260 e1 ECLS Continuous flow VAD Pulsatile VAD Oxygenator Yes No, but can be added No Anticoagulation ACT 180 200 Heparin 1 aspirin Long term LMWH/warfarin 1 aspirin Heparin 1 aspirin dipyridamole [.]
260.e1 eTABLE PediMACS Approved Devices (Age ,19 Years) 28.3 Device Class Device Brand Paracorporeal continuous Thoratec Centrimag Thoratec Pedimag Maquet Rotaflow Sorin Revolution Implantable continuous HeartWare HVAD HeartMate II LVAD Percutaneous Abiomed Impella 2.5/5.0 Tandem Heart Abiomed Impella CP Total Artificial Heart Syncardia Total Artificial Heart LVAD, Left ventricular assist device eTABLE Extracorporeal Life Support vs Ventricular Assist Devices 28.4 ECLS Continuous-flow VAD Pulsatile VAD Oxygenator Yes No, but can be added No Anticoagulation ACT 180-200 Heparin aspirin Long term: LMWH/warfarin aspirin Heparin aspirin dipyridamole Clopidogrel Long term: LMWH/warfarin aspirin dipyridamole clopidogrel Support Cardiac respiratory Cardiac Cardiac Type of ventricular support Biventricular Uni- or biventricular Uni- or biventricular Ventricular decompression May need LA “venting” Via direct drainage cannula in LA or LV apex Via direct drainage cannula in LV apex Risk of air embolus Low Yes (especially with LVAD) Yes (especially with LVAD) Length of support Short term Short/long term Long term Cannulation site Transthoracic or transcervical Transthoracic Transthoracic ACT, Activated clotting time; ECLS, extracorporeal life support; LA, left atrial; LMWH, low-molecular-weight heparin; LV, left ventricular; LVAD, left ventricular assist device; VAD, ventricular assist device CHAPTER 28 Cardiac Failure and Ventricular Assist Devices 261 B A • Fig 28.6 (A) Berlin Heart biventricular assist device showing apical cannulation, which allows better left ventricular unloading and decreased afterload to the right ventricle 1, Deoxygenated blood flows from the body into the right atrium Because the right ventricle is unable to pump blood into the lungs, the blood goes into the device 2, The blood is pumped out from the device into the pulmonary artery 3, Once the blood is oxygenated in the lungs, it flows into the left atrium Because the left ventricle is unable to pump, the blood goes into the device 4, The Berlin Heart pumps blood into the aorta and systemic circulation (B) Set of cannulas for the Berlin Heart assist device (B, Courtesy Berlin Heart, Inc., The Woodlands, TX.) cohort was lower at 75%, and the risk of neurologic dysfunction was similar at 29% Children were more likely to die on EXCOR support if they had significant renal or hepatic impairment at implantation or RV failure requiring BiVAD support In addition, children weighing less than kg did significantly worse These findings demonstrate that EXCOR survival varies considerably and depends heavily on patient characteristics at implantation, underscoring the need for careful patient selection Specifically, excessive delay in implanting a device until renal, hepatic, or RV function has failed increases the risk of death on EXCOR support, whereas implanting too early may also escalate mortality by unnecessarily exposing children to the risks of support (i.e., stroke, death) Most of the neurologic events are secondary to left atrial cannulation; hence, many centers favor ventricular apical cannulation It is encouraging to note that even within the short 3-year time frame of this study, pediatric centers that have refined their patient characteristics over time are observing significantly lower patient mortality.175,203–205 Continuous-Flow Ventricular Assist Devices Short- to Medium-Term Ventricular Assist Device Support Centrifugal pumps have been available since the late 1970s to support postoperative cardiac failure.206 They have been an effective support for infants and children with myocardial failure from a variety of etiologies (e.g., acute myocarditis, dilated cardiomyopathy, acute transplant rejection, anomalous left coronary artery from the PA).207,208 Centrifugal pumps are used for short-term support and are, in essence, mini-ECLS circuits without an oxygenator The CentriMag VAD (Thoratec Corp.) belongs to a class of magnetically levitated devices operating in a bearingless rotor that floats within a rotating magnetic field Because of its contact-free environment and absence of seals or valves, this device minimizes blood trauma, thrombus formation, and hemolysis It is capable of operating over a range of speeds up to 5500 RPM, generating flows up to 10 L/minute The Thoratec PediMag blood pump, a miniaturized version of the CentriMag, is an extracorporeal circulatory support device providing hemodynamics stabilization for small patients (,10 kg) in need of cardiopulmonary assistance It is cleared for clinical use up to hours; thus, it can be used as a short-term solution to support the circulation while longer-term options are considered The device is capable of flowing up to 1.5 L/min These devices are generally used for short- or intermediateterm support for recovery, conversion to a long-term VAD, or as a bridge to transplant.209,210 Other temporary continuous-flow devices include Jostra Rotaflow (MAQUET