RVOT obstruction with a subsequent increase in right-to-left shunt and the development of cyanosis. In the most dramatic situation, there can be near occlusion of the RVOT with profound cyanosis. These episodes are often referred to as "tet spells" or "hypercyanotic spells." (See 'Tet spells' below.)
Presentation — With advances in obstetric ultrasound screening, many infants with TOF are diagnosed prenatally. (See 'Prenatal diagnosis' below.)
For patients not diagnosed prenatally, postnatal presentation depends upon the degree of right ventricular outflow tract (RVOT) obstruction:
●Infants with severe RVOT obstruction and inadequate pulmonary flow typically present in the immediate newborn period with profound cyanosis and require intervention.
●Infants with mild to moderate RVOT obstruction and balanced pulmonary and systemic flow may be asymptomatic initially. They may be referred for cardiology evaluation and diagnosed during evaluation of a murmur noted in the nursery or in the course of well-child care. These children are referred to as "pink tets." Importantly, the degree of RVOT obstruction is progressive over time. An initially asymptomatic and acyanotic child may gradually develop increasing cyanosis and/or present with hypercyanotic ("tet") spells when the gradually increasing RVOT obstruction is abruptly and dynamically increased during periods of excitement, agitation, or hypovolemia. (See 'Tet spells' below.)
●Infants with minimal obstruction are also asymptomatic initially. They may develop symptoms of pulmonary overcirculation and heart failure in the first four to six weeks after birth as the initially elevated perinatal pulmonary vascular resistance falls to normal.
In addition, some affected newborns will be detected by an evaluation prompted by a failed pulse oximetry screening test. (See "Newborn screening for critical congenital heart disease using pulse oximetry".)
In general, the earlier the onset of cyanosis, the more likely that severe RVOT obstruction is present.
In the contemporary era in the United States, most children are diagnosed in infancy; however, this is not true in regions of the world where access to health care is more limited. Rarely, and most often in the course of relocation from those regions, older children with unrepaired TOF may present, usually with some degree of baseline cyanosis, often limiting their own activities to prevent hypercyanotic episodes.
Tet spells — Patients with unrepaired TOF are at risk for episodic hypercyanotic ("tet") spells in which there can be transient near occlusion of the RVOT with profound cyanosis. The exact etiology of these episodes is unclear, although there have been a number of proposed mechanisms, including increased infundibular contractility, peripheral vasodilatation, hyperventilation, and stimulation of RV mechanoreceptors .
Tet spells typically arise when the infant becomes agitated or upset. They may also occur in the setting of pain, fever, anemia, and hypovolemia, as well as after a bowel movement or feeding (or, in older children with uncorrected TOF, after vigorous exercise) . They may occur more commonly in the morning and after feeding, though they can arise at any time .
Tet spells are characterized by hyperpnea (rapid and deep respirations), irritability, inconsolability, and progressively severe cyanosis. An older child experiencing a tet spell will typically squat to recover. Examination during the acute episode may reveal decreased intensity of the heart murmur. Though some episodes may resolve spontaneously, prolonged spells can progress to loss of consciousness and cardiac arrest. Prompt intervention is essential for the acute episode and infants, and children presenting with hypercyanotic episodes should be referred for surgical intervention to prevent potentially life-threatening recurrences. Acute management of tet spells is discussed separately. (See "Management and outcome of tetralogy of Fallot", section on 'Tet spells'.)
Physical examination — On inspection, individuals with TOF are usually comfortable and in no distress. However, during hypercyanotic (tet) spells, they will become hyperpneic and infants will often become agitated. If cyanosis is present, it is most easily seen in the nail beds and lips.
On palpation, one may appreciate a prominent RV impulse and, occasionally, a systolic thrill. Hepatomegaly is uncommon. Peripheral pulses are usually normal, although the presence of prominent pulses may suggest the existence of a significant patent ductus arteriosus or aorticopulmonary collaterals.
