Tetralogy of Fallot (ToF) is a cyanotic congenital heart disease characterized by four key defects:
- Pulmonary stenosis – A narrowing of the pulmonary valve and outflow tract means the heart has to work harder to eject blood into the pulmonary artery and blood flow to the lungs is reduced. You may see this referred to as “right ventricular outflow tract (RVOT) obstruction.
- Right ventricular hypertrophy – The ventricle wall is thicker than it should be due to the right ventricle having to work harder.
- Ventricular septal defect – An opening in the septal wall between the right and left ventricles allows oxygen-poor blood of the right ventricle to mix with oxygen-rich blood of the left ventricle.
- Overriding aorta – Some sources will state the aorta sits over the VSD, while others state the aorta sits over both the left and right ventricle. Both positions allow oxygen-poor blood from the right side of the heart to enter systemic circulation.
Taken as a whole, these four defects allow oxygen-poor blood to be pumped out into systemic circulation leading to hypercyanotic episodes called “tet spells.” These spells occur due to reduced pulmonary blood flow, which is a result of both increased pulmonary vascular resistance (PVR) and decreased systemic vascular resistance (SVR). Let’s dive into this a bit.
When systemic vascular resistance is high, the effect is that blood is shunted from the left side of the heart to the right (through the VSD). When pulmonary resistance is high (which is what is occurring during a “tet spell”) the blood is shunted from the right side of the heart, through that VSD to the left side of the heart.
So in a tet spell, the physiological result is an increase in right-to-left shunting. This means more blood is being sent into systemic circulation than is being sent to the lungs for gas exchange. This can lead to drastically low oxygen saturation levels and cyanosis. Tet spells are often preceded by crying, feeding or nursing, having a bowel movement, waking from a nap, dehydration, fevers, and elevated heart rate (tachycardia). The spells occur most commonly in young infants aged 2-4 months, but can occur in older children and toddlers as well. Many times, the child will instinctively squat when they are short of breath as squatting will increase blood flow to the lungs.
What causes Tetralogy of Fallot?
While the exact cause of ToF is unknown, it has been associated with certain underlying conditions. These include chromosomal abnormalities, untreated gestational diabetes, maternal phenylketonuria, maternal intake of retinoids (such as isotretinoin/Accutane) during pregnancy, maternal alcohol use, viral illness during pregnancy, and simply being pregnant over 40 years of age. ToF accounts for approximately 7% to 10% of congenital defects.
What are the complications of Tetralogy of Fallot?
If left untreated, not only does ToF cause significant hypoxic events, it can also lead to:
- Cerebrovascular accident due to the formation of blood clots in the heart that are circulated to the vessels of the brain
- Brain abscess due to the spread of localized infection (in normal physiology, bacteria are filtered through the pulmonary vascular bed)
- Seizures secondary to hypoxia and embolic neurological events
- Infective endocarditis
- Cardiac arrhythmias
- Heart failure
- Sudden cardiac death
Let’s go through the key things to know about Tetralogy of Fallot using the Straight A Nursing LATTE method. This format helps you focus on the key elements you’ll need to understand for your case studies and exams.
L: How does the patient LOOK?
What do you notice about the patient? What are their signs and symptoms?
Signs and symptoms of ToF can be classified as both acute and chronic. Ongoing or chronic signs include:
- Clubbing of the nails and polycythemia due to chronic hypoxia
- Tiring easily during feeding
- Poor weight gain and failure to thrive (see above)
- Exercise intolerance
- Prolonged crying and irritability
- Heart murmur
- Recurrent infections
- Episodes of syncope
During an acute hypercyanotic episode or “tet spell” you may notice:
- Cyanotic skin and lips that progressively worsens
- In light-skinned infants, cyanosis is a bluish tint to the skin
- In darker skinned children, cyanosis may appear as a gray or whitish discoloration
- In children with a yellow skin tone, the cyanosis can cause a grayish-greenish hue
- The child may be more agitated than usual
- Child may appear distressed and be inconsolable
- Increased RR and depth
- Drastically low oxygen saturation levels
A: How do you ASSESS the patient with Tetralogy of Fallot?
Your first priority when assessing a patient with ToF is to determine if they need immediate medical intervention due to a tet spell or hypercyanotic episode. Quickly assess for cyanosis and get an oxygen saturation level as well as a respiratory rate. Additional assessments include:
- A full set of vital signs
- Auscultate lung sounds as heart failure can cause pulmonary edema
- Auscultate heart sounds to assess for murmur
- A systolic ejection murmur is auscultated at the upper left sternal border and is a result of pulmonary stenosis
- A holosystolic murmur is auscultated at the left sternal border and is a result of VSD
- Palpate pulses noting some could be diminished or even absent
- Monitor the patient’s weight, intake, and output
T: What TESTS will be ordered for a patient with Tetralogy of Fallot?
- Echocardiogram – This is an ultrasound of the heart that shows the anatomical structures and function; this exam plays a vital role in diagnosis and evaluation of ToF.
- Chest X-Ray – A common finding with ToF is a “boot shaped” heart (due to the right ventricle being enlarged).
