Truncus arteriosusDefinition This anomaly consists of a single arterial trunk exiting from the heart through a common valve, giving origin to aorta (systemic circulation), pulmonary artery (pulmonary circulation) and coronary arteries (coronary circulation).

Failure of normal septation and division of the embryonic bulbar trunk into the pulmonary artery & aorta, which results in development of a single vessel that overrides both ventricles. Blood from both the ventricles mixes in the common great artery which leads to desaturation and hypoxemia.

Blood ejected from the heart flows preferentially to the lower pressure pulmonary arteries, so the pulmonary blood flow is increased & systemic blood flow is reduced.

Incidence

It affects males & females equally & accounts for about 1% of all CHD cases. Almost always associated with VSD.

Synonyms

• Truncus arteriosus communis• Common arterial trunk

Embryology

• At 4 weeks of gestation two spiral ridges appear which separate common truncus into aorta & pulmonary artery.

• Failure of septation of the cono-truncal segment gives rise to this anomaly.

Etiology

•Infants of diabetic mothers• Embryonic exposure to retinoic acid•Deletion of 22q11•Siblings of children born with truncus•High association with truncus and DORV•Association with CHARGE syndrome, Digeorge syndrome and CATCH 22

Types

• Type I : A single pulmonary trunk arises near the base of the truncus and divides into the left and right pulmonary arteries.• Type II : The left and right pulmonary arteries arise separately but in close proximity & at the same level from the back of the truncus.• Type III : The pulmonary arteries arise independently from the sides of the truncus.

• Type IV : No pulmonary artery arise from common truncus and lungs are supplied by pulmonary collaterals called pseudo truncus arteriosus .

Hemitruncus When one pulmonary artery arises from ascending aorta and other comes off normally from main pulmonary artery arising from the RV.

Pathophysiology

Blood ejected from the left and right ventricles enters the common trunk, so that pulmonary & systemic circulations are mixed. Blood flow is distributed to the pulmonary and systemic circulations according to the relative resistances of each system. The amount of pulmonary blood flow depends on the size of the pulmonary arteries and the pulmonary vascular resistance. Generally resistance to pulmonary blood flow is less than systemic vascular resistance, which results in preferential blood flow to the lungs. Pulmonary vascular disease develops at an early age in patients with truncus arteriosus.

Hemodynamics

Both ventricles pump into the common trunk which overrides the VSD. Therefore the systolic pressure in ventricles, aorta and pulmonary artery are same.Blood flow to pulmonary bed and systemic bed depends on the resistance to flow in their respective circulation.Soon after the birth :- SVR increased and PVR decreased increased pulmonary flow, if pulmonary flow is adequate, systemic saturation becomes normal.

Truncal regurgitation contributes to volume overload of both ventricles. Volume overload in ventricles and pulmonary circulation Obstructive changes of pulmonary vasculature Increased PVR Pulmonary hypertension Eisenmenger’s complex.

But later, because of increased pulmonary blood flow increased pulmonary venous return to LA and LVCCF within 1st week of birth. The cyanosis is mild or negligible.

Clinical manifestations

CCF in early pregnancy FTT, feeding difficulties, excessive sweating, tachypnea Repeated respiratory infection Hyperdynamic precordium, cardiomegaly, hepatomegaly Minimal cyanosis(not detected in rest, detected only in crying)

High volume pulse

Auscultation: Loud single 2nd heart sound( Loudness- dilation of trunk, Single – closure of one set of valves), Prominent ejection click (Due to opening of truncal valve), loud ejection systolic murmur(increased blood flow through the truncal orifice).

Diagnosis

ECG: Tall, peaked P wave in leadII, III and aVF shows RAE, right axis deviation and RVH.Radiography: cardiomegaly, a high origin of a dilated left pulmonary artery may give rise to comma sign in CXR. Echo : most helpful diagnostic tool.Cardiac catheterization : used to clarify doubt about cardiac anatomy.

Management Medical Control of CCF with diuretics and digoxinCorrection of acidosisTreatment of respiratory infectionsNo oxygen to minimize pulmonary blood flowIf interruption in aortic arch, prostaglandin infusion to keep ductus arteriosus patent. I E prophylaxis

Surgical management

Definite treatment : surgical repair Early surgery is necessary Definite repair using conduit from RV to PA and closure of VSD. Optimum age : Before 3 months. As the child grows this conduit tends to degenerate and calcify, so it needs replacement in futurePalliative surgery: Pulmonary artery banding. It is indicated in infants with large pulmonary blood flow and CCF.

Complications

CCFRepeated respiratory infectionIncreased cyanosis and hypoxemiaBrain abscess CVA Infective endocarditisComplications of surgeryTruncal valve dysfunctionRV conduit obstruction

Prognosis

• Mortality is high if not corrected early• 75% die with in 1st month of life• Average lifespan is 5 week• Survival up to one year is seen only 15%• If survived, features of pulmonary vascular obstructive disease and develops Eisenmenger’s syndrome.

Thank You…

Deepa Merin KuriakoseAssistant Professor

Govt. College of Nursing, Kottayam