DOI: 10.1148/radiol.2461041673
(Radiology 2008;246:328-329.)
© RSNA, 2008
The Boot-shaped Heart Sign1
Ehsan A. Haider, MB BCh
1 From the Department of Radiology, Montreal Children's Hospital, McGill University, 2300 Tupper St, Montreal, QC, Canada H3H 1P3. Received September 29, 2004; revision requested December 2; revision received May 29, 2005; final version accepted August 22.
Address correspondence to the author (e-mail: haider1111{at}hotmail.com).
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APPEARANCE
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The boot-shaped heart sign is seen on the frontal chest radiograph of children with decreased pulmonary vasculature. The left cardiac border resembles the shape of a wooden boot (Figure) (1).
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Frontal chest radiograph of pediatric patient with tetralogy of Fallot (TOF) shows characteristic boot-shaped heart with hyperlucent lungs, diminished central hilar pulmonary vessels, and an upturned cardiac apex. Main pulmonary artery segment is flat to concave, and right aortic arch is seen.
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EXPLANATION
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The boot-shaped heart sign is a conventional radiographic finding in patients with TOF. The toe of the boot is formed by the upward pointing cardiac apex, which makes an acute angle with the diaphragm. The upturned cardiac apex is ascribed to right ventricular hypertrophy and occurs in 65% of patients with TOF (2). The narrower upper part of the boot results from a small or absent main pulmonary artery partly caused by a narrow infundibulum and hypoplastic main pulmonary artery. The latter has been confirmed at angiocardiography in 57% of patients (2). The sign is accentuated by a large lung volume, a small thymus (1), and the lordotic projection. When a normal thymus is present, the left lobe may obscure the sign.
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DISCUSSION
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The boot-shaped heart or coeur en sabot is often seen in patients with TOF, which is the most common cause (75%) of cyanotic heart disease (2). TOF has four components: (a) obstruction of the right ventricular outflow tract, which may be below the pulmonic valve in the infundibulum of the right ventricle; (b) ventricular septal defect (VSD); (c) overriding of the aorta above the VSD; and (d) right ventricular hypertrophy. Right aortic arch occurs in 20%–30% of patients with cyanotic TOF (3,4). When TOF is also associated with an atrial septal defect, it is called the pentalogy of Fallot.
The upturned cardiac apex is usually ascribed to concentric right ventricular hypertrophy. However, this appearance is not seen in patients with severe pulmonic stenosis and an intact ventricular septum, when right ventricular systolic pressure is often much greater than systemic systolic pressure. The appearance, therefore, may be related to right ventricular hypertrophy coupled with altered development of the left ventricle and an abnormal horizontal ventricular septum (3). Interventricular septum attachment may result in minimal indentation of the inferior border of the cardiac apex (3). A report published many years ago claimed that this characteristic upturned cardiac apex is only encountered in congenital heart lesions and not in acquired right ventricular hypertrophy (5).
In infants with TOF, the boot-shaped heart is uncommon (3) and is only seen in moderate to severe cases. Since there is no volume overload, heart size is typically normal. Infants with TOF do not develop right ventricular failure and marked cardiac enlargement, both of which should suggest another diagnosis in infants (2). As the severity of right ventricular outflow tract obstruction increases, so does the upturn of the cardiac apex. In TOF patients with severe pulmonary atresia, the boot-shaped heart is seen more frequently and sooner (6).
The clinical manifestation and radiographic appearance of TOF depend on the size of the VSD and the severity of the right ventricular outflow tract obstruction; patients become cyanotic at birth when severe pulmonary stenosis or atresia is present. Later in life, patients may present with cyanotic spells (7). If the right-to-left intracardiac shunt is minimal, the patient will be only mildly cyanotic and may be diagnosed later in life. The chest radiograph may be essentially normal, and the only clue might be the common association of mirror image right aortic arch (8).
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ACKNOWLEDGMENTS
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I thank Robert Williams, MD, for his advice on the preparation of this article.
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FOOTNOTES
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Author stated no financial relationship to disclose.
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References
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- Condon VR, Jaffe RB. The heart and great vessels. In: Kuhn JP, Solvis TL, Haller JO, eds. Caffey's pediatric diagnostic imaging. 10th ed. Philadelphia, Pa: Mosby, 2004; 1324–1325.
- Johnson C. Fallot's tetralogy: a review of the radiological appearances in thirty-three cases. Clin Radiol 1965;16:199–210. [CrossRef][Medline]
- Perloff JK. Ventricular septal defect with pulmonic stenosis. In: The clinical recognition of congenital heart disease. 2nd ed. Philadelphia, Pa: Saunders, 1978; 442–493.
- Rowe RD, Vlad P, Keith JD. Experiences with 180 cases of tetralogy of Fallot in infants and children. Can Med Assoc J 1955;73(1):23–30.[Medline]
- Foo G. Interventricular notch in differential diagnosis between Fallot's tetrad and tricuspid atresia. Acta Radiol Diagn (Stockh) 1966;4(1):40–46.[Medline]
- Bedford DE. Two cases of Fallot's tetralogy, shown at the section in 1929, exhibiting unusual longevity. Proc R Soc Med 1956;49(6):314–316.
- Walzem DE, Singleton EB. Tetralogy of Fallot: radiologic evaluation before and after surgical treatment. Radiology 1963;81:760–769. [Medline]
- Brickner ME, Hillis LD, Lange RA. Congenital heart disease in adults: second of two parts. N Engl J Med 2000;342(5):334–342. [Published correction appears in N Engl J Med 2000;342(13):988.] [Free Full Text]
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