Chapter 23

    In this malformation, a single vessel arises from the heart, which is usually overriding a VSD with atrophy of the right ventricle outflow tract.
    There are five basic possibilities: type I, II, III, IV and Pseudotroncus.

A. Type I:	Following a common origin, the main pulmonary artery and ascending aorta divide. The pulmonary trunk divides normally into the right and left pulmonary arteries.
B. Type II:	The main pulmonary artery does not exist and both pulmonaries arise independently from the posterior aspect of the truncus arteriosus.
C. Type III:	Both pulmonary arteries originate from the lateral aspect of the common truncus arteriosus.
D. Type IV:	Both pulmonary arteries arise from the lateral aspect of the descending aorta, or there is total absence of the pulmonary artery. Many times in this variety there is not even right or left pulmonary branches and the blood reaches the lung through hypertrophied bronchial arteries arising from the descending aorta.
E. Pseudotroncus:	Extreme variety of Tetralogy of Fallot with complete atresia of the pulmonary artery. For this case bronchial collateral vessel enlargement is necessary for survival.

    All five of these possibilities can also be given with intact ventricular septum and in these cases ASO or FDA is needed for life.

PHYSIOLOGY AND HEMODYNAMICS

    Two different categories can be distinguished depending upon the pulmonary vascular resistance:

1. Low pulmonary vascular resistance (where there is no major impediment for the blood flow to reach the patient's lungs). These patients will behave as a large left to right shunt, with mild to moderate cyanosis.
   
2. High pulmonary vascular resistance (impediment exists for the blood to reach the lungs). These patients will closely simulate Elsenmenger's Complex and Tetralogy of Fallot.
   

CLINICAL PICTURE

    The average age, depending on the type involved, will be between 3 months and 18 months. The clinical findings will depend upon the type of truncus arteriosus. In Type I, II, III with good pulmonary ciculation and normal pulmonary vascular resistance the picture will be the one of left to right shunt with mild cyanosis and differential diagnosis should be made with large VSD, transposition of the great arteries and Tetralogy of Fallot.
    If the pulmonary vascular resistance is more severe or in case of Type IV and Pseudotroncus, the picture will be characterized by more severe cyanosis and may closely simulate at times severe Tetralogy of Fallot and Elsenmenger's Syndrome.
    Failure to thrive is seen in both situations. Congestive heart failure and deformed thorax can be noted from the first months of life.
    First sound is single and is closely followed by an early systolic click. Systolic murmur (protosystolic) is present is the third and fourth left intercostal spaces which is many times accompanied by a thrill. This murmur is similar to the one seen in VSD.) In Type IV, there is a continuous interscapular murmur.
    Early diastolic murmur of regurgitation can also be present (30% of cases), and if PDA is present, a continuous murmur can be heard.
    Single and accentuated S₂ is the rule.
    Signs of right ventricle failure are present after a few months of life.

Cardinal findings:

Cyanosis CHF Growth retardation Pulmonary plethora Significant cardiomegaly Systolic murmur Single loud second sound

ELECTROCARDIOGRAM

    Is not typical.
    Large P pulmonale can be seen.
    The main axis can be normally placed over the frontal plane, at times present right axis deviation if resistance is increased to the pulmonary blood flow.
    Biventricular hypertrophy is almost always the case however.
    Real time echocardiography can be particularly helpful in these patients as proved recently in many cases.

ROENTGENOGRAM

    The appearance will depend upon the type ot truncus arteriosus in question and from the size and location of the right and left pulmonary arteries.
    In Type I,II and III pulmonary flow will be increased with pulsating and engorged pulmonary arteries. If the origin of the pulmonary arteries is close to the aortic notch, truncus arteriosus is to be suspected.
    Right aortic arch is seen in close to 50% of cases of truncus arteriosus.

CARDIAC CATHETERIZATION

    During right cardiac catheterization the catheter may be advanced toward the truncus, and there, depending on the origin of the pulmonary arteries, (Type I,II,III) toward these vessels.
    Saturation in the aorta will depend upon the pulmonary vascular resistance (high resistance = low 0₂ saturation; low resistance = good 0₂ saturation). The 0₂ saturation is the same in the truncus arteriosus and in the pulmonary arteries.
    Selective infection of contrast in the truncus will show the vessel and the abnormal origin of the pulmonary arteries.
    Truncus arteriosus valve insufficiency and right aortic arch can be frequently encountered.
    In Type IV, which is very rare, no pulmonary arteries will be visualized and the lung circulation is singificantly diminished: These patients usually are very hypoxic and die early in life. Typical of this type is the continuous interscapular murmur.

MEDICAL AND SURGICAL TREATMENT

Medical treatment:

a. Prevention of SBE b. Treatment of CHF

SURGICAL TREATMENT

    Repair should be done before age 2. If CHP is present, surgery must be attempted early in infancy.
    Surgical approach differs upon the type of truncus arteriosus as follows:

    Type I, II, III: McGoom, Wallace, Danielson technique, using homograft of aorta to connect right ventricle with pulmonary arteries (hospital mortality between 10 to 20%) with repair of VSD.

    Type IV: No surgical treatment is yet available.

    Pseudotroncus: Palliative surgery can be attempted in early life (Blalock Taussig type). Then later in life the artificial shunt must be closed and insertion of external conduit between right ventricle and pulmonary arteries is done, with surgical closure of the VSD. (Hospital mortality 30%).

Representation of type I truncus arteriosus where the pulmonary artery separates early from the common trunk. Not infrequently these cases can generate a clinical picture similar to isolated ventricular septal defect and pass unrecognized for many years.

Type Ill truncus arteriosus where both pulmonary arteries arise perpendicularly from the aortic artery. The level of the pulmonary arteries is usually higher than normal in these cases.

Diagrammatic portrayal ot type IV truncus arteriosus. In cases there is total abscence of the pulmonary arteries and the pulmonary circulation is established through hypertrophied bronchial arteries.

Pseudotruncus arteriosus. Pulmonary artery atresia with ventricular septal defect present. The picture is a diagrammatic representation of the circulation pattern end specific anatomic features of thin malformation.

Electrocardiogram from a 1 year-old infant with Troncus Arteriosus shows a moderate right axis deviation considering this patient's age, and Biventricular Hypertrophy.

Roentgenogram of an infant with Troncus Arteriosus type III.

Roentgenogram in troncus Arteriosus in a 3 year-old boy. Cardiac catheterization demonstrates type I variety with right aortic arch.