transposition of the great arteries

Transposition of the Great Arteries




Transposition of the great arteries results from failure of the truncus arteriosus to spiral, resulting in the aorta arising from the anterior portion of the right ventricle and the pulmonary artery arising from the left ventricle ( Fig. 3-5 ).

There is complete separation of the pulmonary and systemic circulations such that systemic venous blood traverses the right atrium, right ventricle, aorta, and systemic circulation; and pulmonary venous blood traverses the left atrium, left ventricle, pulmonary artery, and lungs.

Survival is possible only if there is communication between the two circulations in the form of a VSD, ASD, or PDA.

additional cardiac lesions are associated with transposition of the great arteries (D-TGA)

The most commonly associated cardiac anomalies are a persistent patent foramen ovale (PFO), patent ductus arteriosus (PDA), ventricular septal defect (VSD), and subpulmonic stenosis or left ventricular outflow tract (LVOT) obstruction.

　

Figure 3-5 Transposition of the great arteries. The right ventricle (RV) and left ventricle (LV) are not connected in series. Instead, the two ventricles function as parallel and independent circulations, with the aorta (Ao) arising from the RV and the pulmonary artery (PA) arising from the LV. Survival is not possible unless mixing of blood between the two circulations occurs through an atrial septal defect, ventricular septal defect, or patent ductus. IVC, inferior vena cava; LA, left atrium; PV, pulmonary vein; RA, right atrium; SVC, superior vena cava.



the pathophysiology of transposition of the great arteries (D-TGA)

In the parallel arrangement of D-TGA, deoxygenated systemic venous blood recirculates through the systemic circulation without reaching the lungs to be oxygenated. This recirculated systemic

venous blood represents a physiologic right-to-left shunt.

Likewise oxygenated pulmonary venous blood recirculates uselessly through the pulmonary circulation. This recirculated

pulmonary venous blood represents a physiologic left-to-right shunt. Therefore, in a parallel circulation, the physiologic shunt or the percentage of venous blood from one system that recirculates in the arterial outflow of the same system is 100% for both circuits. Unless there is one or more communications between the parallel circuits to allow intercirculatory mixing, this arrangement is not compatible with life.

The sites available for intercirculatory mixing in D-TGA can be intracardiac (patent foramen ovale [PFO], atrial septal defect [ASD], ventricular septal defect [VSD]) or extracardiac (patent

ductus arteriosus [PDA], bronchopulmonary collaterals).

Several factors affect the amount of intercirculatory mixing. The number, size, and position of anatomic communications are

important.

One large, nonrestrictive communication will provide better mixing than two or three restrictive communications.

The position of the communication is also important. Poor mixing occurs even with large anterior muscular VSDs due to their unfavorable position.

Finally, in the presence of adequate intercirculatory mixing sites, the extent of intercirculatory mixing is directly related to total pulmonary blood flow. Patients with reduced pulmonary blood flow secondary to subpulmonary stenosis or pulmonary vascular occlusive disease (PVOD) will have reduced intercirculatory mixing.

the clinical subsets of transposition of the great arteries (D-TGA)

Four clinical subsets based on anatomy, pulmonary blood flow, and intercirculatory mixing can be used to characterize patients with D-TGA.



Anatomy Pulmonary blood flow Intercirculatory mixing

TGA with IVS INCREASED SMALL

TGA with IVS;nonrestrictive ASD or PDA INCREASED LARGE

TGA with VSD INCREASED LARGE

TGA with VSD and LVOT REDUCED SMALL

TGA with PVOD REDUCED SMALL

Diagnosis

Signs and Symptoms

Persistent cyanosis and tachypnea at birth may be the first clues to the presence of transposition of the great arteries. Congestive heart failure is often present, reflecting left ventricular failure due to volume overload created by the left-to-right intracardiac shunt necessary for survival.

The ECG is likely to demonstrate right axis deviation and right ventricular hypertrophy because the right ventricle is the systemic ventricle.

