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Ann Thorac Surg 2001;71:S139-S143
© 2001 The Society of Thoracic Surgeons
a Department of Cardiothoracic Surgery, University of Vienna, Vienna, Austria
b Department of Cardiothoracic Anesthesia and Intensive Care, University of Vienna, Vienna, Austria
c Department of Cardiology, Internal Medicine II, University of Vienna, Vienna, Austria
Address reprint requests to Dr Wieselthaler, Department of Cardiothoracic Surgery, University of Vienna, Waehringer Guertel 18-20, A-1090 Vienna, Austria
e-mail: georg.wieselthaler{at}akh-wien.ac.at
Presented at the Fifth International Conference on Circulatory Support Devices for Severe Cardiac Failure, New York, NY, Sept 15–17, 2000.
Abstract
Background. The bridge to transplantation with pulsatile mechanical assist devices became a standard procedure for patients deteriorating on the waiting list. Recently, continuous flow axial impeller pumps were introduced to clinical application offering new advantages.
Methods. From November 1998 till September 2000, 6 male patients (mean age 53 plus or minus 11 years) with end-stage left heart failure were implanted with a DeBakey ventricular assist device (VAD) axial-flow pump for bridge to transplantation.
Results. Three patients were successfully transplanted after 74, 115, and 117 days, respectively. Two other patients died after 25 and 133 days. One patient is still on the device after 108 days. Because of modification of the implantation technique after the first 2 patients, mean pump-flow within the first 3 weeks was increased from 4.3 ± 0.6 L/min to 6.7 ± 0.3 L/min. Patients were put on regular bicycle-ergometer training and improved their exercise capacities up to a mean maximum oxygen consumption of 20.2 mL/kg/min.
Conclusions. Initial implants of the DeBakey VAD demonstrated support properties comparable to pulsatile pumps but without significant restrictions for extended use.
Patients listed for cardiac transplantation may deteriorate hemodynamically despite maximal pharmacologic support. The bridge to transplantation with mechanical ventricular assist devices offers these patients an opportunity to survive. Tremendous improvements in technology, together with the development of smaller, wearable, and technically reliable pumps and drivers, facilitated wide clinical use and rapid experience with these devices over the past 3 decades. Bridging to transplantation with pulsatile ventricular assist devices (VADs) became a standard clinical procedure and improved morbidity and mortality of patients on the waiting list [1, 2]. Larger series of patients supported with different devices exhibited disadvantages of pulsatile blood pumps [3]. Pneumatically-driven pulsatile blood pumps require stiff drivelines to connect bulky driving units. Electrically-actuated pulsatile pump implants that enhance a patient’s mobility and quality-of-life, allowing home discharges, need quite stiff power ventlines that perforate the skin and bear the danger of ascending infections [4]. Bulky implantable pump chambers limit their use for smaller patients (body surface area less than 1.5 m2) and provoke bleeding problems from large pump pockets. A new generation of blood pumps reduce at least some of the disadvantages of current pulsatile pumps. Nonpulsatile axial-flow impeller pumps hold the potential for small size, low noise, and absence of a compliance chamber. Over the past 10 years, several devices have been developed for clinical use from which three developments have been recently used for clinical implants. The first clinical use of the DeBakey VAD was in November 1998 [5] followed by the Jarvik 2000 Heart [6], and the TCI II (Thermo Cardiosystems Inc, Woburn, MA) [7] in the beginning of the year 2000. We report our initial experience with the first consecutive patients using this new technology, nonpulsatile VAD, and discuss the new features and differences with pulsatile devices.
Material and methods
Patients
From November 1998 to August 2000, 6 male patients, 53 ± 11 years old (mean plus or minus standard deviation) underwent implantation of a DeBakey VAD [8] as a bridge to heart transplantation. All patients suffered from end-stage left heart failure and were listed for cardiac transplantation. Despite maximal pharmacologic support, patients showed signs of acute hemodynamic deterioration and end-organ dysfunction at the time of implantation. None of the patients were on mechanical support or ventilation before implantation. Hemodynamics and pharmacologic support at the time of implantation are presented in Table 1. All patients met inclusion criteria for enrollment in a multiinstitutional study in Europe and provided their written informed consent for implantation. The protocol for the study was approved by the Institutional Review Committee.
