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Suporte circulatório mecânico em ICC em pediatria


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Suporte circulatório mecânico em ICC em pediatria

  1. 1. Indian Heart J 2006; 58: 345–349 345 Seminar INTRODUCTION Acute heart failure commonly occurs in children as a result of hemodynamic insults imposed on the heart by structural defects or in a structurally normal heart with myocarditis. Aggressive treatment of even the most complex congenital heart disease (CHD) is being championed with ever-improv- ing results. Despite good repair, these patients go through various periods of refractory low cardiac output and form an expanding substrate for short-term mechanical support. Various indications for pediatric mechanical support are enumerated in Table 1. When present, acute heart failure in children justifies aggressive therapy because of the high potential for complete recovery. Extracorporeal life support organization (ELSO) data stands testimony to this.1 The international summary for patients on extracorporeal life support (ECLS) for cardiac failure showed that 57% of neonates and 58% of pediatric patients survive ECLS with 38% of neonates and 43% of pediatric patients surviving to hospital discharge or transfer. Achieving circulatory support in the pediatric practice is confounded by the wide range of patient size, the small size and fragility of the vasculature along with significant anatomic variations which may affect cannulation. Finally, heart failure in the pediatric population is often biventricu- lar and is commonly associated with pulmonary dysfunc- tion. The rationale for use of and the devices available for circulatory support are discussed. Why Mechanical Support? Long bypass and aortic cross-clamp ischemia along with an exaggerated inflammatory response for complex cardiac defects, leads to myocardial incompetence presenting as low cardiac output. Further, because of a labile and reactive pulmonary bed, the right ventricle is subjected to variable decrease of after-load excesses, which displaces the inter- ventricular septum to the left impairing left ventricular filling and systolic functions. Post-cardiopulmonary bypass (Post-CPB), cyanotic hearts also tend to be more edema- tous, which impacts coronary perfusion and diastolic and systolic functions. This reperfusion-insulted and energy-depleted stunned myocardium has the potential to recover if given the right support. Unfortunately instinctive support is provided by increasing dosages of pharmacological agents, which further aggravate the myocardial injury. Catecholamines cause variable increase in after-load excesses and tachycar- dia and increase in contractility leading to an increase in myocardial oxygen demand at a time when supply may be sub-optimal due to low pressure and increased transmy- ocardial gradients. Thus energy stores which are needed for myocardial repair and maintenance of ionic homeostasis are expended in contractile work which can result in signifi- cant ongoing myocardial injury that may compromise or prevent cardiac injury. On the other hand, mechanical support reduces myocardial work thereby preserving energy stores and at the same time it maximizes myocardial delivery. Most devices unload the heart which reduces the Mechanical Circulatory Support for Acute Cardiac Failure in Children: The Options Available Sathiakar Paul Collison, Kulbhushan Singh Dagar Department of Neonatal, Pediatric and Congenital Heart Surgery, Escorts Heart Institute and Research Centre, New Delhi Correspondence: Dr Kulbhushan Singh Dagar, Escorts Heart Institute and Research Centre, Okhla Road, New Delhi E-mail: Table 1. Indications for ventricular assist No cardiotomy Acute changes in congenital heart disease patients Acute myocarditis Decompensated cardiomyopathy (“Bridge to transplant”) Salvage for cardiac arrest Management of intractable destabilizing arrhythmias Hypoxia, destabilizing pulmonary hypertensive crises Post-surgical repair CPB-induced Bridge to recovery post-CPB (e.g., late arterial switch, ALCAPA repair) CPB: cardiopulmonary bypass; ALCAPA: anomalous origin of the left coro- nary artery from the pulmonary artery. IHJ_Article_13.qxd 12/2/2006 5:03 PM Page 345
  2. 2. wall stress, thereby reducing the oxygen demand, and also improves sub-endocardial perfusion. When to Initiate Support Mechanical support is a better methodology for myocardial support and resuscitation in hearts refractory to usual levels of pharmacological support. As with most forms of support, results may be directly related to the threshold at which support is initiated. In some series, survival has been found to be greater when ECLS is instituted some time after successful weaning from CPB.2 However, Aharon et al. reported that the initiation of ECLS in the operation theatre for failure to wean from CPB was associated with better survival.3 More recently Chaturvedi et al. showed that odds of survival were improved if there was initiation of extra- corporeal membrane oxygenation (ECMO) in the theatre (64% survival) rather than in the cardiac intensive unit (29% survival).4 The results may be confounding because of different patient subsets and