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Right arrow Mechanical Circulatory Assistance

Ann Thorac Surg 2006;81:1752-1759
© 2006 The Society of Thoracic Surgeons

Original article: Cardiovascular

Mechanical Reliability of the Jarvik 2000 Heart

Michael P. Siegenthaler, MD a , * , O.H. Frazier, MD b , Friedhelm Beyersdorf, MD a , Jürgen Martin, MD a , Hillel Laks, MD c , John Elefteriades, MD d , Asghar Khaghani, MD e , Ulf Kjellman, MD f , Bansi Koul, MD g , John Pepper, MD h , Robert Jarvik, MD i , Stephen Westaby, MD j

a Center for Cardiovascular Disease, University of Freiburg, Freiburg, Germany
b Department of Cardiovascular Surgery, Texas Heart Institute, Houston, Texas
c Department of Cardiothoracic Surgery, University of California at Los Angeles, Los Angeles, California
d Cardiothoracic Surgery, Yale New Haven Hospital, New Haven, Connecticut
e Cardiothoracic Surgery, Royal Brompton and Harefield Hospitals, London, United Kingdom
f Department of Cardiovascular Surgery, Sahlgrenska University Hospital, Goteborg, Sweden
g Department of Cardiovascular Surgery, University Hospital Lund, Lund, Sweden
h Department of Cardiovascular Surgery, Royal Brompton and Harefield Hospital Trust and Imperial College, London, United Kingdom
i Jarvik Heart, Inc, New York, New York
j Department of Cardiovascular Surgery, John Radcliffe Hospital, Oxford, United Kingdom

Accepted for publication December 2, 2005.

* Address correspondence to Dr Siegenthaler, Center for Cardiovascular Disease, University of Freiburg Medical Center, Hugstetterstrasse 55, Freiburg 79106, Germany (Email: siegenth{at}ch11.ukl.uni-freiburg.de).

Presented at the Forty-first Annual Meeting of The Society of Thoracic Surgeons, Tampa, FL, Jan 24–26, 2005.


Doctor Jarvik discloses that he has a financial relationship with Jarvik Heart, Inc.

 

   Abstract
Top
 Abstract
Introduction
 Patients and Methods
 Results
 Comment
 Discussion
 Acknowledgments
 References
 
BACKGROUND: Device failure is a limitation of permanent mechanical circulatory support. We studied the mechanical reliability of the Jarvik 2000 Heart, an axial flow pump with ceramic bearings designed to provide more than 10 years' durability.

METHODS: The Jarvik 2000 Heart was implanted in 102 patients between April 2000 and December 2004. Eighty-three pumps with an abdominal driveline were implanted as a bridge-to-transplantation, and 19 with postauricular power supply as lifetime therapy. Eighteen pumps were recovered intact after clinical use and run continuously on the bench to further assess durability.

RESULTS: No implantable component failure occurred either in patients or during bench testing. The cumulative pump run-time was 110 years: 59 years overall in vivo and 51 years in vitro. The mean support time for bridge-to-transplant recipients was 159 days, and for discharged lifetime-therapy recipients 551 days. Six recipients were supported moer than 2 years, with the longest ongoing approaching 5 years. External cables caused three system failures, with a 95% freedom from system failure at 4 years. Device malfunctions, related to external cables (9) and lack of a backup battery (1), caused no adverse consequences. Before introduction of noncorrosive, gold-plated stainless steel connectors, corrosion was observed on three connectors to the retroauricular power supply.

CONCLUSIONS: The Jarvik 2000 Heart has had no implantable component failure. Meaningful durability data and failure mode can only be established by real-time testing in patients. The reliability and dependability of this device, in addition to the exchangeability of external components, give promise for long-term circulatory support in critically ill heart failure patients.

Device failure has been a major limitation of permanent mechanical circulatory support. Device malfunction and mechanical failure were among the factors limiting lifetime circulatory support in the Randomized Evaluation of Mechanical Assistance for the Treatment of Congestive Heart Failure (REMATCH) trial [1, 2], which studied patients who were supported with an implantable, pulsatile, pusher-plate–type left ventricular assist device (LVAD). Engineering a blood pump to meet the needs of mechanical durability and reliability is an important consideration in the successful long-term use of cardiac assist devices. Axial flow pumps could provide longer failure-free support times than pulsatile pumps, as the rotor is the only moving part and the bearings are the only parts subject to failure due to wear. We retrospectively studied the mechanical reliability of the Jarvik 2000 Heart (Jarvik Heart, Inc, New York, New York), an axial flow pump with ceramic bearings designed to provide more than 10 years' durability.


