Univentricular Heart: Management Options

Transcription

1 Ref. 172/05 Article No. 9 June Symposium on Pediatric Cardiology-I Univentricular Heart: Management Options Usha Krishnan Pediatric Cardiology, NY Medical College, Maria Fareri Children Hospital, Valhalla, NY. Abstract. The term Univentricular Heart encompasses a wide variety of heart defects that functionally and physiologically constitute a single ventricular chamber. The terminology univentricular repair is frequently used in the surgical literature to include those biventricular hearts that are not amenable for a final two ventricle repair and need to go through the same surgical stages as with a functionally univentricular heart, culminating finally in a total cavo-pulmonary connection. Broadly, treatment is focused on controlling the pulmonary blood flow in early infancy, by means of aorto-pulmonary shunting in pulmonary atresia or stenosis, and pulmonary artery banding or pulmonary artery disconnection with aorto-pulmonary shunt placement in high pulmonary blood flow situations. Concomitant repair of other associated conditions is required. Babies with hypoplastic left heart physiology undergo staged Norwood repair resulting in an eventual total cavo-pulmonary connection with the RV functioning as the systemic ventricle. In this review, medical and surgical management of these patients will be discussed, after a brief discussion of nomenclature, anatomic and physiologic considerations. [Indian J Pediatr 2005; 72 (6) : ] Key words: Univentricular heart; Superior and total cavo-pulmonary connections; Norwood repair; Bi-directional Glenn and Fontan procedures. Univentricular heart (UVH) is a term used to describe a wide variety of structural cardiac abnormalities associated with a functional single ventricular chamber. 1 There has been considerable controversy over the nomenclature and classification of these complex conditions. 1-4 Van Praagh et al define UVH as one ventricular chamber that receives both tricuspid and mitral valves or a common atrioventricular (AV) valve. 2 Anderson et al suggest that the entire atrioventricular junction is connected to one ventricular mass, thus including hearts with tricuspid or mitral atresia, which are excluded in Van Praagh s definition. 1,4 The consensus of the STS- Congenital Heart Surgery and the European study group database proposed that the nomenclature of UVH should include double inlet left and right ventricles, absence of one AV connection, common AV valves, and hearts with only one well developed ventricle as unbalanced AV canal and complex conditions with heterotaxy syndromes. 3 This incorporates both the segmental approach by Van Praagh and the sequential approach by Anderson, and uses a descriptive format to define the anatomy in such patients. This nomenclature does not include hypoplastic left heart syndrome (HLHS), pulmonary atresia with intact ventricular septum and certain other biventricular hearts which also undergo the stages of univentricular repair. Medical management of these patients requires a thorough understanding of the physiology of these conditions which in turn is dependent on the anatomy. The reader is referred to various excellent textbooks and Correspondence and Reprint requests : Dr. Usha Krishnan, Asst Professor, Pediatric Cardiology, NY Medical College, Maria Fareri Childrens Hospital, 618 Munger Pavilion, Valhalla, NY Fax : review articles for morphology and classification of UVH. The physiology of UVH in a neonate depends upon certain key anatomical factors. These are: 1. Obstruction to systemic or pulmonary outflows. 2. Obstruction to ventricular inflow and atrial septum and abnormal systemic or pulmonary venous return. 3. Amount of pulmonary blood flow and pulmonary vascular resistance. 