Cardiovascular) It is a centrifugal extracorporeal pump (50 mm in diameter, made of polycarbonate material) It has one point bearing with three magnetic fields powered via an 262 S E C T I O N I V Pediatric Critical Care: Cardiovascular electromagnetic mechanism This levitated mechanism reduces mechanical friction, hemolysis, and overall wear.211 Another system of use in pediatrics is the Tandem Heart (CardiacAssist) VAD It is a centrifugal pump, like the devices already mentioned, that is currently approved by the FDA for clinical use in adults.212 Kulat et al modified the system to include a variable restrictive recirculation shunt to allow lower flows for support in smaller patients.213,214 Advantages of these short-term VAD systems compared with traditional ECLS include lower priming volumes, adequate left (or systemic) ventricular decompression, lower heparin requirements, less hemolysis, ease of transport, and relatively low costs.215 In addition, central cannulation spares the neck vessels These short-term devices are now used also for longer duration of support, up to to weeks.216 Centrifugal LVADs require a functional RV to supply preload to the LV drained by the pump Complications of the centrifugal VAD system include thrombus formation in the circuit, hemolysis, bleeding (including acquired von Willebrand disease217 and infection218) Yarlagadda et al reported the outcome of children listed for heart transplantation between 2011 and 2015 supported with temporary circulatory support (TCS) devices compared with a match control of children supported with ECMO during the same period The number of implanted TCS devices increased from or fewer before 2011 to 50 in 2015 A total of 93 children were implanted (59% LVAD, 23% RVAD, and 18% BiVAD) The most commonly used device was the CentriMag-PediMag system (65%), followed by TandemHeart (18%) and Rotaflow (6%) The support duration was longer for the device cohort (median, 19 days vs days; P , 001) and was longest for CentriMag-PediMag, with 27% supported for more than 60 days The TCS device cohort had longer overall survival (hazard ratio, 0.61; 95% confidence interval, 0.39–0.96), with 90-day mortality before transplant that was modestly reduced (from 45% with ECMO to 39% with TCS).219 Successful use of the TCS as a bridge to implantable VAD and then to heart transplantation in a patient with single-ventricle physiology has recently been reported.220 Long-Term Ventricular Assist Device Support After the first-generation, long-term pulsatile VADs were noted to have significant complications, the use of axial continuous-flow devices increased with the hope to decrease device-related complications The initial long-term axial continuous-flow devices included the Heart Assist MicroMed DeBakey VAD (Fig 28.7) and Jarvik 2000 The MicroMed DeBakey VAD was approved for use in pediatric patients in 2004 It supported pediatric patients as small as 18 kg, providing a wide degree of cardiac support, with blood flows from to 10 L/min This was an implantable LVAD, focusing on bridge to transplantation It represented the first truly miniaturized device The advantages of this device were its small size, relative ease of implant and explant, decreased infection risk, and continuous flow It had a significant risk of thrombosis in addition to the risk for hemolysis.221,222 The Jarvik 2000 was an adult device with a relatively small surface area, measuring 1.8 cm in diameter by cm in length The device usually is implanted into the LV apex via a left thoracotomy, and the outflow graft is placed into the descending aorta Blood flow ranges from to L/min and is determined by impeller speed and systemic vascular resistance, with the usual setting at 9000 RPMs (range, 8000–12,000 RPMs) An infant Jarvik 2000 was under investigation but, owing to issues with hemolysis, had been modified to the Infant Jarvik 2015, which is being tested in the PumpKIN (Pumps for Kids, Infants, and Neonates) trial.223,224 • Fig 28.7 HeartMate II ventricular assist device (Courtesy MicroMed Technology, Houston, TX.) In the context of axial continuous-flow devices, the HeartMate II (Thoratec Corp.) is the most commonly used implantable axialflow rotary pump using blood-immersed mechanical bearings with textured blood-contacting surfaces The percutaneous version is totally implantable The HeartMate II (Fig 28.8) is smaller than the first-generation devices, principally owing to the elimination of the sac or reservoir necessary in pulsatile pumps This CHAPTER 28 Cardiac Failure and Ventricular Assist Devices 263 Flow inducer/impeller Flow straightener Flow diffuser (1) Pre-sealed outflow graft (2) Exclusive flow probe Front bearing A Flow housing Magnet pieces Rear bearing Motor stator B C (3) Near silent pump (4) Rigid titanium inflow cannula Actual size: 71mm × 30mm, 92 grams • Fig 28.8 HeartAssist pediatric ventricular assist device (modern DeBakey ventricular assist device) (A) DeBakey ventricular assist device in a cutaway view (B) HeartAssist with its position in the heart. (C) HeartAssist shown with a US quarter for size comparison (Courtesy Abbott Laboratories, Abbott