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Levitronix CentriMag Third-Generation Magnetically Levitated Continuous Flow Pump as Bridge to Solution

Loforte, Antonio; Montalto, Andrea; Ranocchi, Federico; Lilla Della Monica, Paola; Casali, Giovanni; Lappa, Angela; Contento, Carlo; Musumeci, Francesco

doi: 10.1097/MAT.0b013e31821f2116
Adult Circulatory Support

The Levitronix CentriMag (Levitronix LLC, Waltham, MA) ventricular assist device (VAD) is a magnetically levitated rotary pump designed for temporary extracorporeal support. Between February 2004 and May 2010, 42 consecutive adult patients were supported with Levitronix at our institution (32 men; age 62.3 ± 10.5 years, range: 31–76 years). Indications for support were (group A, n = 37) failure to wean from the cardiopulmonary bypass in the setting of postcardiotomy (n = 23), primary donor graft failure (n = 4), or right ventricular failure after axial left VAD (LVAD) placement (n = 10) and (group B, n = 5) refractory heart failure after acute myocardial infarction. The mean support time was 11.2 ± 6.8 days (range: 3–43 days) in group A and 8.6 ± 4.3 days (range: 5–11 days) in group B. In the postcardiotomy cohort (group A), 11 (47.8%) patients were weaned from support as all were supported graft failure patients. Eight patients of axial LVAD cohort were weaned from right VAD (RVAD). One patient was bridged to heart transplantation (Htx). Thirteen (35.1%) patients died on support in group A. In group B, one patient was bridged to Htx and four died on support. In overall population, bleeding requiring reoperation occurred in 15 (35.7%) cases and cerebral major events in four (9.5%). There were no device failures. Of the 23 (54.7%) patients who recovered and were discharged home, 20 (47.6%) are presently alive, and additionally, two patients of both groups who were bridged to Htx (overall n = 22, 52.3%). The Levitronix proved to be useful in patients previously considered nonsuitable for transplantation or long-term assist device. The device was technically easy to manage, and the results were encouraging.

From the Department of Cardiac Surgery and Transplantation, San Camillo Hospital, Rome, Italy.

Submitted for consideration July 2010; accepted for publication in revised form March 2011.

Partially presented at ASAIO, 55th annual conference, May 27–30, 2009, San Francisco, CA (ASAIO-IFAO Fellowship Award, 2009).

Reprint Requests: Antonio Loforte, MD, Department of Cardiac Surgery and Transplantation, S. Camillo Hospital, P.za C. Forlanini n.1, Rome 00151, Italy. Email: antonioloforte@yahoo.it.

The Levitronix CentriMag (Levitronix LLC, Waltham, MA) ventricular assist device (VAD) is a rotary blood pump designed for extracorporeal support operating without mechanical bearings or seals. The rotor is magnetically levitated (MAGLEV), and rotation is achieved without friction or wear, thus minimizing blood trauma, mechanical failure, and heat generation.1,2

The concept of MAGLEV can be categorized into external motor-driven system, direct-drive system, and self-bearing system. In the external motor-driven system, a motor is used to induce magnetic coupling force to the impeller, whereas a separate levitation system controls the impeller suspension. In the direct-drive system, the impeller becomes the motor rotor, whereas a separate levitation system is built into the system to realize magnetic suspension. In the third system, both the drive and the levitation coils share the same stator core to make it as a “self-bearing” system, as first investigated by Chiba, Bichsel, and Shöb.1 The CentriMag manufactured by Levitronix belongs to the third MAGLEV category.

The aim of this study is to report our early results with the device in terms of 1) the benefit of CentriMag support in patients with cardiogenic shock (CS); 2) postoperative outcome as a bridge to decision making; and 3) overall outcomes, including complications during mechanical support, and survival to recovery and primary transplantation.

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Materials and Methods

Patients

Overall mean age was 62.3 ± 10.5 years (range: 31–76 years). There were two main indications in our experience for placing the temporary Levitronix CentriMag: (group A, n = 37) failure to wean from the cardiopulmonary bypass (CPB) device in the setting of postcardiotomy (n = 23), primary nonfunction of the donor heart (n = 4), or acute right ventricular failure (RVF) after axial long-term left VAD (LVAD) placement (HeartMate II LVAD, Thoratec corp., Pleasanton, CA) (n = 10) and (group B, n = 5) heart failure refractory to medical therapy and intraaortic balloon pump (IABP) support after acute myocardial infarction (AMI).