4. A-V valve regurgitation. OBSTRUCTION TO SYSTEMIC OUTFLOW When there is severe obstruction to systemic outflow (HLHS and its variants, UVH with severe aortic valve or arch obstruction), the neonate is dependent on the ductus arteriosus for maintaining systemic output. If the diagnosis is made antenatally, delivery should be conducted at a center capable of neonatal surgery, and the baby started on prostaglandin E2 (PGE2) immediately after birth, in order to maintain ductal patency. If undiagnosed previously, these infants often have a catastrophic presentation, with severe acidosis and shock, secondary to ductal closure and loss of cardiac output. Therefore, a high index of suspicion is necessary to seek out congenital heart disease as a cause of such presentation, and to differentiate it from sepsis or neonatal metabolic problems leading to acidosis and shock. These babies are usually asymptomatic during the first few days of life until the ductus closes down. A careful 4 limb blood pressure evaluation done prior to discharge from the newborn nursery may reveal a discrepancy between arms and legs, and suggest further Indian Journal of Pediatrics, Volume 72 June,

2 Usha Krishnan evaluation. Four limb pulse oximetry is an important investigation and an oxygen saturation difference between the upper and lower limbs suggests pulmonary origin of the leg blood supply, even before ductal closure and BP differences become apparent. This would facilitate diagnosis of these patients at an appropriate time, even before the PDA closes and clinical deterioration sets in. 5 Physiologically, there is complete mixing of blood within the heart at the atrial and ventricular levels, with all the blood ejected through the pulmonary valve and distributed to the pulmonary and systemic beds by the pulmonary artery branches and PDA respectively. 6 The balance of resistances in these 2 circulations determines the blood flow. OBSTRUCTION TO PULMONARY OUTFLOW: UVH with critical pulmonary outflow obstruction (usually in the form of pulmonary atresia) is an important ductal dependent neonatal congenital heart disease. If associated with heterotaxy syndromes, there may be other critical associated abnormalities of systemic and pulmonary venous return and systemic abnormalities. 1,2 Presentation is usually not as catastrophic as with HLHS, as the neonatal cyanosis is often apparent as the PDA starts to close, and diagnosis may be made prior to hospital discharge. Pulse oximetry done prior to hospital discharge will detect cyanosis before it gets apparent to the naked eye and suggest further evaluation before cardiac decompensation occurs. 5 In this situation, there is complete mixing of blood within the heart and the degree of cyanosis depends on the severity of pulmonary stenosis. Once the ductus is opened using PGE2, the pulmonary and systemic circulations become interdependent on each other, and the resistances in the two circulations determine the amount of flow. Additionally, anatomic obstructions along the pulmonary vascular tree would further influence pulmonary blood flow and distribution. OBSTRUCTION TO SYSTEMIC OR PULMONARY VENOUS RETURN OR VENTRICULAR INFLOWS: Systemic and pulmonary venous abnormalities are often seen in association with other complex congenital cardiac anomalies and especially with heterotaxy syndrome. 7,8 Pulmonary venous obstructions cause severe pulmonary hypertension because of backpressure into the pulmonary capillary bed and need to be detected early and corrected during surgery. 8 Severe mitral or tricuspid stenosis or atresia may be a component of the UVH. In order to ensure unobstructed communication between the two venous inflows and the single ventricular chamber, an unrestricted atrial septal defect is necessary for egress of blood from the atrial chamber with the obstructed valve. In the presence of mitral atresia, a restrictive ASD acts physiologically similar to pulmonary venous obstruction and leads to elevated pulmonary vascular resistance from back pressure. Similarly, in tricuspid atresia, a restrictive ASD causes signs of systemic venous obstruction. The atrial septal defect needs to be widened either by balloon septostomy prior to surgery or by surgical resection of the atrial septum during the first stage of repair. IDEAL PULMONARY BLOOD FLOW. An ideal patient with UVH should have good ventricular function, unobstructed venous return, unrestrictive ASD and optimal pulmonary blood flow. 9 This situation is rarely found in patients with UVH variants and PS, where the amount of pulmonary blood flow is just enough to prevent severe cyanosis as well as avoid development of pulmonary vascular disease. Patients