Continuing Education Activity

Persistent truncus arteriosus (TA) is a rare, congenital, cyanotic heart defect characterized by a ventricular septal defect (VSD), a single truncal valve, and a common ventricular outflow tract (OT). Systemic venous blood and pulmonary venous blood mix at the VSD level, and the resulting desaturated blood is ejected into the single OT. Because the pulmonary arteries arise directly from the truncus, the pulmonary vascular resistance (PVR) will determine the pulmonary blood flow, which is usually torrential. This activity reviews the presentation, pathophysiology, and diagnosis of truncus arteriosus and highlights the role of the interprofessional team in the management of patients with congenital heart disorders.

Objectives:

• Identify the etiology of truncus arteriosus.
• Recall the presentation of an infant with truncus arteriosus.
• List the treatment and management options available for truncus arteriosus.
• Employ interprofessional team strategies for improving care and outcomes in infants diagnosed with truncus arteriosus.

Introduction

Persistent truncus arteriosus (TA) is a rare, congenital, cyanotic heart defect characterized by a ventricular septal defect (VSD), a single truncal valve, and a common ventricular outflow tract (OT). Systemic venous blood and pulmonary venous blood mix at the VSD level, and the resulting desaturated blood is ejected into the single OT. Because the pulmonary arteries arise directly from the truncus, the pulmonary vascular resistance (PVR) will determine the pulmonary blood flow, which is usually torrential. Without surgical intervention, death in infancy is the rule. Long-term surgical outcomes are good, but there are often residual and potential complications that require regular, long-term cardiology follow-up.[1][2]

Etiology

TA results if proper embryological processes fail to create a truncoconal septal wall, and the single truncal root does not divide into the separate aortic and pulmonic outflow tracts. This also inhibits the proper creation of separate aortic and pulmonary valves resulting in a single truncal valve.[3]

While no direct cause is known, TA is frequently associated with 22q11 genetic mutations.[4]

Epidemiology

TA is seen with an annual incidence of seven per 100,000 live births, and while it accounts for less than 1% of all congenital heart lesions, it accounts for 4% of critical congenital heart defects.[5]

Pathophysiology

To understand the pathophysiology of TA, it is first important to understand the path of blood flow and anatomy. In patients with TA, systemic venous blood normally returns to the right atrium and flows into the right ventricle. Pulmonary venous blood from the lungs normally flows through the pulmonary veins into the left atrium and to the left ventricle. The VSD allows oxygenated and deoxygenated blood to mix before it is ejected through a common truncal valve to a single great artery, subsequently supplying the coronary, pulmonary and systemic circulations.

The common semilunar valve may have 1 to 4 cusps with tricuspid most frequently seen. The presence of a single arterial trunk can be associated with several cardiac, aortic, and pulmonary abnormalities. These abnormalities include right-sided, interrupted, or hypoplastic aortic arches, abnormal origins of the coronary arteries, pulmonary artery stenosis, and patent ductus arteriosus. Depending on the origins of the pulmonary arteries, Collett and Edwards (CE) and Van Praagh each classified various forms of TA. Collett and Edwards based their system solely on the origins of the pulmonary vascular system, while Van Praagh also took into account aortic abnormalities.[6][7][8][9][10]

Throughout fetal development and the first week of life, PVR is relatively high, resulting in greater shunting of mixed oxygenated and deoxygenated blood into the systemic circuit causing mild cyanosis. As the PVR drops and PBF increases, pulmonary over-circulation causes congestive heart failure (CHF). If left untreated, pulmonary over-circulation may eventually lead to severe irreversible pulmonary vascular disease and death. As the pulmonary vascular disease worsens, PVR increases. This results in worsening cyanosis or right-to-left shunt (Eisenmenger syndrome).[2][11][12]

The mixing of pulmonary and systemic blood before departure from the heart combined with the degree of pulmonary blood flow (PBF) and pulmonary vascular resistance (PVR) drives the pathophysiology and the clinical picture.[2][5]

History and Physical

The clinical picture is driven by the PBF as well as the presence of valvular abnormalities and aortic arch obstruction. In the first few days after birth, the critical congenital heart defect (CCHD) screen in these patients show pre-and post-ductal oxygen saturation less than 95% with mild or unnoticeable cyanosis. Unscreened infants present within the first two weeks for evaluation of a heart murmur or with symptoms of CHF resulting from increased blood flow to the lungs. These infants exhibit poor feeding, lethargy, tachypnea, costal-sternal retractions, grunting, nasal flaring, tachycardia, or hepatomegaly.[2]

