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Hybrid Procedure for Hypoplastic Left Heart Syndrome: The Nemours Approach

      The management of hypoplastic left heart syndrome (HLHS) has evolved primarily into a sequence of staged surgical interventions originally described by Norwood and colleagues.
      • Norwood W.I.
      • Lang P.
      • Hansen D.D.
      Physiologic repair of aortic atresia-hypoplastic left heart syndrome.
      A significant improvement in early survival following Stage I Norwood in recent years has led to the recognition of conditions associated with “high risk” for poor outcome, including low birth weight, prematurity, noncardiac conditions, and genetic or chromosomal abnormalities.
      • Ashburn D.A.
      • McCrindle B.W.
      • Tchervenkov C.I.
      • et al.
      Outcomes after the Norwood operation in neonates with critical aortic stenosis or aortic valve atresia.
      • Gaynor J.W.
      • Mahle W.T.
      • Cohen M.I.
      • et al.
      Risk factors for mortality after the Norwood procedure.
      • Pizarro C.
      • Malec E.
      • Maher K.O.
      • et al.
      Right ventricle to pulmonary artery conduit improves outcome after stage I Norwood for hypoplastic left heart syndrome.
      The decreased survival in high-risk patients along with the suboptimal neurocognitive function reported among survivors of staged reconstruction
      • Mahle W.T.
      • Wernovsky G.
      Neurodevelopmental outcomes in hypoplastic left heart syndrome.
      have provided the stimulus to explore alternative management strategies.

      Historical Perspective

      Over a decade ago, Gibbs and coworkers reported “a new approach which combined surgery and interventional catheterization, to achieve bilateral pulmonary artery banding, creation of an atrial septal defect and stenting of the arterial duct,” as an alternative form of palliation for HLHS.
      • Gibbs J.L.
      • Wren C.
      • Watterson K.G.
      • et al.
      Stenting of the arterial duct combined with banding of the pulmonary arteries and atrial septectomy or septostomy: A new approach to palliation for the hypoplastic left heart syndrome.
      Almost simultaneously, Ruiz and colleagues reported their experience with stenting of the ductus arteriosus as a bridge to cardiac transplantation in infants with HLHS.
      • Ruiz C.E.
      • Gamra H.
      • Zhang H.P.
      • et al.
      Brief report: Stenting of the ductus arteriosus as a bridge to cardiac transplantation in infants with the hypoplastic left heart syndrome.
      These reports established the feasibility, safety, and efficacy of this strategy to stabilize the circulation in patients with HLHS waiting for heart transplantation. Although in both series, ductal patency by stent implantation was achieved effectively, the overall success of this approach was inconsistent due to difficulty achieving appropriate control of pulmonary blood flow.
      More recently, Mitchell and colleagues documented the effectiveness of mechanical limitation of pulmonary blood flow as a bridge to heart transplantation in older infants with HLHS.
      • Mitchell M.B.
      • Campbell D.N.
      • Boucek M.M.
      • et al.
      Mechanical limitation of pulmonary blood flow facilitates heart transplantation in older infants with hypoplastic left heart syndrome.
      Their approach, which included branch pulmonary artery banding by either a conventional surgical approach or percutaneous placement of bilateral intravascular branch pulmonary artery flow-limiting devices, confirmed that appropriate limitation of pulmonary blood flow could allow successful transplantation of patients with HLHS beyond several months of age.
      Applying the concept of ductal stenting and bilateral pulmonary artery banding to newborns with a broad range of left heart obstructive lesions, Michel-Behnke and colleagues successfully explored the possibility of a hybrid approach leading to either a single-ventricle palliation or a biventricular repair.
      • Michel-Behnke I.
      • Akintuerk H.
      • Marquardt I.
      • et al.
      Stenting of the ductus arteriosus and banding of the pulmonary arteries: Basis for various surgical strategies in newborns with multiple left heart obstructive lesions.
      Following this report, the use of a hybrid approach as the initial palliative intervention leading to a subsequent Fontan procedure has been employed with success at several centers.

