Truncus Arteriosus

INTRODUCTION

Background: Truncus arteriosus (TA) is an uncommon congenital cardiovascular anomaly that is characterized by a single arterial trunk arising from the normally formed ventricles by means of a single semilunar valve (ie, truncal valve). In addition, the pulmonary arteries originate from the common arterial trunk distal to the coronary arteries and proximal to the first brachiocephalic branch of the aortic arch. The common trunk typically straddles a defect in the outlet portion of the interventricular septum (ie, conal septum); however, in rare cases, it may originate almost completely from the right or left ventricle. In patients with a patent and normal caliber aortic arch, the ductus arteriosus is either absent or diminutive.

Embryology

The anomaly is thought to result from incomplete or failed septation of the embryonic truncus arteriosus, hence the persistence of the Latin term truncus arteriosus and its variants. Aortopulmonary and interventricular defects are believed to represent an abnormality of conotruncal septation. Because the common trunk originates from both the left and right ventricles, and pulmonary arteries arise directly from the common trunk, a ductus arteriosus is not required to support the fetal circulation. Accordingly, an inverse relationship typically exists between the caliber of the ductus arteriosus (derived from the fourth branchial arch) and that of distal portion of the aortic arch (derived from the sixth branchial arch). While the hemodynamic consequences of a common arterial outflow may predispose to the development of the fourth or the sixth arch (but not both), it is likely that anomalous development of the arch system is a fundamental aspect of the morphogenetic anomalies that produce TA.

Anatomy

Pulmonary arteries may arise from the common trunk in one of several patterns, which often are used to classify subtypes of TA. Several classification schemes have been proposed, none of which is ideal.

The earliest classification, developed by Collett and Edwards in 1948, includes types I through IV TA, as follows (see Image 1):

  • TA type I is characterized by origin of a single pulmonary trunk from the left lateral aspect of the common trunk, with branching of the left and right pulmonary arteries from the pulmonary trunk.

     

  • TA type II is characterized by separate but proximate origins of the left and right pulmonary arterial branches from the posterolateral aspect of the common arterial trunk.

     

  • In TA type III, the branch pulmonary arteries originate independently from the common arterial trunk or aortic arch, most often from the left and right lateral aspects of the trunk. This occasionally occurs with origin of one pulmonary artery from the underside of the aortic arch, usually from a ductus arteriosus.

     

  • Type IV TA, originally proposed by Collett and Edwards as a form of the lesion with neither pulmonary arterial branch arising from the common trunk, now is recognized to be a form of pulmonary atresia with ventricular septal defect rather than TA (not depicted in figure 1).

Collett and Edwards describe variations of each of these types.

In 1965, Van Praaghs proposed the other commonly cited classification scheme that also includes 4 primary types, as follows (combined with Collett and Edwards types in Image 1):

  • Type A1 is identical to the type I of Collett and Edwards.

     

  • Type A2 includes Collett and Edwards type II and most cases of type III, namely those with separate origin of the branch pulmonary arteries from the left and right lateral aspects of the common trunk.

     

  • Type A3 includes cases with origin of one branch pulmonary artery (usually the right) from the common trunk, with pulmonary blood supply to the other lung provided either by a pulmonary artery arising from the aortic arch (a subtype of Collett and Edwards type III) or by systemic to pulmonary arterial collaterals.

     

  • Type A4 is defined not by the pattern of origin of branch pulmonary arteries, but rather by the coexistence of an interrupted aortic arch. In the vast majority of cases of type A4, which fall into the type I of Collett and Edwards, the pulmonary arteries arise as a single pulmonary trunk that then branches. In any of these patterns, intrinsic stenosis/hypoplasia of one or both branch pulmonary arteries may be present, which may have an effect on management and outcome.

Associated cardiovascular anomalies

A variety of abnormalities may be associated with TA, some of which may have an impact on management and outcome.

Structural abnormalities of the truncal valve, including dysplastic and supernumerary leaflets, are frequently observed, and significant regurgitation (moderate or severe) through the truncal valve may be present in 20% or more patients.

Similarly, proximal coronary arteries are abnormal in many patients, with a single coronary artery and an intramural course as the most important variations.

The other major anomaly associated with TA in a substantial portion of cases is interruption of the aortic arch, which almost always occurs between the left common carotid and subclavian arteries.