The overall support setup included 19 right VADs (RVADs), 14 biventricular assist devices (BVADs), and nine LVADs (Table 1).

Postcardiotomy procedures (n = 23) included coronary artery bypass grafting (CABG) in 11; combined CABG and ascending aorta replacement in three; aortic valve replacement in three; Bentall procedure in two; combined CABG and aortic valve replacement in one; combined mitral valve replacement and tricuspid valve repair in one; mitral valve repair in one; and mitral valve replacement in one (Tables 1 and 2).

The etiology of end-stage heart failure of long-term HeartMate II LVAD recipients requiring a temporary CentriMag RVAD (n = 10) support was ischemic dilated cardiomyopathy in six and idiopathic dilated cardiomyopathy in four. All patients had the Levitronix device inserted simultaneously during the same operative time of HeartMate II LVAD insertion due to acute RVF in two cases and prophylactically in the other eight cases according to similar preoperative echocardiography, hemodynamic, and laboratory parameters (Tables 1 and 3).

The third group involved acute donor graft failure and included two BVADs and two LVADs (Tables 1 and 4). Three patients had the Levitronix device inserted during the same operative transplant procedure due to failure to be weaned from CPB after orthotopic heart transplantation (Htx) using the Lower–Shumway technique, despite inotropic support with adrenaline, noradrenaline, inhaled nitric oxide, and IABP, and one patient was already in the intensive care unit (ICU) and underwent emergency BVAD implantation.

The final group (group B) involved five post-AMI patients on IABP support (Tables 1 and 5), referred from other institutions and already treated by primary percutaneous transluminal coronary angioplasty (PTCA), in whom postprocedure CS eventually occurred. One patient, a 42-year-old man, was referred already on peripheral extracorporeal membrane oxygenation (ECMO) support.

In the studied population, the vital status immediately before CentriMag placement was documented using the simplified acute physiology score (SAPS) II. Briefly, the following data were collected and score points calculated: age, heart rate, systolic blood pressure, body temperature (in °C), Pao2/Fio2, urine output, serum blood urea nitrogen (BUN), white blood cell (WBC) count, serum potassium, sodium and bicarbonate level, bilirubin plasma level, Glasgow coma score, documented history of chronic disease (acquired immunodeficiency syndrome, hematologic malignancy, and metastatic cancer), and type of admission (Tables 3 and 5).

The inotropic score before CentriMag placement was also calculated (Tables 2, 3, and 5). Briefly, the doses of dopamine, dobutamine, and enoximone (in μg/kg body weight/min) were added; the dose of milrinone was multiplied by 15 and doses of epinephrine and norepinephrine by 100 and then added.

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Device

The CentriMag has been manufactured by Levitronix as extracorporeal MAGLEV blood pump and uses the so called “bearingless” or “self-bearing motor.”1 The rotor is suspended and rotated by eight L-shaped iron cores (four pairs) with drive and control winding together. The rotor position and rotation are continuously controlled by a feedback control system in radial directions. Another impeller motion is passively suspended with bias flux between rotor and stator.

The pump system consists of a single-use disposable polycarbonate pump head (priming volume: 31 ml, connectors: 0.375 inch inlet/outlet ports) (Figure 1), motor/bearing drive unit (diameter × height = 87 × 70 mm), cannulae, and a bedside controller. It can deliver a pump flow of up to 9.9 L/min and head pressures of up to 600 mm Hg operated at a rotational speed of up to 5,500 rpm. The pump was specially designed for extracorporeal circulatory support applications as CPB or uni- or biventricular assistance. The device is Conformite Europeenne mark approved for short-term usage for up to 14 days in CS patients.

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Surgical Technique

Transesophageal echocardiography was routinely used in the operating room to exclude eventual intracardiac shunts and aortic valve incompetence and then to confirm the adequate placement of the cannulae.