   Patients and Methods
Top
 Abstract
 Introduction
 Patients and Methods
Results
 Comment
 Discussion
 Acknowledgments
 References
 
Between April 2000 and December 2004, 102 patients had the Jarvik 2000 Heart implanted. All data were collected according to a study protocol, which was approved by the local Ethics Committee, and then retrospectively analyzed. Data were analyzed until May 2005. All patients gave informed consent for the implantation. Eighty-three devices with an abdominal driveline were implanted as a bridge to transplantation, and 19 with a postauricular power supply were implanted as lifetime therapy [3–5]. The device is approved for use as both bridge to transplant and destination therapy in Europe. It is approved only as a bridge to transplant in the United States. During the study period, all damaged and potentially malfunctioning external device components were sent to the manufacturer for detailed analysis and corrective action. All explanted pumps were sent to the manufacturer for postimplantation inspection. Eighteen pumps with intact electrical systems were subjected to extended durability bench testing as described below.

Definitions of Device-Related Events
The definitions for technical device-related events recently reported by the REMATCH group were used [2]. Any reported technical event was included in our analysis. The following definitions were used.

Damaged external device components
Damaged external device components were defined as physically damaged components that were still capable of performing their intended function. This definition included device controller underspeed alarms caused by partial strand breaks in the external power cable. Externally damaged lithium or lead acid batteries or batteries with a shortened lifespan were included in this category as long as they did not lead to a pump stoppage. In October 2004, a protocol for the scheduled exchange of external cables was introduced to minimize the chance of any potentially damaged external component causing a device malfunction.

Left ventricular assist device malfunction
Left ventricular assist device malfunction was defined as any device component failing to perform its intended function and leading to an unintended halt of circulatory support. The cause of LVAD malfunction was further analyzed to determine whether the malfunction was related to external or implantable components, including the abdominal driveline. Operator-dependent malfunctions were also identified. All malfunctions were considered to have the potential for causing serious adverse effects and were subdivided according to whether the actual consequences were serious or nonserious.

Left ventricular assist device system failure
Left ventricular assist device system failure was defined as the inability of the device to provide adequate circulatory support and any event where circulatory support came to an unintended stop and emergency measures, namely, exchange of the external components, failed to solve the problem.

Durability Bench Testing
All pumps that were explanted from patients were returned to the manufacturer (Jarvik Heart, Inc), where they were inspected and tested for damage incurred during explantation, handling, transport, or cleaning. A detailed pump history, including pump explant analysis, was available for each explanted pump. A total of 18 pumps explanted at the time of transplantation or at autopsy owing to death unrelated to device failure underwent further durability bench testing. After a standardized cleaning and decontamination procedure, durability bench testing was done in a designated area of the manufacturing facility separate from production areas and was limited to the 18 available testing stations there. Each pump was tested over a range of pump speeds (8,000 to 12,000 rpm) simulating periods of normal activity, exercise, and rest. All pumps were run in distilled water maintained at approximately 95°F. The following variables were logged: motor voltage, motor current, power supply voltage, and pump rpm.

Statistical Analysis
Because of the competing risks of these patients, the actual method for event-free survival [6, 7] was chosen to calculate the probability of a technical event to occur over time.


   Results
Top
 Abstract
 Introduction
 Patients and Methods
 Results
Comment
 Discussion
 Acknowledgments
 References
 
Pump Run Time
In vivo support
No mechanical failure of the pumps or any implantable components occurred in patients. The cumulative patient support time was 59 years. The mean support time (±SD) for bridge-to-transplant patients was 159 ± 195 days: 124 days in the United States and 262 days in Europe (Table 1). After hospital discharge, the mean support time for lifetime-therapy recipients was 551 days. Six device recipients were supported longer than 2 years, with the longest still ongoing approaching 5 years in June 2005. Details about the support times are summarized in Table 1. Twenty-four years of the observed patient support time was accumulated by patients who were on the device for less than a year; 35 years of the patient support time was accumulated by patients who were on the device for more than 1 year (Fig 1A). The total pump run time for each year of device support is depicted in Figure 1B.


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  		Table 1. In Vivo Support Time With Jarvik 2000 Heart (n = 102)
 

Figure 1
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  		Fig 1. (A) The accumulated patient support time by device recipients who were on the device for less than a year and those supported for more than 1 year (white bar = 1 to 2 years; black bar = 2 to 3 years; gray bay = more than 3 years). (B) The cumulative total pump run-time for each year of device support (white bar = 1 to 2 years; black bar = 2 to 3 years; gray bay = more than 3 years).

