KEY-WORDS: Tetralogy of Fallot

INTRODUCTION
CLINICAL
WORKUP
TREATMENT
MEDICATION
FOLLOW-UP
MISCELLANEOUS
BIBLIOGRAPHY

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INTRODUCTION

Background: Tetralogy of Fallot (TOF) is a complex of anatomic abnormalities arising from the maldevelopment of the right ventricular infundibulum.

Fallot described the anatomy in 1888 as consisting of a sub-aortic ventricular septal defect, right ventricular infundibular stenosis, an aortic valve positioned to override the right ventricle and right ventricular hypertrophy.

Pathophysiology: There is a wide variation in the basic anatomic morphology, pathophysiology, clinical signs and symptoms and surgical methods of therapy. The pathophysiology is primarily dependent upon the severity of the right ventricular outflow tract obstruction. Right-to-left shunting is typical.

Frequency:

Mortality/Morbidity: The natural history is variable.

Sex: Male greater than female (slightly)

• Cyanosis develops within the first few years of life.

• Symptoms generally progress secondary to hypertrophy of the infundibular septum.

• Cyanosis occurs and demands surgical repair.

• Dyspnea on exertion is common.

• Squatting is uniquely characteristic of a right-to-left shunt that presents in the exercising child.

• Hypoxic TET spells are potentially lethal, unpredictable episodes that occur even in non-cyanotic patients with TOF. They can be aborted with relatively simple procedures.

• The rare patient with TOF may remain marginally and imperceptibly cyanotic or acyanotic and asymptomatic into adult life.

• Severe cyanosis may present at birth in a patient with TOF and associated pulmonary atresia.

• Low birth weight

• Retarded growth

Physical:

• Right ventricular predominance on palpation

• Systolic thrill at the lower left sternal border

• Aortic ejection click

• Single S2: Pulmonic valve closure not heard

• Systolic ejection murmur: Varies in intensity inversely with the degree of RVOT obstruction; that is, more cyanotic patients have greater obstruction and a softer murmur.

• An acyanotic pink TET has a long, loud, systolic murmur with a thrill along the RVOT.

• Cyanosis and clubbing are variable.

• Squatting position

• Scoliosis is common.

• Retinal engorgement

• Hemoptysis

Causes:

• Although there is no specific singular genetic abnormality identified, (e.g., chromosomal abnormalities, as in Trisomy 21), there is undoubtedly a genetic etiology to the family of cardiac malformations known as, conotruncal abnormalities (e.g., double outlet right ventricle, interrupted aortic arch type B, transposition of the great arteries, truncus arteriosus and TOF).

• Ablation of cells of the neural crest has been shown to reproduce conotruncal malformations.

• These abnormalities are also associated with the DiGeorge syndrome and branchial arch abnormalities.

• TOF is frequently associated with the following:

• Fetal hydantoin syndrome

• Fetal carbamazepine syndrome

• Fetal alcohol syndrome
  
• Maternal phenylketonuria (PKU) birth defects

• Oximetry and Arterial Blood Gas (ABG)

• Oxygen saturation is variable, but pH and pCO2 are normal unless the patient is in extremis, such as, during a TET spell.

• Oximetry is particularly useful in the dark-skinned patient or the anemic patient whose level of cyanosis is not apparent.

• Cyanosis is not evident until 5.0 mg/dl of reduced hemoglobin is present.

• A decrease in SVR (systemic vascular resistance) during exercise, bathing or fever will potentiate a right-to-left shunt and cause hypoxemia.

• Hematology:

• Prolonged cyanosis causes a reactive polycythemia that will increase the oxygen-carrying capacity.

• Hyperviscosity and coagulopathy often ensue and are particularly deleterious in patients with a right-to-left intracardiac shunt.

• Cerebrovascular accident (CVA) and brain abscess are natural corollaries.