ideologies. However, it is amply clear that if anatomic correction is adequate, early and appropriate support before end-organ injury, severe metabolic derangement occurrence or cardiac arrest can lead to excellent results. INTRA-AORTIC BALLOON COUNTERPULSATION The intra-aortic balloon pump (IABP) is a non-flow generat- ing counter pulsation type of assist. Intra-aortic balloon pump deflation in systole leads to reduced ventricular after-load and ventricular wall stress, thereby improving cardiac perform- ance. Inflation of the balloon in diastole increases the aortic diastolic pressure and hence coronary perfusion and distal runoff (Figure 1). Appreciable measure of the patient’s own cardiac function must be present and the IABP augments this improving cardiac output to the tune of 15–20%. Hence IABP is a poor form of support for total replacement of the function of a ventricle. It is extensively used in the adults where it is a good form of support for coronary flow augmentation. Intra-aortic balloon pump usage in a pediatric popula- tion was first described in 1980s.5 However, its application in children has not been widespread for the following reasons. Unlike adults, an open surgical insertion of the balloon is employed in children.6 The criterion used in selecting a catheter of an appropriate size has been detailed elsewhere.7 Timing of the balloon may be performed by using either electrocardiography tracing or echocardiogra- phy. Recent reports emphasized M-mode echocardiography as the tool to ensure proper timing of balloon inflation and deflation.8 There are also concerns regarding the efficacy of using the IABP in the pediatric population with its high incidence of arrhythmias making optimal timing very diffi- cult. The aorta in children is thought to have greater elastic- ity than that in adults. Hence, much of the energy generated during balloon filling may be transferred to the expansile aorta and diastolic augmentation may be dampened. However, the effect of IABP on systolic unloading of the left ventricle is preserved. Children frequently present with right ventricular failure with or without respiratory failure, both of which cannot be supported by IABP. Hence the role of IABP in pediatric patients is at best restrictive and prob- ably limited to support of isolated left heart failure for short duration. In Pollock’s study, which is the earliest experience of IABP use in children, there was a 43% survival among a group of 14 children.5 Webster and Veasy reported the use of IABP in patients aged between 5 days to 18 years; the smallest child weighed 4.2kg.9 The survival in children aged below 3 years was 75%. Park et al. studied children with left ventricular dysfunction after cardiac surgery and reported 44% survival among those managed with IABP.10 Del Nido et al. reported the successful utilization of IABP support in a 2- kg infant.11 In their series of patients, 37% were long-term survivors. Much of the understanding of the contemporary role of IABP usage and results (Table 2) for Collison and Dagar 346 Indian Heart J 2006; 58: 345–349 Figure 1. Depiction of the aortic systolic and diastolic pressures during a normal cardiac cycle as well as an augmented beat. Table 2. Results of IABP use among individual patient groups Disease Number Survival (%) Medical Cardiomyopathy 8 50 Myocarditis 2 100 HUS 1 100 Blunt trauma 2 100 Surgical ALCAPA 3 100 Fontan 2 100 TOF 3 0 VSD 4 50 Complex conduit repair 4 50 IABP: intra-aortic balloon pulsation; HUS: hemolytic uremic syndrome; ALCAPA: anomalous left coronary artery from pulmonary artery; TOF: tetral- ogy of fallot; VSD: ventricular septal defect. IHJ_Article_13.qxd 12/2/2006 5:03 PM Page 346
  3. 3. temporary mechanical cardiac support in children has come from Pinkey et al.12 Poor results in tetralogy emphasize limitations of IABP in biventricular or predominant right- sided support. EXTRACORPOREAL MEMBRANE OXYGENATION (ECMO) In veno-arterial ECMO (VA-ECMO), the functions of heart and lungs can be partially or totally replaced. A typical ECMO circuit is depicted in Figure 2. Deoxygenated blood is drained from the right atrium through cannula inserted into the internal jugular vein and the blood that has been oxygenated extracorporeally is pumped back into the right common carotid artery, allowing total cardiopulmonary support. Thus, the heart and lung can be bypassed and hence rested, allowing time for the heart to heal in an envi- ronment of normal systemic perfusion and gas exchange. It is this flexibility of the ECMO circuit that makes ECMO versatile in supporting children with acute cardiac failure, where hypoxia, pulmonary hypertension, ventricular failure and cyanosis all contribute to the pathophysiology of acute cardiac failure. It is advisable to maintain moderate levels of ventilator support during ECMO.13 Avoidance of left ventricular distention is essential. When detected, left-sided decompression is achieved by balloon atrial septostomy performed at the bedside under echocardiography guid- ance,14 or surgical insertion of a left ventricular vent. Several studies provide the rationale for the use of ECMO for circulatory support in children.15-25 The central tenets of successful cardiac