      Nemours Cardiac Center Approach

      Analysis of our experience since February 2001, along with a critical review of the published data, has resulted in the current implementation of the hybrid approach at our institution. Selection criteria include patients with significant associated comorbidities or those who present in shock due to delayed diagnosis, conditions which afford an increased mortality under the traditional surgical reconstructive approach.
      • Ashburn D.A.
      • McCrindle B.W.
      • Tchervenkov C.I.
      • et al.
      Outcomes after the Norwood operation in neonates with critical aortic stenosis or aortic valve atresia.
      • Gaynor J.W.
      • Mahle W.T.
      • Cohen M.I.
      • et al.
      Risk factors for mortality after the Norwood procedure.
      • Pizarro C.
      • Malec E.
      • Maher K.O.
      • et al.
      Right ventricle to pulmonary artery conduit improves outcome after stage I Norwood for hypoplastic left heart syndrome.
      Patients are admitted to the intensive care unit, where they receive a PGE1 infusion and manipulations to balance the systemic and pulmonary circulations. Bilateral branch pulmonary artery banding and stenting of the ductus arteriosus are usually performed in the hybrid cardiac catheterization laboratory during the first week of life. In the case of delayed presentation with circulatory failure, pulmonary artery banding is performed in the intensive care unit as part of the resuscitative effort, followed by ductal stenting once the patient has stabilized.
      The surgical approach we have chosen aims to facilitate the procedure and preserve vascular access, which will be required for future hemodynamic studies. Additionally, the surgical placement of pulmonary artery bands avoids the need for transcatheter delivery of “internal bands,” which generally requires a sheath position that creates significant simultaneous semilunar and atrioventricular valve regurgitation, resulting in hemodynamic instability.

      Initial Palliation (Stage I)

