Postcardiotomy cardiogenic shock occurs in up to 0.5–5% of adult cardiac operations.1–3 It is a critical clinical condition that, despite the usage of inotropes, pressors, and eventually intra-aortic balloon pump (IABP) support, has still an high mortality rate.4
Mechanical circulatory support (MCS) treatment is the only option for survival in such a patient’s category.5 Two options are available: short-term ventricular assist devices (VADs) or extracorporeal membrane oxygenation (ECMO) support. Both MCS strategies allow time to assess the eventual myocardial function recovery or evaluate patients’ transplantability or upgrade to a long-term device support. The literature shows that regardless of the device adopted, only a low percentage of patients (25–48%) survive to be discharged home.6–10
The CentriMag (Levitronix LLC, Waltham, MA) is a third-generation extracorporeal blood pump operating without mechanical bearings or seals. The rotor is magnetically levitated and rotation is without friction-reducing blood trauma. The pump produces unidirectional flow up to 10 l/min at lower rotations per minute. The CentriMag system is CE marked and approved for use for up to 30 days. In comparison with other short-term VADs, the CentriMag is cost saving, easy to implant and manage, and has high durability.6, 11, 12 Only a few reports are available in the literature concerning CentriMag in ECMO configuration.13–16
We report our experience with Levitronix CentriMag (Levitronix LLC, Waltham, MA) in the setting of a peripheral or central extracorporeal membrane oxygenation (ECMO) system support as treatment of postcardiotomy cardiogenic shock (CS).
Between January 2007 and August 2011, a total of 5,480 consecutive adult patients underwent cardiac surgery procedures at our institution. Among them, 14 patients (0.25%) required temporary CentriMag ECMO support because of postcardiotomy CS in the setting of failure to be weaned from cardiopulmonary bypass (CPB) (n = 12; 85.7%) or within 48 hours since their arrival at the intensive care unit (ICU) (n = 2; 14.3%). There were 9 males (64.3%) and the mean age was 53.1 ± 14.3 years (range: 25–70 years) Table 1).
Before ECMO support, cardiac surgery procedures included: aortic and/or mitral valve replacement (n = 6); coronary artery bypass grafting (CABG) (n = 5); and Bentall procedures (n = 3).
Preoperatively, six patients had a poor hemodinamics and were already suffering from cardiogenic shock (mean arterial pressure [MAP] < 60 mm Hg, left atrial pressure [LAP] > 20 mm Hg, cardiac index [CI] < 2 l/min/m2, SvO2 < 50, and systemic vascular resistance index > 2400 dyns/cm5/m2, diuresis < 40 ml/h) despite inotropic support, afterload reduction, or the usage of IABP) (Table 1). No cardiac arrest occurred. Among them, five patients underwent emergency cardiac surgery with rapid institution of CPB after a full sternotomy. One patient (n = 14, Table 1) was referred from another hospital already on a peripheral RotaFlow ECMO (Jostra RotaFlow, Maquet Cardiopulmonary AG, Hirrlingen, Germany) support. The patient was operated on the same day and CentriMag ECMO support followed the surgical procedure.
Intravenous pharmacological support before CentriMag consisted of a combination of two or more inotropic and vasoactive drugs such as epinephrine, norepinephrine, dobutamine, dopamine, isoproterenol, and, in detail, the inotropic score17, 18 before mechanical support was calculated (Table 1). Briefly, the dose of dopamine, dobutamine, and enoximone (µg/kg/min) were added; the doses of epinephrine and norepinephrine were multiplied by 100 and then added.
An IABP was employed in all patients before and during CentriMag support. All patients had an Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS)19 level 1 and the indication criteria for mechanical support followed the IABP score as described by Hausmann et al.20
An overview of patient’s population of the two groups is shown in Table 1.