The cardiac exam will be notable for an ejection click and systolic murmur, single loud second heart sound, and a diastolic murmur if truncal valve regurgitation is present. Peripheral pulses may be bounding due to excess runoff into the pulmonary arteries. During diastole, an increased pulmonary vascular flow may correlate with higher pulse pressures.[13][14][15]

Valvular insufficiency and stenosis are common phenomena. Valvular regurgitation, seen in 50% of patients, can worsen symptoms of CHF. Concurrent critical coarctation, seen in 10% of TA patients, can lead to cardiovascular collapse with patients presenting in shock or even death.[11][12][16]

Evaluation

Definitive prenatal diagnosis by fetal echocardiography requires visualization of a single arterial outflow tract, a VSD, and the absence of a pulmonary valve. Postnatal diagnosis is suggested by the history and physical findings mentioned above along with abnormal results of the CCHD screening test. An electrocardiogram shows non-specific changes in early infancy with LV or RV hypertrophy, or higher QRS and P-wave voltages in older patients with increased PBF. Chest plain films will depict cardiomegaly and increased pulmonary vascular markings. Echocardiogram confirms the diagnosis and can delineate the anatomy in great detail. Cardiac magnetic resonance imaging (MRI), catheterization, and angiography can be used to assess the anatomy and cardiac function further if needed for pre-surgical planning and post-surgical evaluation. Genetic testing is recommended for all patients born with truncus arteriosus due to the frequent association with 22q11 genetic mutations.[2][4][17][18][19]

Treatment / Management

The initial management revolves around stabilization of the patient and balancing the amount of blood flow through the pulmonary and systemic circuits. Care is typically provided in a neonatal or cardiac intensive care setting.

Treatment of Pulmonary Congestion and CHF[20]

1. Use loop and thiazide diuretics to help achieve proper fluid balance
   1. Improve LV failure by reducing excess volume, filling pressure, and pulmonary congestion.
   2. Improve RV failure by maintaining control of systemic venous congestion.
2. Patients in respiratory distress may require additional positive-pressure support (CPAP, SiPAP, endotracheal intubation).
3. Avoid the use of supplemental oxygen as this may worsen pulmonary over-circulation.
4. Correct any metabolic derangements, electrolyte abnormalities, hypoglycemia, and anemia to prevent worsening heart failure.[2]

Prostaglandin Infusion

Promote ductal patency with prostaglandin infusion if there is a concurrent aortic arch anomaly.[7]

Definitive Surgical Correction with a Single-Stage Repair Within the First Month of Life

1. Procedure for TA without truncal valve or aortic arch abnormality[7]
   1. Mobilization of pulmonary arteries from the truncus to the RV with conduit-based RVOT reconstruction
   2. Closure of the VSD with a patch
2. Aortic arch abnormalities and the truncal valve should also be fixed at this time.[21]
3. Primary palliation with pulmonary arterial banding and delayed surgical repair may be required to allow the infant to grow. This two-stage correction is not routinely recommended due to higher rates of morbidity and mortality.[22]

Immediate Post-Operative Care Should be Provided in a Cardiac Intensive Care Unit.[23]

1. Fluid and electrolyte management, sedation and pain control, respiratory control, cardiovascular management, renal function, neurological status, infection control, nutritional status are all important factors to consider during the post-operative period.
2. While noninvasive monitoring of the heart rate, respiratory rate, and oxygen saturation are the most basic requirements, invasive pulmonary and atrial catheters with central and arterial lines can be used for closer continuous monitoring.

Differential Diagnosis

New technological advances have improved the rate of correctly diagnosing TA prenatally to greater than 90%. However, TA may be misdiagnosed as tetralogy of Fallot (ToF) with pulmonary atresia if structures cannot be identified correctly on prenatal echocardiography. Postnatally, the two may be differentiated clinically by the presence of a murmur in TA but no murmur in ToF as well as the greater degree of cyanosis in ToF. Some lesions that may cause a similar degree of mild cyanosis include tetralogy of Fallot with pulmonary atresia, critical pulmonary stenosis, tricuspid atresia, total anomalous pulmonary venous return/circulation, and hypoplastic left heart syndrome. Postnatally, the differential diagnosis for cardiac lesions causing hemodynamic shock also includes hypoplastic left heart syndrome and critical coarctation of the aorta.[17][24]