      Figure thumbnail gr1
      Figure 1This procedure is performed in the cardiac catheterization laboratory or hybrid suite, with the capability of performing a surgical procedure using cardiopulmonary bypass support if necessary.
      After induction of general anesthesia, ventilation is commonly established with 21% FiO2 with or without inspired carbon dioxide to balance the circulations. A milrinone infusion is routinely used. A median sternotomy is performed. Following excision of the thymus gland, the upper portion of the pericardium is opened and tacked to the edges of the incision. A purse-string is placed on the right atrial appendage, and a single lumen line is inserted for vascular access and pressure monitoring. (A) Downward traction on the atrial purse-string allows exposure of the right pulmonary artery (RPA) between the superior vena cava and ascending aorta. After incising the pericardium over the RPA, a right-angled clamp is used to pass a 2-0 Tevdek tie while the assistant provides slight traction of the main pulmonary artery (MPA) to the left. The RPA is occluded with a tourniquet, effectively decreasing the volume load on the ventricle and improving systemic perfusion. To avoid compression or distortion of the ascending aorta, particularly in the low birth weight patient with aortic atresia, the tourniquet is positioned to the right (surgeon's side), away from the ascending aorta. In the case of hemodynamic instability or during resuscitation, manipulation is minimized and the RPA is occluded using an angled vascular clamp immediately after opening the pericardium.
      (B) Bands of polytetrafluoroethylene (PTFE) are prepared by cutting a 5-mm PTFE tube longitudinally outside the blue lines on the graft, creating a band about 2 mm wide. A length >3 cm is desirable to facilitate manipulation. Once the bands are ready, the RPA tourniquet is released and pulled anteriorly. (C) A PTFE band is passed behind the RPA with minimal further dissection and then closed over a 2.5-mm coronary probe placed alongside the anterior aspect of the vessel, using a medium-size vascular hemoclip. Special attention should be paid to avoid compression of the diminutive ascending aorta in patients with aortic atresia, or compression of the right upper lobe artery. (D) The coronary probe is removed and the band is tacked to the adventitia with two 6-0 Prolene stitches, to prevent migration. The long ends of the band are then trimmed. RPA = right pulmonary artery.
      Figure thumbnail gr2
      Figure 2Banding of the left pulmonary artery (LPA) is more challenging due to the short length of the intrapericardial portion of the vessel, and the limited view due to the large ductus. It should also be noted that this vessel has a rather posterior course. To facilitate exposure, the left pulmonary artery is mobilized beyond the pericardial reflection. This is best accomplished using scissors and establishing a plane immediately over the adventitia, to avoid a phrenic nerve injury. The use of rightward traction on the MPA by the surgeon and counter-traction on the opposite pericardial edge by the assistant allow the LPA to become straight and elongated, facilitating the exposure. Once a clear opening behind the LPA, between the ductus arteriosus and LPA, is established, a PTFE band is passed around the artery using a short nose right angle or a Dennis Brown dissector. Care should be taken to avoid injury of the left atrial appendage, which is usually very prominent in the volume-loaded heart and can obscure the view of the most inferior margin of the LPA. Gentle downward traction on the left atrial appendage using a forceps assists with the exposure. The LPA is then banded over a 2.5-mm coronary probe placed alongside and parallel to the vessel, using a vascular hemoclip. The probe is removed and two tacking sutures are placed. We empirically band over a 2.5- to 3.0-mm probe for patients over 3 kg, and a 2.0- to 2.5-mm probe for patients under 3 kg. Pressure distal to the bands is not measured. Our aim is to achieve an arterial oxygen saturation of approximately 80%. Once a desirable saturation is achieved, oxygen is transiently administered to confirm that the saturation can be increased with supplemental oxygen if necessary. If additional tightening of the bands is needed, we favor tightening the RPA band first, which is more accessible to repair if necessary. Branch pulmonary artery banding is performed preceding the stent deployment to facilitate exposure of the LPA and to avoid potential distortion or displacement of the stent at the time of the banding. Additionally, this is the logical sequence to effectively balance the circulation in patients who present in shock. RA = right pulmonary artery; Ao, aorta; MPA, main pulmonary artery; LPA = left pulmonary artery.
      Figure thumbnail gr3
      Figure 3(A) Using a 5-0 monofilament suture, a purse-string is placed on the main pulmonary artery immediately proximal to the takeoff of the right pulmonary artery. Due to the short distance between the sinotubular junction and the RPA origin, the location of the sinuses should be noted to avoid injury to the anterior commissure of the pulmonary valve. A needle is inserted through the purse-string, directed along the long axis of the ductus, and a guide wire is advanced into the descending aorta under fluoroscopic guidance. (B) A 5-F or 6-F sidearm sheath with a marker band at the tip is advanced over the guide wire into the MPA until the marker band completely enters the MPA; the sheath is secured with a tourniquet. (C) A hand injection of contrast using the lateral projection is used to delineate the ductal anatomy and perform measurements to select the appropriate stent. Unusual ductal curvature may require additional angiography in different projections to profile the ductus properly. Angiography also is the last confirmation of the adequacy of the distal arch opening in the juxtaductal area, an issue of special consideration for patients with aortic atresia. After determination of the ductal dimensions and depending on the anatomy, either a balloon-mounted or a self-expandable stent is advanced through the sheath system and deployed into position, followed by an angiogram to assess the stent position. (D) Balloon-mounted stents require more distance between the intended proximal stent end and the sheath tip, to accommodate the shoulder of the balloon during inflation. In small patients it may be necessary to withdraw the sheath for stent deployment, possibly even out of the MPA, while tightening the purse-string. Self-expandable stents can be deployed directly from the sheath tip and do not require sheath withdrawal; however, their shortest available length of 20 mm precludes their use in very small patients. Although most operators prefer self-expandable stents, balloon-expandable stents appear to perform equally well. Self-expandable stents have the advantage of unobstructed ductal flow during deployment. However, balloon inflation to deploy balloon-mounted stents is short in duration and usually not associated with significant hemodynamic disturbance. Balloon expandable stents also allow later redilation to account for growth. Minor positional adjustments during deployment are possible with both stent types. Although it is desirable to keep the stent as short as possible, longer stents offer more margin of error in positioning and prevent distal embolization. Placement of short, balloon expandable stents may require deployment of a second overlapping stent to cover the entire ductus. Generally, stent length ranges from 12 mm for premature infants to 20 mm for term infants. Stent diameter ranges from 5 mm for premature infants to 9 mm for term infants (typically 8 mm). The stent diameter is selected to exceed the smallest duct diameter by 1 to 2 mm and to be in good apposition to most of the ductal wall. Self-expandable stents are more suitable for unusual ductal curvature but tend to straighten with time. Stent misplacement or dislodgment is best prevented by careful initial measurements and proper stent selection. Otherwise, stent misplacement can sometimes be corrected by re-inflating the balloon inside the stent and carefully moving the stent/balloon assembly into a more favorable position. A baseline echocardiographic study with estimation of the velocity across the stented ductus, and examination of the retrograde flow in the aortic arch, is performed at the end of the procedure.
      It should be emphasized that accurate delineation of the ductal anatomy is extremely important before deployment of the ductal stent. If the stent does not cover the entire length of the ductus, this will likely result in ductal narrowing and systemic outflow obstruction. Conversely, if the stent is too long, it could potentially obstruct retrograde flow into the proximal arch and ascending aorta, which could be catastrophic in patients with aortic atresia. LPA = left pulmonary artery; RPA = right pulmonary artery. (Color version of figure is available online at http://www.optechtcs.com.)