with tricuspid atresia and pulmonary stenosis occasionally have optimal pulmonary flow which allows for the patient to wait and undergo a superior cavo-pulmonary connection or even a direct Fontan procedure during early childhood, without going through staged repair. Such fortuitous situations are not common. In patients with aortic obstruction, often pulmonary blood flow is unrestricted and since the pulmonary and systemic outputs are interdependent, this situation leads to excessive pulmonary blood flow and consequently, low cardiac output and hemodynamic decompensation. Similarly, when the ductus is kept open, to supply either the systemic or pulmonary circulation, the patient s pulmonary blood flow has to be very carefully fine tuned in the pre-operative period in order to maintain appropriate cardiac output. 6 THE GOAL OF CORRECTIVE PROCEDURES The single most important principle in UV circulation is that the systemic and pulmonary circulations balance each other and this critical balance is maintained by the ratios of the respective resistances. The goal of initial surgical palliation is to provide unobstructed systemic outflow, restricted pulmonary blood flow to maintain normal pulmonary pressures and unobstructed systemic and pulmonary venous return to the heart. Patients with UVH and pulmonary atresia or critical stenosis undergo aortopulmonary shunting. If the pulmonary vascular tree is suspected to be inadequate or abnormal, a pre-operative angiography to delineate the pulmonary arterial tree is performed. The smallest size shunt that will allow enough pulmonary circulation to maintain saturations in the low 80s is placed. Management in the ICU involves ventilator care and manipulating the systemic Vs pulmonary resistances especially if a larger size shunt is placed. In such situations, the baby may need diuresis and anti failure management in the initial few months until the baby grows into the shunt. Very small shunts run the risk of acute blockade and thrombosis and usually babies with 520 Indian Journal of Pediatrics, Volume 72 June, 2005

3 Univentricular Heart: Management Options shunts are maintained on aspirin for its anti-platelet effect. A baby with pulmonary atresia and pulmonary circulation solely via aortopulmonary collaterals is a potentially difficult management situation as surgery would entail unifocalization of the collaterals along with staged procedures leading to a total cavo-pulmonary connection (TCPC). Such procedures are exceedingly high risk and may not be feasible or advisable in our setting. Such babies may be referred for a heart- lung transplant in the Western world and there is very high mortality awaiting transplant as well as following it. The patient then undergoes the next stage of procedure, the Bi-directional Glenn or the superior cavopulmonary shunting at around 6 months of age. Cardiac catheterization is performed in many centers to evaluate the pulmonary pressures and anatomy of the pulmonary tree and to occlude aortopulmonary collaterals that may complicate the post- Glenn course. Careful attention to the systemic venous anatomy is necessary, especially evaluation for the presence of a left sided SVC or a levoatrio-cardinal vein and its communication with the right SVC is necessary (using a balloon occlusive injection in the innominate vein). If such a vein is found, with adequate communication with the SVC, it is closed at the time of surgery. If there is no communicating vein, then a bilateral bi-directional Glenn is performed, connecting the LSVC to the LPA and RSVC to RPA. Any obstructions or distortions to the pulmonary tree because of the previous shunt or native anatomy are corrected during this repair. Opinions vary on the advisability of leaving some forward flow through the pulmonary valve creating a pulsatile Glenn. 