Other relatively common but minor associations include right aortic arch, left superior caval vein, aberrant subclavian artery, and atrial septal defect. In addition to these defects found in the usual spectrum of TA, several other major but rare associated anomalies are reported, including complete atrioventricular septal defect, double aortic arch, and various forms of functionally univentricular heart.

Sepsis is probably the most important noncardiac problem in the differential diagnosis of neonates with TA, as well as other forms of complex congenital heart disease. Young infants with TA frequently present in shock because of high output heart failure with significant pulmonary overcirculation. This scenario may resemble the presentation of neonatal sepsis, especially when the ratio of pulmonary-to-systemic blood flow is sufficiently high that the patient is not cyanotic.

Pathophysiology: Pathophysiology of TA is typified by cyanosis and systemic ventricular volume overload. Outflow from both ventricles is directed into the common arterial trunk. Pulmonary blood flow is derived from this combined ventricular output, and its magnitude depends on the ratio of resistances to flow in the pulmonary and systemic vascular beds. Given the mixing (although not complete) of left and right ventricular output that occurs primarily during systole and at the level of the common arterial trunk, subnormal systemic arterial oxygen saturation is common. Similarly, because the systemic and pulmonary circulations are essentially in parallel, pulmonary blood flow typically is at least 3-fold higher than systemic blood flow, with pulmonary overcirculation and increased myocardial work that results in increased resting oxygen demand and decreased metabolic reserve.

Frequency:

  • In the US: TA represents 1-2% of congenital heart defects in liveborn infants. Based on an estimated incidence of congenital heart disease of 6-8 per 1,000 liveborn children, TA occurs in approximately 5-15 of 100,000 live births. Among aborted fetuses and stillborn infants with cardiovascular anomalies, TA represents almost 5% of defects.
  • Internationally: No significant difference in the incidence of TA is noted among those born in the United States compared to other countries.

Mortality/Morbidity:

  • The natural history of TA without surgical intervention is not well characterized. In a number of earlier series, the median age at death without surgery ranged from 2 weeks to 3 months, with almost 100% mortality by 1 year. Cases of patients surviving into adulthood with unrepaired TA are reported, but they are extremely uncommon. Cause of death in unrepaired patients usually is cardiac arrest or multiple organ failure in the face of systemic perfusion that is inadequate to meet the body's metabolic demands; progressive metabolic acidosis and myocardial dysfunction results.
  • Currently, for patients undergoing complete repair in the neonatal or early infant periods, early postoperative mortality generally is less than 10%. This represents a substantial improvement from earlier eras; as recently as 20 years ago, the early mortality rate after complete repair was higher than 25% in most series. Among patients surviving the initial postoperative period, the survival rate at a 10- to 20-year follow-up is higher than 80%, with most deaths resulting from sequelae of late repair (pulmonary vascular obstructive disease), reinterventions, or residual/recurrent physiologic abnormalities.
  • Although rarely used today, surgical palliation by banding of the pulmonary artery to protect the pulmonary vascular bed was a frequently employed strategy until the 1970s and early 1980s. This practice resulted in only minor improvement in the natural history of the disease, with substantial early and intermediate mortality rates.

Race:

  • Based on limited data, no racial predilection is apparent.

Sex:

  • Although many series report a slight male predominance, no significant predilection based on sex is apparent.

Age:

  • TA is a congenital anomaly that is present from early in embryonic gestation. Currently, TA is diagnosed on prenatal ultrasound in a small percentage of patients. Among patients diagnosed after birth, the median age at presentation generally is a few days, which is significantly earlier than was the case 20 or more years ago. Occasionally, patients are not diagnosed until later in infancy, childhood, or even adulthood, although such cases are exceedingly rare in the United States and Europe.

CLINICAL

History:

  • Historical presentation of patients with TA who are not diagnosed before the onset of symptoms typically consists of the following:
    • Poor feeding
    • Diaphoresis
    • Tachypnea
    • Cyanosis
  • Symptoms are variable, and may be more or less pronounced, depending on specific anatomic features and age at presentation. For example, patients with significant truncal valve regurgitation tend to present earlier with more profound symptoms of congestive heart failure.

