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Ann Thorac Surg 2002;73:1628-1629
© 2002 The Society of Thoracic Surgeons
a department of Cardiology, Niguarda Hospital, Milan, Italy
b department of Cardiovascular Surgery, Niguarda Hospital, Milan, Italy
Accepted for publication October 10, 2001.
* Address reprint requests to Dr Russo, Department of Cardiac Surgery "A. De Gasperis," Niguarda Hospital, Piazza Ospedale Maggiore, 3, 20162 Milan, Italy
e-mail: cf.russo{at}tiscalinet.it
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Abstract |
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Introduction |
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The DeBakey VAD (MicroMed Technology, Inc, Houston, TX) [1] is an electromagnetically actuated, implantable titanium axial flow blood pump designed for LV support. The pump connects the apex of LV to the ascending aorta and is smaller compared with other kinds of VADs. An ultrasonic Doppler flow probe is placed around the outflow conduit (Fig 1). The device is connected by a percutaneous cable to an external controller. The pump does not have valves and can produce up to 10 L/min continuous flows, with a rotor speed of 7,500 to 12,500 rpm. The rotor speed can be adjusted through the external unit. The wearable external controller continuously displays pump operating indicators: speed, flow, power, and battery charge. Power is supplied by a central unit, or during patient mobilization, by two 12-V rechargeable batteries.
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After approval by the ethics committee and the patient’s informed consent, she was enrolled in the DeBakey VAD European multicenter, nonrandomized study. We decided to implant a DeBakey VAD because of the small body surface area (1.4 m2) of the patient. The device was implanted with extracorporeal circulation and cardioplegic arrest. Extracorporeal circulation was discontinued when the VAD index was more than 2.5 L · min-1 · m-2. The implantation procedure was uneventful. A Gore-Tex sheet (W. L. Gore & Associates, Flagstaff, AZ) was wrapped around the device to prevent adhesions [2]. At the end of the operation the patient was stable and the mechanical support was working properly; mixed venous O2 saturation was more than 70% and cardiac index was more than 2.5 L · min-1 · m-2. The position of the inflow cannula in the LV and the right ventricle function were assessed by transesophageal echocardiography.
The early postoperative period was uneventful: mean blood pressure was always more than 90 mm Hg and end-organ dysfunction recovered. After a first phase of intravenous heparin, a combined anticoagulation protocol was used: dipyridamole, penthoxyfilline, aspirin, warfarin sodium, and low molecular weight heparin [3]. The international normalized ratio and partial thromboplastin time were controlled daily and once a week a thromboelastogram was studied. Ten days after implant, the patient was discharged from the intensive care unit without inotropic medical support; she was confident with the device and she attended a rehabilitation program. Laboratory tests and echocardiography were performed regularly. No hemolysis occurred.
On the 112th postoperative day, the patient experienced increasing dyspnea. The pump controller indicated an abnormal increase in current from 0.6 A to 1.4 A and in power from 7.8 W to 15 W—changes suggestive of increasing friction on the pump impeller, possibly due to VAD thrombosis. Despite the patient’s adequate anticoagulation profile (international normalized ratio 3.3, partial thromboplastin time 60 seconds), we immediately started intravenous heparin administration. Transthoracic echocardiography did not demonstrate endoventricular thrombus, and no stenosis was observed at the anastomosis of the outflow graft. Contrast computed tomography scan did not show obstruction or kinking of the outflow graft. The patient’s condition continued to deteriorate; the pump controller’s current and power indicators remained higher than normal and flow rate decreased to 2.1 L/min. The VAD stopped twice but the pump restarted both times, owing to its automatic restart program.
We suspected a pump thrombosis. According to the manufacturer’s technical support staff advice, we decided to perform endoventricular thrombolysis delivering recombinant tissue plasminogen activator into the LV. We considered low-dose local administration safer than systemic thrombolysis. Angiography was not performed because we were concerned that radiopaque contrast could further increase blood viscosity, worsening pump friction. Three hours later a 5F pigtail catheter was inserted through the right femoral artery into the LV, close to the inflow cannula. The aortic valve was easily crossed by the catheter, which remained stable in the LV despite the continuous negative pressure caused by the VAD. Three recombinant tissue plasminogen activator boluses (12, 10, and 10 mg) were administered into the LV over 15 minutes; after the last dose, a 50-mg sodium heparin bolus was administered. After 20 minutes, pump power and current values decreased, flow rate increased, and the patient’s clinical status improved. After 3 hours the pump indicators were normal, the flow was 4.5 L/min, and there was complete hemodynamic recovery.
No neurologic events occurred; only transient hematuria occurred. The pump continued to work properly. We controlled more strictly the coagulation profile but we did not change our protocol. On the 142nd day after VAD implant, the patient underwent heart transplantation and was discharged. At VAD explantation, no clot was found in the LV, in the vascular graft, or at the aortic anastomosis. We could not assess the inner part of the pump but, considering the effectiveness of thrombolysis, it made sense that if a clot had been in the device, it would not be possible to find it anymore.
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Comment |
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In our experience, the device dysfunction was apparently caused by a VAD thrombus and, indeed, immediate intraventricular thrombolysis fixed the pump failure. This case represents the only adverse event in our series of 9 DeBakey VAD implants. The immediate administration of low-dose LV thrombolysis was safe and effective. This approach is justified to avoid the risk of high-dose systemic thrombolysis or device replacement.
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This article has been cited by other articles:
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  C. Decoene, G. Fayad, S. Al-Ruzzeh, T. Modine, F. Crepin, A. Pol, and H. Warembourg Right ventricular assist device thrombosis during biventricular heart assistance Perfusion, December 1, 2004; 19(6): 365 - 367. [Abstract] [PDF]
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 E. Vitali, M. Lanfranconi, E. Ribera, G. Bruschi, T. Colombo, M. Frigerio, and C. Russo Successful experience in bridging patients to heart transplantation with the MicroMed Debakey ventricular assist device Ann. Thorac. Surg., April 1, 2003; 75(4): 1200 - 1204. [Abstract] [Full Text] [PDF]
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