Chapter 4

ANATOMICAL ABNORMALITY

    There are many different types of ASD depending upon in the interauricular septum.

1. Persistent patent foramen ovale (Vieussens valve)
2. Ostium secundum type
3. Sinus venosus type
4. Low posterior defect type (Inferior vena cava type)
5. Ostium primum type (Endocardial cushion defect)
6. Single atrium (Cor triloculare)

Prevalence of different types of ASD

1. Patent foramen ovale: frequent during first few months of life
2. Ostium secundum type: 70 % of cases
3. Sinus venosus type: 5 % of cases
4. Inferior vena cava type: 15 %
5. Other types: 10 % of cases

Associated Abnormalities

1. Anomalous pulmonary venous return (one to two pulmonary veins draining in the superior vena cava). This is more frequently seen in the sinus venosus type or superior vena caval type of ASD.
2. Left superior vena cava draining into the left atrium. This anomaly is frequently seen in the infero-posterior type of ASD (Inferior vena cava type).
3. In case of single atriums asplenia syndrome is not uncommon, as the Elis-Van Crewald Syndrome and Trisomy 13-15.

ANATOMICAL CONSEQUENCES

    Enlargement of the right atrium, right ventricle and pulmonary artery which will vary depending upon the volume of shunting.
    The size of the aorta can be reduced due to the low systemic cardiac output.
    If the defect is less than 1 cm2 usually the anatomical consequences are minimal.

HEMODYNAMICS

    If the ASD size is below 2 cm² the gradient of pressures between both atriums will be maintained.
    If the size is larger than 2 cm² both atrial pressure will be equal with a bidirectional shunt with a predominant left to right passage due to the lower right side ventricular and pulmonary resistance.
    As in PDA and VSD, ASD is an evolving pathology in the sense that there is slow progression toward pulmonary hypertension. The pace of this progression will depend on the size of the ASD. However, the rate of progression toward pulmonary hypertension and Eisenmenger Complex is slower than in VSD and PDA.
    If the ASD size is less than 1 cm² the pulmonary pressure increases usually so slowly that even at 40 years it may be normal or only moderately elevated.

VSD = Early pulmonary hypertension
ASD = Pulmonary hypertension tends to appear later in an advanced stage of the evolution.

CLINICAL PICTURE

    ASD patients usually have a much slower evolution toward Grade III and IV than VSD and PDA.
    Many times (mainly if the defect size is smaller than 2.0 cm²) the patient may persist in Grade II until age 40 and even 60, but more frequently (defects between 1 and 2 cm²) after 25 years of age will appear moderate pulmonary hypertension (30 to 60 mm Hg) which brings moderate symptoms such as easy fatigability and shortness of breath.

PHYSICAL FINDINGS

Will depend on the hemodynamic grade and condition of the disease.

Grade I and II

1. Hyperdynamic right ventricle with systolic left parasternal lift.

2 year-old girl with Atrial Septal Defect (ASD) and moderately severe Pulmonary Hypertension.

2. Systolic pulsation of the pulmonary artery when MPA pressure is higher than 40 mm Hg, located in the second left intercostal space.
3. Systolic ejection murmur in the pulmonary area (II to IV)
4. Fixed splitting of S₂ (does not vary during respiration)
5. L.L.S.B. mid diastolic rumble

    If CHF is present (rare) JVD will be present with hepatomegaly.
    Second sound (S₂) will be palpable when the MPA pressure is higher than 40 or 50 mm Hg.
    Systolic thrill will be present as far as no severe pulmonary hypertension is present; once marked pulmonary hypertension develops the thrill disappears (greater than 60 mm Hg).
    The pulmonary systolic murmur almost diappears during the pressure phase of the valsalva maneuver, and increases after Amyl Nitrate.
    Occasionally Tricuspid opening snaps and right ventricle S₃ will be present. (large shunt volume)

Grade III

    When the MPA pressure is higher than 60 mm Hg the shunt volume diminishes and pulmonary hypertension symptoms will prevail.
    The systolic murmur reduces its intensity.
    The systolic thrill disappears.
    The fix splitting of S₂ will be narrow and sometimes will be only a loud and single pulmonary valve closure sound.
    Early diastolic murmur of pulmonary insufficiency will appear (Graham Still murmur).
    In case of Cor Triloculare (single atrium) early congestive failure is usual, with not rare early death, and electrocardiography which resembles endocardial cushion defect.

