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(Circulation. 2000;101:356.)
© 2000 American Heart Association, Inc.
Brief Rapid Communications |
First Clinical Experience With the DeBakey VAD Continuous-Axial-Flow Pump for Bridge to Transplantation
From the Department of Cardiothoracic Surgery (G.M.W., H.S., G.L., E.W.), the Department for Cardiothoracic Anesthesia and Intensive Care (M.H.), and the Department of Cardiology, Internal Medicine II (R.P.), University of Vienna, Austria, and the Department of Surgery, Baylor College of Medicine, The Methodist Hospital, Houston, Tex (G.P.N., M.D.).
Correspondence to Georg M. 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
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Abstract |
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 Top Abstract IntroductionMethodsResultsDiscussionReferences |
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Background—A shortage of donor organs and increased numbers of deaths of patients on the waiting list for cardiac transplantation make mechanical circulatory support for a bridge to transplantation a standard clinical procedure. Continuous-flow rotary blood pumps offer exciting new perspectives.
Methods and Results—Two male patients (ages 44 and 65 years) suffering from end-stage left heart failure were implanted with a DeBakey VAD axial-flow pump for use as a bridge to transplant. In the initial postoperative period, the mean pump flow was 3.9±0.5 L/min, which equals a mean cardiac index (CI) of 2.3±0.2 L · min-1 · m-2. In both patients, the early postoperative phase was characterized by a completely nonpulsatile flow profile. However, with the recovery of heart function 8 to 12 days after implantation, increasing pulse pressures became evident, and net flow rose to 4.5±0.6 L/min, causing an increase of mean CI up to 2.7±0.2 L · min-1 · m-2. Patients were mobilized and put through regular physical training. Hemolysis stayed in the physiological range and increased only slightly from 2.1±0.8 mg/dL before surgery to 3.3±1.8 mg/dL 6 weeks after implantation.
Conclusions—The first clinical implants of the DeBakey VAD axial-flow pump have demonstrated the device to be a promising measure of bridge-to-transplant mechanical support.
Key Words: heart failure • heart-assist device • DeBakey VAD
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Introduction |
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Ashortage of suitable donor grafts prolongs the waiting time for cardiac transplantation and increases the number of patients who die while on the waiting list. Bridge-to-transplant programs with mechanical assist devices were successfully installed to overcome the problem of acute hemodynamic deterioration in patients on the waiting list. Development of technically reliable pulsatile mechanical assist devices over the past 3 decades guarantees their feasibility for long-term bridge-to-transplantation support up to 2 years. However, device size and noise and infection of the power/vent line limit the use of these devices.
Axial-flow impeller pumps, with their potential for small size, low noise, and absence of a compliance chamber, have been developed for clinical use during the past 10 years. Of 4 potential candidates (Jarvik 2000 Heart,1 DeBakey VAD,2 Nimbus/Pittsburgh axial-flow blood pump,3 and Sun Medical/HIJ/Waseda/Pittsburgh intraventricular axial-flow blood pump4 ), the DeBakey VAD was the first clinically used. We report the first successful clinical implants of the continuous-flow DeBakey VAD for bridge to transplant in 2 patients in our institution.
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Methods |
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DeBakey VAD
The electromagnetically actuated DeBakey VAD is a miniaturized, fully implantable titanium axial-flow blood pump (Figure 1
). A titanium inflow cannula connects
the pump to the apex of the left ventricle, and a Vascutec Gelweave
vascular graft as an outflow conduit connects the pump to the ascending
aorta. An ultrasonic flow probe is placed around the outflow conduit.
Together with the flow probe’s wiring, the pump motor cable exits the
skin superior to the right iliac crest and attaches to the VAD’s
external controller system. The pump is designed to achieve 5 L/min
against 100 mm Hg pressure, with a rotor speed of 10 000 rpm and
a power input of <10 W. The measured pump flow is displayed either on
the external VAD controller or when connected on the clinical data
acquisition system (CDAS) together with pump speed, power consumption,
and current signals from the pump. Adjustments to the pump speed can be
performed only when it is connected to the CDAS. For optimal
mobilization of the patient and freedom to move, power can be delivered
by two 12-V DC batteries for several hours.
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Patients
Two male patients suffering from end-stage left heart failure
received a DeBakey VAD as a left ventricular assist device
for bridge to transplantation (Table 1). Both patients were listed for
cardiac transplantation and showed signs of acute
hemodynamic deterioration and end-organ dysfunction at
the time of implantation. These 2 patients were the first in our center
to enroll in a multi-institutional study in Europe. The protocol for
the study was approved by the Institutional Review Committee, and both
patients provided written informed consent.