Cardiac auscultation — On auscultation, the first heart sound is normal and the second heart sound is most commonly single because the pulmonic component is rarely audible. Third and fourth heart sounds are uncommon. An early systolic click along the left sternal border may be heard, which is thought to be due to flow into the dilated ascending aorta. (See "Approach to the infant or child with a cardiac murmur", section on 'Heart sounds'.)
Murmur — The murmur in TOF is due primarily to the RV outflow obstruction, not the ventricular septal defect (VSD). The murmur is typically a systolic, crescendo-decrescendo murmur with a harsh ejection quality; it is appreciated best along the left mid- to upper sternal border with radiation posteriorly. It can, however, have a more regurgitant quality that can be easily mistaken for a VSD. (See "Approach to the infant or child with a cardiac murmur".)
The murmur is due both to the degree of obstruction and to the amount of flow across the obstruction. In TOF, unlike isolated valvar pulmonary stenosis, the amount of flow across the RVOT will decrease as the obstruction increases, due to the shunting of blood right-to-left across the VSD. Thus, as the obstruction increases, the murmur will become softer. During severe hypercyanotic ("tet") spells, the murmur may actually disappear due to the markedly diminished flow across the obstruction. (See "Management and outcome of tetralogy of Fallot", section on 'Tet spells'.)
PRENATAL DIAGNOSIS — Improvements in prenatal screening and fetal echocardiography have led to an increase in rates of prenatal diagnosis of TOF [27-29]. Fetal diagnosis allows for advanced planning for delivery and perinatal management, which is particularly important if there is evidence of severe right ventricular outflow tract (RVOT) obstruction necessitating prostaglandin therapy to maintain ductal patency. (See "Management and outcome of tetralogy of Fallot", section on 'Neonates with severe RVOT obstruction'.)
Prenatal risk factors predicting the need for perinatal intervention continue to be identified and include the direction of ductal shunting, pulmonary valve Z scores, pulmonary velocity, pulmonary valve/aortic valve diameter ratios, and subpulmonary/descending aorta ratios [30-35].
The approach to screening, evaluation, and pregnancy management of suspected fetal cardiac abnormalities is discussed separately. (See "Congenital heart disease: Prenatal screening, diagnosis, and management".)
POSTNATAL DIAGNOSIS — The diagnosis of TOF is generally made by echocardiography. Other tests that are often performed during the evaluation of TOF include electrocardiogram (ECG) and chest radiography. Findings from the ECG and chest radiograph are often suggestive but not conclusive for the diagnosis of TOF.
Other advanced imaging modalities (eg, high-resolution computed tomography [CT], cardiac magnetic resonance imaging [MRI]) are sometimes used to provide additional anatomic information related to pulmonary artery anatomy, coronary artery anatomy, and the presence of aorticopulmonary collateral vessels. Cardiac catheterization is sometimes needed to further delineate anatomy and hemodynamic changes.
Echocardiography — Two-dimensional echocardiography and Doppler examination allow assessment of all essential features of TOF and play a crucial role in diagnosis and preoperative evaluation. Complete echocardiographic evaluation may obviate the need for other imaging or diagnostic studies before surgical repair. Most of the information can be achieved with transthoracic echocardiography, but, occasionally, transesophageal echocardiography may be helpful for specific questions raised with transthoracic echocardiography. A complete study must address:
●Location and number of ventricular septal defects (VSDs)
●Anatomy and severity of RVOT obstruction
●Coronary artery and aortic arch anatomy
●Presence of any associated anomalies
Additional details of the echocardiographic evaluation are as follows:
●VSD – The characteristic large, malaligned VSD must be evaluated in multiple views. The degree of aortic override can be best assessed in parasternal long-axis and apical views (movie 1 and movie 2). The extension of the defect from the membranous septum, beneath the tricuspid valve, and into the infracristal outlet septum is well seen in the parasternal short-axis view; extension into the supracristal region, if present, can be seen in this view as well (movie 3). Potential extension of the defect posteriorly toward the inlet septum, or apically into the trabecular septum, can be examined in apical views; the transducer is swept through serial imaging planes from the more caudal views of the inlet septum to the anteriorly angulated views, showing the overriding aorta in continuity with both the mitral and tricuspid valves.
