Chapter 10

    Ventricular septal defects account for 15 to 25 % of the congenital heart diseases (Wood 11.0 %, Keith 25 %, Nadas 19.87 %, De Soldati 10 to 15 %). It can be encountered as the principal heart malformation or forming part of other anomalies as Tetralogy of Fallot, Truncus arteriosus, Complete transposition of the great arteries, Tricuspid atresia, etc.

ANATOMICAL ABNORMALITY

    There are two basic different locations to be distinguished.

1. VSD located over the Crista Supraventricularis (less frequent). Defect located in the outflow tract of the right ventricle. Both the right and posterior coronary aortic valves are directly over the defect. Many times there is aortic insufficiency and rarely the aortic orifice can override the septal defect.
2. VSD located below the Crista Supraventricularis (more frequent). The defects located in front of the Conus Papillary muscle and behind the Crista are the most common variety.

    There are defects behind the Conus Papilary muscle which are the posterior and basal VSD. Usually in this variety the defect size is larger than in the previous type.
    There is a third variety located in the muscular interventricular septum (single or multiple orifices) (Roger disease).

PHYSIOLOGY AND HEMODYNAMICS

    The hemodynamics in VSD will depend upon:

1. The size of the VSD (most important factor)
2. Degree of pulmonary hypertension, if any, and pulmonary vascular resistance.
3. Location of the VSD.

    Usually if the size is less than 1 cm² the shunt allows the pulmonary vasculature to accommodate to the new hemodynamic condition without pulmonary hypertension. The shunt is always from left to right. Good clinical tolerance is the rule with none or minimal LVH. (The Roger Syndrome belongs to this category.)
    If the size is lower than 2 cm2 there is a progressive volume (diastolic) overload in both ventricles. There is major tendency toward development of pulmonary hypertension, initially due to excessive blood flow through the pulmonary vasculature and finally, due to reactive arteriolar contraction.
    Finally a high pulmonary resistance will tend to change the direction of the cardiac shunt and, when it is similar or higher than the systemic pressure, the picture of Eisenmenger Syndrome develops with right to left shunt and predominant right ventricular overload.
    In patients with large VSD the normal reduction of pulmonary resistance after birth does not occur and these patients behave as Eisenmenger Syndromes with early cyanosis noticed a few weeks after birth.
    Patients with large VSD invariably are symptomatic after a few weeks or months of life.

CLINICAL PICTURE
Grade I

    Small ventricular septal defect (less than 1.5 cm2) Patient is asymptomatic. Murmur can be present since a few days after birth.
    VSD is an evolving congenital heart disease. Small defects tend many times to disappear. Middle size and large defects tend to evolve however, from a total asymptomatic picture toward Eisenmenger complex in a few months or many years.

Grade II

    Frequent respiratory tract infections. CHF (rare). Cyanosis is absent even during exercise. Functional aerobic capacity is usually moderately reduced with early fatigability but unusual CHF.

Grade III

    More frequent respiratory tract infections. Defective growth. Moderate cyanosis at times with exertion Congestive heart failure frequent in the first years of life (one of the most frequent causes of CHF during the first year of life). Functional capacity markedly reduced.
    Grade IV or Eisenmenger Complex is analyzed in another chapter.

PHYSICAL FINDINGS

    The most typical findings are:
    Thrill in 80 % of patients on L.L.S.B.
    Wide splitting of S₂ which varies with respiration. S₂ can be palpable as the pulmonary artery pressure increases. S₃ is commonly present at apex due to left ventricle volume overload.
    II to IV murmur of regurgitation (usually pansystolic), harsh in character many times, located at 3rd, 4th, and 5th left parasternal, intercostal spaces.
    In case of severe VSD with pulmonary hypertension, this murmur diminishes its intensity, and a second murmur, ejective, located in the pulmonary area appears with an early diastolic murmur of pulmonary insufficiency. In case of progressive pulmonary hypertension, the second sound splitting tends to be less significant but S₂ many times is louder.
    When the patient is in the last stage or Grade IV known as Eisenmenger Syndrome, the clinical picture and most of the physical findings are the ones of this complex, and will be the same regardless of the shunt site (V.S.D., A.S.D., P.D.A.).
    Ammyl Nitrate increases the murmur of VSD (regurgitant type of murmur).