Physical:

  • Patients with TA often present with cyanosis and typically are found to have decreased systemic arterial oxygen saturation.
    • Cyanosis may not be evident, especially in very young neonates in whom pulmonary vascular resistance remains elevated.
    • Even in slightly older neonates and young infants, pulmonary overcirculation and streaming of left and right ventricular outflow into the aorta and pulmonary arteries, respectively, may occasionally result in systemic oxyhemoglobin saturation well above 90%.
  • Symptoms and signs of congestive heart failure are probably more common findings than cyanosis in patients presenting early in life.
    • Symptoms of failure typically manifest as pulmonary vascular resistance falls and pulmonary overcirculation increases.
    • With progressively increasing pulmonary blood flow and, consequently, myocardial work, the initial symptoms of congestive heart failure (eg, poor feeding, diaphoresis, mild lethargy) become more evident as failure to thrive ensues.
  • Patients occasionally present in extremis, with the usual high output failure exacerbated by significant regurgitation of the truncal valve. Patients with associated interruption of the aortic arch may exhibit a shocklike picture of cardiovascular collapse during ductal closure, although the arterial duct frequently remains patent in patients with truncus and interrupted arch, even without pharmacologic therapy.

Causes:

  • As with most forms of congenital heart disease, the causes of TA are not known. In experimental animal models, TA has been linked to abnormal development of cells from the neural crest that normally inhabit the outflow region of the developing heart. This is thought to be an important etiologic factor in at least some cases of human TA also.

     

  • As with various other congenital cardiac anomalies of the conotruncal region, a substantial number of patients with TA (approximately 35%) have microdeletions within chromosome band 22q11.2. This particular type of chromosomal deletion is thought to affect migration or development of cardiac neural crest cells and may contribute to the pathogenesis of TA in certain cases. Patients with TA and anomalies of the branch pulmonary arteries, such as stenosis or separate origin from the undersurface of the aortic arch, may have a higher incidence of association with band 22q11 deletion. Other specific features of TA that may be related to chromosomal deletion have yet to be characterized. A specific gene product left deficient by band 22q11 deletion has not been identified definitively in humans, thus the association between TA and band 22q11 deletion remains simply an empiric association; a causal association is not established. Extensive research regarding TA and band 22q11 association is being conducted.
  • For the most part, other factors that may cause TA in humans have not clearly been identified.
    • One report found that children of mothers with significant diabetes mellitus during pregnancy had an increased incidence of TA; however, this is not widely recognized as a significant risk factor.
    • Although certain teratogens (eg, retinoic acid, bis-diamine) have been found to predispose to TA in animal models, no evidence suggests that these or others contribute importantly to this anomaly in humans.
  • DiGeorge syndrome or velocardiofacial syndrome, often included together as variations of CATCH-22 syndrome, are present in approximately 30-35% of patients with TA; most of these patients have deletions in band 22q11.
  • The most common noncardiac anomalies in patients with TA are those typically found in association with CATCH-22 syndrome, such as velopharyngeal insufficiency, cleft palate, and thymic and parathyroid dysfunction.
  • Other noncardiac anomalies found sporadically in patients with TA include renal abnormalities, vertebral and rib anomalies, and anomalies of the alimentary tract.

DIFFERENTIALS

Acidosis, Metabolic
Aortopulmonary Septal Defect
Double Outlet Right Ventricle, Normally Related Great Arteries
Double Outlet Right Ventricle, With Transposition
Hypoplastic Left Heart Syndrome
Shock
Shock and Hypotension in the Newborn
Tetralogy of Fallot With Absent Pulmonary Valve
Tetralogy of Fallot With Pulmonary Atresia
Total Anomalous Pulmonary Venous Connection
Transposition of the Great Arteries


Other Problems to be Considered:

Sepsis


WORKUP

Lab Studies:

  • Routine laboratory studies in the neonate with TA generally aid in determining therapeutic strategy rather than diagnosis.
    • An important exception in some cases is an arterial blood gas measurement, which helps to evaluate the degree of acidosis on presentation and may aid in differentiating cardiac disease from primary pulmonary pathology when performed before and after administration of 100% inspired oxygen (hyperoxia test).
    • Note that a hyperoxia test may be misleading in patients with TA and torrential pulmonary blood flow, both because of severe mismatch between pulmonary and systemic blood flow and, in some cases, because of streaming of left and right ventricular outflow into the systemic and pulmonary arterial systems, respectively.