Complications

There are few complications associated with TA before surgical intervention. If a patient has DiGeorge syndrome, then one must monitor for complications associated with hypocalcemia. In the older, unrepaired infant who has received little or no cardiac care, a higher risk of infections is present if 22q11 deletions are present. Most complications occur post-operatively and usually in the first 48 hours postoperatively. Specific postoperative complications include pulmonary hypertensive crisis and low cardiac output syndrome. Decreased manipulation and mobilization of patients may achieve a decreased rate of pulmonary hypertensive crisis during the immediate post-operative phase. Right bundle branch block and arrhythmias such as supraventricular tachycardia were also noted. Complications requiring surgical re-intervention in the immediate post-operative period include mediastinal bleeding, pleural effusion, pneumothorax, cardiac tamponade. Problems common to any surgery included seizures and other nervous system injuries, prolonged bleeding times, and renal failure.[25]

As patients outgrow their RV-PA conduit or truncal valve insufficiency worsens, re-interventions are inevitable. By the 10-year, postoperative period, approximately 75% of patients required re-intervention, with the number one cause being RVOT reconstruction, followed by valve repair/replacement, and relief of aortic obstruction.[25][26][27]

Without the recommended single-stage repair, patients often die before two months of age. The 1-year survival rate for unrepaired patients is less than 20%. By age 4, pulmonary vascular obstructive disease becomes so severe that surgery is futile and patients die before the second decade due to cardiac failure. After the primary repair, patients have a 20-year survival rate over 80%, but the rate of reoperation remains high. Therefore, long-term follow-up is recommended.[5][25]

Deterrence and Patient Education

Life-long follow-up with a cardiologist trained in CHD should be emphasized to all patients. In the long-term, patients and physicians should pay close attention to changes in exercise tolerance, history of palpitations or syncope, or the emergence of edema and dyspnea. It is important to note any diastolic murmur as a sign of valve insufficiency or conduit regurgitation, pulmonary congestion and peripheral edema as a sign of CHF, and elevated jugular venous pulse or hepatomegaly as a sign of increasing right heart pressures.[21][26]

Routine testing with serial echocardiography is recommended to evaluate the RV-PA connection, biventricular function, and truncal valve stenosis or insufficiency. Patients with symptoms of heart failure or arrhythmia will require more frequent evaluations with electrocardiography, echocardiography, or stress-testing. If these tests are insufficient, further testing with MRI or computed tomography is useful.[28]

Pearls and Other Issues

Latin for single artery, truncus arteriosus, results in too much blood flow to the lungs and too little oxygenated blood delivered to the body.

Surgery is the only definitive treatment, but repeat interventions are ubiquitous, so long-term follow-up with a congenital heart disease specialist is advised. Without surgical intervention, most patients would die before their first birthday.

Enhancing Healthcare Team Outcomes

To improve outcomes, an interprofessional approach to truncus arteriosus is recommended.

Team-based healthcare delivery starts very early after conception for these patients with high-risk obstetricians and fetal cardiac imaging specialists. After delivery, the timing of surgical re-intervention and/or trans-catheter intervention is also important to enhance outcomes. Especially given the common association with 22q11 microdeletion syndromes, and the need for open-heart surgery in the newborn period, team-based case in childhood should include the pediatric cardiologist, a pediatric cardiac surgeon, an intensivist, residents or fellows, geneticist, and a radiologist. As patient care most often occurs in a neonatal or cardiac intensive care unit, specific team members are vital. In addition to the physicians mentioned above, teams should also have a charge nurse and bedside nurse, respiratory therapist, nutrition specialist, social worker, pharmacist, and radiographers.[21][29] (Level IV) [4][30][31] (Level V)

With increasing success in surgical and post-operative management and the advent of new technological advances, children with congenital heart disease are surviving well into adulthood. This, however, comes with an array of questions revolving around transitions of clinical care, recommendations for daily and competitive activity, medications and adherence, routine medical and dental care, acquisition of proper insurance and healthcare providers, reproductive issues including pregnancy and contraception, and education and career planning. Physicians should be aware that impairments in cognition, social interactions, communication skills, and executive functioning are well documented in children with complex heart disease, so as these patients reach adolescence and adulthood, an important consideration should be given to addressing these issues at the appropriate times and with the appropriate members of the care team. For the adult, a specialist in adult congenital heart disease (ACHD) is ideal, but an electrophysiologist and interventional cardiologist may also be required. Additionally, an internal medicine provider may prove beneficial in coordinating required care with a high-risk obstetrician, neurologist, psychologist/psychiatrist, endocrinologist, and geneticist. Other critical members of the ACHD team include nurses and nurse practitioners, physician assistants, cardiac anesthesiologists with training in CHD, a hepatologist, and a cardiac pathologist. Services that may be required include rehabilitation services, psychological services, social services, and financial counselors. The smooth transition of care to adult medicine is critical.[28][32][33] (Level V)