Imaging Studies:

• Chest Roentgenography:

• Coeur en sabot (boot-shaped heart) secondary to uplifting of the cardiac apex from right ventricular hypertrophy and the absence of a normal main pulmonary artery segment

• Normal heart size due to the lack of pulmonary blood flow and congestive heart failure

• Decreased pulmonary vascularity

• Right atrial enlargement

• Right aortic arch (25% of patients)

• May be normal in acyanotic TOF or may resemble findings of small to moderate size VSD with mild RVH, right atrial enlargement and increased pulmonary vascular markings

• Echocardiography reveals a large VSD with an overriding aorta and variable degrees of right ventricular outflow tract obstruction.

• Electrocardiogram:

• Right axis deviation (+120 to +150 degrees)

• Right or combined ventricular hypertrophy

• Right atrial hypertrophy

Procedures:

• Cardiac Catheterization:

• Assesses pulmonary annulus size and pulmonary arteries

• Assesses the severity of right ventricular outflow obstruction

• Locates the position and size of the VSD
  
• Rules out possible coronary artery anomalie

• Any infant with cyanosis and/or respiratory distress requires 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 IV, especially if not skilled in pediatric IV starts.

• An intraosseus insertion could be an immediate lifesaving tool.

• Hypoxic TET Spell:
  
  Hypercyanotic episodes are characterized by paroxysms of hyperpnea, prolonged crying, intense cyanosis and decreased intensity of the murmur of pulmonic stenosis.

• Mechanism:
  
  Secondary to infundibular spasm and/or decreased systemic vascular resistance with increased right-to-left shunting at the VSD, resulting in diminished pulmonary blood flow.

• If left untreated, the following may result in syncope, seizure, CVA or death.

• Treatment for the acute setting of hypercyanosis includes:

• Knee-chest position: Place the baby on the mother's shoulder with the knees tucked up underneath. This provides a calming effect, reduces systemic venous return and increases systemic vascular resistance.

• Oxygen is of limited value since the primary abnormality is reduced pulmonary blood flow.

• Morphine sulfate, 0.1-0.2 mg/kg SC or IM, may reduce the ventilatory drive and decrease systemic venous return.

• Phenylephrine (Neo-Synephrine), 0.02 mg/kg IV, is used to increase SVR.

• Treat acidosis with sodium bicarbonate. It may reduce the respiratory center stimulating effect of acidosis.

• General anesthesia is a last resort.

• Palliative surgery:

• Blalock-Taussig shunt

• Pott's procedure

• Waterson's shunt

• Total surgical correction with patch closure of the VSD and relief of the ventricular outflow obstruction is preferred.

Further Outpatient Care:

• Good dental hygiene

• Endocarditis prophylaxis

Complications:

• Erythrocytosis

• Brain abscess

• Acute gouty arthritis

• Infective endocarditis

• Cerebrovascular thrombosis

• Delayed puberty

• Postoperative Complications:

• Residual outflow obstruction, VSD and/or pulmonic regurgitation

• Ventricular arrhythmias, right bundle branch block (RBBB) or left anterior hemiblock

• Infective bacterial endocarditis

Prognosis:

• Uniformly fatal if not surgically corrected
  

• Hypoxic TET spells

• Physical and mental growth impairment

• Brain abscess and CVA, secondary to the right-to-left shunt

• Infective endocarditis

• Polycythemia

• Fyler DC : Tetralogy of Fallot. Nadas Pediatric Cardiology 1992; 471-493.
• Kirklin JW, Barrett-Boyes BGF: Ventricular septal defect and pulmonary stenosis or atresia. Cardiac Surgery 1993; 2: 861-1012.
• Park MK: Tetralogy of Fallot. Pediatric Cardiology or Practitioners 168-175.
• Silverman NH : Tetralogy of Fallot and related lesions. Pediatric Echocardiography 1993; 195-214.
• Snider AR, Serwer GA : Defects in cardiac septation. Echocardiography in Pediatric Heart Disease 1990; 150-153.
• Zuberhuler JH: Tetralogy of Fallot. Heart Disease in Infants, Childrenand Adolescents 1995; II: 998-1026.