All procedures were performed through a median sternotomy. Anticoagulation management was based on activated clotting time (ACT)-guided heparinization. The patients reunderwent a CPB running in group A. Differently, in group B, CPB installation was not achieved.

The aortic and pulmonary “outflow” arterial cannulae were placed through double-layer purse-string 4-0 polypropylene sutures with multiple pledgets. Both atrial cannulas were placed through double-layer purse-string 4-0 polypropylene sutures with multiple pledgets. For additional stability, multiple 2-0 Tevdek ties were placed around the cannula and the snares. The cannula of choice for aortic and pulmonary artery cannulation was the Medtronic elongated one-piece arterial cannula (20F or 22F). The choice of cannula for atrial cannulation was an angled (Medtronic) venous cannula (24F or 28F). The choice of cannula size was customized to the patient's body surface area. The cannulae were tunneled through subcostal incisions.

In the LVAD configuration, the inflow cannula was inserted in the left atrium at the level of the junction between the right superior pulmonary vein and the left atrium. The outflow cannula was placed directly into the ascending aorta in all but one case. In this case, a long-term Thoratec cannula (Thoratec Corp., Pleasanton, CA), having a woven polyester graft section, was sewn to the aorta with a continuous 4-0 polypropylene running suture, whereas the left ventricle apex was drained by usage of an appropriate Thoratec apical cannula (Thoratec Corp., Pleasanton, CA).3 If a right-side support system was needed, the inflow cannula was placed in the right atrium and the outflow cannula was inserted in the main pulmonary artery. The right and left outflow cannulae were placed anteriorly at the front of the heart, whereas the inflow cannulae were lying in the pericardium on the right side of the right atrium.

The CentriMag pump heads and tubing were prepared and primed extracorporeally. The tubing was then divided within the operating field and appropriately connected to each cannula, carefully avoiding any air in the system. LVAD support was then initiated, followed by RVAD support, in case of biventricular support. The speed of each pump was increased to provide a cardiac index of >2.2–2.4 L/min. Once satisfactory flows were achieved, protamine was given, and hemostasis was performed. The sternotomy was closed conventionally with surgical steel wires, and the patient was returned to the ICU. In case of coagulopathy with ongoing mediastinal bleeding, the patient's chest was packed and left open.

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Device Weaning

Termination of support due to recovery of myocardium was elective procedure for all patients, except for one patient with accidental dislocation of the “outflow” cannula of the isolated RVAD in a HeartMate II LVAD recipient who emergently joined the operating theater with successful RVAD removal.

The weaning was initiated when the heart began to show signs of recovery, consisting of increasing amplitude of the arterial waveform, decreased need for pharmacotherapy, and increased left and right heart contractility on echocardiography.

Elective weaning in the ICU setting was done by Swan–Ganz catheterization with transesophageal echocardiography. The flows for the single heart compartment were gradually weaned down to 1 L/min for a couple of minutes while rising the intravenously heparin infusion dosage and inspecting for any change in recordings of central venous pressure (CVP), pulmonary artery, and wedge pressure, as well as contractility on echocardiography.

In the BVAD group, CVP and systemic and pulmonary pressure recordings were inspected with left-side flow maintained and then with both VADs weaned to 1 L/min. A decision to remove the VAD was made if hemodynamic and pulmonary catheter parameters, and echocardiography showed improvement. It was required that there is no rise in CVP or increase in inotropic support and good contractility in the presence of two or more consultant surgeons before explantation of the device.

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Anticoagulation

We did not administer any anticoagulation for the first 12–18 hours to normalize the clotting profile. Once the drainage was <50 ml/h, an heparin infusion was started without a bolus to maintain a partial thromboplastin time (PTT) of 50–60 seconds, and it was continued for the duration of support. No antiplatelet agents were given.

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Statistical Analysis

Categoric factors are expressed as the number and percentage of patients. Continuous parameters are given as mean and standard deviation. Paired data were compared by a one-tailed Student's t-test. p < 0.05 was considered statistically significant. Outcomes are presented as operative mortality within 30 days and survival to discharge from the hospital.

All analyses were performed using SPSS for Windows Release 11.5 (SPSS Inc., Chicago, IL).

