Meeting Reviews
Session II: Focus on A Lesion – Truncus Arteriosus
By Jamie Sinton, MD and Annelisa Cossu, MD
The mid-morning session, Focus on a Lesion, was moderated by Laura Downey, MD (Children's Healthcare of Atlanta) and Viviane G. Nasr, MD (Boston Children’s Hospital) and was centered around Truncus Arteriosus.
Truncus Arteriosus: Diagnosis and Pre-Op Physiology
Jill Savla, MD, MSCE
Children’s Hospital of Philadelphia
The diagnosis and preop physiology of Truncus Arteriosus (TA) was presented by Jill Savla, MD, MSCE, a pediatric cardiologist from Children’s Hospital of Philadelphia. Dr. Savla’s presentation focused on the subtypes of TA, associated anomalies, and the pathophysiology of TA. TA is a conotruncal defect with a single great artery arising from the heart and giving origin to the aorta, one or more coronary arteries, and at least one pulmonary artery.
Dr. Savla explained the Van Praagh Classification (Types 1-4) of TA, the most commonly used classification system. In Type I TA, the branch pulmonary arteries arise from the left or anterior side of the truncus. Although Type 1 is characterized by the presence of a main pulmonary artery (PA), it is often not a true main PA when viewed from interior aspect of the truncus as the right and left branches bifurcate closely together. This arrangement necessitates bilateral PA band placement on the branch PAs versus one band on the main PA. In Type 2 TA, the branch PAs arise separately from the posterior aspect of the truncus. A surgical challenge to Van Praagh Type 2 TA is that the two branch PAs may arise from the truncus posteriorly and placement of a right ventricular to pulmonary arterial (RV to PA) conduit may lead to a detrimental anatomic impact on the branch PAs. Type 3 is comprised of an isolated branch PA from the truncus and a second source of pulmonary blood from the ductus arteriosus or a collateral artery. Type 4 is associated with an aortic arch interruption, atresia, or coarctation.
Dr. Savla briefly mentioned the Collett and Edwards classification. In Type 1, branch PAs arise from a main PA segment. In Type 2, branch PAs arise directly from the truncus with one or two orifices in close proximity to each other. In Type 3, the branch PAs arise from the truncus with two separate orifices that are further apart, typically from the posterior aspect of the truncus. In Type 4, branch PAs arise from the descending aorta, which is actually on the spectrum of Tetralogy of Fallot with pulmonary atresia and multiple aortopulmonary collaterals (TOF/PA/MAPCAs) and not TA. She ended the classification section with the Anderson descriptive classification which groups TA variations as either more aortic or more pulmonary dominant.
Dr. Savla then discussed the morphological structures of importance in TA, including the ventricular septal defect (VSD), the subtruncal conus or infundibulum, the truncal valve, and coronary abnormalities. The truncal valve can have a variable number of leaflets (tricuspid, bicuspid or quadricuspid). The leaflets can of be different sizes, thickened, dysplastic, and asymmetric. Due to these abnormalities, the valve may be stenotic or have coaptation gaps resulting in regurgitation. Additionally, there may be abnormalities in the coronary arteries such as abnormal or eccentric origins. The normal origin of a coronary artery is in the middle of a sinus of Valsalva where there is maximal diastolic blood flow.
However, in TA the coronary origin may be directly above a commissure or above the sinotubular junction. This can lead to impaired coronary filling. Additionally, there may be coronary ostial stenosis with a slit-like ostium or an intramural course of a coronary artery. These abnormalities can predispose a patient to coronary ischemia and, therefore, worsen postoperative outcomes. Other common associations include right aortic arch, 22q11 microdeletion syndrome, and variable presence of the patent ductus arteriosus depending on the type of TA. Additional cardiac findings include complete atrioventricular canal and a persistent left superior vena cava.
Dr. Savla next described the preoperative physiology of Truncus Arteriosus. Patients with TA are cyanotic at birth because there is complete mixing of systemic and pulmonary venous blood. With the normal decline in pulmonary vascular resistance over the first days to weeks of life, systemic oxygen saturation increases due to increased pulmonary blood flow. Increased pulmonary blood flow and pulmonary venous return to the left atrium results in increased left ventricular end diastolic blood volume. Blood is ejected across the truncal valve and will either enter the aorta, pulmonary arteries, or the coronary arteries.
As pulmonary vascular resistance falls, blood will follow the path of least resistance into the pulmonary arterial bed. This comes at a cost to systemic and coronary perfusion and lowers diastolic blood pressure due to diastolic runoff of truncal blood into the branch PAs. A wide pulse pressure develops due to diastolic run off and can lead to coronary ischemia. Symptomatic heart failure will develop in the first days to weeks of life with tachypnea, increased work of breathing, poor weight gain due to feeding difficulty, and diaphoresis with feeds. If left unrepaired, patients with TA will develop progressive metabolic acidosis and failure to thrive.