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Operation
Like other left ventricular assist devices, this
pump is implanted through a median sternotomy with extracorporeal
circulation (ECC). The pump was placed in a small, left-sided
extracardiac pocket. A sewing ring was attached to the apex of the
beating heart with circumferentially placed buttressed sutures. An
inflow cannula was inserted into the ventricle, and a Dacron skirt of
the cannula was sutured to the apical ring. The Vascutec outflow graft
was placed extrapericardially and anastomosed to the ascending aorta.
The VAD was easily deaired, and the pump was started while ECC was
gradually discontinued. A combined cardiac and pump output was
maintained at a cardiac index of 
2.0 L ·
min-1 · m-2
obtained with a Swan-Ganz catheter.
Anticoagulation
The study protocol allowed individual anticoagulation regimens
according to each center’s previous device experience. During ECC and
implantation of the pump, the patient received heparin 300 U/kg body wt
IV, and the heart-lung machine was primed with 1 000 000 IU
aprotinin. After discontinuation of ECC, heparin was reversed with an
appropriate dose of protamine. Intravenous heparin was
instituted 6 hours after surgery to achieve activated partial
thromboplastin target times of 50 to 60 seconds. Platelet
antiaggregation therapy with 150 mg/d aspirin and 225 mg/d
dipyridamole was started after removal of all chest
drains. Administration of heparin was stopped when anticoagulation with
coumarin reached target levels of INR 2.5 to 3.5.
Statistic Analysis
All results for continuous variables are expressed as
mean±SD. Students paired or unpaired t test, if
appropriate, was used to compare continuous variables between 2
subgroups. A value of P<0.05 was considered indicative of
statistical significance.
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Results |
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Clinical Course
The intraoperative course in both patients was uneventful, and the pump showed good performance, with flow rates of 3 to 5 L/min after gradual discontinuation of ECC, and adequate tissue perfusion was achieved with mixed venous oxygen saturation >60%. However, full unloading of the extremely enlarged ventricles in this early period could not be achieved, but transesophageal echocardiography showed a closed aortic valve, and no pulsations in the aortic blood pressure curve could be detected. Pump flow increased within the first days after surgery and stabilized at flow rates of 4.5±1.2 L/min after postoperative week 3 (Figure 2
). Because the aortic valve stayed
closed all the time (as shown by echocardiography),
we calculated a cardiac index of 2.7±0.2 L ·
min-1 · m-2. After
initial early extubation, both patients needed surgical reinterventions
on postoperative days 5 and 6, respectively. Anticoagulation
overtreatment caused bleeding in patient 1; patient 2
presented a laceration of the subclavian vein caused by
catheter insertion. Subsequently, both patients were mobilized,
and inotropic support for sufficient right heart function could be
discontinued. Both patients were moved from the intensive care unit to
an intermediate care ward and were put through regular physical
training to rebuild the muscle mass lost during prolonged periods of
preoperative immobilization.
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Hemodynamic Changes
The initial period after implantation of the DeBakey VAD was
characterized by complete nonpulsatile arterial blood
pressure in both patients. Despite the aortic valve staying closed,
modulation of pulsatility with low amplitude to the nonpulsatile blood
flow produced by the VAD could be achieved by varying pump flow. Mean
arterial blood pressures were always kept in the range of
70 to 90 mm Hg, and flow rate was adjusted to obtain mixed venous
oxygen saturation >60%. After this initial nonpulsatile period,
low-amplitude pulsations became more frequent and were associated with
recovered left ventricular contractility,
but at all times nonpulsatile flow patterns could be produced with an
increase in pump speed.
Device Performance
In both patients, the DeBakey VAD provided adequate flow to
maintain sufficient tissue perfusion expressed by mixed venous oxygen
saturation >60% in the early perioperative period.
Pump speed was set between 9000 and 11 000 rpm and was adjusted
manually in this early phase to avoid excess suction with
ventricular collapse, which was easily detected in the pump
flow curve. With hemodynamic stabilization of the
patients, pump flow increased gradually from 3.9±0.5 L/min in
postoperative week 1 up to 4.5±0.6 L/min after postoperative week 3,
with peak flows >6 L/min. Sudden pump desynchronizations followed by
automatic restarts could be detected in both patients but did not
dramatically affect patients in their daily routine. On postoperative
day 60, 1 patient encountered an 18-minute, probably connector-related
pump stop, which occurred during his daily exercise on the bicycle. The
patient tolerated a regurgitation of 1.3 L/min through
the pump, although he needed short-term intravenous
inotropic support. He recovered immediately when the pump was
successfully restarted and provided flows of >5 L/min.
Hemolysis
Table 2 shows indices of
hemolysis for both patients before surgery and at 1, 2, 3, 4, 5, and 6
weeks after implantation. No statistically significant elevation of
mean plasma-free hemoglobin was detected. Serum creatinine
levels declined from a slightly elevated preoperative level to normal.