ELECTROCARDIOGRAM

    In this congenital problem (ASD), the electrocardiogram is of major importance. The ECG can differentiate the common type of atrial septal defect from the ostium primum type. In the majority of cases of ostium secundum (most commmon type), moderate right axis deviation will be noted. In the majority of cases of ostium primum (less frequent cases), a tendency to left axis deviation will be observed (also seen in common atno-ventricular canal). In an atrial septal defect due to ostium secundum, the magnitude of the right axis deviation will depend on the degree of pulmonary hypertension (resistance) and the magnitude of the shunt (overload). Normally, normal sinus mechanism will drive the heart, although in less than 10% of the cases, atrial fibrillation may be present.
    Probably the most characteristic electrocardiographic feature in atrial septal defect is the presence of incomplete right bundle branch block, which will be seen in 85-90% of the cases. Complete right bundle branch block is unusual in young patients but is frequently observed in adult cases.
    As a consequence of this incomplete right bundle branch block, which is probably due to the right ventricular diastrolic overload, wide S wave will be seen in leads I, II and V₆ and rSR', rsR', or rSr' complex will be seen in lead V₁ and at times in V₂.
    R' wave high appears to correlate with a degree of hypertrophy of the cristasupraventricularis which almost always will be enlarged in this disease. R wave taller than 10 mm. in lead V₁ frequently is observed in significant right ventricular hypertrophy, which at times is the case in this disease. Over estimation of the right ventricular size can result from this rule due to the numerous exceptions, where a very tall R or R' wave in lead V₁ does not correlate with significant right ventricular hypertrophy.
    If systemic pulmonary hypertension is the case in atrial septal defect, no real electrocardiographic differences will exist with ventricular septal defect or patent ductus arteriosus in the same hemodynamic stage (Eisenmenger syndrome).

ROENTGENOGRAM

    Moderate right ventricular hypertrophy more easily appreciated in lateral view with clockwise heart rotation on the longitudinal axis.
    Enlargement of pulmonary artery arch.
    Right atrium enlargement, more easily appreciated in lateral or oblique views.
    The aorta frequently is smaller than normal.
    The left atrium is normal in size.
    Dilated hilar vessels. Clear peripheral lung fields with tremendous enlargement of the pulmonary artery and marked hilar congestion will characterize the roentogenogram of severe pulmonary hypertension (more than 60 mm Hg.).

ECHOCARDIOGRAM IN ASD

    Although the septal defect only exceptionally can be visualized, echocardiography can be useful in assessing the right ventricular volume overload proper of this disease, where dilation of the right ventricular chamber associated with abnormal interventricular septal motion is noted. Some findings, however, can eventually be observed in any situation leading to right ventricular volume overload as pulmonary insufficiency, tricuspid insufficiency, pulmonary anomalous venous return, etc.

HEMODYNAMIC AND ANGIOGRAPHIC STUDY

    The ASD diagnosis can be made without problems by the physical exam, electrocardiography and roentgenogram. However, the hemodynamic study helps in categorizing the functional stage and is essential to discover associated congenital malformations.
The right side catheterization will typically reveal:

1. Blood oximetry demonstrate right atrium step up difficult to evaluate at times (unless large ASD) due to blood streams inside the right atrium with different oxygen concentration.
       At times this step up is manifested only at ventricular level. Superior vena cava step up can indicate anomalous venous return.
2. Passing of the catheter toward left atrium documented by entering of the pulmonary veins and by oximetry.
3. Pulmonary valve gradient is not unusual due to high blood flow (functional). A gradient higher than 30 mm Hg however, indicates real anatomical stenosis or infundibular stenosis due to "defensive" infundibular hypertrophy.

    A complete right cardiac catheterization will reveal the real hemodynamic magnitude of the problem revealing the degree of pulmonary hypertension.
    Angiocardiography indications are questionable in the sense that a very accurate diagnosis can be reached in a simpler manner. Angiography however, is particularly useful in case of ostium primum and anomalus pulmonary vein drainage. In this case, injection of the contrast material in the main pulmonary artery will visualize the pulmonary vasculature and pulmonary veins, then the left atrium and left ventricle and the dye will pass to the right atrium visualizing the right sided chambers.
    Special attention must be given in adults to the condition of the Mitral valve during catheterization (rule out Mitral Stenosis before surgery is attempted).

MEDICAL AND SURGICAL TREATMENT

    The medical management is limited to the early treatment of upper respiratory tract infections and prevention of congestive failure.
    Atrial fibrillation may be complicated with congestive heart failure too and should be rapidly converted to NSR with Quinidine or electrocardioversion using direct current counter shock.
    SBE is uncommon in ASD. Most of researchers favor antibiotics prophylactically.
    Surgical correction is advisable if signs of pulmonary hypertension or congestive heart failure develop.
    The ideal age for surgical correction is 5 to 8 years.
    Direct suture of the defect is usually enough in ostium secundum type. If anomalous venous defect is present a special pericardial patching is necessary as explained elsewhere.

Diagrammatic representation of different types of atrial septal defects. The superior one is a sinus venous type which in the majority of cases associates with partial anomalous pulmonary venous return. The second defect represents a case of ostium secundum type. The inferior one is a low posterior defect also known as inferior vena cava type.

16 year-old female with ASD.

34 year-old with Ostium Secundum type of ASD. There was minimal elevation of his MPA pressure.

Diagrammatic representation of the hemodynamic findings in a case of atrial septal defect (pressures are given in mm Hg and the picture depicts percentage of oxygen saturation too).
    Indocyanine green dye curves are shown on the right. The abbreviations indicate the injection site on the left and the sampling site on the right. In the left ventricle to femoral artery curve nothing abnormal is seen. The injections in both pulmonary arteries and inferior vena cava finally indicate that the level of shunt is located in the atrial septum.