A subset of TA patients with particularly high risk are those with truncal valve regurgitation. Regurgitation increases the volume load on the ventricle and thereby increases myocardial oxygen demand. Additionally, regurgitation will further lower diastolic blood pressure at the cost of coronary and systemic perfusion. This may lead to mesenteric ischemia and necrotizing enterocolitis. Coronary ischemia can lead to myocardial dysfunction, arrhythmia, and low cardiac output - which further worsens end-organ perfusion.
All in all, truncal valve regurgitation increases the risk of poor postoperative outcomes. Conversely, branch pulmonary artery stenosis may be beneficial to patients with TA. With a mild amount of branch PA narrowing or PA hypoplasia or with Van Praagh Type 3 (small ductus arteriosus or collateral vessel), there is reduced risk of increased pulmonary blood flow. These patients are less likely to develop early heart failure symptoms, which may ultimately delay the timing of surgery.
Ideal timing of surgery is in the first week of life to prevent the development of pulmonary arterial hypertension. If left untreated, the natural history of TA is the development of irreversible pulmonary vascular disease, increased right to left shunting as in Eisenmenger’s syndrome, and death. Factors that may delay neonatal surgery include early gestational age, low birth weight, and organ immaturity. Prematurity predisposes patients to bronchopulmonary dysplasia, pulmonary hypertension, and chronic lung disease. In a 2017 study, a high mortality rate was demonstrated in premature infants at 25 - 32 weeks post gestational age. An alternative approach, therefore, is bilateral PA band palliation followed by complete repair.
Truncus Arteriosus: Surgical Repair
Carlos Mery, MD, MPH
Dell Children’s Medical Center
Carlos Mery, MD, MPH, a congenital heart surgeon in practice at Dell Children’s Medical Center, provided insight into the surgical repair of truncus arteriosus, risk factors for poor postoperative outcomes, and short- and long- term outcomes after surgical repair of Truncus Arteriosus. His lecture began with a clinical case describing a 1.7 kg, ex 34-week premature neonate with intrauterine growth restriction, DiGeorge syndrome and Truncus Arteriosus with Type B interrupted aortic arch and severe truncal valve insufficiency.
Although this newborn was small, he opted for complete repair rather than PA band palliation. He recognized that other centers may offer palliation and allow the infant to grow prior to complete repair. The goals of a complete repair with the Rastelli operation include the following: 1) septation of the heart, 2) separation of the aorta and pulmonary artery, 3) restoration of right ventricular to pulmonary artery continuity, and 4) repair of any associated anomalies, such as truncal valve insufficiency or interrupted aortic arch.
Dr. Mery mentioned the challenge of the prebypass management of these patients. He emphasized the importance of avoiding large decreases in pulmonary vascular resistance and maintenance of adequate diastolic perfusion pressure to prevent myocardial ischemia. Partial surgical snaring of the branch pulmonary arteries may be necessary to limit diastolic run off and improve systemic perfusion.
The surgical strategy of TA repair depends on the type of TA: aortic dominant (Van Praagh Type 1 and 2) versus pulmonary dominant (Van Praagh Type 4 with interrupted aortic arch). Starting with aortic dominant TA, the cardiopulmonary bypass strategy includes aortobicaval cannulation with the aortic cannula placed distally. The pulmonary arteries are snared immediately after going on bypass to avoid runoff. Moderate hypothermia is used at Dr. Mery’s institution. Myocardial preservation is performed by instillation of cardioplegia into the aortic root or directly into the coronary ostia if there is significant truncal valve insufficiency. LV venting is performed through a right atriotomy and a patent foramen ovale or through the right upper pulmonary vein. The branch PAs are detached from the truncus as a unit and then the truncus can be closed primarily or with an autologous pericardial patch.
Dr. Mery favors complete transection of the truncus followed by harvesting the pulmonary arteries which allows better visualization of the left coronary artery. An end-to-end anastomosis can be performed between the proximal and distal truncus. Next, the ventricular septal defect (VSD) is typically closed with autologous pericardial patch or a synthetic patch. The inferior rim of the VSD is often remote from conduction tissue unless the VSD extends into the perimembranous region, in which case the conduction system may be vulnerable to injury. Right ventricular to pulmonary artery (RV to PA) continuity is established by an aortic or pulmonary homograft conduit. The Contegra conduit is an additional type of conduit that is made of bovine jugular vein.
