Tetralogy of Fallot

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Gross heart from a dog which died of Tetralogy of Fallot. Green arrow indicates right ventricular hypertrophy, blue arrow ventricular septal defect[1]

Tetralogy of Fallot is a rare congenital heart disease of dogs, constituting less than 1% of congenital heart defects in this species[2].

A number of variants forms of this congenital anomaly have been reported, including:

This disease has been reported in the Keeshond, English Bulldog, Miniature Poodle, Miniature Schnauzer, Dachshund, Japanese Shiba, Japanese tosa, Bernese Mountain Dog, Beagle, Airedale Terrier, Havanese and Wirehaired Fox Terrier.

In the Keeshond, conotruncal malformation is frequently observed in closely related dogs as a multifactorial autosomal-dominant disease, resulting in type I (subarterial) ventricular septal defects due to failure of fusion of the conal cushions[5].

Concurrent patent ductus arteriosus has also been reported in the German Shepherd[6].

Clinical signs are normally seen in young dogs (under 6 months of age) and usually present with exercise intolerance, dyspnea, cyanosis and a detectable murmur.

Blood tests are usually unrewarding, although polycythemia may be evident in some cases.

A tentative diagnosis can be established by auscultation of a high thrill murmur at the right cardiac apex.

Routine ECG shows deep S waves and right axis shift characteristic of right ventricular enlargement and bundle branch block. Arrhythmias are infrequent.

Radiographs often show right cardiomegaly and undersized pulmonary vessels.

Echocardiography is usually required for a definitive diagnosis, usually revealing rightward displacement of the aortic root, right ventricular hypertrophy, and a ventricular septal defect. The left-sided chambers may be small as a result of decreased pulmonary venous return. Routine contrast echocardiography demonstrates shunting from right to left at the level of the ventricular septal defect. Flow through the defect can also be detected by Doppler echocardiography.

A differential diagnosis would include subaortic stenosis, ventricular septal defect[7], double-chambered right ventricle[8], hyperthyroidism, cardiomyopathy, Duchenne muscular dystrophy, endocarditis, pulmonic stenosis, mitral valve endocardiosis and infections with Dirofilaria spp.

Treatment options include surgical and medical management. Atenolol and pimobendan are usually prescribed.

Corrective surgery, using surgical valvuloplasty[9], balloon valvuloplasty, or open heart surgery involving transannular pericardial patch graft[10] or a modified Blalock-Taussig shunt procedure[11] are options that are available.

The prognosis is guarded, but animals with mild to moderate shunting may reach adulthood.

References

  1. Paslawska, U (2012) A retrospective study of tetralogy of Fallot in dogs. Turk J Vet Anim Sci 36(1):10.3906
  2. Tidholm A (1997) Retrospective study of congenital heart defects in 151 dogs. J Small Anim Pract 38(3):94-98
  3. Park IC et al (2007) Pentalogy of Fallot in a Korean Sapsaree dog. J Vet Med Sci 69(1):73-76
  4. Werner P et al (2005) The keeshond defect in cardiac conotruncal development is oligogenic. Hum Genet 116(5):368-377
  5. Patterson, DF et al (1974) Hereditary defects of the conotruncal septum in Keeshond dogs: pathologic and genetic studies. Am J Cardiol 34:187–205
  6. McEntee K et al (1998) Clinical vignette. Tetralogy of Fallot associated with a patent ductus arteriosus in a German shepherd dog. J Vet Intern Med 12(1):53-55
  7. Guglielmini C et al (2002) Atrial septal defect in five dogs. J Small Anim Pract 43(7):317-322
  8. Fukushima R et al (2011) Epidemiological and morphological studies of double-chambered right ventricle in dogs. J Vet Med Sci 73(10):1287-1293
  9. Weber UT et al (1995) Palliative treatment of tetralogy of Fallot using a PTFE (polytetrafluoroethylene) vascular graft. Schweiz Arch Tierheilkd 137(10):480-484
  10. Lew LJ et al (1998) Open-heart correction of tetralogy of Fallot in an acyanotic dog. J Am Vet Med Assoc 213(5):652-657
  11. Brockman DJ et al (2007) Long-term palliation of tetralogy of Fallot in dogs by use of a modified Blalock-Taussig shunt. J Am Vet Med Assoc 231(5):721-726