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All patients needed inotropic support initially after implantation for adequate right heart function. To protect the impaired right ventricle, the target cardiac index was not to exceed 2.5 L/min/m2 within the first 24 to 48 hours after implantation, and to also achieve a mixed venous-oxygen saturation greater than 60% for adequate tissue perfusion. If necessary, nitric oxide was used to reduce elevated pulmonary vascular resistance. However, in the first 2 patients, this target cardiac index could not be reached because flow restrictions limited increases of pump flows over 4 L/min. Because of modified placement of the inflow cannula (Wieselthaler GM, Schima H, Grimm M, Wolner E. Special considerations on implantation technique for the DeBakey VAD axial pump. Submitted for publication.) a significant increase in pump output was achieved after these first 2 patients (Table 2). After the initial postoperative period, pump speed was manually adjusted to obtain mixed venous-oxygen saturation greater than 70% with mean arterial blood pressures 
65 mm Hg. In all patients, except patients 4 and 6, the initial postoperative period after implantation was characterized by complete nonpulsatile arterial blood flow. Pulsatility with low amplitude reappeared in all patients after a period of 6 to 10 days, whereas the aortic valve stayed closed all the time. Echocardiography examination showed that the aortic valve opened only under forced exercise.
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Results
Clinical outcome
All patients, except patient 5, were extubated as early as possible and mobilized. After patients were moved to an intermediate ward, they underwent regular physical training with a bicycle-ergometer. Finally, 3 of the 6 patients were successfully transplanted after 74, 115, and 117 days, respectively. Patient 6 is still on the device after 110 days of uncomplicated pump support, and has been discharged from the hospital for more than 6 weeks. Patient 3 was discharged from the hospital after 60 days of pump support; readmission to the hospital was necessary after 14 days at home because of an infectious complication with pneumonia that required intubation after postoperative day 114. The patient finally died in multiorgan failure after 142 days. Patient 5 suffered from bicycle ischemic cardiomyopathy and an infarction of the right coronary artery immediately after uncomplicated implantation of the DeBakey VAD; he developed acute right heart failure and needed an additional mechanical support of the right ventricle. He was never weaned from the right ventricular assist device and died in multiorgan failure after 25 days.
Hemolysis
No clinically relevant elevation of mean plasma-free hemoglobin was detected (physiologic range zero to 4 mg/dL), except for a slight increase over longer pumping periods. Only patient 5, with the additional right ventricular assist device presented increased plasma-free hemoglobin after prolonged biventricular support (Table 3) shows indices of hemolysis for all patients (except patient 5) before surgery and at 1, 2, 3, 4, 10, and 15 weeks after implantation. Interestingly, lactate dehydrogenase increased in patients 2, 4, and 6 over the time of support with no correlation of single peaks in plasma-free hemoglobin. Patient 2 presented lactate dehydrogenase peak levels greater than 800 U/L after 4 weeks of implantation together with elevated levels of µ-glutamyl transferase, and again with no correlation of peaks in plasma-free hemoglobin. A correlation with a concomitant application of antibiotics in this patient is discussed.
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Infectious complications
Patient 1 and patient 5 presented pneumonia-like infiltrations in the lung shortly after implantation of the DeBakey VAD and needed reintubation. Adequate antibiotic therapy completely resolved the inflammation. Patient 3 had positive blood cultures with methicillin-resistant Staphylococcus aureus after intermittent attacks of fever 4 weeks after implantation of the VAD. Antibiotic therapy with vancomycin resolved the septic state and fever but methicillin-resistant Staphylococcus aureus was cultured continuously over the whole pumping period. Fifteen weeks after implantation, septic complications caused uremia with the need to hemofiltration and intubation. This patient finally died as a result of septic complications.
Discharge from hospital
The first patient in the world with an implanted continuous axial-flow blood pump was discharged home on December 10, 1999. Patient 3 recovered extremely well and showed improving results in weekly performed spiro-ergometry tests. The patient was discharged from the hospital in excellent physical condition on postoperative day 60. He had follow-up hospital visits twice a week for check-ups. Fourteen days after the patient left the hospital, he had to be readmitted because of a constant increase of arterial blood pressure, drop of pump flow, gain of weight, dyspnea, and peripheral edema. Echocardiography showed impaired right ventricular function with congestion of the lungs. Hemodynamic and pump parameters are shown in Figure 1. Institution of intravenous diuretic therapy, together with short-term mild inotropic support, improved the patient’s condition within days. Subsequently this patient left the hospital only for single day trips.
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Since the bridge to transplantation with mechanical ventricular assist devices became a standard procedure for patients deteriorating on the waiting list, primarily pulsatile blood pumps were used. Over the years, electrically-driven pumps became fully implantable and drivers were miniaturized and wearable. With these technically reliable systems, patients could be discharged from the hospital to wait at home for transplantation. For the last 10 years, strong efforts were made to develop a new generation of pumps. Nonpulsatile rotary pumps with their potential for small size, low noise, and absence of compliance chambers were thought to improve the quality-of-life of patients supported with mechanical ventricular assist devices. However, some concerns against these pumps remain and still need to be clarified. Initial implants in humans demonstrated that low pulsatility of blood flow, as produced by these pumps, was not detrimental to human life. At least for a period of up to 4 months, this nonphysiologic blood flow pattern was tolerated well by patients [5]. Small pump sizes bring definitive advantages during implant procedures with the potential of less complications of bleeding because of smaller incisions and pump pockets. The absence of a compliance chamber leads to thin and flexible drivelines. In contrast to implantable pulsatile pumps with stiff power or ventlines, mechanical irritation of the exit site of thin, flexible cables is reduced. No infectious complications of the exit site were detected in any of our patients.