10 Proponents argue that the pulsatility allows continues normal growth of the pulmonary tree, whereas opponents contend that the additional blood flow hampers the smooth flow from the SVC to the pulmonary arteries by increasing the pulmonary artery pressures and creating competing flow. The final stage of conversion from a parallel circulation to one in series is the total cavo-pulmonary connection (TCPC) or Fontan procedure. This is ideally performed between 18 months to 4 years of age. Most anatomical details are obtained on echocardiography, including a-v valve competence and adequacy; inter-atrial communication adequacy, systemic and pulmonary venous return and presence of collaterals. Cardiac catheterization is performed in most centers to evaluate the pulmonary pressures and resistances, to occlude aorto-pulmonary or systemic venous collaterals and evaluate ventricular function and end diastolic pressures. TCPC can be performed using either extra cardiac conduit between the IVC to the PA or an intracardiac baffle. 11 The extra cardiac TCPC is now the procedure of choice in most centers as studies have shown a reduced incidence of new onset arrhythmias as compared to the lateral tunnel procedure. 11 A fenestration is usually placed in between the conduit and the atrium to allow for a pop off especially during the early postoperative period, when the PA pressures may be higher and thus pressures in the venous circuit. This has been shown to reduce the incidence and length of effusions which are related to high venous pressures and early Fontan failures. 12 Patients may run lower oxygen saturations due to right to left shunting across the fenestration. These fenestrations can be closed with devices, using transcatheter techniques, months to years later, once systemic venous pressures are demonstrated to be low by cardiac catheterization. 13 Patients without fenestrated TCPC may need a subsequent fenestration performed because of long standing effusions. Some centers perform a transcatheter completion of Fontan, where a covered stent from the SVC to the IVC is used to complete the Fontan baffle. 14,15 Such patients are prepared during the Glenn or hemi Fontan stage, by leaving the SVC to RA connection intact and patch closing the atrial opening, for a future transcatheter completion. Long term complications following TCPC include atrial and ventricular arrhythmias, heart blocks needing dual chamber pacing, protein losing enteropathy, development of venovenous and arteriovenous communications, worsening a v valve incompetence and ventricular failure leading to death or needing cardiac transplantation. Patients with unrestricted pulmonary as well as systemic blood flow need initial palliation by means of either PA banding or PA disconnection with creation of an aortopulmonary shunt to limit pulmonary blood flow and achieve normal pulmonary artery pressures. 16,18 Placing a band may lead to development of sub aortic stenosis or narrowing of a bulboventricular foramen, and may need to be tackled in the second stage surgery by either sub aortic resection or a Damus Kaye Stansel procedure. 16 It has been shown that long standing PA bands are associated with worse outcomes after the Fontan procedure. 18 It may be difficult to accurately judge the effectiveness of a band in restricting pulmonary circulation, especially in very young infants with high pulmonary resistances. Even though such infants are allowed to grow into their bands, the residual pulmonary pressures and resistances may be high and lead to a much worse outcome after completion of Fontan. 19 It has been suggested by Chowdhury et al that patients with mean PA pressures more than 25mm and resistance more than 4 wood units are poor candidates for TCPC, with high morbiditiy and mortality, and the PA banding should be considered as final palliation in such patients. 19 Systemic Outflow obstructions associated with UVH usually necessitate Norwood Procedure or its variations for repair. (Fig 1) The Norwood repair involves conversion of the pulmonary artery into the systemic artery or neo-aorta. The small native aorta is anastomosed to the neo aorta and serves to carry blood retrograde to the coronary arteries. The aortic arch is augmented and then connected to the neoaorta. The branch pulmonary arteries are transected and connected to the systemic circulation by means of a Gore-Tex shunt. 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4 Usha Krishnan Fig 1. Diagrammatic Representation of the Norwood Stage 1 surgery for Hypoplastic left heart syndrome, involving connection between the PA and the dimunitive ascending aorta, arch repair and aorto-pulmonary shunting, with PA distally disconnected. Fig 2. Diagrammatic Representation of the Hybrid Procedure, Ductal stenting to create the arch, ASD stenting to keep the ASD open, bilateral branch PA banding. Fig 3. Norwood stage 2- Bilateral SVC-PA Connection (Glenn) Fig 4. Stage 3: Extracardiac total cavo-pulmonary connection (Fontan) 522 Indian Journal of Pediatrics, Volume 72 June, 2005