Levitronix CentriMag is an extracorporeal, centrifugal (VAD) that uses magnetically levitated bearingless motor technology thus minimizing blood trauma, mechanical failure, and heat generation. The rotor is suspended and roted by eight L-shaped iron cores with the drive and control winding together. The rotor position and rotation are continuously controlled by a feedback control system in the radial direction. The risk of thrombus formation is reduced by uniform unidirectional flow and less stagnation, whereas reduced shearing stress attenuates hemolysis. The pump was designed for single or biventricular support and a maximum flow of 9.99 l/min can be achieved at a maximum operating pressures of 600 mm Hg, maximum pump speed of 5500 revolutions per minute and a priming volume of 31 ml.11, 12
ECMO Installation and Management
We assembled the CentriMag device with an ECMO circuit (A.G.I.L.E., phosphorilcoline coated), which included an hollow fiber membrane oxygenator Medos® Hilite 7000 LT (MEDOS Medizintechnik AG, Stolberg, Germany) (n = 10 patients) or Eurosets A.L.ONE (EUROSETS srl, Medolla, Modena, Italy) (n = 4 patients).
Central cannulation has been used in eight patients: the inflow cannula was placed into the right atrium (angled venous cannula, DLP Medtronic, 30 Fr) while the outflow cannula was positioned in the ascending aorta (straight arterial cannula, Medtronic DLP, 24 Fr, or EOPA Medtronic 22 Fr). All cannulas were secured with pledgeted reinforced pursestring prolene sutures. Routinely, a left ventricular venting through the upper right pulmonary vein (Terumo Sarns, 20 Fr) was inserted in all patients to unload the left heart and was connected to the right atrial drainage thorough a Y connector (EUROSETS srl, Medolla, Modena, Italy). The ECMO cannulas were tunneled through sub-costal incisions and then connected to the circuit, avoiding air in the system.
Peripheral cannulation (n = 6) was established after groin-vessel exposure by using the femoral vein (Cardiovations QD, 22 Fr) as inflow and the femoral artery for arterial return (Medtronic Biomedicus, 19 Fr). In all patients, distal perfusion through a 10 Fr catheter (Gundry®, a Medtronic retrograde coronary sinus perfusion cannula with a manual inflating cuff) was used to avoid deleterious leg ischemia.
All patients had intraoperative transesophageal echocardiography to monitor left and right ventricular function, any patency of foramen ovale, aortic valve competence, and adequate placement of cannulas.
The ECMO blood flow was adequately adjusted during the first 24–48 hours to maintain cardiac index of 2.6 l/min/m2, mixed venous oxygen saturation (SvO2) around 70%, and mean arterial pressure (MAP) of 60–65 mm Hg.
Heparin was antagonized to maintain an activated clotting time (ACT) of 170–190 seconds with full ECMO flow. However, in case of mediastinal bleeding, anticoagulation was safely avoided for 24 hours, while keeping an ECMO flow of 4 l/min, without signs of pump malfunction because of trombosis or embolic events.
When possible, the chest was closed traditionally, and in case of excessive bleeding, it was packed and left open (n = 5).
All patients needed blood transfusions to achieve a hematocrit of 28–30%, and platelet units were given when the platelet count was less than 50.000–60.000.
An IABP was employed in all patients to reduce the cardiac afterload, improve the coronary perfusion, and maintain a pulsatile flow. All ECMO support cases were conducted in normothermia.
Mechanical ventilation was continued throughout ECMO support with the same management for every patient. Ventilator setting was commonly set at a tidal volume less than 8 ml/kg, 8 breaths/min, positive end expiratory pressure less than 10 cm H2O, and a FiO2 of 0.40–0.60. Two patients were extubated during ECMO support, thus reducing the risk of pneumonia.
Weaning from ECMO was initiated when the heart showed signs of recovery as defined by increase of arterial waveforms despite low pharmacological support, improvement of cardiac index as monitored by the Swan-Ganz catheter and improvement of heart contractility as well on echocardiography. The pump flow was gradually decreased of 500–800 ml every day, while rising the intravenously heparin infusion dosage and monitoring haemodynamics and cardiac function. The CentriMag was removed when pump flow reached 1.5 l/min. It required no rise of CVP, no increase of inotropic support, and good contractility.
In all patients, the IABP support was maintained for at least 5 days after ECMO removal.
Statistical analysis was performed using SPSS 12.0 for Windows (SPSS, Inc, Chicago, IL). Categorical variables are expressed as proportions and continuous variables as mean values and standard deviation or as median and ranges.