Classically, the cardiac silhouette on the chest radiograph is described as being “egg-shaped with a narrow stalk.”

Two-dimensional echocardiography is the diagnostic modality of choice in the diagnosis and assessment of infants with D-TGA. It accurately establishes the diagnosis of D-TGA and reliably, identifies associated abnormalities such as VSD, mitral and tricuspid valve abnormalities, and LVOT obstruction. It also reliably delineates coronary artery anatomy

Treatment

The immediate management of transposition of the great arteries involves creating intracardiac mixing or increasing the degree of mixing. This goal is accomplished with infusions of prostaglandin E to maintain patency of the ductus arteriosus and/or balloon atrial septostomy (Rashkind procedure). Administration of oxygen may decrease pulmonary vascular resistance and increase pulmonary blood flow. Diuretics and digoxin are administered to treat congestive heart failure.



Two surgical switch procedures have been used to treat complete transition of the great arteries.



Arterial anatomic repair: arterial switch (Jatene) operation

The arterial switch operation (ASO) anatomically corrects the discordant ventriculoarterial connections and is the procedure of choice for patients with transposition of great arteries (DTGA).

Following repair, the right ventricle (RV) is connected to the pulmonary artery (PA) and the left ventricle (LV) to the aorta.

The ASO was originally described in patients with D-TGA and a large ventricular septal defect (VSD) or a large patent ductus

arteriosus (PDA). In these patients, the pulmonary ventricle (LV) remains exposed to systemic pressures, and the LV mass remains sufficient to support the systemic circulation. For this

subset of patients, the ASO is generally performed within the first 2 to 3 months of life, before intractable congestive heart failure (CHF) or irreversible pulmonary vascular occlusive disease (PVOD) intervene.

In patients with D-TGA and intact ventricular septum (IVS), there is a progressive reduction in LV mass as the physiologic pulmonary hypertension present at birth resolves progressively over

the first weeks following birth. Adequate LV mass to support the systemic circulation exists in these patients for only the first 2 or 3 weeks following birth. In patients with D-TGA and IVS, the

ASO can be performed primarily or as the second phase of a staged procedure.

A successful primary ASO must generally be performed within the first 3 weeks of life. Previously, favorable candidates for the procedure in the neonatal period were shown to have an LV to RV pressure ratio of at least 0.6 by catheterization. Currently, two-dimensional echocardiography is used to

noninvasively assess the LV to RV pressure ratio. Three types of ventricular septal geometry have been described. Patients in whom the ventricular septum bulges to the left (type 3), indicating a low pressure in the pulmonary ventricle (LV), are not candidates for a neonatal ASO. Patients with septal bulging to the right (type 1), indicating a high pressure in the pulmonary ventricle (LV), and those patients with an intermediate septal position (type 2) are considered good candidates. Most neonates with D-TGA and IVS who are sui table candidates for an ASO have type 2 septal geometry.

The staged ASO for D-TGA with IVS is used for those neonates in whom surgery cannot be performed in the first few weeks of life secondary to events such as prematurity, sepsis, low birth weight (<1.0 kg), or late referral. The LV is retrained to accept the systemic workload within the first 2 months of life. The preparatory surgery involves creation of a nonrestrictive atrial septum

(if it does not already exist), placement of a PA band, and creation of an aortopulmonary shunt with entry to the PA distal to the band. The band must be tight enough to increase pressure in the pulmonary ventricle (LV) to approximately one half to two thirds of that in the systemic ventricle (RV). This wi ll increase the afterload sufficiently to stimulate an increase in LV mass.

Historically, after 3 to 6 months the PA was debanded, the shunt taken down, and an ASO performed. Currently a rapid two-stage repair is undertaken in which the ASO is performed as early as 1 week after preparatory PA banding, often during the same hospitalization. This approach is based on the fact that a doubling of LV mass is seen after 1 week of PA banding.