      Special Considerations

      Atrial Septum

      According to hemodynamic and echocardiographic data, adequacy of the atrial septal communication is assessed. Routine echocardiographic assessment is done on arrival to the intensive care unit and weekly until discharged. Usually there is an adequate size defect and no immediate intervention is necessary. Subsequently a balloon septostomy or atrial stent deployment is performed in the cardiac catheterization laboratory as needed. In the presence of important restriction (mean gradient >5 mm Hg) or nearly intact atrial septum, this is addressed immediately after birth. The ductus is then kept open with a PGE1 infusion, and pulmonary artery banding is not performed until the pulmonary vascular resistance drops, as evidenced by increasing retrograde diastolic flow through the ductus, clearing of the chest X-ray, and a decrease in oxygen requirement.

      Retrograde Flow in the Aortic Arch

      In patients with aortic atresia, the coronary and brachiocephalic perfusion depends on retrograde flow across the arch. Due to reports of interstage death, increased attention has been paid to the characteristics of the retrograde flow through the distal arch opening into the juxtaductal area. Although no conclusive data are available, increased velocity of retrograde flow or a distal arch opening less than 2.5 mm on echocardiogram either pre- or posthybrid palliation has prompted consideration for the empiric placement of a MPA to innominate artery shunt, or performing a Norwood procedure.