The median CentriMag ECMO support time was 5 days (range 1–55 days). Weaning off ECMO was obtained in overall 7 (50%) patients (n = 3, peripheral; n = 4, central). Six (42.8%) patients died on ECMO (n = 3, peripheral; n = 3, central) because of multiple organ failure. One patient died on ECMO after transfer to the referral hub center while waiting for heart transplantation (Htx). Six (42.8%) patients were successfully discharged home (n = 3, peripheral; n = 3, central).
Overall median time in the intensive care unit (ICU) was 300 hours (range 10–1824 hours). Overall mechanical ventilation time was 268 hours (range 10–1440 hours) (Table 2). Two patients were successfully extubated during ECMO support.
The main postoperative complication was mediastinal bleeding (n = 9, 64.3%), mostly in case of central ECMO support, which required repeat bedside surgical exploration in the ICU and replacement of blood loss. Overall, a median number of packed red blood cells (PRBCs) of 39 (range: 8–130) and a median number of fresh frozen plasma (FFP) and platelet (PLT) units of 18 (range: 2–34) were necessary during ECMO support. The patients who survived and were weaned from ECMO got a lower number of PRBCs (median 29, range: 8–66) when compared with those who did not survive on support (median 51.5, range: 10–130) and a lower number of PLT and FFP (median 12, range: 3–32 vs. median 23.5, range: 2–34). The central ECMO patients had a higher rate of blood transfusions, in terms of PRBCs, if compared with the peripheral ECMO patients (median 50.5, range: 8–130 vs. median 30, range: 22–52), and similarly analyzing FFP and PLT (median 17.5, range: 2–34 vs. median 10, range: 7–27).
Renal failure requiring continuous venovenous hemofiltration (CVVHF) occurred in seven patients (50%), pneumonia in four (28.6%) and sepsis in six (42.8%).
By comparing the two ECMO group populations, the central setting showed a bigger incidence of re-exploration for bleeding (75% vs. 50%) and need of CVVHF (62.5% vs. 33.3%) (Table 2).
Platelet counts were measured and a moderate reduction was observed (overall, average 237.5 ± 81.1 K/µl, before ECMO, vs. 151.3 ± 91.6 K/µl, already at 48 hours of ECMO support but with no significant further reduction at the overall average time of ECMO support and no significant difference between survivors and nonsurvivors). No heparin-induced thrombocitopenia cases were observed.
The average plasma-free hemoglobin (PFH)-hemolysis marker was 9.8 (range 2.4–211) IU. Among survivors, the average PFH was 8.4 (range 2.4–203) IU, whereas for nonsurvivors it was 16.2 (range 3.1 –211) mmol/l.
No major cerebral events occurred. No peripheral complications concerning groin vessels access were observed.
Only two patients were considered suitable candidates for Htx since no myocardial recovery was obtained. Both died during ECMO support (n = 1 at our institution; n = 1 at the referral hub center after transfer). The question of whether to bridge to transplant or use a long-term device has remained controversial. Our goal was to adopt the CentriMag ECMO support as a bridge to Htx since the average waiting time to Htx is shorter than in the United States (40 vs. 250 days).
Patients who underwent cardiac surgery procedure emergently and who had a CS before surgery (n = 6) had a poor outcome (n = 2 [33.3%], weaned off from ECMO). Eight patients were operated on urgently (n = 2) or electively (n = 6) and the weaning rate was 62.5% (n = 5).
Only in one patient (n = 9) the oxygenator was changed every 14 days (55 days of support) when the pressure drop was bigger than 130 mm Hg and the PaO2 was less than 70 at a FiO2 of 100%. In all, the other 13 patients the oxygenator was never changed. No gas exchanger (Sechrist) replacement was necessary in all patients.
Of the six patients who recovered and were discharged home, all (100%) are presently alive.
Postcardiotomy cardiogenic shock is a critical condition. Several short-term VADs have been adopted as treatment for such a delicate clinical scenario, but the mortality rate actually remains still high (70–90%).21, 22
Short-term VADs include the Abiomed BVS 500 (Abiomed Inc., Danvers, MA), the Bio-Medicus systems (Medtronic Bio-Medicus, Inc., Minneapolis, MN) and percutaneous devices such as the Tandem Heart (CardiacAssist Inc, Pittsburgh, PA). Disadvantages of these modalities of support include the limited duration of support, the need for pump exchanges at short intervals of time, the high incidence of complications with increasing duration of support, the need for fairly stringent anticoagulation, and the requirement of an experienced team.