Intraatrial physiologic repairs: mustard and senning procedures

Both the Mustard and the Senning procedures are atrial switch procedures that surgically create discordant atrioventricular (AV) connections in D-TGA. Systemic venous blood is routed to the LV and the PA whereas pulmonary venous blood is routed to the RV and the aorta.

This arrangement results in physiologic but not anatomic correction of D-TGA as the morphologic RV becomes the systemic ventricle. Given the current success with and the almost universal application of the more definitive ASO these intraatrial switch procedures are primarily of historic interest in patients with D-TGA.

Rastelli procedure

it is a method of anatomically correcting D-TGA with VSD and left ventricular outflow tract (LVOT) obstruction. This surgery is used when LVOT obstruction in the form of subpulmonic and/or pulmonic stenosis is surgically uncorrectable.

Performance of an ASO under these circumstances would leave the infant with residual LVOT obstruction (aortic or subaortic stenosis).



Management of Anesthesia

preoperative interventions to help stabilize a patient with transposition of the great arteries (D-TGA)

Intact ventricular septum

Prostaglandin E1, (0.01 to 0.05 μg/kg/minute) is administered to dilate and maintain the patency of the ductus arteriosus. This will be effective in increasing effective pulmonary and systemic blood flow, and in improving PaO2 and tissue oxygen delivery if

(a) pulmonary vascular resistance (PVR) less than systemic vascular resistance (SVR) and (b) there is a nonrestrictive

or minimally restrictive atrial septal communication. In some centers, all neonates stabi lized on prostaglandin E1 alone have a balloon atrial septostomy to enlarge the atrial septal communication so that prostaglandin E1 can be stopped and surgery scheduled on a semielective basis.

Prostaglandin E1 infusion is associated with apnea, pyrexia, fluid retention, and platelet dysfunction.

If prostaglandin E1 does not improve tissue oxygen delivery, then an emergent balloon atrial septostomy is performed in the catheterization laboratory utilizing angiography or in the

intensive care unit (ICU) utilizing echocardiography.

These patients also require tracheal intubation and mechanical ventilation. This allows reduction of PVR through induction of a respiratory alkalosis and elimination of pulmonary ventilation/pefusion (V/Q) mismatch. Sedation and muscle relaxation reduce oxygen consumption, thereby increasing mixed venous O2 saturation.

extracorporeal membrane oxygenation (ECMO) (either venoarterial [VA] or venovenous [VV]) support to improve tissue oxygenation and to reverse end-organ insult and lactic acidosis before surgery is an alternative approach to emergent surgery in a critically i ll neonate.

Ventricular septal defect

Infants in this subset are mildly cyanotic with symptoms of congestive heart failure (CHF).

These patients are commonly stable enough not to require immediate surgical or catheterization laboratory intervention. They are, however, candidates for an arterial switch operation (ASO) before intractable CHF or advanced pulmonary vascular occlusive disease (PVOD) occur.

Ventricular septal defect and left ventricular outflow tract

obstruction

The degree of cyanosis in these infants will depend on the extent of left ventricular outflow tract (LVOT) obstruction. LVOT obstruction reduces pulmonary blood flow and intercirculatory mixing, and it protects the pulmonary vasculature from the increased pressures and volumes that accelerate the development of PVOD. The more severe the LVOT obstruction, the less effective will be the efforts to increase pulmonary blood flow by decreasing PVR. When LVOT obstruction is severe, the infant is severely cyanotic and progressively develops polycythemia.

These infants may require a palliative aortopulmonary shunt to increase pulmonary blood flow.

Ideally, a definitive repair in the form of a Rastelli procedure is performed in the neonatal period.

Pulmonary vascular occlusive disease

The goal of diagnosis and treatment of infants with D-TGA is to intervene surgically before the development of PVOD. As PVOD advances, the child becomes progressively cyanotic and polycythemic.