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Results

All patients were in cardiac failure refractory to medical therapy, and the majority of them had IABP adjunctive therapy at the time of Levitronix placement, which continued for 72 hours. The decision to place a temporary VAD device as opposed to a long-term device was based on the clinical judgment that these patients needed timely ventricular support with little means of determining their neurologic status and long-term outcome.

The mean support time was 11.2 ± 6.8 days (range: 3–43 days) in group A and 8.6 ± 4.3 days (range: 5–11 days) in group B. In group A, the postcardiotomy cohort had a mean duration of support of 8.8 ± 2.8, the graft failure cohort of 7.7 ± 0.9 days, and the RVAD support in HeartMate II LVAD recipients cohort of 18.6 ± 9.2 days (Table 1).

There was no significative difference in duration support if BVAD, LVAD, and RVAD patient cohorts were compared but excluding HeartMate II LVAD recipients.

In the postcardiotomy cohort of group A, 11 (47.8%) patients were successfully weaned from support and discharged from hospital (Table 1). One patient (post-CABG) was successfully bridged to Htx after 10 days of support. The main cause of death was multiple organ failure (MOF) in 10 patients and severe hemorrhage in one case due to accidental dislocation of CentriMag LVAD outflow cannula in the ICU. Age, preoperative BUN value, and surgical crossing clamping time resulted to be predictors of early death in the postcardiotomy cohort by comparing preoperative and postoperative parameters of survivors and nonsurvivors (Table 2).

All four supported graft failure patients were weaned and discharged as well (Table 1). Eight (80%) patients of HeartMate II LVAD cohort were successfully weaned from RVAD and discharged home (Tables 1 and 3). In six patients, RVAD removal was performed through a right mini thoracotomy without repeat sternotomy. One patient died after 43 days of support due to respiratory failure despite additional ECMO placement. One patient with preoperative severe fixed pulmonary hypertension died after 8 days of support due to pulmonary hemorrhage.

Thirteen (35.1%) patients died on support in group A (Tables 1 and 3). There were two (5.4%) hemorrhagic strokes (postcardiotomy cohort), and 12 (32.4%) patients required rethoracotomy for bleeding.

In group B, none of the patients recovered and was weaned from CentriMag. One patient was successfully bridged to Htx after 11 days of support (Table 1). Four patients died on support due to MOF. There were one ischemic and one hemorrhagic strokes (40%), and three (60%) patients required rethoracotomy for bleeding. Group B comprised a preoperative severely ill cohort of patients, all late referred by other institutions, with an average preoperative SAPS II of 49.6 (range: 45–55) (Table 5). In the 42-year-old patient, already on peripheral ECMO support, bleeding and septic events occurred before CentriMag placement. The Levitronix circuit was connected to the Thoratec VAD cannulae as described earlier. After 7 days of support, the circuit had thrombus formations at the connectors sites, and the patient resulted to be the one in group B with an ischemic stroke.

In overall population, bleeding requiring reoperation occurred in 15 (35.7%) cases and cerebral major events in four (9.5%). There were no device failures. Of the 23 (54.7%) patients who recovered and were discharged home, 20 (47.6%) are presently alive, and additionally, the two patients of both groups who were bridged to Htx (overall n = 22, 52.3%).

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Device Performance and Related Complications

During support, the survived patients were extubated when feasible (n = 16, 64%) and began to mobilize in the ICU. A total of four patients underwent replacement of the external tubing and pump head at bedside. Two of these patients had elective replacement at 4 weeks after implantation and two required emergent replacement due to clot formation in the tubing at 2 weeks. There were no instances of mechanical failure of the device. With accumulating experience, we have found that device exchange could be safely extended to 4 weeks.

Reoperation for bleeding occurred in 15 patients. The result was correlated to the beginning of our experience when higher ranges of PTT for anticoagulation were used with even consequent three hemorrhagic stroke events. With accumulating experience, the anticoagulation therapy was better managed.

The only one ischemic stroke event was correlated to the use of silicone connectors between Thoratec cannulae and CentriMag circuit.