      Combined Stage II Reconstruction

      Figure thumbnail gr4
      Figure 4Stage II reconstruction is performed at 4 to 6 months of age, following complete hemodynamic, angiographic, and echocardiographic evaluation. Stage II reconstruction consists of amalgamation of the proximal ascending aorta with the main pulmonary artery, removal or resection of the ductus/stent complex, aortic arch reconstruction, atrial septectomy (with or without removal of atrial septal stent), removal of the branch pulmonary artery bands with arterioplasty if necessary, and superior cavopulmonary connection. Central venous catheters are avoided and transesophageal echocardiography is routinely used.
      Following a redo sternotomy, the patient is cannulated for cardiopulmonary bypass using a single venous cannula. Most commonly the arterial cannula is placed in the proximal MPA. Cooling on cardiopulmonary bypass to 18°C is initiated and the branch pulmonary arteries are occluded with tourniquets. The brachiocephalic vessels are mobilized and encircled with snares in preparation for deep hypothermic circulatory arrest. The aorta, main pulmonary artery, and the stented ductus are mobilized. As there may be evidence of resolving inflammation or fibrosis surrounding the ductal area, care should be exercised to avoid injury to the left recurrent laryngeal nerve, which can be adherent in this area.
      Figure thumbnail gr5
      Figure 5(A) After deep hypothermia is reached, circulatory arrest is instituted; the brachiocephalic vessels are occluded with tourniquets, and cannulae are removed. Then crystalloid cardioplegia is administered in the aortic root. An atrial septectomy is performed through the atrial cannulation site. If an atrial stent has been previously placed, this is removed through a limited right atriotomy. As the stent is usually intimately adherent to the atrial septum, particularly in the presence of a thick and muscular septum, it is excised with a margin of tissue. An incision is made using a number 11 blade, parallel to the plane of the stent, starting at 11 or 12 o'clock according to the surgeon's view. Once the left atrium has been entered, the resection is carried under direct visualization around the perimeter, close to the stent to avoid injury to adjacent structures. After removal of the stent, care is taken to eliminate any loose debris. The right atriotomy is then closed with a running 5-0 Prolene suture. In the case in which a hemi-Fontan superior cavopulmonary connection is to be performed, removal of the stent is postponed, and the stent is removed through the opening in the dome of the right atrium at the time of the hemi-Fontan connection. (B) Stent removed from the atrial septum with a cuff of muscle. Note that the entire length of the stent has been covered with atrial septal tissue, becoming a conduit rather than an open cell structure. ASD = atrial septal defect; SVC = superior vena cava. (Color version of figure is available online at http://www.optechtcs.com.)
      Figure thumbnail gr6a
      Figure 6(A) After transection of the MPA proximal to its bifurcation, the ductal stent is visualized and removed while providing traction with a forceps. In some cases the deposition of neointima on the stent is minimal, so the stent can be easily retrieved (“endarterectomy-like”), removing much of the stent either bare or partially covered with intima and a portion of the media without disruption of the ductal wall. (B) Specimen of self-expandable stent removed by partial endarterectomy of the ductus. (C) As the posterior aortic wall remains intact, less mobilization is required; therefore, the aortic arch reconstruction is facilitated, unless a prominent coarctation shelf requires resection. The residual ductus is resected at both the pulmonary and the aortic ends. The opening left at the aortic end is then extended distally about 1 to 2 cm into the descending aorta and proximally along the underside of the aortic arch toward the sinotubular junction. The isthmus of the aorta is inspected for the presence of residual neointimal flaps or a coarctation shelf. (Color version of figure is available online at http://www.optechtcs.com.)
      Figure thumbnail gr6b
      Figure 6(A) After transection of the MPA proximal to its bifurcation, the ductal stent is visualized and removed while providing traction with a forceps. In some cases the deposition of neointima on the stent is minimal, so the stent can be easily retrieved (“endarterectomy-like”), removing much of the stent either bare or partially covered with intima and a portion of the media without disruption of the ductal wall. (B) Specimen of self-expandable stent removed by partial endarterectomy of the ductus. (C) As the posterior aortic wall remains intact, less mobilization is required; therefore, the aortic arch reconstruction is facilitated, unless a prominent coarctation shelf requires resection. The residual ductus is resected at both the pulmonary and the aortic ends. The opening left at the aortic end is then extended distally about 1 to 2 cm into the descending aorta and proximally along the underside of the aortic arch toward the sinotubular junction. The isthmus of the aorta is inspected for the presence of residual neointimal flaps or a coarctation shelf. (Color version of figure is available online at http://www.optechtcs.com.)
      Figure thumbnail gr7a