Park, IL.) device has two cannulas (inflow and outflow) without valves It has smooth surfaces in the inlet and outlet stators but still requires anticoagulation Clinical experience shows that the HeartMate II LVAD provides excellent support, with significant improvement in functional capacity HeartMate II is approved for both destination therapy and bridge to heart transplantation In a retrospective review of the Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS) data from 2008 to 2011, there were 28 pediatric patients, with (25%) undergoing device placement in a pediatric hospital At 6-month follow-up, the composite of survival to transplantation, ongoing support, or recovery was 96% for the pediatric group, which was not significantly different from the young adult group Bleeding complications requiring surgical intervention were more common in the pediatric group.225 The FDA has already approved the HeartMate II as a bridge to transplant and for destination therapy The device has low thrombogenicity and low thromboembolic risk, making it a good device option for destination therapy The newer generations of continuous-flow devices over the past 10 years include centrifugal continuous-flow pumps with an impeller or rotor suspended in the blood flow path using a noncontact bearing design, which uses either magnetic or hydrodynamic levitation The levitation systems suspend the moving impeller within the blood field without any mechanical contact, eliminating frictional wear and reducing heat generation This feature hopes to promise longer durability and higher reliability with a low incidence of device failure and need for replacement Usually, magnetic levitation devices are larger owing to the need for a complex position sensing and control system Examples of thirdgeneration devices are the DuraHeart (Terumo, Inc.), HVAD (HeartWare Corp.), HeartMate III (Abbot Inc.) and EVAHEART LVAS (Sun Medical Technology Research Corp.).226,227 The HeartWare HVAD system (Medtronic) has gained significant popularity in the pediatric world for its use in older children and adolescents given its smaller size Its ability to be intracorporeally implanted allows the patient to be discharged home on VAD support The HVAD system was approved by the FDA in 2012 for adults through the ADVANCE (Evaluation of the HeartWare LVAD System for the Treatment of Advanced Heart Failure) trial, and its application in pediatrics has increased since the first reported use as a bridge to heart transplantation in an adolescent.228 As the implantable continuous-flow devices continued to increase in pediatrics so did the use of the HVAD VanderPluym et al reported the outcome of children supported with an intracorporeal continuous-flow LVAD who were entered in the Pediatric Interagency Registry for Mechanical Circulatory Support (PediMACS), the pediatric portion of INTERMACS They identified 192 children from 2012 to 2017 with a median weight of 51.5 kg and a median support of 2.8 months Twelve children weighed less than 20 kg at time of implant, and the majority (58.3%) had CHD compared with 11.7% in children who weighed 20 kg or more Serious adverse events in children included infection (27%), major bleeding (23%), device malfunction or pump thrombosis (11%), and stroke (10%) Interestingly, children who weighed less than 20 kg at time of implant had lower major bleeding complications, infections, and stroke compared with the older counterparts Almost half of the children who weighed 20 kg or more were discharged home as they waited for a transplant as opposed to only 33% of children who weighed less than 20 kg.229 The HeartMate III, as opposed to the HeartMate II (axial continuous-flow device) is a centrifugal flow, fully levitated, selfcentering rotor pump with intrinsic pulsatility The HeartMate III was approved by the FDA in 2018 for destination therapy following the MOMENTUM trial.230 The study showed that although 264 S E C T I O N I V Pediatric Critical Care: Cardiovascular the disabling thromboembolic complications were similar, the rates of overall stroke and pump malfunction were lower in the HeartMate III than in the HeartMate II.227,231 The use of this device in the pediatric population continues to increase not only in children with dilated cardiomyopathy but also in those with CHD.225,232 Total Artificial Heart Total artificial heart (TAH) devices completely replace the patient’s native ventricles and all four cardiac valves The SynCardiaSystems TAH is the modern version of the Jarvik implanted in 1982 It is the only FDA-approved TAH in the United States It is used as destination therapy and, more recently, as a bridge to heart transplant As the device has evolved, so too have its indications and its name, from Symbion TAH to CardioWest TAH, to the SynCardia TAH most recently The 70-mL SynCardia-t TAH is suitable for patients with BSA of 1.7 m2 or greater The SynCardia-t TAH is approved for outpatient use, allowing many patients to be discharged home The development of the 50 mL SynCardia TAH addressed the need for a smaller pump for use in small adults and adolescents down to a BSA of 1.2 m2 Indications for