Canis ISSN: 2398-2942

Heart: tetralogy of fallot

Contributor(s): Serena Brownlie, Mark Rishniw, Liz Bode

Introduction

  • Combination of 3 defects: pulmonic stenosis, ventricular septal defect (VSD), dextroposition/overriding aorta; plus right ventricular hypertrophy (physiological response).
  • Hereditary (polygenic), in Keeshond Keeshond.
  • Exaggerated forms include: pulmonary artery hypoplasia/atresia, aortic anomalies.
  • If pulmonic stenosis is severe (such that right ventricular pressure is greater than left ventricular pressure), will lead to right-to-left shunt through VSD.
  • Signs: usually stunted and cyanotic.
  • If pulmonic stenosis is mild and VSD is left-to-right shunting, patient less severely compromised ('Pink tetralogy').
  • Diagnosis: radiography, echocardiography.
  • Treatment: symptomatic.
  • Prognosis: guarded.

Pathogenesis

Etiology

  • Embryological developmental anomaly affecting closure of the membranous interventricular septum and differentiation of the conotruncus - affecting the pulmonary trunk, pulmonic valve and the aorta - secondary to deviation of the outlet septum.

Predisposing factors

General

  • None? Breed lines?

Specific

  • Hereditary; polygenic in Keeshound.

Pathophysiology

  • Embryological developmental anomaly, manifested as a (peri)membranous VSD and pulmonic stenosis.
  • Conotruncal abnormality results in a degree of dextroposition of the aorta, often with a hypoplastic pulmonary trunk.
  • Right ventricular hypertrophy compensates for the pressure overload due to pulmonic stenosis.
  • Increased right ventricular pressures lead to right-to-left shunting across the VSD.
  • With severe dextroposition of the aorta - overriding the VSD - some right ventricular ejection is into the aorta, exacerbating the right-to-left shunting Tetralogy of fallot pathology.
  • Depends on severity of pulmonic stenosis and ventricular septal defect.
Severe
  • Increased right ventricular pressure → shunting from right-to-left ventricle → cyanosis → hypoxia → hypoxic kidneys release erythropoietin → increased red blood cell production → polycythemia → animal incapacitated by hypoxia.

Timecourse

  • Since birth.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Chetboul V, Pitsch I et al (2016) Epidemiological, clinical and echocardiographic features and survival times of dogs and cats with tetralogy of Fallot: 31 cases (2003-2014). JAVMA 249 (8), 909-917 PubMed.
  • Orton E C, Mama K, Hellyer P & Hackett T B (2001) Open surgical repair of tetralogy of Fallot in dogs. JAVMA 219 (8), 1089-1093 PubMed.

Other sources of information

  • Fox, Sisson & Moise (Eds) (1999)Textbook of Canine and Feline Cardiology.2nd edn. Philadelphia: W B Saunders, p 533.


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