Persistent truncus arteriosus
Overview
Persistent truncus arteriosus occurs when, during fetal development, the primitive truncus does not divide into the pulmonary artery and aorta, resulting in a single large arterial trunk that overlies a large, perimembranous, infundibular ventricular septal defect. Consequently, a mixture of oxygenated and deoxygenated blood enters systemic, pulmonary, and coronary circulations. Symptoms include cyanosis, poor feeding, diaphoresis, and tachypnea. A normal S1 and a loud single S2 are common; murmurs may vary. Diagnosis is by echocardiography or cardiac catheterization. Medical treatment for heart failure is typically followed by surgical repair. Endocarditis prophylaxis is recommended. Persistent truncus arteriosus accounts for 1 to 2% of congenital heart anomalies. About 35% of patients have DiGeorge syndrome or velocardiofacial syndrome. There are 4 types. In type I, the main pulmonary artery arises from the truncus, then divides into the right and left pulmonary arteries. In types II and III, the right and left pulmonary arteries arise separately from the posterior and lateral aspects of the truncus, respectively. In type IV, arteries arising in the descending aorta supply the lungs; this type is now considered a severe form of tetralogy of Fallot. Other anomalies (eg, truncal valve insufficiency, coronary artery anomalies, atrioventricular septal defect, double aortic arch) may be present and may contribute to the high surgical mortality rate. Physiologic consequences of type I include mild cyanosis, heart failure (HF), and significant pulmonary overcirculation. In types II and III, cyanosis is more noticeable and HF is infrequent because pulmonary blood flow is normal or only slightly increased.
Symptoms
Neonates with type I present with mild cyanosis and symptoms and signs of HF (tachypnea, poor feeding, diaphoresis) in the 1st few weeks of life. Neonates with type II or III present with more noticeable cyanosis, but HF is less likely to develop. Physical examination may detect a hyperdynamic precordium, increased pulse pressure, a loud and single S2, and an ejection click. A grade 2 to 4/6 holosystolic murmur is audible along the left sternal border. A mid-diastolic mitral flow murmur may be audible at the apex when pulmonary blood flow is increased. With truncal valve insufficiency, a high-pitched diastolic decrescendo murmur is audible over the mid left sternal border.
Diagnosis
Diagnosis is suspected clinically, supported by chest x-ray and ECG, and established by 2-dimensional echocardiography with color flow and Doppler studies. Cardiac catheterization is often necessary to delineate associated anomalies before surgery. Chest x-rays show varying degrees of cardiomegaly with increased pulmonary vascular markings, right aortic arch (in about 30%), and relatively high position of pulmonary arteries. ECG commonly shows combined ventricular hypertrophy. Substantial pulmonary overcirculation may produce evidence of left atrial hypertrophy.
Treatment
HF is treated vigorously with diuretics, digoxin Some Trade Names DIGITEK LANOXIN Click for Drug Monograph , and ACE inhibitors, followed by early surgical repair. IV prostaglandin infusion is not beneficial. Surgical management consists of complete primary repair. The ventricular septal defect is closed so that the left ventricle ejects into the truncal artery. A conduit with or without a valve is placed between the right ventricle and the confluence of the pulmonary arteries. Surgical mortality rate is 10 to 30%. All patients require endocarditis prophylaxis