- Electrocardiogram – A 12-lead EKG will determine if cardiac arrhythmias are present
- Cardiac Catheterization – This is a more invasive procedure that allows the physician to evaluate the structure and function of the hearts and its vessels.
- Cardiac MRI – This test may be conducted if the MD needs additional anatomical details. Note that children (especially those under 7 years old) will require anesthesia for this diagnostic exam.
- Holter Monitor – A Holter monitor may be ordered to observe for associated arrhythmias on a continuous basis. Most monitors are worn for 24-48 hours.
T: What TREATMENTS are provided for someone with Tetralogy of Fallot?
Treatment is aimed at responding appropriately to tet spells, preventing infection, managing heart failure if present, and surgical correction of the anomaly.
Tet Spells – If the child is having a “tet” spell or hypercyanotic episode, the general guidelines are to:
- Draw the child’s knees up to their chest to increase systemic vascular resistance. This increases the amount of blood flow out of the right ventricle and into the pulmonary vasculature.
- Provide oxygen.
- The MD may order additional therapies, including an IV narcotic and fluid bolus of 10-20 ml/kg. The mechanism of how narcotics help is unclear, but the fluids help improve preload and pulmonary blood flow.
- A beta blocker may be used to decrease right-ventricular outflow tract obstruction, thereby increasing pulmonary blood flow.
- If these measures do not produce the desired result, the MD may progress to ordering a vasoconstrictor such as phenylephrine to increase SVR and promote flow into the pulmonary circulation vs the aorta.
Antibiotics – Since children with ToF are at high risk for serious infection, they are likely to receive prophylactic antibiotics until the defects can be surgically repaired.
Heart Failure – Many patients with ToF will have heart failure which must be managed. Mainstays of treatment are digoxin and a loop diuretic such as furosemide. Interestingly, the reason ACE-inhibitors and ARBs are not used in patients with Tetralogy of Fallot are that these medications can reduce SVR, which would potentiate a hypercyanotic episode.
Surgery – Most patients with ToF will have surgery by one year of age (under six months of age is most likely). Surgery can range from a complete repair done all at once to a more localized correction that is followed by a complete repair at a later date. The choice of procedure will depend on the severity of the condition.
- Complete repair is done in most cases with a goal of creating a full distinction between pulmonary and systemic circulation. This includes closing the VSD and correcting outflow obstructions from the right ventricle. Addressing these two issues corrects the other two defects associated with ToF.
- Shunts – A Blalock-Taussig shunt involves a small tube that creates a connection between the right subclavian artery and the right pulmonary artery. This will not alleviate all cyanosis, but the goal is for some improvement in oxygenation. The shunt is considered temporary and is removed once the complete surgical repair is done.
It’s important to note there are some potential complications the child may experience after surgery. These include, but are not limited to:
- Severe pulmonary regurgitation – When a patch is used to improve right ventricular outflow, it can result in chronic (and severe) pulmonary regurgitation.
- Right ventricular enlargement, which can lead to or potentiate heart failure.
- Ascending aorta dilation – This condition puts the patient at risk for aortic valve insufficiency. Though aortic dissection has occurred, it is a rare complication.
- Continued right ventricular outflow obstruction – If the obstruction is mild it is generally well-tolerated. Severe obstructions may require additional intervention.
- Arrhythmias – The most common are monomorphic ventricular tachycardia and atrial tachycardia including atrial fibrillation/flutter.
- Sudden cardiac death – Identifying patients at risk for SCD prior to surgery is vital and may require ICD implantation.
Prostaglandins (alprostadil) – Children with severe right ventricular outflow obstruction who are significantly hypoxic and cyanotic may receive prostaglandins to maintain ductal patency and blood flow to the pulmonary vasculature.
E: How do you EDUCATE the family?
In addition to basic teaching about the anatomical abnormalities present in ToF, you’ll also want to teach caregivers what to do during a tet spell, when to seek emergency medical treatment, and how to care for the child after surgery.
- Teach parents how to recognize a tet spell and what to do. The general guidelines are to raise the child’s knees to their chest, which helps improve blood flow to the lungs. Teach parents of older children that the child may instinctively squat down when they feel short of breath, and that this position also increases blood flow to the lungs.
- Teach parents when to seek medical attention as defined by their physician. This can include, but is not limited to, cyanosis, seizures, losing consciousness, and difficulty breathing.
- Lifestyle modifications include smaller, more-frequent meals (since baby tires easily), keeping the child calm as additional stress or energy expenditure can precipitate a tet spell, avoiding activity in extreme weather, and ensuring adequate rest between activities.
- Teach the parents that the child will require surgery at some point, and that this may be done in one procedure, or multiple procedures with shunt placement occurring first.
- Teach the parents about the need for prophylactic antibiotics. Even after surgical repair, the child will need antibiotics prior to any invasive or dental procedures. The parents should always consult their cardiologist before any procedure to ensure adequate protection for the child.
- Teach the parents to keep their child’s gums and teeth healthy to help reduce the risk of endocarditis.
- Teach the parents that most children are able to be active after recovering from ToF surgical repair. The cardiologist will determine the appropriate activity level based on each individual child.
I hope this helps you understand Tetralogy of Fallot for your nursing school case studies and exams. Interested in other pediatric topics? Browse our current articles here.
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