General statements about all ASDs

  • There are four types of ASD-
    • Secundum ASD- 75%
    • Primum ASD- 20%
    • Sinus venosus ASD- 5%
    • Coronary sinus ASD- 1%
  • Secundum ASD is sometimes called secondary ASD as it develops over the existing foramen ovale while the others are called primary ASD.
  • ASD was the first recognized congenital heart disease.

Embryology

  • Septum primum grows up from the AV junction.
  • Septum secundum grows down from the atrial roof.
  • Septum primum is on the left.
  • Septum secundum forms the limbus of the fossa ovalis.
  • Septum primum forms the valve of the fossa ovalis.
  • Functional closure of foramen ovale occurs at birth while anatomical closure occurs (in 80%) at 1 year. In 20% anatomical closure does not occur (probe patent foramen ovale).
  • Secundum ASD occurs when septum primum and septum secundum do not unite.

Incidence (all ASDs)

  • Incidence-
    • ASD alone- 6 to 10% of all congenital heart diseases.
    • ASD alone or with other heart diseases- 20% of all congenial heart diseases.
  • Females are 3 times more affected.
  • ASD is the commonest congenital heart disease in adults.
  • ASDs of less than 3 mm close in first year of life while those of more than 8 mm do not usually close.
  • Frequency of MVP in secundum ASD is 8 to 37%.

Hemodynamics

  • Restrictive ASD-
    • Pressure difference between the atria.
    • Qp/Qs is less than 1.5:1.
    • No RV volume overload.
  • Non-restrictive ASD-
    • Both atria have same pressure.
    • Qp/Qs is more than 1.5:1.
    • RV volume overload is present.
  • Flow across ASD depends on
    • Size of the ASD
    • Relative compliances of RV and LV
  • Pulmonary vascular obstructive disease (PVOD) develops late in ASD because normal involution of pulmonary arteries is allowed to occur as there is no transmission of pressure to pulmonary vasculature.
  • PVOD occurs earlier in ASD with Down’s syndrome.
  • RA is dilated. LA is dilated in adults.
  • PAPVC of RUPV to RA occurs in 10%.
  • Causes of cyanosis-
    • LSVC to LA
    • Large Eustachian valve directing IVC blood to LA

Clinical features

  • Small ASD-
    • Risk of paradoxical embolism is present.
  • Large ASD –
    • Late childhood or adulthood-
      • Dyspnoea on exertion
      • Palpitations on exertion
      • Fatigue
      • Platypnoea-orthodeoxia- dyspnoea with standing, relieved by rest
    • After 40 years, deterioration due to-
      • Atrial fibrillation
      • Increased left to right shunt due to hypertension and CAD which decrease LV compliance
      • Cyanosis due to PVOD which occurs in 10%.
  • Holt-Oram syndrome- accessory or hypoplastic thumb or fingers, abrachia.
  • Pulse-
    • No variation in rate or volume with Valsalva.
  • JVP-
    • a and v waves have equal height- a reflection of LA waves
    • a wave becomes taller when-
      • age advances (due to decreased LV compliance)
      • PVOD occurs (due to decreased RV compliance)
    • Pressure increases when RV or LV failure occurs- usually in elderly.
  • Left parasternal impulse.
  • RV apex.
  • Systolic pulsations in second and third LICS- due to dilated PA.
  • Pulmonary systolic thrill is absent. If present-
    • PS
    • MS
  • S1-
    • Wide split
    • T1 is loud
  • RV S3.
  • S2-
    • Wide split due to
      • Increased RV ejection time
      • Increased pulmonary hangout interval
    • Fixed split due to
      • Reciprocal changes in the shunt during respiration
      • No respiratory variation in pulmonary hangout interval
    • P2 is loud due to
      • Increased recoil of the dilated PA
      • Close proximity of dilated PA to chest wall.
    • Split may not be fixed in
      • Restrictive ASD
      • AF- lesser split after short diastole
  • Pulmonary MSM-
    • Ends well before S2
    • Due to increased RV stroke volume
  • Tricuspid MDM-
    • Does not vary with respiration
  • Changes with PVOD-
    • Fatigue increases, dizziness develops
    • Cyanosis
    • a wave becomes more prominent
    • JVP elevates if HF occurs
    • Left parasternal impulse changes to heave
    • S1 split disappears
    • S2 has wide fixed split with louder P2
    • PES, Graham Steell murmur
    • Pulmonary MSM becomes less intense, tricuspid MDM and RV S3 disappear.
    • Tricuspid PSM which has Carvallo’s sign.

ECG

  • Peaked P
  • First degree heart block
  • Right axis deviation
  • Incomplete RBBB pattern in v1
    • Mechanism is disproportionate thickness of crista supraventricularis
    • Height does not exceed 15 mm- if it does, suspect PS or PVOD
  • AF after fourth decade

Chest X-ray

  • RA, RV and MPA prominence with inconspicuous aorta- jug handle cardiac silhouette
  • Increased pulmonary vascularity
  • Adults especially with AF- LA enlargement
  • PVOD- RA and RV become more prominent, inverted comma PA branches

Echocardiography

  • True echo dropout in septum has thickening of margins called “T sign”.
  • Paradoxical IVS motion indicates RV volume overload.

Cardiac catheterization

  • Oxygen step-up of 10 % (15% if single sample).
  • In non-restrictive ASD, pressure gradient between atria is less than 3 mmHg.
  • Other causes of oxygen step-up in RA-
    • Anomalous pulmonary venous connections to RA, vena cavae or CS
    • Gerbode defect
    • VSD with TR
    • RSOV to RA
    • Coronary AV fistula to RA or coronary sinus

Differential diagnosis

  • PAPVC-
    • S2 has wide variable split
  • PS-
    • PES
    • Wide variable S2 split
    • R in v1

Treatment

  • Indications for closure-
    • Qp/Qs more than 1.5:1.
    • Paradoxical embolism
  • Device closure-    
    • ASO
  • Surgery-
    • Midline sternotomy
    • Partial sternal split