If good tissue perfusion is obtained through adequate pump flows, patients recover very fast after implantation. Because all our patients were in severe end-stage cardiac failure at the time of implantation and needed initial inotropic support for sufficient right ventricular function, we tried to provide pump flows in the range of 5 to 6 L/min to maintain adequate tissue perfusion with mixed venous-oxygen saturations greater than 60%. Reduction of pump speed and, consequently, pump flow limited patients mobility in daily life. Three of 6 patients were fully immobilized for a long period of time before VAD implantation. Therefore, physical training was instituted as early as possible after the operation to rebuild the patients’ muscle mass and improve their general condition for the upcoming transplantation. As reported previously, patients on VADs have the ability to improve their exercise capacity during support [9, 10]. Regular daily training on a bicycle-ergometer improved anerobic thresholds. Despite nonphysiologic blood flow patterns, conditioning was assessed weekly by spiro-ergometry. In one patient, VO2max increased up to 20.2 mL/kg/min when exercising with 125-watt workload (Wieselthaler GM, Quittan M, Schima H, et al. Assessment of exercise capacity in patients with an implanted continuous axial flow DeBakey VAD. Submitted for publication). In addition, it was demonstrated that an increase in pump speed with higher pump flows during exercise resulted in an increase of anerobic threshold and a drop of lactate production in these patients. Our findings provide evidence that patients can exercise with a constant pump speed but could improve exercise capacity when a physiologic control algorithm was implemented in their drivers. Also changed demands in blood flow because of circadian rhythm could be better attained with physiological control algorithms rather than adjusting pump flows manually.
In contrast to pulsatile pumps with artificial valves, rotary blood pumps are not occlusive when they fail. In both patients with pump stops regurgitant flow of 1.3 to 1.5 L/min was measured with the implanted flow probe. None of the patients tolerated this amount of backflow for an extended period of time, and after initial administration of mild inotropes the outflow graft had to be ligated. Embolization with thrombus formation caused one pump stop but no peripheral neurologic deficit was detected. Again, in contrast to pulsatile pumps, axial flow impeller pumps stop when a large embolus enters the pump; this prevents peripheral thromboembolism.
In conclusion, these first implants of the continuous axial flow DeBakey VAD in patients demonstrated support properties and feasibility in patients comparable to pulsatile pumps. Because patients tolerated nonphysiologic blood flow patterns for a period of up to 4 months, we believe that no principal restriction for extended use for this new generation of pump exists.
Acknowledgments
We thank MicroMed Technology Inc, The Woodlands, TX for providing the DeBakey VAD devices for this clinical multiinstitutional study.
References
This article has been cited by other articles:
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  M. J. Wilhelm, D. Hammel, C. Schmid, A. Rhode, T. Kaan, M. Rothenburger, J. Stypmann, M. Schafers, C. Schmidt, H. A. Baba, et al. Long-term support of 9 patients with the DeBakey VAD for more than 200 days J. Thorac. Cardiovasc. Surg., October 1, 2005; 130(4): 1122 - 1129. [Abstract] [Full Text] [PDF]
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 G. M. Wieselthaler, H. Schima, and E. Wolner Special considerations on the implantation technique for the MicroMed-DeBakey ventricular assist device axial pump Ann. Thorac. Surg., December 1, 2003; 76(6): 2109 - 2111. [Abstract] [Full Text] [PDF]
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 J.M. Grinda, C.H. Latremouille, P. Chevalier, N. D'Attelis, F. Boughenou, R. Guillemain, A. Deloche, and J.N. Fabiani Bridge to transplantation with the DeBakey VAD(R) axial pump: a single center report Eur. J. Cardiothorac. Surg., December 1, 2002; 22(6): 965 - 970. [Abstract] [Full Text] [PDF]
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 M. Rothenburger, M. J. Wilhelm, D. Hammel, C. Schmidt, T. D. T. Tjan, D. Bocker, H. H. Scheld, and C. Schmid Treatment of Thrombus Formation Associated With the MicroMed DeBakey VAD Using Recombinant Tissue Plasminogen Activator Circulation, September 24, 2002; 106(12_suppl_1): I-189 - I-192. [Abstract] [Full Text] [PDF]
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H. J. Ankersmit, G. Wieselthaler, B. Moser, S. Gerlitz, G. Roth, G. Boltz-Nitulescu, and E. Wolner Transitory immunologic response after implantation of the DeBakey VAD continuous-axial-flow pump J. Thorac. Cardiovasc. Surg., March 1, 2002; 123(3): 557 - 561. [Abstract] [Full Text] [PDF]
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