According to literature, the Levitronix CentriMag VAD usage seems to overcome the previously mentioned limitations and improve the outcome with an average success rate of 42–47% as treatment of postcardiotomy CS.6, 9, 23, 24 De Robertis et al.6 reported the usage of CentriMag VAD in 12 cases and showed a discharge rate of 42% after a mean duration of support of 8.3 days. Similar results were reported by Shuhaiber et al.23 (n = 7 postcardiotomy cases: 3 of them were alive after a mean support time of 8 days) and Loforte et al.9 (n = 23 postcardiotomy cases: 11 of them [47.8%] were weaned and discharged home). Recently, a multicenter trial concerning the Levitronix CentriMag ventricular assist system for short-term circulatory support was published by John et al.24: 38 patients were supported by CentriMag at 7 centers and 12 of them after cardiodomy. They reported 33% of survival to discharge and 17% (2/12) of 6 month survival.
A recent option is the adoption of CentriMag ECMO support.13–16 In general, ECMO offers several advantages: (1) it provides cardiac and pulmonary support; (2) the peripheral insertion of cannulas into vessels is simple and rapid, thus avoiding a sternotomy incision; (3) it can be performed during cardiopulmonary resuscitation; (4) it provides time to assess eligibility for Htx or long-term VAD; and (5) it is less costly than other forms of MCS.8, 10, 25
The first usage of Levitronix as peripheral ECMO support was reported by Saeed et al.13 in 2007: the patient was a 56-year-old woman with postcardiotomy cardiogenic shock treated by the percutaneous implantation of a femoro-femoral CentriMag, which was installed in the ICU. Khan et al.14 described the CentriMag ECMO support, implanted both peripherally and centrally, after lung transplantation as treatment of primary graft failure in three patients and resulted to be safe, technically easy to implant and manage. Thereafter, concerning the treatment of CS, the peripheral CentriMag ECMO was described by Aziz et al.15 who reported a series of 10 patients. The average duration of support was 5.8 days and overall survival to discharge was 60%. Only 2 patients (20%) had a postcardiotomy cardiogenic shock with a survival rate of 50%. Russo et al.16 adopted the CentriMag ECMO in 15 patients as both central (n = 7, 46.6%) and peripheral setting (n = 8, 53.4%). Only three of them had postcardiotomy etiology, one patient has been transplanted, one weaned from ECMO and one dead-on device support.
At our institution, the CentriMag ECMO was easily installed in all our patients both peripherally and centrally without complications, worked well while providing adequate support, and significantly reduced expected mortality in critically ill patients.
The bearingless, magnetic levitation (maglev) rotor technology of Levitronix CentriMag device appears appropriate for ECMO support. It works with minimal shear trauma to blood cells, therefore reducing the risks of hemolysis and thrombus formation. We had no clotting of both device and ECMO circuit.
Full circulatory support by CentriMag ECMO rapidly improves patients’ hemodinamics and end-organ function. In case of postcardiotomy CS we believe that a rapid ECMO installation is essential to achieve an acceptable outcome thus avoiding the complications associated with a long CPB time, high-dosage of inotropic infusions, and prolonged low peripheral perfusion.
In six patients, the femoral route was used for ECMO support since preference of the surgeon in order to reduce the risk of bleeding and infection and help nursing care in the ICU (Table 2). Left ventricular decompression was sufficiently achieved by usage of IABP only. However, such an approach still requires more investigations.
In conclusion, we have found that the Levitronix CentriMag ECMO system is a reliable and easy temporary circulatory support system as a bridge to decision in patients with postcardiotomy refractory acute CS.
The first limitation of this study is the small cohort of patients. Preliminary results were provided concerning such a MCS strategy and further investigations will be necessary to draw robust conclusions. This study is also subject to all limitations concerning such a retrospective and nonrandomized analysis. We started recently an ECMO support program by adoption of the CentriMag pump, thus no comparisons with other kinds of ECMO and MCS systems are actually available.
The authors thank the entire MCS team at the Deutsches Herzzentrum Berlin, Berlin, Germany, for continuous support.
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Levitronix CentriMag; extracorporeal membrane oxygenation; postcardiotomy cardiogenic shock