5 Univentricular Heart: Management Options Fig. 5. Pulmonary angiogram revealing the stented ductal arch, and banded branch Pas, constituting the hybrid procedure. Fig. 6. Same patient, after an ASD stent placement to keep the closing foramen open. The smallest shunt size to supply enough pulmonary blood flow to maintain normal PA pressures and systemic circulation in the high 70s to low 80s is placed. The baby is ventilated in the post operative period with a strategy to maintain the PCO2 in the 50s and PO2 in the 40s range. This ensures that the pulmonary arterial resistance is maintained on the higher side, to prevent pulmonary over circulation, which would be at the expense of systemic output. A recent modification of this procedure, popularized by Sano et al involves using a RV to PA Gore-Tex shunt to supply the pulmonary arteries rather than an aorto-pulmonary shunt. 20 This modification has been shown by Norwood himself, to improve the outcome and make postoperative ventilation easier to handle. 21 The RV to PA shunt avoids the diastolic run-off that happens in aorto-pulmonary shunts, which lead to compromised coronary flow and poor ventricular myocardial perfusion and ultimately death. 20,21 A combined catheterization and surgical approach to achieve the same goals has been performed in some centers. 22 In this hybrid approach, the neo-aortic arch is created by stenting the ductus (Figure 2). This ensures continued presence of a ductal arch to function as a new systemic arch. The arch vessels and coronaries are perfused by reterograde flow. The atrial septal defect is widened by septostomy or stenting the ASD if required. The branch pulmonary arteries are initially individually banded in a closed heart procedure, to limit pulmonary blood flow. This hybrid procedure offers the physiological results of a Norwood surgical procedure, without subjecting these ventricles to cardio-pulmonary bypass, and the neonate to deep hypothermic circulatory arrest. To date, this procedure has been used in higher surgical risk babies- namely, those with ventricular dysfunction, late presentation in shock or prolonged acidosis and those with very diminutive ascending aortas where repair may be associated with very high mortality. In the future, as further data is obtained, the risks and benefits of this procedure will become more apparent. The second stage of Norwood procedure, namely the superior cavo-pulmonary connection is guided by the same principles as previously mentioned. When the transcatheter procedure is used for the first stage, the second stage repair becomes more complex, involving extensive aortic reconstruction, as well as pulmonary artery reconstruction, and removal of the ductal (and atrial) stents. The final stage of Norwood procedure is the TCPC with resultant separation of the systemic and pulmonary circulations. It must be noted that the long term outlook for a single left ventricle is better than a single ventricle of RV morphology. In conclusion, the clinical presentation in patients with a single ventricle depends on the physiology of the systemic and pulmonary circulations. A thorough knowledge of the anatomic variables involved, anticipatory management of the problems involved is required for improvement in outcome. Balance of the systemic and pulmonary circulations to maintain cardiac output and oxygenation is necessary both in the pre and post-operative periods in the neonate with UVH. Management of subsequent stages of repair has also undergone multiple modifications, with the goal of achieving a perfect palliation and prevention of long term complications associated with the Fontan procedure. Indian Journal of Pediatrics, Volume 72 June,