Lactate dehydrogenase increased significantly during the postoperative
period, but only patient 2 developed peak levels of >800 U/L 4 weeks
after implantation, together with elevated levels of 
-glutamyl
transferase and no correlation with single peaks in plasma-free
hemoglobin.
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Discussion |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Pulsatile blood pressure profile was always considered necessary to maintain sufficient tissue perfusion in mammals. Early studies with nonpulsatile blood flow in calves performed by Johnston et al5 in 1976 gave the first evidence of tolerance of this nonphysiological blood flow pattern. Later, Golding et al6 were able to sustain survival for up to 34 days. Yada and associates7 supported calves with nonpulsatile blood flows for >3 months but hypothesized a need for an
20%
higher blood flow than with pulsatile perfusion to avoid transient
physiological disorders. In our patients, we could
demonstrate for the first time that continuous blood flow, generated by
an implanted axial-flow pump, over a period of >60 days is well
tolerated in humans. The pumps generated low hemolysis, within
physiological ranges. In accordance with the early
animal experiments, these first clinical implants provide no evidence
of disadvantages of this unphysiological
continuous-flow condition in humans. This generates optimism for a more
widespread use of implantable rotary blood pumps as long-term
mechanical support. In contrast to the electric pusher-plate pumps,
axial-flow pumps are silent, are smaller in size, have lower energy
requirements, and provide the prospect of low device costs.
Nevertheless, a number of questions are as yet unanswered. Some of them
are general concerns applicable to all kinds of rotary blood pumps,
such as the absence of an inherent Frank-Starling mechanism and its
consequences during exercise, as well as the definition of control
parameters to optimize pump-speed adjustments and avoid
excess suction.8 9 Such questions as noninvasive
measurement of nonpulsatile or low-pulsatile blood pressures of fully
mobilized and exercising patients will have to be addressed in the
future. Furthermore, episodes of stalling and consecutive pump stops
and restarts have not yet been sufficiently explained. Other questions
involve construction specifications of the pump, such as the geometry
and diameter of the pump inflow cannulas. In conclusion, the first clinical implants of the DeBakey VAD axial-flow pump have demonstrated the feasibility of continuous-blood-flow pumps as a promising measure of bridge-to-transplant mechanical support. This new technology opens exciting possibilities with evident advantages, but a number of questions remain open with regard to use of the pumps in humans.
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Acknowledgments |
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The DeBakey VAD devices were provided according to an Ethics Committee–approved study protocol by MicroMed Technology Inc.
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Footnotes |
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Guest Editor for this article was Eric A. Rose, MD, Columbia-Presbyterian Medical Center, New York, NY.
Received March 3, 1999; revision received November 10, 1999; accepted November 23, 1999.
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References |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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1. Macris MP, Parnis SM, Frazier OH, Fuqua JM Jr, Jarvik RK. Development of an implantable ventricular assist system. Ann Thorac Surg. 1997;63:367–370.
2. DeBakey ME, Benkowski R. The DeBakey/NASA axial flow ventricular assist device. In: Akutsu T, Koyanagi H, eds. Heart Replacement and Artificial Heart 6. Tokyo, Japan: Springer Verlag; 1998:407–413.
3. Butler K, Thomas D, Antaki J, Borovetz H, Griffith B, Kameneva M, Kormos B, Litwak P. Development of the Nimbus/Pittsburgh axial flow left ventricular assist system. Artif Organs. 1997;21:602–610.[Medline] [Order article via Infotrieve]
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5.
Johnston GG, Hammill F, Marzec U, Gerard D, Johansen
K, Dilley RB, Bernstein F. Prolonged pulseless perfusion in
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6. Golding LR, Jacobs G, Murakami T, Takatani S, Valdes F, Harasaki H, Nose Y. Chronic nonpulsatile blood flow in an alive, awake animal 34-day survival. Trans Am Soc Artif Intern Organs. 1980;26:251–255.[Medline] [Order article via Infotrieve]
7. Yada I, Golding LR, Harasaki H, Jacobs G, Koike S, Yozu R, Sato N, Fujimoto LK, Snow J, Olsen E, Murabayashi S, Vekatesen VS, Kiraly R, Nose Y. Physiopathological studies of nonpulsatile blood flow in chronic models. Trans Am Soc Artif Intern Organs. 1983;26:520–525.
8. Schima H, Trubel W, Moritz A, Wieselthaler G, Stöhr H, Thoma H, Losert U, Wolner E. Noninvasive monitoring of rotary blood pumps: necessity, possibilities, and limitations. Artif Organs. 1992;16:195–202.[Medline] [Order article via Infotrieve]
9. Holzer S, Scherer R, Schmidt C, Schwendenwein I, Wieselthaler G, Noisser R, Schima H. A clinical monitoring system for centrifugal blood pumps. Artif Organs. 1995;19:708–712.[Medline] [Order article via Infotrieve]
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