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Ann Thorac Surg 2007;83:1865-1867
© 2007 The Society of Thoracic Surgeons
a Department of Anesthesia, Deutsches Herzzentrum Berlin, Berlin, Germany
b Department of Cardiothoracic and Vascular Surgery, Deutsches Herzzentrum Berlin, Berlin, Germany
c Department of Perfusion, Deutsches Herzzentrum Berlin, Berlin, Germany
Accepted for publication November 16, 2006.
* Address correspondence to Dr Koster, Deutsches Herzzentrum Berlin, Augustenburger Platz 1, Berlin, 13305 Germany (Email: koster{at}dhzb.de).
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A 40-year-old, 55 kg, woman was transferred to our institution for implantation of a ventricular assist device. The patient’s history showed the repair of an acute aortic type A dissection with a mechanically valved conduit (Carbomedics, Austin, TX, 21 mm) and a single venous coronary artery graft to the right coronary artery. One day after surgery the patient had a massive biventricular failure develop due to myocardial infarction caused by graft thrombosis, which required mechanical circulatory support with a closed uncoated ECMO system (Levitronix, Waltham, MA) with cannulation of the right atrium and the ascending aortic graft. Anticoagulation for ECMO was performed with intravenous unfractionated heparin guided by target activated clotting time (ACT) values of 200 to 250 seconds.
After the patient’s arrival to our intensive care unit, transesophageal echocardiography was performed at an ECMO flow of 2 L/min showing a left ventricular ejection fraction of 30% and a right ventricular ejection fraction of <30%. Immediate implantation of a biventricular assist device was considered, but it was rejected as the first choice option because of the danger of thrombosis of the mechanical aortic valve under conditions of the left heart unloading through the left ventricular assist device. The volume of the thorax precluded implantation of a total artificial heart. Therefore it was decided to wait for potential recovery of ventricular function. On day 5 of ECMO support, the transesophageal echocardiography revealed a partial recovery of left ventricular function but persistent severe impairment of right ventricular activity, so that implantation of an RVAD within the next few days was considered. However, on the following day the platelet count, which had remained stable before at approximately 80,000/nL, suddenly decreased to 20,000/nL, and the suspected diagnosis of acute HIT was confirmed in an antibody test (Particle GEL immune assay [Diamed AG, Cresier Sur Morat, Switzerland]) and in the heparin-induced platelet aggregation assay.
After confirmation of the diagnosis, heparin was stopped. After obtaining the informed consent of patients’ relatives and notifying the local ethics committee, bivalirudin therapy (Angiox [Nycomed, Roskilde, Denmark]) was initiated with a bolus of 0.5 mg/kg followed by a continuous infusion of 0.5 mg/kg/h. Although initial ACT values (Hepcon HMS ACT, [Medtronic, Minneapolis, MN]) were 420 seconds, presumably due to the remaining heparin effects, during the following hours the ACT values slowly decreed to 200 to 220 seconds and remained stable during continuous bivalirudin infusion. During the next day, platelet counts increased to values of 45,000/nL and implantation of an RVAD was scheduled for the following day.