Infants with advanced PVOD (PVR >10 Wood units; histologic grade 4) are generally candidates only for palliative therapy. These patients are candidates for a palliative intraatrial physiologic repair without closure or with fenestrated closure (4- to 5-mm hole in the center of the VSD patch) of the VSD.

management of anesthesia

Preoperative Evaluation and Preparation

The preoperative evaluation should begin with a careful history and physical examination.

Gestational age, birth complications, family history, and any other medical problems should be noted. A comprehensive airway evaluation should be performed and the previous endotracheal

tube size and leak pressure noted. Arterial and intravenous access should be assessed. A type and cross must be sent to the blood bank to ensure adequate red cells and blood component therapies are available in the operating room (OR).

The preoperative electrocardiography (ECG) and chest roentgenogram should be reviewed. The preoperative echocardiograms should be reviewed. Particular attention should be paid to septal geometry, biventricular function, coronary anatomy, and adequacy of mixing at the atrial septal

and ductal levels.

Prostaglandin E1 was discontinued in the patient but the ductus arteriosus may remain patent.

Laboratory data should include a complete blood count, electrolytes, platelet count, arterial blood gas, calcium, blood urea nitrogen (BUN), creatinine, liver function tests (LFT)s and glucose.



the anesthetic goals before cardiopulmonary

bypass (CPB)

Maintain HR, contractility, and preload to maintain cardiac output; decreases in cardiac output decrease systemic venous saturation with a resultant fall in arterial saturation.

Maintain ductal patency with prostaglandin E1 (0.01 to 0.05 μg/kg/minute) in ductal - dependent patients.

Avoid increases in pulmonary vascular resistance (PVR) relative to systemic vascular resistance (SVR); increases in PVR will decrease pulmonary blood flow and reduce intercirculatory mixing; in patients with pulmonary vascular occlusive disease (PVOD), ventilatory interventions should be used to reduce PVR; in patients with left ventricular outflow tract (LVOT) obstruction that is not severe, ventilatory interventions to reduce PVR increase pulmonary blood flow and intercirculatory mixing.

Reductions in SVR relative to PVR should be avoided; decreased SVR increases recirculation of systemic venous blood and decreases arterial saturation.

In patients with D-TGA and ventricular septal defect (VSD) with symptoms of congestive heart failure (CHF), ventilatory interventions to reduce PVR are not warranted as they will produce small improvements in arterial saturation at the expense of systemic perfusion.

method of induction

Management of anesthesia in the presence of transposition of the great arteries must take into account separation of the pulmonary and systemic circulations. Drugs administered intravenously are distributed with minimal dilution to organs such as the heart and brain. Therefore, doses and rates of injection of intravenously administered drugs may have to be decreased.

Conversely, the onset of anesthesia produced by inhaled drugs is delayed because only small amounts of the inhaled drug reach the systemic circulation.



This infant would have an IV catheter in place on transfer to the operating room (OR).

Anesthesia is generally induced and maintained using a synthetic opioid-based (fentanyl or sufentanil) technique.

These opioids may be used alone in high doses (25 to 100 μg/kg fentanyl or 2.5 to 10 μg/kg sufentanil) or in low to moderate doses (5 to 25 μg/kg fentanyl or 0.5 to 2.5 μg/kg sufentanil) in combination with an inhalation agent (generally isoflurane or sevoflurane) or a benzodiazepine (generally midazolam).

The high-dose technique is particularly useful in neonates and infants. High-dose opioids provide hemodynamic stability, do not depress the myocardium, and blunt reactive pulmonary hypertension.

In order to avoid bradycardia, pancuronium (0.1 mg/kg) is administered in conjunction with the opioid; its vagolytic activity

offsets the vagotonic activity of the narcotics.

induction and maintenance of anesthesia are alternatively accomplished with ketamine combined with muscle relaxants to facilitate tracheal intubation. Ketamine can be supplemented with opioids or benzodiazepines for maintenance of anesthesia.

