Felis ISSN 2398-2950

Heart: tetralogy of fallot

Contributor(s): Serena Brownlie, Phil Fox, Penny Watson, Liz Bode

Introduction

  • About 6% of feline congenital heart defects.
  • Cause: combination of defects - pulmonic stenosis, high ventricular septal defect (VSD), dextroposition/overriding aorta; plus right ventricular hypertrophy (physiological response).
  • Signs: usually stunted and cyanotic.
  • If pulmonic stenosis is mild and VSD is left-to-right shunting, patient less severely compromised ('Pink tetralogy').
  • Diagnosis: radiographic signs of right-sided enlargement, cardiac murmur, echocardiography.
  • Treatment: none/medical therapy/cardiac surgery, depends on severity.
  • Prognosis: poor to grave.

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.

Pathophysiology

  • Embryological developmental anomaly manifested as a membranous VSD, abnormal position of septum 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.
Severe
  • Secondary right ventricular hypertrophy  →  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

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