 
In vitro durability bench testing
None of the 18 explanted pumps that have undergone bench testing have failed to date. The mean durability, namely, the run time in the patient and in vitro is 2.8 years. Overall, the cumulative in vitro run time is 51 years (Fig 2). To date, there have also been no significant changes in motor current, motor voltage, or pump speed (rpm) at any given pump setting.


Figure 2
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  		Fig 2. Total run-time of all 18 pumps subjected to durability bench testing. Black bars indicate the patient support time (days) in vivo; gray bars indicate the pump run-time (days) in vitro.

 
Technical Events Related to Implantable Device Components
LVAD malfunctions and LVAD system failures
There were no LVAD malfunctions or system failures caused by the implantable components, either in vivo or in vitro. Freedom from device failure or device explantation due to failure of implantable components was 100% at 1 to 4 years (Figs 3 and 4). Go The failure mode of the implantable Jarvik 2000 technology remains unknown, as none of the devices has been pumped to failure to date.


Figure 3
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  		Fig 3. Freedom from left ventricular assist device component failure using cumulative incidence curves [6]. This actual curve plots the actual probability of internal and external component failure versus time (months). The circles depict the time of last follow-up in ongoing cases, the time of transplantation, device explantation, or death.

 

Figure 4
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  		Fig 4. Freedom from left ventricular assist device explantation with switch to a different device due to problems with circulatory support using cumulative incidence curves [6]. This actual curve plots the actuarial probability of freedom from device explantation versus time (months). Reasons for explantation included device thrombosis (n = 1), insufficient support with this system (n = 1), and external component failure (ie, cable break; n = 1). The circles depict the time of last follow-up in ongoing cases, the time of transplantation, device explantation, or death. (Note: no single device explantation or switch was due to internal component failure.)

 
Technical Events Related to External Device Components
Simple external damage and wear and tear
In lifetime-therapy patients, there was wear of external components. Most of the damaged external components were simply exchanged by the patient or a caregiver and did not lead to LVAD malfunction. Batteries were the most frequently replaced external components due to external (ie, patient-related) damage to light-emitting diodes, which are important for assessing battery charges, although the battery continued to function properly. The manufacturer has corrected that problem by introducing a sturdier battery pack and more robust power cables. The most frequently damaged external components were the power cables (Fig 5) and batteries; plugs were damaged owing to trauma to the battery or faulty handling of the power connectors. New cables with a tensile strength of approximately 200 lb will replace the present cables, which have a tensile strength of approximately 35 lb. The average usage time for external cables was about 9 to 12 months in lifetime-therapy recipients who were discharged. Lithium batteries lasted from 6 months to more than 2 years, depending on the frequency of use. Twelve to 18 months' use for the larger lead-acid batteries used at night was typical.


Figure 5
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  		Fig 5. Photo of a damaged (but still functioning) head cable that was incidentally noticed at a routine follow-up visit. (Note: the patient was still taking showers with this cable.) The damage occurred at the zone of the maximal flexing strain on the external head cable.

 
Corrosion of head pestal power connector
Early in the study, corrosion of gold-plated, beryllium-copper external power connectors occurred in 3 lifetime-therapy recipients whose devices were equipped with a postauricular power supply. In 2 of these cases, the problem was solved by cleaning the pedestal pins. In the third case, the corrosion led to a preventable LVAD system failure, which caused serious patient harm and was operator dependent. In that case, corrosion damaged a postauricular connector pin, and the problem was exacerbated when the pin was further damaged by medical staff. Corrective action was taken to replace all beryllium-copper connectors with noncorrosive, gold-plated stainless steel connectors.

Flex failure of the external postauricular cable
In the early implants of devices with a postauricular power supply, the skull-pedestal power connector was oriented so that the cable could run posteriorly behind a patient's shoulder. However, the patients always carried the cable in front of the shoulder, which led to mechanical flexing strain on the head cable where it connected to the skull-mounted pedestal. In these early patients, cable heat generation or device underspeed alarm was occasionally observed after several months owing to internal strand breaks within the external power cable. This problem was solved by orienting the power cable in a more downward position in later patients and by instituting a regular program of exchanging the head power cable. A total of 8 cables in 5 lifetime-therapy patients showed internal strand breaks. These breaks led to two episodes of confirmed LVAD malfunction, which were corrected simply by exchanging the head cable. No LVAD failure occurred as a result of this problem, nor has any such failure occurred since instituting the regular cable exchange protocol and reorienting the skull-mounted pedestal.

Loss of consciousness with battery change
In early use, every battery exchange led to a short pump stoppage, as the used battery had to be disconnected before connecting the new battery. Pump stoppage during routine battery exchange was not categorized as LVAD malfunction. Three patients lost consciousness for short periods when they changed their batteries. The problem was solved by introducing a Y-cable that allows patients to connect the recharged battery before disconnecting the discharged one. No additional events have occurred since the Y-cable was introduced.