Imaging Studies:

  • Chest radiography
    • On presentation, obtain a chest radiograph in most patients with TA.
    • Cardiomegaly and increased pulmonary vascular markings typically are present, and fullness in the region of the truncal root may possibly be discerned. In patients with a right aortic arch, this radiographic finding in association with increased pulmonary vascular markings suggests TA.
  • Echocardiography
    • Echocardiography with cross-sectional and Doppler flow analysis is sufficient to confirm diagnosis of TA and fully characterize the various anatomic features in most patients. A full complement of echocardiographic views is necessary to ensure complete and accurate definition of the anatomy and potential associated anomalies.
    • Using subcostal coronal and parasternal long-axis images is the best way to demonstrate the single arterial trunk arising from the ventricles, with variable override of the ventricular septum. These views also demonstrate the thickness and mobility of the truncal valve leaflets. In general, the subcostal coronal view allows delineation of the pulmonary arterial origin(s) from the common trunk, although additional views are helpful to more completely characterize the pulmonary arterial anatomy. Morphology of the truncal valve and origins and course of the proximal coronary arteries are best observed from the parasternal short-axis window.
    • Doppler color imaging from these windows is critical to evaluate pulmonary arterial flow and regurgitation or stenosis of the truncal valve. Imaging from the high parasternal and suprasternal notch views is necessary to define the aortic arch and provide additional perspective on the anatomy of the central pulmonary arteries. Standard approaches to imaging of the ventricular masses, atrioventricular valves, and atriums are important for full characterization of their structure and function.
  • Magnetic resonance imaging
    • Magnetic resonance imaging (MRI) rarely is necessary in patients with TA.
    • MRI modality provides excellent imaging for characterizing anatomy, and may be especially useful in reconstructing complex pulmonary arterial anatomy in older patients with TA.

Other Tests:

  • Electrocardiography
    • Electrocardiographic (ECG) findings in young infants with TA do not distinguish this lesion from others on the differential diagnosis.
    • A normal sinus rhythm, normal intervals, and either a normal QRS axis or minimal right-axis deviation generally are observed. Biventricular hypertrophy is a characteristic finding.
    • In patients with substantial pulmonary overcirculation, left ventricular forces are especially prominent with evidence of left atrial enlargement.

Procedures:

  • Cardiac catheterization
    • Standard angiographic images from the truncal root can aid in the assessment of coronary arterial anatomy, if echocardiography is inadequate, and of regurgitation through the truncal valve.
    • Cardiac catheterization generally is not required in neonates and young infants with TA. Currently, its use aids in the assessment of hemodynamics, most importantly pulmonary vascular resistance, in older patients. In patients with unrepaired TA who survive beyond the first few months of life, pulmonary vascular obstructive disease can have major clinical importance.
Histologic Findings: Histologic examination generally is not indicated in the evaluation of patients with TA. In the rare older patient with evidence of elevated pulmonary vascular resistance, pulmonary biopsy occasionally is performed as a means of assessing the extent of pulmonary vascular obstructive disease.

TREATMENT

Medical Care:

  • Medical care before surgical repair depends on clinical presentation.
  • Most neonates with TA display some evidence of congestive heart failure for which they usually are treated with digitalis and diuretic medicines.
  • Intravenous prostaglandin often is initiated in patients with TA on presentation because the differential diagnosis includes a number of anomalies with duct-dependent systemic or pulmonary blood flow. However, it is beneficial only in patients with associated interruption of the aortic arch or aortic coarctation.
  • Other preoperative medications generally are not indicated, although specific circumstances may dictate afterload reducing agents, inotropic medications, or antiarrhythmics.

Surgical Care:

  • Indications
    • TA invariably requires operative repair.
    • Symptoms typically develop in the early neonatal period, indicating that complete repair is required at this point.
  • Techniques
    • Surgical management of TA has undergone significant evolution over the past 30 years. Complete repair was first performed in 1967, but until neonatal and early infant repair became routine in the 1980s, palliative pulmonary artery banding was common, with complete repair performed at an older age. At many centers, primary complete repair has been standard for the past 15-20 years; repair in the neonate and young infant has been routine for the past 10 years.
    • Currently, surgical management consists of complete primary repair, with closure of the ventricular septal defect, committing the common arterial trunk to the left ventricle, and reconstruction of the right ventricular outflow tract.
    • In patients with both branch pulmonary arteries arising from the common trunk, the standard method of right ventricular outflow tract reconstruction entails removing the central pulmonary arteries from the common trunk en bloc and placing a valved conduit from the right ventricle proximally to the central pulmonary arteries distally. Also, the most common type of conduit employed is a cryopreserved valved aortic or pulmonary allograft. Before allograft conduits became widely available, and, currently, in areas where the cost and availability of conduits prohibit their routine use, other forms of pulmonary outflow reconstruction are employed. Such alternatives include xenograft valves housed in synthetic tube grafts, direct anastomosis of the pulmonary arteries to the right ventriculotomy, or autologous flaps of pulmonary or aortic tissue augmented with synthetic patch material.
    • In patients with one pulmonary artery arising from the common trunk and one from the underside of the aortic arch, the pulmonary arteries are disconnected separately and first anastomosed together and then to the conduit or anastomosed to the conduit independently.
    • Coexisting anomalies are repaired as appropriate with cardiopulmonary bypass, cardioplegia, and sometimes deep hypothermic arrest, depending on anatomic features and the preference of the surgeon.

