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Heart: tetralogy of fallot
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.
Presenting signs
- Stunted, cyanotic, severe exercise intolerance.
- Exercise intolerance with pink tetralogy, congenital heart murmur.
- Severe polycythemia may lead to hyperviscosity syndrome and neurological signs.
Acute presentation
- Die from venous to arterial embolism of the brain or heart, eg after IV injections.
- Sudden death.
Age predisposition
- Weeks or months old.
Breed/Species predisposition
- Terrier types; Wirehaired Fox Terrier Fox Terrier -Wire, West Highland White Terrier West Highland White Terrier.
- Bulldog Bulldog.
- Keeshond Keeshond.
Special risks
Associated with right-to-left shunt
- IV injections: air or particulate matter may embolize across right-to-left shunt into cerebral or coronary circulation and lead to death.
- Stress (chronically hypoxic; fails to respond to oxygen supplementation).
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
.
- 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.