Congenital heart malformation in which one great
artery emerges from the heart and subsequently gives origin to the coronary
arteries, pulmonary arteries, and systemic arteries.
0.4 to 2.8% of all congenital heart disease.
Autosomal recessive. Gene map locus is at
Embryologically, truncus arteriosus results from
failure of septation of the bulbus cordis, which usually occurs at about 5
weeks' gestation. Failure of conal septation is usually present and results
in a ventricular septal defect. Collett and Edwards, and Van Praagh have
suggested different classifications for truncus arteriosus based on the
origin of the pulmonary arteries and associated anomalies such as
hypoplastic aortic arch. Physiologically the pulmonary and systemic
circulations are in parallel, with high flow through the low-resistance
pulmonary circuit causing left ventricular volume overload and failure. The
right ventricle pumps at systemic pressures to maintain truncal flow and is
“pressure overloaded.” Ventricular function may be compromised further by
abnormal coronary anatomy or stenosis, causing ischemia, and by low
diastolic pressures as a consequence of excessive flow through the pulmonary
circuit, resulting in hypoperfusion of the endocardium. Systemic and
pulmonary venous blood mix at the level of the ventricular septal defect,
tending to cause desaturation of systemic blood. Continued high pulmonary
flow will ultimately result in pulmonary vascular occlusive disease,
Eisenmenger syndrome, and death.
Clinical findings. Echocardiography and angiographic
Symptoms are predominantly those of ventricular
failure, tachypnea, tachycardia, and feeding difficulties. In older infants,
cyanosis and recurrent chest infections become more common. The clinical
signs are nonspecific and include various heart murmurs and a collapsing
pulse caused by high flow through the low-resistance pulmonary circulation.
Facial abnormalities, including micrognathia, may be present as part of the
conotruncal anomaly face syndrome. The chest radiograph usually demonstrates
increased vascular markings, cardiomegaly, and a “globular or egg-shaped
cardiac contour.” If one pulmonary artery is absent, there may be
hypoplasia of the affected hemithorax. Rarely, left or right main bronchus
compression by the abnormal vasculature causes pulmonary collapse. The ECG
shows signs of ventricular hypertrophy. Echocardiography and
angiocardiography are required to confirm the diagnosis and to define the
individual anatomy. Only 18% of affected individuals survive beyond 6
months of age without an operation. Those patients who survive childhood
usually die as a result of pulmonary hypertension causing Eisenmenger
syndrome in the third decade of life.
History and examination for evidence
of ventricular failure and respiratory compromise. Examine for possible
airway anomalies. Respiratory assessment: chest radiography; consider
measurement of arterial blood gases. Cardiovascular assessment: review ECG,
echocardiographic, and angiocardiographic data. Continue treatment for
ventricular failure preoperatively.
The major considerations are ventricular
failure, parallel pulmonary and systemic circulations, and the risk of
myocardial ischemia. Premedication is desirable. Avoid decreases in
pulmonary vascular resistance (i.e., avoid hyperoxia and hypocapnia).
Moderate reductions in systemic vascular resistance may improve the
pulmonary:systemic flow ratio, but may further compromise endocardial
perfusion by lowering the ...