Consultations:

  • Unless specific associated anomalies or problems are identified, consultations generally are not necessary.
  • Band 22q11 deletion is present in approximately one third of patients with TA, and consultation with a geneticist may be appropriate in some of these patients. Although patients with this chromosomal anomaly may have subtle associated abnormalities that are more likely to be identified if an experienced clinical geneticist is consulted, there is no evidence that outcomes or management considerations differ in patients with or without chromosomal deletion.
  • Consult a cardiologist before beginning, changing, or discontinuing cardiac medications in these patients.

Diet:

  • No special dietary considerations are indicated in patients with TA, other than a diet that might be dictated by associated conditions.
  • Resume enteral feeding once the patient is hemodynamically stable.
  • Resume oral feedings when the patient has been removed from mechanical ventilatory support and is adequately alert to take orally feed safely. In patients with deletion in band 22q11, velopharyngeal insufficiency or cleft palate are frequently present and oral feedings should be resumed with the aid of feeding specialists.

Activity:

  • Specific restrictions on activity are not indicated in patients with TA.
  • Patients with repaired TA and either residual defects or regurgitation of the right ventricle to pulmonary artery conduit may have limited exercise capacity best addressed on an individual basis.

MEDICATION

Pharmacologic therapy in patients with TA depends on a variety of factors, including clinical status, associated lesions, and where in the course of management (eg, preoperative, early postoperative) the patient is when drug therapy is provided. The major classes of cardiac drugs administered to patients with TA include diuretics, digoxin, afterload reducing agents, inotropic medications, and antiarrhythmics if necessary. Consultation with a cardiologist is imperative before beginning, changing, or discontinuing cardiac medications in these patients.