The subcostal views are also helpful to delineate the bounds of the VSD, allowing particularly good representation of the relationship between the defect and the tricuspid and aortic valves. The subcostal right oblique view, obtained by rotating the transducer counterclockwise from the coronal views, is also helpful in identifying any potential extension of the defect into the supracristal region. In the rare cases of restrictive VSD in this lesion, this view also defines abnormal tricuspid valve attachments [36,37].
●RVOT obstruction – The multiple levels and severity of obstruction in the RVOT can also be evaluated by echocardiography (image 4 and movie 4). Parasternal short-axis and subcostal coronal and sagittal views allow the best examination of the infundibulum and pulmonary valve. These views demonstrate the anterior deviation of the conal septum and the infundibular muscle bundles that contribute to infundibular obstruction. The size of the usually hypoplastic pulmonary annulus can be assessed and compared with normal values for patient size and body surface area. This is important to establish the potential need for a transannular patch. The pulmonary valve may appear thickened and may dome in these views.
●Pulmonary arteries – The size and anatomy of the main pulmonary artery, the pulmonary arterial confluence, and the proximal branch pulmonary arteries can also be assessed in parasternal short-axis views. The proximal branch pulmonary arteries should be assessed as far distally as possible in high parasternal views and in suprasternal notch long- and short-axis views, directing the transducer into the left and right chest (movie 5 and movie 6).
●Coronary arteries – The proximal coronary anatomy should be defined echocardiographically in patients with TOF. In addition to examining the coronary anatomy in the traditional short-axis view, the examination should include sweeping the transducer anterior to the pulmonary outflow tract in parasternal long- and short-axis views (movie 7) [38-40]. This permits the identification of variations in coronary anatomy, including the origin of the left anterior descending from the right coronary artery or dual vessel supply to the anterior descending distribution; in these situations, coronary branches crossing anteriorly complicate the surgical approach to relief of RVOT obstruction.
●Aortic arch – Aortic arch situs and the branching patterns of the brachiocephalic arteries are defined in the suprasternal notch long- and short-axis views. Complete evaluation of the arch in these views is also important in delineating the presence of additional potential sources of pulmonary blood flow, including aorticopulmonary collaterals and a patent ductus arteriosus (see "Clinical manifestations and diagnosis of patent ductus arteriosus (PDA) in term infants, children, and adults"). Dilation of the ascending aorta may be present.
●Atrial and ventricular septa – The echocardiographic evaluation of patients with TOF is completed by using both two-dimensional imaging and color flow mapping of the atrial septum and ventricular septum in multiple imaging planes. This assessment defines additional atrial and VSDs and also evaluates potential abnormalities of pulmonary and systemic venous return and the rare associated occurrence of left-sided obstructive lesions.
●Hemodynamic echocardiographic assessment – As previously discussed, the large and generally unrestrictive defect in this lesion permits equalization of right and left ventricular pressures. The direction and degree of shunting is determined by the balance of resistance to flow into the systemic and pulmonary circulations and, to a large degree, by the severity of RVOT obstruction. The modified Bernoulli equation, applied to the peak flow velocity measured in the RVOT, can be used to calculate the outflow tract gradient:
ΔP = 4V2
Where ΔP = peak pressure gradient between the RV and the pulmonary artery (mmHg), and V = velocity obtained by continuous-wave Doppler interrogation of the RVOT
The pulmonary artery pressure can be estimated by subtracting this pressure gradient from the systemic blood pressure. (See "Principles of Doppler echocardiography", section on 'Relationship between Doppler velocity and pressure gradient'.)
While the modified Bernoulli equation is not valid in the setting of tunnel-like and/or multiple levels of obstruction, values obtained with this method correlate with those obtained in the cardiac catheterization laboratory . In practice, the contributions of the infundibulum value and branch pulmonary arteries cannot be separated by Doppler interrogation.