In cases of pulmonary dominant TA with an interrupted arch, Dr. Mery favors arterial cannulation through a graft sewn onto the innominate artery, allowing antegrade cerebral perfusion, and an additional arterial cannula through the ductus arteriosus to provide lower body perfusion. Bicaval cannulation is utilized as well. One reparative technique involves separating the branch pulmonary arteries from the truncus, making an incision on the ascending aorta and the descending aorta, and performing a partial anastomosis between the ascending and descending aorta. A piece of autologous pericardium can then be used to augment and enlarge the communication between the two ends of the aorta and relieve the tension on the two ends.
In cases of significant truncal valve insufficiency, valve repair is also necessary. There are several principles of truncal valve repair including the following: 1) stabilization of incomplete leaflets, 2) debridement of thickened leaflets, 3) elimination of inadequate leaflets (tricuspidization), 4) reduction in the valvular annular dimension, and 5) improvement of leaflet coaptation.
In the case of a quadricuspid valve with one deficient leaflet, the deficient leaflet can be excised with its corresponding sinus and then the remainder of the valve brought together surgically. This is referred to as tricuspidization of the valve.
Dr. Mery then discussed postoperative outcomes and risk factors. In a large study using the Society of Thoracic Surgeons database, 527 patients had TA repair. Early mortality was 11%. Risk factors for early mortality included truncal valve surgery and/or an interrupted aortic arch. A recent multicenter study from three Australian centers included 255 patients with an early mortality of 13.3%. Risk factors included presence of an interrupted aortic arch in univariate analysis and age at the time of repair and low birth weight in multivariate analysis. Risk factors for late mortality included coronary anomaly and low birth weight.
A study from Boston Children’s Hospital found that 204 patients had TA repair from 1984 to 2018. Early morality was 14%. Incidence of reoperation on the truncal valve was much more common in patients with a quadricuspid truncal valve. Long term quality of life in adults with repaired TA is not well studied; however, one Australian study demonstrated no difference in global quality of life when compared to the general population. However, physical function and self-reported general health was worse in patients with a history of TA repair versus the general population.
Dr. Mery closed with further discussion of the case described at the beginning of his presentation. The patient underwent successful initial repair with arch reconstruction, truncal valve repair, and placement of a 7 millimeter RV to PA conduit. However, the patient had progressive truncal valve insufficiency and at four months of age required reoperation. The truncal valve was replaced along with replacement of the RV to PA conduit.
In conclusion, Dr. Mery emphasized the high perioperative mortality of TA repair despite advances in care. Risk factors include low birth weight, interrupted aortic arch, and truncal valve insufficiency/quadricupsid truncal valve. These patients are likely to require reintervention during their lifetime. Long term quality of life in adults is still unknown.
Perioperative Management of the Neonate with Truncus
Denise Joffe, MD
Seattle Children’s Hospital
This session ended with a presentation on the anesthetic management of the patient with truncus arteriosus by Denise Joffe, MD of Seattle Children’s Hospital in Washington. The specifics discussed include the preop assessment and anesthetic management of neonates for primary repair, a step-by-step description of the surgical repair of TA, and anesthetic considerations of re-operative cardiac or non-cardiac surgery.
The presentation began with a discussion of the preanesthetic evaluation starting with the history. Patients with TA will be in the neonatal age range and present with shortness of breath and congestive heart failure. Certainly, any history of excessive crying can indicate coronary ischemia. DiGeorge syndrome, also known by a variety of other names, may occur with TA. These patients have an increased risk of conotruncal defects such as Tetralogy of Fallot and Truncus Arteriosus.
Patients with DiGeorge syndrome have altered calcium metabolism (absent parathyroid glands), abnormal cellular mediated immunity (absent thymus) with increased risk of infection, and increased incidence of airway anomalies such as cleft palate and thus, potential difficult airway. Dr. Joffe emphasized the importance of a good cardiopulmonary physical exam. Pre and post ductal oxygen saturation were noted to be important in any patient with congenital heart disease with particular attention paid to whether the saturations match expectations. Regarding the EKG, attention should be paid to evidence of ischemia. Labs should be checked for low ionized calcium. The chest x-ray should be checked for findings of pulmonary edema and for signs of bronchial compression. Typically, TA is diagnosed with an echocardiogram; though further imaging may be necessary to identify collateral blood vessels. Preoperative orders for patients with DiGeorge syndrome should include irradiated blood.
Dr. Joffe noted that the operating room must be ready for the induction of anesthesia and the surgical procedure. It is important to monitor the EKG closely for signs of ischemia. The induction must be judicious and slow with the following goals: 1) maintain heart rate, 2) maintain sinus rhythm, 3) maintain or slightly decrease preload, 4) maintain contractility by avoiding drugs with negative inotropic effects such as propofol and inhalational agents, 5) maintain or slightly decrease systemic vascular resistance to promote forward blood flow, and 6) most importantly, avoid decreases in pulmonary vascular resistance by minimizing hyperoxia (use room air) and hyperventilation.