Drug Category: Inotropis agents -- Provide inotropic and chronotropic support in the early postoperative period, when postoperative myocardial edema and ischemia-reperfusion injury may result in varying degrees of residual ventricular dysfunction. Also used at low doses to optimize renal perfusion to facilitate diuresis.
Drug Name
 Dopamine (Intropin) -- Stimulates adrenergic and dopaminergic receptors, with a predominant dopaminergic effect at low doses, beta-adrenergic and dopaminergic effects at intermediate doses, and primarily alpha-adrenergic effects at high doses.
Pediatric Dose Renal dose: 3-5 mcg/kg/min IV
Inotropic/chronotropic dose: 5-20 mcg/kg/min IV
Contraindications Documented hypersensitivity; pheochromocytoma or ventricular fibrillation
Interactions Phenytoin, alpha- and beta-adrenergic blockers, general anesthesia, and MAOIs increase and prolong effects of dopamine
Pregnancy C - Safety for use during pregnancy has not been established.
Precautions Extravasation may cause tissue necrosis; closely monitor urine flow, cardiac output, pulmonary wedge pressure, and blood pressure during the infusion; before infusion, correct hypovolemia as indicated
Drug Category: Diuretic agents -- Used to mobilize edema in the early postoperative period and facilitate fluid homeostasis. Also used for treatment of hypertension.
Drug Name
 Furosemide (Lasix) -- Increases excretion of water by interfering with chloride-binding cotransport system, which, in turn, inhibits sodium and chloride reabsorption in ascending loop of Henle and distal renal tubule.
Adult Dose 20-80 mg/d PO/IV/IM; titrate up to 600 mg/d for severe edema
Pediatric Dose 1-6 mg/kg/d PO divided q6-24h
1-2 mg/kg/dose IV q6-24h
Contraindications Documented hypersensitivity; hepatic coma, anuria, and severe electrolyte depletion
Interactions Metformin decreases furosemide concentrations; furosemide interferes with hypoglycemic effect of antidiabetic agents and antagonizes muscle relaxing effect of tubocurarine; auditory toxicity appears to be increased with coadministration of aminoglycosides and furosemide; hearing loss of varying degrees may occur; anticoagulant activity of warfarin may be enhanced when taken concurrently with this medication; increased plasma lithium levels and toxicity are possible when taken concurrently with this medication
Pregnancy C - Safety for use during pregnancy has not been established.
Precautions Perform frequent serum electrolyte, carbon dioxide, glucose, creatinine, uric acid, calcium, and BUN determinations during first few months of therapy and periodically thereafter
Drug Category: Cardiac glycoside, antiarrhythmic -- Used to increase myocardial contractility, slow atrioventricular node conduction time, and potentiate the effects of furosemide.
Drug Name
 Digoxin (Lanoxin, Lanoxicaps) -- Acts directly on cardiac muscle, increasing myocardial systolic contractions. Its indirect actions result in increased carotid sinus nerve activity and enhanced sympathetic withdrawal for any given increase in mean arterial pressure.
Adult Dose 0.125-0.375 mg PO qd
Pediatric Dose 1 month - 2 years:
Loading dose: 35-60 mcg/kg PO (1/2 dose initially, 1/4 dose in each of 2 subsequent doses at 6- to 12-h intervals)
30-50 mcg/kg IV/IM (1/2 dose initially, 1/4 dose in each of 2 subsequent doses at 6- to 12-h intervals)
Maintenance dose: Infants: 6-8 mcg/kg/d PO
2-5 years: 10-15 mcg/kg/d PO
5-10 years: 7-10 mcg/kg/d PO
>10 years: 3-5 mcg/kg/d PO
<10 years: Bid dosing recommended
Contraindications Documented hypersensitivity; beriberi heart disease, idiopathic hypertrophic subaortic stenosis, constrictive pericarditis, and carotid sinus syndrome
Interactions Medications that may increase digoxin levels include alprazolam, benzodiazepines, bepridil, captopril, cyclosporine, propafenone, propantheline, quinidine, diltiazem, aminoglycosides, oral amiodarone, anticholinergics, diphenoxylate, erythromycin, felodipine, flecainide, hydroxychloroquine, itraconazole, nifedipine, omeprazole, quinine, ibuprofen, indomethacin, esmolol, tetracycline, tolbutamide, and verapamil
Medications that may decrease serum digoxin levels include aminoglutethimide, antihistamines, cholestyramine, neomycin, penicillamine, aminoglycosides, oral colestipol, hydantoins, hypoglycemic agents, antineoplastic treatment combinations (including carmustine, bleomycin, methotrexate, cytarabine, doxorubicin, cyclophosphamide, vincristine, procarbazine), aluminum or magnesium antacids, rifampin, sucralfate, sulfasalazine, barbiturates, kaolin/pectin, and aminosalicylic acid
Pregnancy C - Safety for use during pregnancy has not been established.
Precautions Hypokalemia may reduce positive inotropic effect of digitalis; IV calcium may produce arrhythmias in digitalized patients; hypercalcemia predisposes patient to digitalis toxicity, and hypocalcemia can make digoxin ineffective until serum calcium levels are normal; magnesium replacement therapy must be instituted in patients with hypomagnesemia to prevent digitalis toxicity; patients with incomplete AV block may progress to complete block when treated with digoxin; exercise caution in hypothyroidism, hypoxia, and acute myocarditis
Drug Category: ACE inhibitor, afterload reducing agent -- To decrease systemic vascular resistance, which is beneficial in patients with hypertension, impaired ventricular function, or aortic/truncal valve regurgitation.
Drug Name
 Captopril (Capoten) -- Inhibits activity of the angiotensin-converting enzyme, preventing conversion of angiotensin I to angiotensin II, which is a potent vasoconstrictor. Decreased levels of angiotensin II lead to increased plasma renin activity and decreased circulating aldosterone.
Adult Dose 6.25-12.5 mg PO tid; not to exceed 150 mg tid
Pediatric Dose Neonates: 0.05-0.1 mg/kg/dose PO q6-24h; titrate dose up to 0.5 mg/kg/dose prn
Infants: 0.15-0.3 mg/kg/dose PO q6-24h; titrate dose up; not to exceed 6 mg/kg/d in 2-4 divided doses prn
Children: 0.3-0.5 mg/kg/dose PO q6-24h; titrate dose up; not to exceed of 6 mg/kg/d in 2-4 divided doses prn
Contraindications Documented hypersensitivity
Interactions NSAIDs may reduce hypotensive effects of captopril; ACE inhibitors may increase digoxin, lithium, and allopurinol levels; rifampin decreases captopril levels; probenecid may increase captopril levels; the hypotensive effects of ACE inhibitors may be enhanced when given concurrently with diuretics
Pregnancy D - Unsafe in pregnancy
Precautions Caution in renal impairment, valvular stenosis, or severe congestive heart failure