In patients with minimal RVOT obstruction, the gradient across the RVOT will be low, the estimated pulmonary arterial pressure will be elevated, and shunting through the VSD (as assessed by pulsed Doppler and color flow mapping) will be predominantly left to right through much of the cardiac cycle. (See "Isolated ventricular septal defects (VSDs) in infants and children: Anatomy, clinical features, and diagnosis".)
In patients with a large left-to-right shunt, left atrial and left ventricular dilation may be apparent by two-dimensional imaging. In patients with more severe RVOT obstruction, the estimated pulmonary artery pressure is normal and pulsed Doppler and color flow mapping demonstrate increasing right-to-left shunting at the VSD during the cardiac cycle.
Electrocardiogram — The electrocardiogram in TOF typically shows right atrial enlargement and RV hypertrophy. Right-axis deviation, prominent R waves anteriorly and S waves posteriorly, an upright (waveform 1) T wave in V1 (after two days of life), and a qR pattern in the right-sided chest leads may also be seen (waveform 1). (See "ECG tutorial: Chamber enlargement and hypertrophy".)
Chest radiograph — The classic chest radiograph of a patient with TOF demonstrates a "boot-shaped" heart with an upturned apex and a concave main pulmonary artery segment (image 5). The heart size is often normal, and pulmonary flow will appear normal or decreased. A right aortic arch can be seen in 25 percent of patients.
Cardiac catheterization — Although echocardiography can reveal the anatomy in many patients with TOF, cardiac catheterization may still be necessary to further delineate the anatomy. It is particularly helpful for assessing levels of RVOT obstruction, branch pulmonary artery stenosis or hypoplasia, coronary artery anatomy, presence of aorticopulmonary collaterals, and presence of accessory VSDs.
The hemodynamic findings at catheterization typically reveal normal or only mildly elevated filling pressures. The left and RV systolic pressures are equal and systemic due to the presence of the large VSD. Pulmonary artery pressures are normal or low. Saturations will indicate the degree of right-to-left shunting.
Angiographic assessment should be geared toward the information that is needed; biplane angiography is ideal. An RV injection will often adequately demonstrate the multiple levels of RV obstruction as well as the anatomy of the branch pulmonary arteries (image 2). This is typically done with the anteroposterior camera angled in a cranial and left anterior oblique projection, which allows better delineation of the branch pulmonary arteries. The lateral camera is kept in straight lateral projection, which provides excellent visualization of the infundibular and pulmonary valve anatomy (image 6).
An aortic root injection will usually provide adequate identification of the coronary arteries, although selective injections may occasionally be needed. The coronary arteries usually are seen well with the anteroposterior camera in a right anterior oblique projection and the lateral camera in a long-axial oblique projection (70LAO/20Cranial). The arch and descending aorta may also be seen in this view and provide evidence of the presence of a patent ductus arteriosus or collateral vessels. If collateral vessels are identified, selective injections are helpful to assess the areas of the pulmonary bed that they supply and whether they are the sole supply to these areas. Embolization of collaterals can be considered if they supply flow to regions that are also supplied by the native pulmonary arteries.
The VSD is best seen from a left ventricular injection in a long-axial oblique projection (image 1). With the anteroposterior camera in an right anterior oblique projection, one will often also see the infundibular obstruction from left-to-right flow across the VSD (image 7).
Cardiac catheterization can also play a therapeutic role in some patients with TOF. Balloon valvuloplasty of the pulmonary valve can improve pulmonary flow in many children; there may also be an increase in pulmonary valve annulus size that may decrease the need for transannular patch repair [42,43]. Stent implantation in the RVOT or the patent ductus arteriosus have also been used in the perinatal period to augment pulmonary flow and allow complete repair to be deferred to a later age and larger size. This is discussed separately. (See "Management and outcome of tetralogy of Fallot", section on 'Palliative intervention'.)
Other imaging studies — In situations where additional anatomic information is needed beyond what echocardiography provides, CT and MRI imaging can be useful .
