Chapter 6

 

PERSISTENT COMMON ATRIO VENTRICULAR CANAL
ENDOCARDIAL CUSHION DEFECT

ANATOMICAL ABNORMALITY

  1. Atrial Septal defect located in the very low part of the interatrial septum, below the fossa ovalis (Ostium Primum Type of ASD)
  2. Cleft anterior leaflet of the Mitral valve (frequently present but not always)
  3. Cleft septal leaflet of the Tricuspid valve (less frequent than the Cleft M.V.)
  4. Poor formation of the Membranous interventricular septum
    As a consequence of the previous defects there is inter-atrial communication in all cases. Frequently associated with mitral insufficiency of different degree, and often tricuspid incompetence. In the case of defective formation of the membranous aspect of the interventricular septum, multiple interatrioventricular shunting will be present (persistence of the common atno-ventricular canal).
    There are two varieties of this defect:
  1. Incomplete type.
    Crescent shape ASD with frequent cleft mitral valve and occasionally tricuspid incompetence.
  2. Complete type (common atno-ventricular canal)
    Multiple directional shunt with large mitral insufficiency and bilateral ventricular hypertrophy. (Atrio-ventricularis Comunis).

PHYSIOLOGY AND HEMODYNAMICS

    Will vary depending upon the presence of complete or incomplete variety of ostrium primum (endocardial cushion defect).

  1. Incomplete variety
    Left to right shunt at atrial level (pure ostium primum defect) with or without mitral and/or tricuspid insufficiency.
    In general, the patient will behave as the common variety of ASD (ostium secundum type).
    Occasionally direct regurgitation from left ventricle to right atrium may be seen (cleft mitral valve). In such cases, the enlargement of the right atrium will be more significant than in the common ASD.
    In the case of small ostium primum defect with large mitral incompetence, the enlargement will be prevalent at the left ventricle and left atrium with normal right atrial size.
  1. Complete variety (Atrioventricular Comunis)
    There is not only communication at the atrial level, but, at the ventricular level too with mitral and tricuspid incompetence.
    At times the ventricular defect at the level of the membranous septum is so large that both ventricles can behave as a common cavity.
    The valvular regurgitation is usually multiple directional. There is, as in the common variety of ASD, right ventricular hypertrophy, but the left ventricular enlargement is prevalent, which is typical of endocardial cushion defect.
    Left to right shunt is the rule but tendency to pulmonary hypertension is greater than in common ASD, with consequent potential reversal of the shunt direction (right to left).

CLINICAL PICTURE

Incomplete variety: clinical picture is similar to ASD.
Complete variety: the appearance is also similar to common ASD but major tendency to early CHF, pulmonary hypertension and Eisenmenger Syndrome is noted.

PHYSICAL FINDINGS

Incomplete variety: findings similar to common ASD.
Complete variety: findings of common ASD plus murmur of the mitral competence with or without thrill in apical area radiation to back and left axila. The murmur many times can be indistinguishable from that of VSD).    As in the common ASD, the patient will present basal ejection murmur at the pulmonic valve level.
    Typical Jugular contour of tricuspid insufficiency when present, and hepatic pulse.

VECTORCARDIOGRAM

    Deviation of the QRS loop toward the left and superior quadrants. Counter clockwise rotation in the frontal plane.

ECHOCARDIOGRAM IN ENDOCARDIAL CUSHION DEFECT

    No special findings can be made by M mode or cross sectional echocardiography other than those mentioned for ASD. The left ventricular enlargement often seen in these cases will produce its proper changes in the sonog ram. Real time echo may be helpful.
    In cases of cleft mitral leaflets, abnormal motion and insertion of the valve is described in the literature, which, however, is far from being characteristic of this entry.

ELECTROCARDIOGRAM IN ENDOCARDIAL CUSHION DEFECT

    The anatomical, abnormal communication produced between different chambers by the endocardial cushion defect (ostium primum) will be fundamentally divided into two categories. The first category involves an abnormal communication between both atriums and both ventricles but without mitral or tricuspid regurgitation (both valvular structures are normal). The second category will result in the involvement of the mitral valve, more frequently, and at times the tricuspid valve, with concomittant mitral and/or tricuspid regurgitation. The first category of patients will behave clinically as the most common type of atrial septal defect (ostium secundum). In the second type, signs of mitral and tricuspid regurgitation will be present.
    The electrocardiogram is fundamental to recognize this type of defect. Although not typical of this problem, it will allow the physician to rule out ostium secundum and ostium primum without mitral insufficiency, where the electrocardiography is significantly different.
    The electrocardiogram will show:

  1. Incomplete right bundle branch block in 90% of the cases.
  2. Left axis deviation over the frontal plane (not right axis deviation as in ostium secundum).
  3. At times, P wave configuration of right or bilateral atrial overload will be present.     This kind of association of electrocardiographic features is rather characteristic of ostium primum with mitral regurgitation (complete variety). As a matter of fact, similar electrocardiograms can be seen only in very few congenital cardial diseases as tricuspid atrecia and intraventricular septal defect with tricuspid insufficiency.
  4. Exceptionally complete right bundle branch block may be observed but, most frequently, the QRS duration will be normal. A Q wave in lead I with a deep S wave in leads II and III and aVF will be present. The typical configration of incomplete right bundle branch block will be seen in leads V1 and V2, but the QRS may look normal in V5 and V6.
  5. The electrocardiogram usually will not show hypervoltage in the left precordial leads correlating with a marked left axis deviation.
  6. In more than 50% of the patients, first degree AV block may be seen.
  7. If pulmonary hypertension supervenes, the electrocardiogram will lose the typical characteristics previously mentioned and in systemic pulmonary hypertension, right axis deviation with signs of right ventricular hypertrophy and right ventricular systolic overload will appear in the electocardiogram. In these cases, the electrocardiogram and the clinical picture will be similar to the one described for the Eisenmenger's complex, and, no differences can be established in the ECG tracing regardless of the shunt site. (For more information in this regard, read the chapter of Electrocardiogram in Eisenmenger Syndrome).

ROENTGENOGRAM

    May be similar to ASD, but often it depicts typical left ventricular hypertrophy and bilateral atrial enlargement.

CATHETERIZATION AND ANGIOCARDIOGRAPHY

    Catherization and Angiocardiography is essential for the final anatomical diagnosis and hemodynamic evaluation of each patient. The anatomical condition of the interventricular septum and quantification of mitral incompetence are essential in view of any surgical correction.
    The catherization will demonstrate easy passage of the catheter from the right atrium and right ventricle toward left atrium and left ventricles (low passage of catheter).
    As compared with common ASD these patients will present:

  1. Frequent association with Down's Syndrome.
  2. Symptoms usually occur earlier in infancy.
  3. Left ventricular failure can be seen, which is rare in common ASD.
  4. More pronounced growth delay and respiratory tract infections.
  5. Pulmonary Edema can be seen in terminal cases, and, is not unusual in early infancy.
  6. Signs of hemodynamic decompensation such as cough, paroxysmal nocturnal dyspnea, distention of jugular veins, tachypnea, pulsus alternans, etc.
  7. The prognosis is poor and most of these patients will die before age 3. "Compensatory" infundibular hypertrophic Stenosis can protect the patient from severe pulmonary hypertension and help prolong life.

Oxygen studies will show:

  • Left to right shunt at the atrial level as in ASD.
  • In the complete variety, a second increase in Oxygen saturation can be seen at the ventricular level due to membranous septum defect.
  • A pulmonary gradient of 10 to 15 mm Hg can be seen without real Pulmonic Stenosis due to large blood flow across a normal valve.
  • Occasionally reactive (protective) infundibular, hypertrophic stenosis can appear and a chamber phenomenon register in the pull back pressures across the pulmonary valve.
  • Pulmonary Systolic pressure and right ventricular systolic pressures are below 50 mm Hg if no significant pulmonary hypertension is present.
  • The angiocardiography with injection of contrast material in the left ventricle (positioning the patient in right anterior oblique projection), will render information regarding the shunt level and degree of Mitral incompetence.
  • Left ventricular angiography can produce "Swan Neck" contour which is classically described in this entity. It is probably due to the ventricular prolapse of the abnormal anterior mitral leaflet during systole.

    Biplane angiography is most helpful.


Complete form of atrioventricular canal in endocardial cushion defect.


Diagrammatic representation of multichamber arrangement in endocardial cushion defect. Complete form of common atrioventricular canal.


Complete Endocardial Cushion Defect in a 9 year-old patient with Down's Syndrome. Left axis deviation and biventricular hypertrophy are noted. Incomplete RBBB is not present in this case, however.


Roentgenogram of an infant with complete type of Endocardial Cushion Defect.


Roentgenogram in a case of Ostium Primum in a 14 year-old girl.