TAH implantation are numerous, with the most common being biventricular failure In patients younger than 19 years, cardiomyopathy comprises 61% of the indications, with dilated cardiomyopathy being the most common.233 Although initially designed for use as destination therapy, most of the implants worldwide have been used as a bridge to transplantation Progression to transplant occurs at a reported rate of 60% to 80% in the adult population.234,235 Morales et al.236 reported the worldwide experience for all patients supported with a TAH between 2005 and 2015 (n 43) The most common diagnoses included dilated cardiomyopathy (42%), followed by transplant rejection (19%) and CHD (16%) Successful bridge to transplantation varied by diagnosis; 75% of the patients with dilated cardiomyopathy were bridged to transplant, whereas only 25% of the patients with graft rejection were transplanted Children and adolescents supported with a TAH had survival rates similar to adults with the TAH or biventricular devices Preclinical in vivo trials are underway for continuous flow (CF) TAH devices The Cleveland Clinic valveless, sensorless, pulsatile pediatric continuous-flow TAH (p-CFTAH) promises its use in small children Anatomic fit studies correlating BSA with vertebral-sternal distance projects that the p-CFTAH could be suitable for children with BSA as small as 0.3 m2.237 Device Selection Three factors drive device selection: type of support (cardiopulmonary or cardiac), planned duration of support, and BSA Short-term support (,14 days) is used for acute myocarditis, graft dysfunction after cardiac transplant, and postcardiotomy Venoarterial ECMO/ECLS has been successfully used and is the most widely available form of short-term biventricular support ECLS is commonly employed when there is failure to wean from CPB When compared with temporary VADs, it has the advantage of peripheral cannulation, which can be done in the intensive care setting Temporary VADs, on the other hand, spare cervical vessel loss, allow for better decompression of the LV, and minimize the inflammatory response given the absence of an oxygenator Compared with ECLS, it can provide longer support time (2–4 weeks) as a bridge to decision for a long-term VAD Temporary VADs are • Fig 28.9 Pediatric Jarvik 2015 shown with a paperclip for size comparison better suited to semi-elective cases before the onset of cardiac failure has resulted in secondary lung injury.238,239 Long-term support is often used in patients with cardiomyopathy and in some patients with CHD who fail to improve on a short-term device The Berlin EXCOR continues to be the device of choice for infants and toddlers, while the HVAD is predominantly implanted in pediatric patients with a BSA greater than 0.60 to 0.65 m2 The HeartMate II is an excellent option for adolescents with BSA approximately 1.3 m2 or larger According to the PediMACS registry, continuous-flow VADs account for more than 60% of long-term device implantations in the United States However, the continuous-flow devices used are designed for adults, leading to a patient-device size mismatch, especially in small children The PumpKIN trial, initially a two-arm randomized study (Jarvik 2015 vs Berlin Heart EXCOR) is now being reevaluated with a potential transition to single-arm testing the Infant Jarvik 2015 (Fig 28.9), which is the first continuous-flow VAD specifically designed for small children.224 Indications and Management In general, the use of MCS in pediatric patients with acute or chronic end-stage HF is indicated when conventional medical therapy has failed Newer considerations include inability to wean mechanical ventilator support with aggressive use of inotropic support, which prevents appropriate nutritional and physical rehabilitation Indication for VAD implant in pediatrics has now evolved from the traditional bridge to transplant to include bridge to recovery as well as bridge to decision The use of MCS as destination therapy has been a traditional option in the adult population Although limited in pediatrics, it is garnering more interest240 and has been recently reported in patients with Duchenne muscular dystrophy.241 Contraindications to the use of VADs in pediatric patients include irreversible end-organ dysfunction; risk of intracranial bleed, as with congenital AV malformations (e.g., moyamoya disease); underlying risk of increased bleeding, such as coagulation factor deficiencies; or, conversely, thrombotic disorders, such as factor V Leiden deficiency Also, active malignancy and morbid ... centers favor ventricular apical cannulation It is encouraging to note that even within the short 3-year time frame of this study, pediatric centers that have refined their patient characteristics... operating in a bearingless rotor that floats within a rotating magnetic field Because of its contact-free environment and absence of seals or valves, this device minimizes blood trauma, thrombus... blood flows from to 10 L/min This was an implantable LVAD, focusing on bridge to transplantation It represented the first truly miniaturized device The advantages of this device were its small