      Figure 7(A) Alternatively, if the stent cannot be removed by pulling, the ductus arteriosus/proximal descending aorta complex is resected, which commonly disrupts the continuity of the posterior aorta. As the entire juxtaductal area is removed, this provides an ample coarctectomy. The underside of the aortic arch is opened in a retrograde fashion toward the sinotubular junction. (B) Following extensive mobilization of the descending aorta, aortic arch, and brachiocephalic vessels, the posterior aortic wall is reconstructed without tension using a 5-0 Prolene suture. Adequate mobilization is extremely important not only to avoid bleeding or disruption of the anastomosis but also to prevent compression on the left mainstem bronchus. The aortic arch is reconstructed using a gusset of pulmonary artery homograft. Depending on the exposure and anatomy, the reconstruction can be performed using regional cerebral perfusion by placing the arterial cannula through a purse-string at the base of the innominate artery, or directly into the innominate lumen, while the cannula is secured in place with a tourniquet. Placement of an angled coarctation clamp on the distal thoracic aorta can facilitate the exposure and prevents backbleeding into the field. In this case venous return is established with a single venous cannula in the right atrium, or separate cannulation of the superior vena cava, if a bidirectional Glenn is planned. Subsequently, the ascending aorta is amalgamated with the proximal MPA using a 5-0 Prolene suture, and the aortic reconstruction is completed. As in the previous scenario, the arch reconstruction is performed using a patch of cryopreserved pulmonary artery homograft, which is anastomosed to the amalgamation between the ascending aorta and main pulmonary artery. Systemic and myocardial perfusion are re-established while warming to 30°C is initiated.
      The bands on the branch pulmonary arteries are removed using sharp dissection to take down all adhesions. The bands usually come off easily, leaving minimal residual distortion. Through the distal main pulmonary artery, the branches are gently probed with dilators to estimate their true size. The distal MPA is then patch-closed with cryopreserved pulmonary artery homograft using a running 5-0 Prolene suture. Similarly, the opening of the pulmonary end of the ductus is inspected for loose intima or neointima and closed in a similar manner, assuring no areas of stenosis.
      Figure thumbnail gr7b
      Figure 7(A) Alternatively, if the stent cannot be removed by pulling, the ductus arteriosus/proximal descending aorta complex is resected, which commonly disrupts the continuity of the posterior aorta. As the entire juxtaductal area is removed, this provides an ample coarctectomy. The underside of the aortic arch is opened in a retrograde fashion toward the sinotubular junction. (B) Following extensive mobilization of the descending aorta, aortic arch, and brachiocephalic vessels, the posterior aortic wall is reconstructed without tension using a 5-0 Prolene suture. Adequate mobilization is extremely important not only to avoid bleeding or disruption of the anastomosis but also to prevent compression on the left mainstem bronchus. The aortic arch is reconstructed using a gusset of pulmonary artery homograft. Depending on the exposure and anatomy, the reconstruction can be performed using regional cerebral perfusion by placing the arterial cannula through a purse-string at the base of the innominate artery, or directly into the innominate lumen, while the cannula is secured in place with a tourniquet. Placement of an angled coarctation clamp on the distal thoracic aorta can facilitate the exposure and prevents backbleeding into the field. In this case venous return is established with a single venous cannula in the right atrium, or separate cannulation of the superior vena cava, if a bidirectional Glenn is planned. Subsequently, the ascending aorta is amalgamated with the proximal MPA using a 5-0 Prolene suture, and the aortic reconstruction is completed. As in the previous scenario, the arch reconstruction is performed using a patch of cryopreserved pulmonary artery homograft, which is anastomosed to the amalgamation between the ascending aorta and main pulmonary artery. Systemic and myocardial perfusion are re-established while warming to 30°C is initiated.
      The bands on the branch pulmonary arteries are removed using sharp dissection to take down all adhesions. The bands usually come off easily, leaving minimal residual distortion. Through the distal main pulmonary artery, the branches are gently probed with dilators to estimate their true size. The distal MPA is then patch-closed with cryopreserved pulmonary artery homograft using a running 5-0 Prolene suture. Similarly, the opening of the pulmonary end of the ductus is inspected for loose intima or neointima and closed in a similar manner, assuring no areas of stenosis.
      Figure thumbnail gr8
      Figure 8A completed reconstruction is shown. A superior cavopulmonary connection is created to establish a source of pulmonary blood flow while normalizing the volume work of the ventricle. A bidirectional Glenn is performed at the site of the RPA band, effectively repairing any potential deformity of this vessel. To reduce the length of the circulatory arrest and simplify the surgery, a bidirectional Glenn is preferred to a hemi-Fontan connection. It should be noted that, based on our experience and to minimize the possibility of important postoperative hypoxemia, the decision to carry out a superior cavopulmonary connection at this stage is made during the surgery, and only if the procedure has progressed without significant issues. Due to the lengthy cardiopulmonary bypass necessary for this procedure, it is not uncommon to encounter some degree of postoperative pulmonary dysfunction. As a consequence, oxygen requirement is higher than after a routine bidirectional Glenn. A milrinone infusion and nitric oxide are used routinely.

      Comments

      The use of ductal stenting and bilateral pulmonary artery banding offers a number of attractive features as the initial intervention for HLHS. It avoids the need for an extensive surgical procedure in the newborn period and combines the major reconstructive surgery with a less demanding physiology at a later date. It also avoids the use of cardiopulmonary bypass and circulatory arrest in the neonate; this is particularly important in patients who have suffered severe preoperative circulatory collapse and present with multi-organ dysfunction. At the same time, the hybrid approach eliminates the need for an immediate decision regarding the possibility of biventricular repair in patients with borderline anatomy and provides appropriate palliation while extending the waiting period for patients in need of heart transplantation. Due to these features, the hybrid approach continues to gain interest, and its implementation continues to evolve. Increasing experience and longer follow-up will allow additional technical improvements and the refinement in patient selection necessary to achieve better outcomes.

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