Shortly before the start of the operation, an additional bolus of 0.25 mg/kg bivalirudin was given and the infusion rate increased to 1.0 mg/kg/h, which translated into ACT values of 300 to 350 seconds. These higher values were considered safer due to the activation of the hemostatic system during surgery. After opening the chest, the pulmonary artery was partially clamped and a cannula for the pneumatic pulsatile Berlin Heart (Berlin Heart AG, Berlin, Germany) was implanted. Next, single pledgeted sutures were placed in a circle in the right atrium, the atrium was opened, and the right atrial cannula was inserted. During implantation of both cannulas care was taken by retrograde filling with saline and distal clamping so that no blood entered the cannula to prevent generation of a stagnant blood column with the immanent risk of thrombus formation during bivalirudin anticoagulation [4, 5]. Then the RVAD support was started, and the patient was weaned from ECMO with modest inotropic support. The intraoperative blood loss was 1,250 mL, and the transfusion requirement was 4 units of red blood cells, 6 units of fresh frozen plasma, and 1 platelet concentrate. Although the ACT values during constant bivalirudin infusion remained in the range of 300 of 350 seconds, the values gradually decreased after initiation of RVAD support and termination of bivalirudin infusion, and the chest was closed after 90 minutes at an ACT value of 160 seconds (Fig 1). During the entire period of ECMO support the creatinine clearance remained in the range of 40 to 50 mL/min corresponding to serum creatinine values of 1.8 mg/dL. Six hours after the operation, anticoagulation was continued with argatroban (Argatra [Mitsubishi Pharma Europe, Düsseldorf, Germany]) using a dose of 0.05 mg/kg/h. The blood loss during the postoperative 24 hours was 950 mL. The patient could be weaned from mechanical ventilation 10 days after RVAD implantation. After 6 weeks of mechanical support the contractility of the right ventricle had recovered so that the RVAD could be explanted. This procedure could be performed without the use of CPB.
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The acute development of HIT required immediate institution of alternative anticoagulation. Lepirudin and argatroban are potentially valuable treatment options in the condition of HIT. In contrast to the other options, the bivalirudin elimination half-life (ie, approximately 25 min) is shorter and essentially independent of renal and hepatic function, so that the safety profile is more favorable, particularly in a patient with such a severe clinical condition. In view of these considerations, the potential need to switch from ECMO to CPB encouraged the decision to use bivalirudin as a treatment option [6].
Although experience has been gathered in the use bivalirudin during cardiac surgery with and without CPB, no dosing regimen for anticoagulation of a completely closed ECMO system exists. The dose of 0.25 mg/kg/h currently used for intravenous thrombosis prophylaxis seemed to be rather low, whereas a high dose (as used during coronary intervention or off- pump cardiac surgery) of 1.75 mg/kg/h or 2.5 mg/kg/h during CPB seemed to be too high. Therefore we decided to use an intermediate dose of 0.5mg/kg/h, with the option of a gradual increase to achieve the target ACT of 200 to 250 seconds. This was deemed suitable for safe support on a completely closed uncoated ECMO system, but at the same time it was expected to prevent diffuse bleeding in a thrombocytopenic patient.
Two perfusion strategies for implantation of the RVAD were considered. First the switch from ECMO to a conventional CPB circuit, which would have permitted cardiotomy suction and allowed better handling of air entering the system, but would have required a considerable increase in anticoagulation. The alternative was to implant the RVAD during ECMO support, which due to the completely closed system allowed reduced dosing of bivalirudin, but involved the danger of a system crash if air entered the ECMO system. It was decided to implant the RVAD on ECMO support, but with a completely filled CPB system as a back-up in the operation room with the use of a cell saver. However, during surgery, which leads to a massive release of activated tissue-factor and activation of the hemostatic system, a target ACT of 200 seconds was evaluated as being too low. Therefore bivalirudin dosing was increased by administration of a further small bolus and increase of the infusion rate to 1 mg/kg/h to achieve a target ACT of 300 to 350 seconds.
Using this protocol the ECMO flow was maintained without problems and postoperative inspection of the system revealed no thrombus formation.
The current experience indicates that bivalirudin can be used for treatment of acute HIT syndrome, as observed by an increase of the patient’s platelet count after institution of bivalirudin therapy. We were able to show that moderate dosages of bivalirudin of 0.5 mg/kg/h enable anticoagulation during support with a completely closed ECMO system. In addition we demonstrated that in using such a closed ECMO system, selected cardiac surgical procedures that do not require cardiotomy suction or permit air to penetrate the circuit may be performed with bivalirudin doses considerably lower than those currently recommended for anticoagulation during off-pump and on-pump surgery [2, 3]. The reduced degree of anticoagulation conceivably contributed to relatively low perioperative blood loss, moderate transfusion requirements, and short chest closure time even under these complex conditions of VAD implantation after major aortic surgery and prolonged ECMO support. Further detailed studies in this regard are warranted.
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