FOLLOW-UP

Further Inpatient Care:

  • Administer routine postoperative care, initially in the cardiac intensive care unit, following correction of TA.
  • Support patients with mechanical ventilation, inotropic medications, and sedation as necessary.
  • Restore fluid balance with diuretic therapy and continue tube thoracostomy until pleural and pericardial effusions have resolved.
  • Focus remainder of inpatient stay on providing sufficient enteral nutrition, parental education, and elucidation of the maintenance pharmacologic regimen (if any) that is adopted.
  • Postoperative care after repair of TA requires attention to issues that are common to patients with complex congenital heart disease (eg, support of cardiac output) and prevention or management of arrhythmias and end-organ dysfunction.
  • Management issues include maintenance of intravascular volume and ventricular filling, inotropic support, and acid-base and electrolyte homeostasis.
  • In addition, potential issues that are of particular concern in patients with TA include pulmonary hypertensive crisis and volume overload in patients with persistent truncal valve regurgitation. Because of the lability of the pulmonary resistance vessels that may occur with and following elimination of elevated pulmonary blood flow at high pressures, pulmonary hypertensive crisis currently is less of an issue in early neonatal repair than it was with later repair. Nevertheless, patients may experience episodes of paroxysmal elevation of pulmonary vascular resistance.
  • Management with extended periods of anesthesia, including neuromuscular blockade and continuous fentanyl infusion, often is helpful. Ventilatory strategies aimed at minimizing pulmonary vascular resistance also may be effective. In refractory cases, inhaled nitric oxide or extracorporeal membrane oxygenation may be indicated.

Further Outpatient Care:

  • Maintain close follow-up care in young children after repair of TA.
  • Young infants often are discharged on cardiac medications and usually may be weaned over the following months.
  • Frequently, a mild degree of regurgitation occurs through the right ventricle–to–pulmonary arterial conduit but, in most cases, does not pose a significant load on the heart.
  • In most patients, conduit regurgitation and obstruction (see below) becomes an important issue after early repair; however, reintervention usually is not required for a year or more.
  • Truncal valve regurgitation, which may progress even if it was not severe before repair, may become an important cause of persistent failure to thrive, and repair or replacement of the valve may be indicated.
  • In patients with associated interruption of the aortic arch, pay particular attention to potential recurrent arch obstruction and compression of the bronchi, both of which may manifest within weeks or months of the initial repair.
  • Routine clinical and echocardiographic follow-up care is sufficient to monitor most patients.
  • Cardiac catheterization may be performed for the purpose of balloon dilation of the pulmonary arteries or pulmonary outflow conduit, for evaluation of the pulmonary vascular bed in patients who are older and have evidence of pulmonary hypertension, or for other diagnostic indications according to the preference of the physicians.

Transfer:

  • After stabilization in the intensive care unit, removal from mechanical ventilatory and inotropic support, and discontinuation of intracardiac monitoring catheters, transfer the patient to the regular inpatient care area for advancement of feedings and additional postoperative care, depending on the experience and comfort level of the nursing staff on the ward.

Deterrence/Prevention:

  • No known methods to prevent the development of TA in the fetus are known.
  • On screening obstetric ultrasound, 4-chamber and great vessel views are sufficient to identify that cardiac anomalies are present. In such an event, the parents should be referred for fetal echocardiography, with which the anatomy of TA can be more fully defined. Diagnosis in utero allows for greater parental choice, and may facilitate planned delivery at a tertiary care center and immediate neonatal stabilization, thus preventing the potential hemodynamic sequelae that can result from the natural history of the lesion.

