Persistent Truncus Arteriosus

Persistent truncus arteriosus should be diagnosed early during childhood, despite the fact that cyanosis may sometimes be mild, especially in newborns, that normally have increased pulmonary resistance. It is a cyanotic heart disease and clinician's attention should be first drawn by heart failure signs: diaphoresis, poor feeding, failure to thrive and tachypnea. These gradually appear, as the pulmonary blood flow and, consequently, myocardial work increase.

Clinical examination reveals a hyperdynamic precordium, an ejection click, and a single, loud second heart sound, due to the fact that a single truncal valve exists. If this valve is insufficient, the regurgitant flow causes a murmur that is characterized as high-pitched, decrescendo and diastolic. Some studies [1] [2] find regurgitation to be an important risk factor for mortality, while others [3] [4] fail to do so. The severity of the regurgitation is, however, clinically important because, if severe, it leads to more pronounced and earlier heart failure symptoms. Auscultation is completed by a mild or intense systolic murmur along the left sternal border. A mid-diastolic mitral flow murmur can also be noted. This is because of the high pulmonary blood flow. Pulmonary over-circulation, if present, prevents severe desaturation and cyanosis.

The presentation is usually much more dramatic if patients also have an interrupted aortic arch and patent ductus arteriosus that is about to close. In this case, the clinician will diagnose cardiogenic shock.

Blood workup in persistent truncus arteriosus should include measurement of arterial blood gas, performed before and after a hyperoxia test if the diagnosis is uncertain. This test can also reveal acidosis if present. Electrolytes, especially total and ionized calcium should also be measured, due to the frequent association of truncus arteriosus with DiGeorge syndrome.

The thoracic radiograph shows raised pulmonary vascular markings due to pulmonary over-circulation along with cardiomegaly. A right aortic arch may coexist and be seen with this method [5]. The pulmonary arteries originate high from the common trunk.

The electrocardiogram usually shows both right and left ventricular hypertrophy. A left atrial enlargement may be present if pulmonary over-circulation is marked. Axis may slightly deviate to the right.

Echocardiography is used to establish the diagnosis. Subcostal and parasternal long axis views are key when aiming to demonstrate the single trunk arising from both ventricles and the existence of a ventricular septal defect. The trunk may override the interventricular septum in variable degrees, therefore originating more from the left or from the right ventricle. It is also important to characterize the truncal valve in terms of anatomy and function (stenosis or regurgitation) and this can be performed by doppler color imaging. The subcostal view is also used to observe the origins of the pulmonary and coronary arteries.

Prenatal echocardiography can raise disease suspicion, but differential diagnosis with similar malformations may prove difficult [6]. Four-dimensional fetal echocardiography may improve accuracy [7].

Cardiac catheterization is only used when coronary artery origin and anatomy cannot be properly characterized using echocardiography, in a preoperative setting [8].

1. Rajasinghe H, McElhinney D, Reddy V, et al. Long-term follow-up of truncus arteriosus repaired in infancy: a twenty-year experience. J Thorac Cardiovasc Surg. 1997;113:869–879.
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3. Brown J, Ruzmetov M, Okada Y, et al. Truncus arteriosus repair : Outcomes, risk factors, reoperation and management. Eur J Cardiothorac Surg. 2001;20:221–227.
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7. Turan S, Turan OM, Desai A, et al. First-trimester fetal cardiac examination using spatiotemporal image correlation, tomographic ultrasound and color Doppler imaging for the diagnosis of complex congenital heart disease in high-risk patients. Ultrasound Obstet Gynecol. 2014;44(5):562-567.
8. Rao PS. Diagnosis and management of cyanotic congenital heart disease: part I. Indian J Pediatr. 2009;76(1):57-70.