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Heart: atrial septal defect

icanis

Synonym(s): ASD


Introduction

  • Uncommon, often associated with other defects. Rare as isolated defect.
  • Cause: congenital defect due to failure of normal development.
  • Signs: may be asymptomatic, congestive heart failure in severe cases.
  • Diagnosis: clinical examination, radiography, electrocardiography, 2-D and Doppler echocardiography.
  • Treatment: medical treatment of congestive heart failure or surgery to close defect.
  • Prognosis: good in mild cases, fair for congestive heart failure.

Pathogenesis

Etiology

  • Embryological failure of normal development of the interatrial septum. Can involve septum primum or septum secondum.

Specific

  • Hereditary?

Pathophysiology

  • Defect in interatrial septum → communication between left atrium and right atrium → degree of bidirectional shunting occurs, depending on size of the defect and relative compliance of the ventricles → left atrial systolic pressure greater than right atrial pressure and right ventricular compliance is higher than left → normally net left-to-right systolic shunt → volume overload of right atrium, right ventricle, pulmonary circulation.
  • Primum ASD - defect low in atrial septum adjacent to atrioventricular valves. May involve defects of atrioventricular valves.
  • Secundum ASD - defect in mid atrial septum in region of fossa ovalis.
  • Sinus venosus ASD - high in atrial septum adjacent to cranial or caudal vena cava.
  • Coronary sinus ASD - defect between coronary sinus and left atrium (very rare).
  • Allows shunting of blood predominantly from left-to-right atrium, although mild bidirectional shunting occurs in most cases.
  • Rarely a clinical problem as driving pressure from left-to-right atrium is low; low pressure gradient across the defect.
  • Flow across ASD rarely causes murmur, but increased blood flow through the normal pulmonary valve may cause a murmur called a 'murmur of relative pulmonic stenosis'.

Severe

  • Left-to-right atrial shunt → overloads right atrium and ventricle → pulmonary hypertension → increased right atrial and right ventricular pressures → possibly right-sided CHF.
  • If pulmonary overcirculation is sufficient → vascular changes → pulmonary hypertension → right ventricular hypertrophy (but rarely right-sided CHF) → right-to-left atrial shunt results and may lead to cyanosis.
  • Atrial stretch → dysrhythmias (especially atrial).

Timecourse

  • From 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.
  • Guglielmini C, Diana A,  Pietra M & Cipone M (2002) Atrial septal defect in five dogs. JSAP 43, 317-322 PubMed.
  • Monnet E, Orton E C, Gaynor J, Boon, J Peterson D and Guadagnoli M (1997) Diagnosis and surgical repair of partial atrioventricular septal defects in two dogs. JAVMA 211 (5) 569-572 PubMed.
  • Eyster G E (1994) Atrial septal defect and ventricular septal defect. Seminars in Veterinary Medicine and Surgery (Small Animal) (4), 227-233 PubMed.
  • Jeraj K, Ogburn P N & Johnston G R (1980) Atrial septal defect (sinus venosus type) in a dog. JAVMA 177 (4), 342-346 PubMed.

Other sources of information

  • Bonagura J D & Lehmkuhl L B (1999) Congenital Heart Disease. In:Textbook of Canine and Feline Cardiology. 2nd edition. Fox P R, Sisson D & Moise N S (eds), W B Saunders, Philadelphia. pp 471-535.

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