ECMO are enumerated in Table 3. Besides, any child with cardiac disease who requires increas- ing ventilation or escalating dosages of inotropes with persistent borderline cardiac output and evidence of end- organ failure must be considered for ECMO support. Several studies showed the benefit of early institution of ECMO support over delayed support. Institution of ECMO is contraindicated in the presence of incurable malignancy, advanced multi-systemic organ failure, extreme pre-maturity and severe central nervous system damage. Several centers reported consistent results of ECMO for cardiac failure in children. Overall the weaning rate is 50–80% and hospital survival is 30–70% depending on the underlying diagnoses. In general, two-thirds of patients can be weaned off ECMO and 40% of the original population will eventually survive to hospital discharge.15-25 Table 4 gives details of the results of ECMO, as derived from the ELSO registry.1 Special mention must be made of the emerging role of ECMO in patients with fulminant viral myocarditis. This is an entity that is extremely difficult to manage and affected children have a guarded prognosis. It was believed that a significant percentage of children with acute myocarditis would develop dilated cardiomyopathy, ultimately needing cardiac transplantation. However, current data suggest that the survival rate for children with acute myocarditis can be improved by using ECMO.26,27 The ELSO data suggest that 58% of these patients can be weaned off the support. Another recent multi-centric study reported an overall survival of 80%.28 An important finding of this study was that all non-transplanted survivors were alive with normal ventricular function suggesting that children with acute myocarditis, if successfully supported during the acute phase of the illness, may have an overall favorable outcome. Mechanical Circulatory Support for Acute Cardiac Failure in Children Indian Heart J 2006; 58: 345–349 347 Figure 2. Depiction of a typical veno-arterial ECMO circuit. ECMO: Extracorporeal membrane oxygenation. Table 3. Pre-requisites for cardiac ECMO Potential for myocardial recovery should exist Adequate anatomic repair without residual lesions Appropriately managed associated reversible factors, such as pulmonary hypertensive crises and post-operative myocardial edema The timing of initiation of ECMO in a controlled fashion before circulatory collapse is essential in preventing organ injury ECMO: extracorporeal membrane oxygenation. Table 4. Survival of patients undergoing ECMO for cardiac diseases* Diagnosis Percentage survived Medical Cardiomyopathy 50 Myocarditis 58 Surgical Left to right → R shunt 41 Left-sided obstruction 30 Right-sided obstruction 43 Hypoplastic left heart 32 Cyanotic, increased Qp 40 (TGA) Cyanotic, decreased Qp 40 (tetralogy) *Data from extracorporeal life support organization registry. ECMO: extracorporeal membrane oxygenation; TGA: transposition of the great arteries. IHJ_Article_13.qxd 12/2/2006 5:03 PM Page 347
  4. 4. The need for continued ventilation in an intensive care setting and constraints related to trained manpower and obvious financial implications prevented its widespread use in India. Also, when it is expected that recovery will take longer than a week, the ventricular assist devices (VADs) have an obvious advantage over ECMO. VENTRICULAR ASSIST DEVICES Ventricular assist devices are mechanical pumps that can perform the function of either one or both of the ventricles, restoring perfusion and maintaining end-organ function, while the heart recovers from the precipitating insult.29 The different types of devices available are detailed in Table 5. Ventricular assist devices may be required for right ventric- ular support (RVAD) or for left ventricular support (LVAD). For an LVAD, a Dacron tube graft is inserted into the left ventricular (LV) apex or pulmonary vein and connected to the pump (afferent limb). From the pump, blood is ejected through a Dacron graft into the descending aorta (efferent limb). To maintain unidirectional flow, prosthetic valves are incorporated into both limbs of the circuit. For an RVAD, usually the right articular appendage and the main pulmonary artery are cannulated to create the circuit. Implantation is generally done without CPB, and can be performed either through a median sternotomy or by lateral thoracotomy. Infection, thromboembolic events, bleeding and neurological complications are common. Right-sided circulatory failure can occur in patients supported by an LVAD in 10–15% cases. In spite of optimization of all parameters, the right-sided failure persists. This is an indi- cation for the addition of RVAD. The most commonly used centrifugal device is the para- corporeal Bio-Medicus pump.30 For infants weighing less than 10kg, a 50-ml pump is available; for other children, an 80-ml pump is available. The cannulation required is stan- dard, and as described above, this system can provide support to the right ventricle as well as the left ventricle. Karl et al. reported 34 patients with a median age of 60 days and median weight of 3.7 kg;31 LVAD using a centrifugal device allowed 24–45% survival in these patients. The youngest patient in