●High-resolution CT – With improving technology, high-resolution CT scans can be performed with low radiation exposure and often without anesthesia even in infants, providing excellent intracardiac and extracardiac anatomic detail. This can be useful when evaluating branch pulmonary artery anatomy and collateral vessel distribution. Three-dimensional reconstruction provides detailed appreciation of spatial resolution.
●Cardiac MRI – Cardiac MRI provides additional anatomic detail and volumetric and hemodynamic measurements that can be useful in clinical decision-making. Anesthesia is typically required for cardiac MRI in patients under seven years of age.
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Congenital heart disease in infants and children".)
INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.
Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)
●Basics topic (see "Patient education: Tetralogy of Fallot (The Basics)")
SUMMARY AND RECOMMENDATIONS
•Right ventricular (RV) hypertrophy
•Ventricular septal defect (VSD)
•RV outflow tract (RVOT) obstruction
●Prevalence – The prevalence of TOF is approximately 4 per 10,000 live births. TOF accounts for 7 to 10 percent of all CHD. (See 'Epidemiology' above.)
●Association with genetic disorders and other CHD defects – Although TOF typically occurs sporadically without other anomalies, it can be present as part of a known syndrome or genetic disorder, such as Down, Alagille, or DiGeorge (22q11 deletion) syndromes. Other associated cardiac anomalies occur in approximately 40 percent of patients with TOF. (See 'Genetic factors' above and 'Associated cardiac features' above.)
●Pathophysiology – The pathophysiology of TOF largely depends upon the degree of RVOT obstruction. The direction of blood flow across the VSD is determined by the relative resistance to flow into the pulmonary and systemic circulations, and not by the size of the VSD. If the resistance to the RV outflow is lower than systemic resistance, then there is a predominant left-to-right flow and the patient is not cyanotic. However, with significant RVOT obstruction, there will be a right-to-left shunt across the VSD, resulting in cyanosis (figure 1). (See 'Pathophysiology' above.)
●Clinical presentation – Many infants with TOF are diagnosed prenatally. For those who present postnatally, the clinical presentation depends upon the degree of RVOT obstruction, which determines whether there is a left-to-right (acyanotic) or right-to-left (cyanotic) shunt. In general, the earlier the onset of systemic hypoxemia, the more likely it is that severe RVOT obstruction is present. (See 'Clinical features' above.)
●Hypercyanotic ("tet") spells – Patients with TOF may intermittently experience hypercyanotic ("tet") spells, in which there can be transient near occlusion of the RVOT with profound cyanosis. Tet spells typically arise when the infant becomes agitated or upset. They are characterized by hyperpnea (rapid and deep respirations), irritability, inconsolability, and progressively severe cyanosis. Prolonged spells can lead to loss of consciousness and cardiac arrest. Thus, prompt intervention is warranted. (See 'Tet spells' above and "Management and outcome of tetralogy of Fallot", section on 'Tet spells'.)
●Physical examination findings – Typical findings on cardiac auscultation in patients with TOF include a crescendo-decrescendo harsh systolic ejection murmur and a single second heart sound. (See 'Cardiac auscultation' above.)
●ECG and chest radiograph findings
•Chest radiograph – The classic chest radiograph of a patient with TOF demonstrates a "boot-shaped" heart with an upturned apex and a concave main pulmonary artery segment (image 5). The heart size is often normal, and pulmonary flow will appear normal or decreased. (See 'Chest radiograph' above.)
●Diagnosis – The diagnosis of TOF is typically made by echocardiography, which can usually delineate the location and number of VSDs (movie 1 and movie 2 and movie 3), anatomy and severity of RVOT obstruction (movie 4 and movie 5 and movie 6), coronary artery and aortic arch anatomy (movie 7), presence of any associated anomalies, and hemodynamic abnormalities associated with the anatomical defects. (See 'Echocardiography' above.)
ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Thomas Graham Jr, MD, who contributed to an earlier version of this topic review.
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