Nitrous oxide has limited application in these patients, as it is important to administer high inspired oxygen concentrations.

Dehydration must be avoided during the perioperative period. These patients may have hematocrits in excess of 70%, which may contribute to the high incidence of cerebral venous thrombosis. This finding suggests that oral fluids should not be withheld from these patients for prolonged periods. If fluids cannot be ingested orally, an intravenous infusion should be initiated during the preoperative period. Atrial dysrhythmias and conduction disturbances may occur postoperatively.



further readings



Intraatrial physiologic repairs: Mustard and Senning procedures

In both procedures the interatrial septum is excised, creating a large atrial septal defect (ASD).

In the Mustard procedure, a baffle made of native pericardium or synthetic material is then used to redirect pulmonary and systemic venous blood. In the Senning procedure, autologous tissue

from the right atrial wall and interatrial septum is used in place of the pericardium or synthetic material. In either case, pulmonary venous blood flows over the baffle and is directed across the

tricuspid valve into the RV and out the aorta. Systemic venous blood flows on the underside of the baffle to be directed across the mitral valve into the left ventricle (LV) and out the PA. This

arrangement resul ts in physiologic but not anatomic correction of transposition of the great arteries (D-TGA), as the morphologic RV becomes the systemic ventricle. These procedures are

performed with hypothermic cardiopulmonary bypass (CPB), bicaval cannulation, and aortic cross clamping during cardioplegic arrest. Intervals of low-flow CPB are customarily used.

Arterial anatomic repair: arterial switch (Jatene) operation

The PA and the aorta are transected distal to their respective valves. The coronary arteries are initially explanted from the ascending aorta with 3 to 4 mm of surrounding tissue. The explant

sites are repaired either with pericardium or synthetic material. The coronary arteries are reimplanted into the proximal PA (neoaorta). The distal PA is brought anterior to the aorta

(LeCompte maneuver) to be reanastomosed to the old proximal aorta (right ventricular outflow) and the distal aorta reanastomosed to the old proximal PA (left ventricular outflow). As a result

the great arteries are swi tched to create ventriculoarterial concordance with both an anatomic and physiologic repair achieved. The ASO is done using hypothermic CPB with aortic cross clamping and cardioplegic arrest. Intervals of low-flow CPB are customari ly used. A short interval of deep hypothermic circulatory arrest (DHCA) may be employed to close the atrial

septum or ventricular septal defect (VSD) if a single venous cannula rather than bicaval venous cannulation is used. Closure of a VSD is preferential ly done transatrially through the tricuspid

valve. It is desirable to avoid approaching a VSD through the RV, because an incision in the RV may contribute substantially to postoperative RV dysfunction.

Rastelli procedure

The PA is transected and ligated just distal to or at the level of the pulmonary valve. A right ventriculotomy is performed, and the VSD is closed with a patch tunnel such that the LV is in continuity with the aorta. The VSD may have to be enlarged, in some cases, to prevent subaortic stenosis. Right ventricle (RV) to PA continuity is achieved by placement of valved conduit or valved homograft between the right ventriculotomy site and the proximal main PA. The result is LV to aortic continuity and RV to PA continuity with bypass of the subpulmonic and pulmonic stenosis. This procedure is performed with hypothermic CPB, bicaval cannulation, and aortic cross clamping during cardioplegic arrest. Intervals of low-flow CPB are customarily used.

Historically, most of these patients had a palliative systemic to PA shunt placed in the newborn period and then returned for the Rastell i procedure and take down of the shunt at 2 to 3 years of

age. The delay was felt necessary to avoid performing a right ventriculotomy in infants with immature myocardium and limited contracti le elements and to allow adequate growth of the RV

and pulmonary arteries to permi t placement of an RV to pulmonary artery (PA) conduit. In the current era with improvements in myocardial protection, CPB technology, and surgical technique this procedure can be performed as a primary procedure in the neonatal period.