whom the Bio-Medicus pump has been placed was two days of age and weighed 1.9kg. Pulsatile devices can be located at the bedside, para- corporeally, or may be implantable. These devices, however, can only be used in adolescents with adequate body surface area (BSA) typically >1.5m2 for implantable, and at least > 0.7m2 for paracoporeal devices. Merkle et al. have reported on 45 pediatric patients supported by the Berlin Heart which is the commonest device used in chil- dren.32 Of these, there was 70% survival after separation from the VAD, with long-term survival in 56%. Hetzer et al. used the Berlin Heart system for various indications; the survival rate was 40%.33 The main constraint of VAD in children is the limited space available in the child’s thoracic cavity for these devices, especially in cases requiring biven- tricular support and hence needing four cannulae. However, the Berlin Heart has been used successfully for biventricu- lar support. The results of Medos VAD have been comparable with the Berlin Heart. Konertz et al. managed 12 children with ages between 8 hours and 25 days.33 In their study, the survival for LVAD use was 80% and for RVAD use was 33%. Goldman et al. studied children undergoing bridge to transplantation with the Medos VAD. Fifty-five percent eventually survived transplantation.35 Axial pumps generally consist of electromagnetically coupled, integrated motor-impeller pump assemblies.36 Depending on size, flows up to 3.3 L/min can be achieved. The Jarvik 2000 is approved for implantation in patients with a BSA of 1–1.5 m2 , but so far there has not been any implantation in a pediatric patient.37 The MicroMed Debakey VAD is approved by FDA in USA for use in patients aged between 5–16 years, and can be placed in children with a BSA as low as 0.7m2 .38 Mechanical circulatory support in children will play an ever increasingly important role in the future practice of congenital cardiac surgery. If their full potential is to be utilized, their early use should be integrated into the deci- sion-making cascade for low cardiac output, rather than being relegated to the realm of rescue therapy. More aggressive and earlier implementation of support will lead to superior outcomes. As of today, arteriovenous ECMO holds promise because of its flexibility of use in different age groups and its ability to provide biventricular support along with respiratory support. Its use beyond 5–7 days is associated with poor results. Slow recovery should prompt consideration of switch to VAD as bridge to further recov- ery or transplantation in patients with BSA >0.7 m2 . With miniaturization, axial flow pumps probably hold great promise for pediatric patients. Centrifugal pumps and IABP may have a role for isolated short-term support of the failing ventricle like after ALCAPA (anomalous origin of the left coronary artery from the pulmonary artery) repair or late arterial switch operation. The use of IABP would continue to be anecdotal in pediatric cardiac practice. Devices exclusively for pediatric use like the Pedia Flow VAD (University of Pittsburg), Ensions p CAS, the Pediatric Collison and Dagar 348 Indian Heart J 2006; 58: 345–349 Table 5. Ventricular assist devices (VADs) Device Examples Centrifugal assist devices Medtronic Bio-Medicus pump Axial flow pumps MicroMed Debakey VAD, Pediatric Jarvic 2000 Pulsatile Paracorporeal Berlin Heart VAD, Medos HIA VAD Implantable Thoratec VAD, Heartmate VAD IHJ_Article_13.qxd 12/2/2006 5:03 PM Page 348
  5. 5. Jarvik 200039 are under various stages of development and hold great promise for the future. REFERENCES 1. ECMO registry report: Extra corporeal life support organization. Ann Arbour MI 2004. 2. Walters HI, Hakimi M, Rice MD, et al. Pediatric cardia surgical ECMO: multivariate analysis of risk factors for hospital death. Ann Thorac Surg 1995;60:329–37. 3. Aharon AS, Drinkwater DC, Churchwell KB, et al. ECMO in children after repair of congenital cardiac lesions. Ann Thorac Surg 2001; 72:2095–2102. 4. Chaturvedi RR, Macrae D, Brown KL, et al. Cardiac ECMO for biventricular hearts after pediatric open heart surgery. Heart 2004; 90:545–51. 5. Pollock J, Charlton MC, Williams WG, et al. Intra aortic balloon pumping in children. Ann Thorac Surg 1980;29;522–28. 6. Veasy LG, Webster HF, McGough EC. Intra-aortic balloon pumping. Adaptation for pediatric use. Crit Care Clin 1986;2:237–49. 7. Booker PD. Intra-aortic balloon pumping in young children. Paediatr Anaesth 1997;7:501–07. 8. 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J Thorac Cardiovasc Surg 1996;111:13–18. 37. Frazier OH, Myers TJ, Jarvik RK, et al. Research and Development of an implantable, axial-flow left ventricular assist device: the Jarvik 2000 heart. Ann Thorac Surg 2001;71:125–32. 38. Goldstein DJ. Worldwide experience with the MicroMed De Bakey Ventricular Assist Device as a bridge to transplantation. Circulation 2003;108:1272–77. 39. Baldwin JT, Borovetz HS, Duncan BW, et al. The National Heart, Lung, and Blood Institute Pediatric Circulatory Support Program. Circulation 2006;113:147–55. Mechanical Circulatory Support for Acute Cardiac Failure in Children Indian Heart J 2006; 58: 345–349 349 IHJ_Article_13.qxd 12/2/2006 5:03 PM Page 349