Dr. Joffe recommended placing an IV prior to induction if not already present. She then recommended using doses of 2 mcg/kg of fentanyl with 3-4% sevoflurane and titrating additional fentanyl to effect. After the patient has become unconscious, Dr. Joffe recommended the administration of muscle relaxant and awaiting the appropriate time for pharmacologic effect. In cases of tachycardia with laryngoscopy, she recommended stopping and giving more fentanyl or intravenous lidocaine to blunt the sympathetic response in order to avoid myocardial ischemia. The particular vasoactive drug used must be chosen with consideration as to its physiologic effect given the hemodynamics of TA. Given the risk of ischemia and decompensation during induction of anesthesia, the surgeons and perfusionists should be present in the operating room.
Dr. Joffe suggested using a noninvasive blood pressure cuff on a lower extremity to determine any gradient in blood pressure after repair of an interrupted aortic arch. Arterial line placement was recommended to be on the opposite side of an aberrant subclavian artery and to be radial in location. In regards to recommendations for a central line, Dr. Joffe suggested deferring if the patient becomes unstable. If placing a central line, a transesophageal echocardiogram (TEE) can be used to demonstrate the wire in the right atrium and the left internal jugular vein should be avoided in cases of a persistent left superior vena cava. In cases of an interrupted aortic arch, the patient can be cooled with ice on the head.
Dr. Joffe emphasized the importance of communication with the surgeon regarding excessive pulmonary blood flow. She warned against administration of vasoactive medications and suggested requesting surgical (temporary) banding of the branch pulmonary arteries to increase the pulmonary vascular resistance (PVR) thereby increasing coronary and systemic blood flow. She stressed the importance of vigilance and monitoring for signs of ischemia via the EKG and TEE.
Dr. Joffe then discussed the intraoperative repair and how it affects anesthetic management. Important factors to pay attention to include arterial cannula placement, pump pressures and pump flow. During or following cardiopulmonary bypass (CPB), ascites and hematuria suggest inferior vena cava cannula misplacement while postoperative mitral regurgitation suggests a left ventricular vent misadventure. With the truncus surgically opened, the coronary arteries, pulmonary arteries and valve leaflets are in close proximity to each other and are thus at risk for injury during repair.
With anastomosis of the truncal root to the distal portion of the aorta, obstruction is possible in the postoperative phase. During closure of the VSD, a right ventriculotomy may lead to an injury of the conal branch of a coronary artery with ensuing ventricular dysfunction or there may be a residual VSD. The VSD is often very close to the truncal valve and thus there is potential to injure the truncal valve during VSD closure. A patent foramen ovale is often left at the end of the procedure to permit right to left shunting in the case of elevated PVR. Dr. Joffe concluded the intraoperative discussion with emphasis on snaring the PAs upon initiation of bypass to avoid hypotension. She also noted that the left ventricle may dilate due to worsening truncal valve regurgitation and to use the TEE to reevaluate function such that cardioplegia may be given early. The pulmonary artery may enlarge as well necessitating the LeCompte maneuver.
Upon separation from CPB, Dr. Joffe routinely starts inhaled nitric oxide to reduce PVR. In contrast to prebypass management, the ventilation strategy should focus on reducing PVR with use of inspired oxygen, low airway pressures and hyperventilation. Standard monitors should be used to monitor for ischemia, arch obstruction, and decreased oxygen saturation. The TEE is important to determine ventricular function, coronary blood flow, direction of flow through the PFO, and truncal valve function among other things. She concludes with caution around postbypass hemorrhage and warns that transfusion of several blood volumes may be required. And finally, she emphasized vigilance surrounding transfer of care to the intensive care unit as this can be a physiologically dynamic, tumultuous time for the patient.
The final portion of the presentation centered around the perioperative care of adults with a history of TA. Adults with congenital heart disease typically have poor follow up. Many have a good quality of life but still have limitations in functional status like single ventricle patients. Adult patients with a history of TA are likely to have pulmonary regurgitation if they have not yet undergone RV to PA conduit revision. Though there may be normal echocardiogram parameters in terms of ventricular function, these patients often have right ventricular dilation and elevated right ventricular end diastolic pressure. Thus, in the presence of a PFO, there may be right to left shunting and decreased oxygen saturation. Many of these patients have persistent aberrant vessels, absence of a left subclavian artery, or a residual aortic arch gradient.
In conclusion, Dr. Joffe relays the paucity of evidence-based guidelines for the anesthetic care of adults with a history of TA.