The average plasma-free hemoglobin (PFH) hemolysis marker was 8.7 (range: 1.4–210) IU. Among survivors, the average PFH was 7.5 (range: 1.3–205) IU, whereas for nonsurvivors, it was 11.1 (range: 1.2–211) mmol/L.1,2

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Discussion

The technology of MAGLEV was first applied for rotating machinery by the University of Virginia research group in 1950.1 Application for rotary blood pumps was then reported by Akamatsu et al. in 1992 and Allaire et al. in 1996.1

The progress of rotary blood pump technology has been so fast that during the last years. The so-called second-generation rotary blood pumps with blood-immersed bearings such as the MicroMed (Houston, TX) DeBakey VAD,4 the Jarvik 2000 FlowMaker (Jarvik Heart, Inc., New York, NY),5 and the HeartMate II (Thoratec corp., Pleasanton, CA)6 whose developments had been started in 1995 have been implanted in selected end-stage cardiac patients for bridge to transplantation and for destination therapy. Although considered unphysiological, the continuous flow or reduced pulsatility continues to work in humans for a duration of as long as 5.5 years.7 Beyond second-generation devices, third-generation mechanical noncontact devices using magnetic suspension mechanisms, such as the Terumo DuraHeart (Terumo Heart, Inc., Ann Arbor, MI)8 and the Berlin Heart INCOR system (Berlin Heart GmbH, Berlin, Germany),9 and hydrodynamic bearing mechanisms, such as Arrow International's (Reading, PA) CorAide and Ventracor's (Chatswood, NSW, Australia) Ventr-Assist VADs,10,11 are making their way into clinical applications.

Several short-term VADs have been used for refractory postcardiotomy CS that occurs in 0.5%–5% of patients who underwent cardiac surgery operation as for CS that complicates 7%–10% of patients with AMI. For both groups, it described an high mortality rate (75%–90%).12,13

Short-term VADs include Abiomed BVS 5000 (Abiomed Inc., Danvers, MA)14 and Bio-Medicus systems (Medtronic Bio-Medicus, Inc., Minneapolis, MN).15 However, disadvantages of these modalities of support include the limited support duration and the need for pump exchanges at short intervals of time, a high incidence of complications with increasing duration of support, the need for fairly stringent anticoagulation, and the requirement of an experienced team of personnel to allow for their safe use (Table 6).14–20

According to the recent results reported in literature, the novel Levitronix CentriMag VAD usage seems to reduce morbidity and mortality in such kind of delicate patients population.16–20

Our criteria for placement of temporary circulatory support followed the IABP score criteria described by Hausmann et al.21 and the choice if biventricular or monoventricular support followed Berlin algorithm.22

The decisive management for optimal timing of device insertion and duration of support to either bridge or recovery is difficult to provide in a precise fashion but remains a key confounder when comparing different transplant unit experiences.

Moreover, the question of whether to bridge to transplant or use a long-term device has remained controversial. Therefore, our goal was to adopt the Levitronix as a bridge to Htx if there was no evidence of recovery after weaning attempt(s) after neurologic recovery and multiple-organ improvement as the average waiting time to Htx is shorter than in the United States (90 vs. 250 days).

In only one patient we adopted the CentriMag LVAD combination with long-term Thoratec VAD cannulae in case of eventual exchange for long-term Thoratec paracorporeal device.3 The young patient was on ECMO with frequent hemorrhagic events and sepsis. The neurologic status was good, and it was decided to support him temporarily by means of CentriMag even encouraged by similar reports.23 The patient died due to an ischemic stroke, and thrombus formations were found in the circuit at the silicone connectors sites. The bad outcome was probably correlated to the absence of titanium connectors in the circuit as suggested by the Berlin Heart experience.3

Despite the established use of implantable VADs as bridge to recovery or transplant, the use of implantable VADs in primary graft failure is still controversial.17,19 Literature experiences have shown that cardiac retransplantation for early graft failure and acute rejection is associated with high mortality risk. A good solution is the quick restoration of the appropriate cardiac output after diagnosis with mechanical circulatory support (MCS), avoiding the complications associated with a long CPB time, high-dose inotrope infusions, and low peripheral perfusion. CentriMag proved to be effective in such patient population.16–20 We successfully used CentriMag in four consecutive cases with recovery of all grafts function.