ELECTROCARDIOGRAM

    Electrocardiography is very useful for the clinical evaluation of this entity reflecting quite accurately the real hemodynamic situation of the patient.
    If we classify the ventricular septal defect in four different stages regarding the progressive hemodynamic deterioration of the patient, in the first stage, the electrocardiogram in general will be normal or near normal.
    In the second stage, the electrocardiogram may remain practically normal but occasionally will show moderate changes of left ventricular hypertrophy. At times, in the second stage of the ventricular septal defect, hypertrophy of both right and left ventricles can be seen which will correlate more closely with the pulmonary hypertension than with the significance of the ventricular shunt.
    Signs of left ventricular hypertrophy are frequent in this category (second stage), indicating that pulmonary hypertension is only moderate. qRs or QRS complex may be seen with a P wave taller than usual in V₅ and V₆. Q wave can be very deep (more than 10.0 mm.) in the same leads, which is useful in the differential diagnosis with patent ductus arteriosus where deep Q waves are unusual in the anterolateral leads.
    It is important to remember that ventricular septal defect and PDA may have very similar electrocardiographic changes. The T wave usually is positive in the same leads (antero-lateral leads), and tall R wave may be seen in leads V₅ and V₈ in both congential diseases due to diastolic left ventricular overload (volume overload), which is common to both conditions.
    Typically, in early stages, when left ventricular diastolic overload is more important hemodynamically than pulmonary hypertension, tendency to the left axis deviation will be seen. When pulmonary hypertension is higher than 50 mm Hg, the electrocardiogram will start showing biventricular hypertrophy.
    In the third stage and more typically in the fourth stage, the electrocardiogram shows predominantly, signs of significant right ventricular systolic overload, and, as mentioned for patent ductus arteriosus, the enlargement of the left ventricle will be totally masqueraded by the right ventricular hypertrophy. Electrocardiographic changes due to RV hypertrophy however, rarely will be so significant as in marked pulmonary stenosis with intact intraventricular septum, but can be similar to the one seen in Tetralogy of Fallot (right axis deviation with tall R wave in leads V₁, V₂ and V₃ associated with T wave inversion in the same leads or at times biphasic T waves).
    PR interval prolongation was described several times in these congenital situations (VSD), but, the incidence of AV block is not necessarily high. In 25 % of the cases of ventricular septal defect, enlargement of the right atrium may be noted with tall P waves in leads II and V₁.

ROENTGENOGRAM

ECHOCARDIOGRAM IN VSD

    The defect (VSD) is usually extremely difficult to visualize with M mode scan. Exceptionally a discontinuity between the aorta and the introventricular septum can be visualized in patients with supracristal defects. However, a normal membranous intraventricular septum can eventually produce the same geographic findings.
    Cross sectional echocardiography, although more promising than M mode sonogram, is still highly unreliable for direct visualization of the ventricular defect itself. As in other malformations the ratio between left atrial and aortic diameters allegedly can provide information on the magnitude of the shunt.
    In case of systemic pulmonary hypertension complicating VSD, right ventricular englargement can be easily visualized with signs of pulmonary hypertension at the pulmonary valve level.

HEMODYNAMIC AND ANGIOGRAPHIC STUDY
Grade I

    Right atrium and right ventricular pressures are normal, due to the low volume shunt. Oxymetry can be misleading, showing only a mild step up in oxygen saturation at ventricular level.
    Indicator dilution curves are usually more sensitive in these cases than plane oxymetry.
    The passage to the left ventricle with the catheter is often possible.

Grade II

    Elevation of right ventricular pressure and pulmonary hyperdynamics hypertension (moderate) due to large pulmonary flow.
    Blood oxygen measurements will show typical right ventricular oxygen step up. If the defect is located over the Crista Supraventricularis the step up can only be seen at the pulmonary artery level. (The maximal normal step up between vena cava and atrium is 2 Vol % and between RV and MPA 0.5 Vol %; any difference over such figures must be considered abnormal.)
    The analysis of the catheter position as the left ventricle is entered, is useful but not conclusive in the diagnosis.

Grade III

    The pressure tends to equalize between right and left ventricles but with a still predominant left to right shunt. Significant blood oxygen step up is noted.
    With exertion, the normal peripheral arterial oxygen saturation is reduced. Significant pulmonary hypertension exists (close to systemic). There is marked R.V.H.

Grade IV: See Eisenmenger Complex

    In all categories the calculation of the shunt flow is useful because it provides a quantitative figure, which in terms categorizes the patient more accurately before deciding on surgery.
    The angiography study is usually not very important, and continues to be a debatable subject whether or not it is indicated for the routine evaluation of these patients.
    Many times, however, the surgeon has a valuable extra information with this "graphic" method.
    Angiography can be essential also in very small VSD where it can demonstrate the anomaly even in cases without significant blood oxygen step up.
    Left ventricle angiogram is done if the VSD has predominant shunt from left to right. The injection should be in the right ventricle in case of right to left direction. The patient ideally must be positioned in a left anterior oblique projection for proper visualization of the septum.

TREATMENT

1. Prevention of SBE
2. Treatment of left ventricular failure, prevalently during the first three years of life (more frequent in the first year of life).
3. If the CHF is severe during the first few months, pulmonary artery binding is indicated (mainly during first month of age).
4. After a few months, surgical correction of VSD can be attempted, putting special emphasis on doing the corrective surgery in youngsters before 2 years of age if the shunt is large in volume.
       If the defect is moderate and there are no signs of intractable CHF andlor severe pulmonary hypertension, surgery should be postponed until age 6 to 8. VSD patching at that time, via the right ventricle or right atriotomy depending on the location of the defect is then indicated.

The diagram depicts the different locations of VSD in relation to the Crista Supraventricularis.

Electrocardiogram of an infant with large VSD and moderate Pulmonary Hypertension.

Diagrammatic portrayal of pressures and oxygen staturation findings at different chambers in a patient with ventricular septal defect. The Indocyanine green dye dilution curves injecting in the main pulmonary artery indicate pattern of recirculation typical of a moderate left to right shunt. the shunt is at the ventricular level as indicated by the early appearance of the dye in the pulmonary artery when injected in the left ventricle, but not when injected in the aorta, ruling out PDA and aorto-pulmonary window.