6 Usha Krishnan REFERENCES 1. Anderson RH, Cook AC. Morphology of the functionally univentricular heart. Cardiol Young 2004; 14 (Suppl. 1): Van Praagh R. Nomenclature and classification: Morphologic and segmental approach to diagnosis. In: Moller JH, Hoffman JIE (eds). Pediatric Cardiovascular Medicine. New York, Churchill Livingstone 2000, pp Jacobs ML, Mayer JE Jr. Congenital Heart Surgery Nomenclature and Database Project: single ventricle. Ann Thorac Surg 2000; 69(4 Suppl):S Anderson RH, Becker AE, Tynan M, Macartney FJ, Rigby ML, Wilkinson JL. The univentricular atrioventricular connection: getting to the root of a thorny problem. Am J Cardiol 1984; 54(7) : Hoke TR, Donohue PK, Bawa PK, Mitchell RD, Pathak A, Rowe PC, Byrne BJ. Oxygen saturation as a screening test for critical congenital heart disease: a preliminary study. Pediatr Cardiol 2002; 23(4) : Nelson DP, Schwartz SM, Chang AC. Neonatal physiology of the functionally univentricular heart. Cardiol Young 2004; 14 Suppl. 1 : Heinemann MK, Hanley FL, Van Praagh S, Fenton KN, Jonas RA, Mayer JE Jr, Castaneda AR. Total anomalous pulmonary venous drainage in newborns with visceral heterotaxy. Ann Thorac Surg 1994; 57(1) : Ishiwata T, Kondo C, Nakanishi T, Nakazawa M, Imai Y, Momma K. Non obstructive ASD creation to qualify patients for the Fontan operation: effects on pulmonary hypertension due to restrictive left atrioventricular valve and interatrial communication. Catheter Cardiovasc Interv 2002; 56(4) : Sharma R. Surgical therapy for the univentricular heart. Indian J Pediatr 2000; 67(7) : Caspi J, Pettitt TW, Ferguson TB Jr, Stopa AR, Sandhu SK. Effects of controlled antegrade pulmonary blood flow on cardiac function after bidirectional cavopulmonary anastomosis. Ann Thorac Surg 2003; 76(6) : ; discussion Nurnberg JH, Ovroutski S, Alexi-Meskishvili V, Ewert P, Hetzer R, Lange PE. New onset arrhythmias after the extracardiac conduit Fontan operation compared with the intraatrial lateral tunnel procedure: early and midterm results. Ann Thorac Surg 2004; 78(6) : Lemler MS, Scott WA, Leonard SR, Stromberg D, Ramaciotti C. Fenestration improves clinical outcome of the fontan procedure: a prospective, randomized study. Circulation 2002; 105(2) : Goff DA, Blume ED, Gauvreau K, Mayer JE, Lock JE, Jenkins KJ. Clinical outcome of fenestrated Fontan patients after closure: the first 10 years. Circulation 2000; 102(17) : Galantowicz M, Cheatham JP. Fontan completion without surgery. Semin Thorac Cardiovasc Surg Pediatr Card Surg Annu 2004; 7 : Klima U, Peters T, Peuster M, Hausdorf G, Haverich A. A novel technique for establishing total cavopulmonary connection: from surgical preconditioning to interventional completion. J Thorac Cardiovasc Surg 2000; 120(5) : Jensen RA Jr, Williams RG, Laks H, Drinkwater D, Kaplan S. Usefulness of banding of the pulmonary trunk with single ventricle physiology at risk for subaortic obstruction. Am J Cardiol 1996; 77(12) : Bradley SM, Simsic JM, Atz AM, Dorman BH. The infant with single ventricle and excessive pulmonary blood flow: results of a strategy of pulmonary artery division and shunt. Ann Thorac Surg 2002; 74 (3) : Malcic I, Sauer U, Stern H, Kellerer M, Kuhlein B, Locher D, Buhlmeyer K, Sebening F. The influence of pulmonary artery banding on outcome after the Fontan operation. J Thorac Cardiovasc Surg 1992; 104(3) : Chowdhury UK, Airan B, Kothari SS, Sharma R, Subramaniam GK, Bhan A, Saxena A, Juneja R, Venugopal P. Surgical outcome of staged univentricular-type repairs for patients with univentricular physiology and pulmonary hypertension. Indian Heart J 2004; 56(4) : Sano S, Ishino K, Kawada M, Honjo O. Right ventriclepulmonary artery shunt in first-stage palliation of hypoplastic left heart syndrome. Semin Thorac Cardiovasc Surg Pediatr Card Surg Annu 2004; 7 : Pizarro C, Norwood WI. Right ventricle to pulmonary artery conduit has a favorable impact on postoperative physiology after Stage I Norwood: preliminary results. Eur J Cardiothorac Surg 2003; 23(6) : Akintuerk H, Michel-Behnke I, Valeske K, Mueller M, Thul J, Bauer J, Hagel KJ, Kreuder J, Vogt P, Schranz D.Stenting of the arterial duct and banding of the pulmonary arteries: basis for combined Norwood stage I and II repair in hypoplastic left heart. Circulation 2002; 105(9) : Indian Journal of Pediatrics, Volume 72 June, 2005