Truncus Arteriosus Communis

At a glance

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.

Incidence

From 0.4 to 2.8% of all congenital heart disease.

Genetic inheritance

Autosomal recessive. Gene map locus is at 22q11.

Pathophysiology

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.

Diagnosis

Clinical findings. Echocardiography and angiographic findings.

Clinical aspects

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. The majority patients with Truncus Arteriosus Communis and 22q11 deletion also have other anomalies such as hypoplasia or aplasia of the thymus or parathyroid glands and immune deficits (T-cell deficiency), calcium metabolism disorder (hypocalcemia), palatal defects, learning and speech disorder, craniofacial anomalies, and neuropsychological abnormalities.

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