Tetralogy of Fallot (TOF) is one of the most common cyanotic congenital heart conditions 1,5 and continues to be a major source of morbidity.

Epidemiology

Tetralogy of Fallot accounts for 10% of all congenital heart disease, and in approximately 15% of cases it is associated with a deletion on chromosome 21q11 6-7.

Clinical presentation

Presentation is dictated by the degree of right ventricular outflow obstruction. Typically this is significant, resulting in cyanosis evident in the neonatal period, as a result of the right to left shunt across the VSD. In cases where outflow obstruction is minimal, cyanosis may be inapparent (pink tetralogy) resulting in delayed presentation, even into adulthood, although this is rare. 90% of untreated tetralogy patients succumb by the age of 10 years 6.

Pathophysiology

A tetralogy of Fallot is classically characterised by four features:

1. ventricular septal defect (VSD)
* may be multiple in ~ 5% of cases 6
2. right ventricular outlfow tract obstruction (RVOTO) due to:
* infundibular stenosis, or
* hypoplastic pulmonary valve annulus, or
* bicuspid pulmonary valve, and / or
* hypoplasia of pulmonary artery
3. over riding aorta
4. right ventricular hypertrophy

The right ventricular hypertrophy is a result of the VSD and right ventricular outlet obstruction, both contributing to elevated resistance to right heart emptying 6.

Associations

* right sided aortic arch : seen in 25% of cases
* pulmonary hypoplasia +/- atresia : particularly important in determining treatment 8 : when there is pulmonary atresia it is sometimes termed pseudotruncus arteriosus 9
* atrial septal defect (ASD) or patent ductus arteriosus (PDA) (termed pentalogy of Fallot)
* coronary artery anomalies : seen in 3% of cases 6
* persistent left sided superior vena cava

Radiographic features

Plain film

Can classically show a "boot shaped" heart with an upturned cardiac apex due to right ventricular hypertrophy and concave pulmonary arterial segment. Most infants with TOF however may not show this finding 2.

MRI

MRI has the great advantage of providing both exquisite anatomical details and functional information without ionising radiation. Detailed assessment of the pulmonary artery is particularly important because repair of the cardiac defects without addressing pulmonary artery hypoplasia / stenosis has a poor outcome 8.

The main pulmonary artery or right pulmonary artery diameter should be compared to that of the ascending aorta. A ratio of < 0.3 usually signifies that primary repair would be unsuccessful and a bridging shunt operation may be of benefit 8.

Assessment of coronary artery origin is also essential to surgical planning.

Images Source : Radiopaedia

Treatment and prognosis

Over the years many surgical approaches were performed, until current primary repair was developed. Shunts are now days only performed as a palliative procedure in inoperable cases or to bridge patients until repair can be carried out, typically in the setting of pulmonary arterial hypoplasia 8.

Shunt operations included 6:

* shunts : designed to reduce cyanosis
* Pott shunt
* Waterston shunt
* Blalock-Taussig shunt : still performed in selected cases

Primary repair is now the preferred treatment and is usually performed at the time of diagnosis.

Common post-surgical complications include 6:

* conduction abnormalities
o right bundle branch block (RBBB) : 80 - 90% of cases
o bifasicular block : 15% of cases
o premature ventricular contractions : ~ 50% of cases
o sustained ventricular tachycardias : ~ 5% of cases
o atrial arrhythmias : common
* valvular dysfunction
o tricuspid regurgitation
o pulmonary regurgitation

Prognosis is largely dependent on how soon the defect is diagnosed and corrected, with the best outcome seen in patients repaired before the age of 5 6. Overall there is a 90 - 95% survival rate at 10 years of age, however residual right ventricular dysfunction is common. Up to 10% of patients require re-operation within 20 years 6.

Etymology

Named after Etienne-Louis Arthur Fallot : French physician (1850 - 1911)

Differential diagnoses

Findings on chest x-ray are non-specific and other cyanotic congenital heart diseases should be considered.

Article Source : Dr Yuranga Weerakkody, Radiopaedia

References

* 1. Mirowitz SA, Gutierrez FR, Canter CE et-al. Tetralogy of Fallot: MR findings. Radiology. 1989;171 (1): 207-12. Radiology (abstract) - Pubmed citation
* 2. Haider EA. The boot-shaped heart sign. Radiology. 2008;246 (1): 328-9. doi:10.1148/radiol.2461041673 - Pubmed citation
* 3. Haramati LB, Glickstein JS, Issenberg HJ et-al. MR imaging and CT of vascular anomalies and connections in patients with congenital heart disease: significance in surgical planning. Radiographics. 22 (2): 337-47. Radiographics (full text) - Pubmed citation
* 4. Wiant A, Nyberg E, Gilkeson RC. CT evaluation of congenital heart disease in adults. AJR Am J Roentgenol. 2009;193 (2): 388-96. doi:10.2214/AJR.08.2192 - Pubmed citation
* 5. Bardo DM, Frankel DG, Applegate KE et-al. Hypoplastic left heart syndrome. Radiographics. 21 (3): 705-17. Radiographics (full text) - Pubmed citation
* 6. Topol EJ, Califf RM. Textbook of cardiovascular medicine. Lippincott Williams & Wilkins. (2007) ISBN:0781770122. Read it at Google Books - Find it at Amazon
* 7. Lu JH, Chung MY, Hwang B et-al. Prevalence and parental origin in Tetralogy of Fallot associated with chromosome 22q11 microdeletion. Pediatrics. 1999;104 (1): 87-90. doi:10.1542/peds.104.1.87 - Pubmed citation
* 8. Mirowitz SA, Gutierrez FR, Canter CE et-al. Tetralogy of Fallot: MR findings. Radiology. 1989;171 (1): 207-12. Radiology (abstract) - Pubmed citation
* 9. Margaret A. StuII et.al, Chest Case of the Day, AJR 154:1318-1324, June 91990