Prognosis:

  • Among patients surviving the early postoperative period, prognosis generally is very good. Few published, long-term, follow-up data exist on patients undergoing repair in the neonatal and early infant periods because this management strategy came into widespread application only approximately 15 years ago. Moreover, techniques of myocardial protection and perioperative management have changed dramatically even within this period, thus, existing data, limited as they may be, still are likely to underestimate outcome in contemporary patients.
  • Although late mortality among patients undergoing early repair is minimal, a substantial proportion of premature deaths among such patients are likely to be related to reinterventions. Because the right ventricular outflow tract is reconstructed with a nonviable conduit, which does not grow along with the patient, reinterventions for conduit replacement, revision, or dilation are essentially inevitable.
  • In a recent series following infants younger than 4 months with surgically repaired TA, freedom from conduit-related reintervention was less than 50% at 5 years and less than 10% at 10 years.
  • Patients who have the conduit replaced earlier in life often require a subsequent intervention on the right ventricular outflow tract. Reintervention for truncal valve regurgitation (often within the first year after repair) or for branch pulmonary arterial stenosis also is required in a substantial number of patients.
  • At major centers in North America, survival to hospital discharge after complete repair of TA is approximately 90-95%. Prognosis appears somewhat less favorable for patients with complicating associated conditions, such as severe truncal valve regurgitation of interruption of the aortic arch. Significant perioperative morbidity is uncommon and includes issues common to many forms of complex congenital heart disease, such as transient arrhythmias, low cardiac output, and sequelae of cardiopulmonary bypass.

Patient Education:

  • For the early posthospital period, educate parents about the signs and symptoms of congestive heart failure, proper administration and potential adverse effects of any maintenance medications, and management of the sternotomy incision.
 

MISCELLANEOUS

Medical/Legal Pitfalls:

  • Failure to properly diagnose
  • Failure to consider a variety of abnormalities that may be associated with TA, some of which may have an impact on management and outcome
  • Failure to consider potential issues that are of particular concern in patients with TA, including pulmonary hypertensive crisis and volume overload in patients with persistent truncal valve regurgitation
  • Failure to use routine laboratory and imaging studies (to include a full complement of echocardiographic views) in the neonate with TA to aid in determining therapeutic strategy and assist diagnosis
  • Failure to consult with a cardiologist before beginning, changing, or discontinuing cardiac medications in these patients

PICTURES

 

Caption: Picture 1. Anatomic subtypes of truncus arteriosus (TA), according to the classification systems of both Collett and Edwards (I, II, III) and the Van Praaghs (A1, A2, A3, A4).
Click to see larger picture
Picture Type:
Caption: Picture 2. Pathologic specimen with truncus arteriosus (TA), viewed through the opened right ventricle and truncal valve. The common trunk (CT) can be seen giving off the ascending aorta (AA) as well as the left (LPA) and right (RPA) pulmonary arteries. The truncal valve straddles the ventricular septal defect (VSD). The tricuspid valve (TV) also is labeled. (Photograph courtesy of Robert H. Anderson, MD)
Click to see larger picture
Picture Type: Photo
Caption: Picture 3. Pathologic specimen with truncus arteriosus (TA) and interruption of the aortic arch between the left (L) common carotid (CCA) and subclavian (SCA) arteries, viewed from the anterior aspect. The common trunk (CT) is seen arising from the ventricular mass, including the right ventricular (RV) infundibulum. Pulmonary arteries arise as a single trunk from the leftward aspect of the common trunk, which then divides into left and right branches (not shown) and the arterial duct (DA), which continues into the descending aorta, from which the left subclavian artery arises. The ascending aorta (AA), which supplies only the right (R) and left common carotid arteries (the right subclavian artery, which arises anomalously as the last brachiocephalic branch, is not shown), continues from the rightward aspect of the common trunk and is much smaller than in patients without an interrupted arch. RA=right atrial appendage. (Photograph courtesy of Robert H. Anderson, MD)
Click to see larger picture
Picture Type: Photo
Caption: Picture 4. Echocardiographic images of truncus arteriosus (TA). The top image is from the subcostal coronal window (SC COR) and shows the common trunk (TR) arising from the left ventricle (LV), overriding the interventricular septum. The common trunk branches into the pulmonary trunk and the ascending aorta (AO). The left pulmonary artery (LPA) may be seen branching from the pulmonary trunk. RA=right atrium; RPA=right pulmonary artery. In the bottom image, which is from the suprasternal notch sagittal window, the truncal origin and course of the pulmonary trunk and left pulmonary artery can be appreciated. DAO=descending aorta; IV=innominate vein; LA=left atrium.
Click to see larger picture
Picture Type: ECG