Cardiogenic shock remains a leading cause of death for patients with AMI. Rapidly reestablishing infarct-related arterial blood flow is essential in the treatment of such patients, and the strategy of early revascularization remains superior to initial aggressive medical therapy. Despite the advantages of early surgical or nonsurgical revascularization, once shock is diagnosed, the mortality rate remains high (>60%) despite intervention, and half of all deaths occur within the first 48 hours. The 17 major studies of LVAD support for CS complicating acute MI reported a survival rate of 40%,13 and LVAD support seems to give no survival improvement. This is also supported by our poor results in group B which additionally resulted to be a preoperative severely ill cohort of patients (Table 5), all late referred by other institutions, with preoperative high SAPS II and inotropic scores. However, further investigations are required.

Pulmonary vascular hypertension (PVH) is a common complication of severe, long-lasting chronic heart failure and remains a risk factor for mortality after Htx. Literature highlighted that chronic unloading with LVAD resulted in significant reduction of pulmonary vascular resistance, thus ultimately leading them to successful Htx.24 One of our HeartMate II LVAD recipient with preoperative fixed secondary severe pulmonary hypertension had an RVAD by CentriMag to help the right ventricle in the early postoperative period. The patient died after 8 days of support when the procedure of weaning from temporary RVAD had been just started since the improving of right ventricle contractility. Pulmonary hemorrhage occurred and was probably correlated to the extremely severe preoperative disease of both lungs with a pulmonary hypertension which lasted since 5 years.

The preoperative prediction of right ventricle function after LVAD implantation is crucial for device selection and patient outcome. When patients at high risk for failure of isolated LVAD support are identified, proceeding as a primary option to a BVAD implantation is suggested as it could be hypothesized that the early institution of a “temporary” biventricular support results in improvement of outcome.25–27

The use of a temporary RVAD placement and its further removal could allow patients to be in long-term implantable LVAD support only with good outcome and quality of life as well as long time of mechanical support.27 This supports our current strategy of usage of a CentriMag RVAD in axial LVAD recipients with actually good results.

In conclusion, we have found that the Levitronix CentriMag system is a reliable and facile temporary circulatory support system as a bridge to decision in patients with refractory acute CS in various clinical scenarios.

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Limitations

The aim of the study has been to describe retrospectively our early experience with CentriMag MCS device despite the small cohorts of patients. According to literature,17 we preferred to describe two populations of patients: group A, failing to wean from CPB and group B, suffering from refractory CS due to AMI. The cohorts of patients belonging to group A were not statistically compared each other due to their absolutely different clinical scenarios. Further investigations result to be necessary, thus leading to a more robust analysis.

Bleeding output and blood transfusions were not discussed. However, we think that the results obtained in terms of free Hb only are an important indicator in terms of device-related complications, shear-stress, and hemolysis, which are clearly different if survivors and nonsurvivors are compared as we can notice in literature concerning such kind a mechanical support.16–20

Between 2002 and 2010, 150 long- and short-term MCS devices implants have been performed at our institution. Levitronix CentriMag in VAD configuration has been used since the beginning of our experience as short-term MCS. Actually, we use ECMO systems additionally by usage of Jostra RotaFlow (Maquet Cardiopulmonary AG, Hirrlingen, Germany) associated with Quadrox PLS (Maquet Cardiopulmonary AG, Hirrlingen, Germany) oxygenator and recently Levitronix CentriMag Levitronix CentriMag (Levitronix LLC) associated with EUROSETS A.L. One oxygenator. Further analysis of our data will get us able to show our own MCS protocol management. A comparison of the two latter MAGLEV centrifugal pumps should be investigated. Since a few months only we adopted the HeartWare HVAS implantable MAGLEV third-generation flow pump, this confirms our only initial experience with MAGLEV flow pumps, which needs to be more investigated further.

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Acknowledgment

The authors thank all MCS team of Deutsches Herzzentrum Berlin, Germany, for continuous support and advices. The study was carried out within Dr Loforte's, PhD, Program in “Transplantation” awarded by Rome Tor Vergata University, Italy, in cooperation with the Deutsches Herzzentrum Berlin, Germany.

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