LVAD malfunction
In total, there were 10 instances of LVAD malfunction: 6 due to failure of external cables, 3 due to loss of consciousness during battery exchange, and 1 due to the patient's lack of a backup battery. Even if these events had the potential for causing serious problems, only one resulted in adverse effects on the patient. Since October 2004, when the protocol for routine exchange of external cables was introduced, no device malfunctions due to external components have been reported.

LVAD system failure
There were three LVAD system failures caused by exchangeable external components. All of these adverse events were serious and were operator dependent. Freedom from LVAD system failure due to external components was 98% at 6 months and 95% at 1 to 4 years (Fig 3). Details about the specific failure modes are listed in Table 2. Early in the experience, 1 patient with amyloidosis died when alone at home and was found with his battery disconnected. Ventricular arrhythmia, common in patients with amyloidosis, was the most likely cause for his death, and his death was not attributed to LVAD system failure. However, loss of consciousness when changing the battery leading to subsequent LVAD system failure could not be completely ruled out.


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  		Table 2. Technical Events in Patients Supported With the Jarvik 2000 Heart
 
Device explantation and device switch due to problems associated with mechanical circulatory support
There were three device explantations followed by a switch to another LVAD due to problems associated with mechanical circulatory support. Causes included hemodynamic insufficiency and aortic valve thrombus in 1 patient, insufficient support in a large patient with a body surface area of 2.3 m2 and virtually absent myocardial function, and an unrecognized malfunction of an external power cable in 1 patient. Freedom from device explantation due to problems associated with mechanical circulatory support was 97% at 1 to 4 years (Fig 4).


   Comment
Top
 Abstract
 Introduction
 Patients and Methods
 Results
 Comment
Discussion
 Acknowledgments
 References
 
Device Durability
There have been no failures of the implanted component of the Jarvik 2000 Heart in more than 100 patients. The observed cumulative patient support time was 59 years, of which 35 years were observed in 17 recipients who were on the device for more than a year. The longest-lived survivor on this device remains in New York Heart Association class I-II after almost 5 years of support [3, 5].

The long-term durability and reliability of the Jarvik 2000 Heart is enhanced by the simplicity of its design and the clinical quality of its blood-immersed bearings. The pump's intraventricular implantation eliminates any inflow cannula. The absence of valves or other moving parts besides the rotor and the absence of implanted electronics or sensors are unique to this technology. This simplicity also allows for more reliable control and consistency of the manufacturing process. As a result, the axial-flow Jarvik 2000 Heart is limited mainly by potential bearing wear and by build-up of hematologic elements, or the internal power cable may eventually prove to be the limiting component. Exposure to blood and real cable flex conditions can only be assessed in vivo, which makes in vivo testing of axial flow pumps more meaningful than in vitro durability testing. Nonetheless, there have been no bearing failures in 18 Jarvik 2000 Hearts operated continuously in water for an average of almost 3 years.

Damage to External Components
In this series, we have reported damage to external components, which may reflect the normal life activities (for example, mountain climbing, hiking, biking) of long-term device recipients. To date, these problems have not occurred in the largest single-center experience in the United States (at the Texas Heart Institute), which includes a cumulative outpatient experience of 9 years. The outpatient experience in the United States is more limited as bridge-to-transplant patients were only allowed to be discharged starting August 2002.

One advantage of this technology has been the exchangeability of its external device components, which makes modification to the cables or connectors possible. Results obtained with the postauricular pedestal connector are promising, with successful ongoing use for as long as 4.9 years and few complications. Minor modifications, such as addition of a short segment of velour cable covering near the pedestal, improved electrical contact materials to eliminate corrosion, and better surgical implant technique, have all been implemented and are expected to further enhance the clinical results.

Accidental Pump Stops
A consideration often overlooked in designing an LVAD system for reliability is the device's ability to withstand prolonged pump-off conditions without damage or thrombosis. These events can never be completely avoided as the "human factor" becomes more important with activities of a normal lifestyle. When pusher plate pumps are turned off, they are generally poorly washed out by flow-through. When centrifugal pumps are turned off, they generally exhibit a reverse flow path of lower resistance direct from the outlet to the inlet and a peripheral area that is not well washed out by flow-through. In contrast, the flow-through in axial pumps is more uniform than in either pusher plate or centrifugal pumps. When the Jarvik 2000 is turned off, its rotor spins during backflow, which improves washout [8].

Operator Dependence
There were three observed LVAD system failures, all of which could have been avoided with different operator handling. This finding underscores how crucial ease of use and training of hospital staff, patients, and caregivers are to system reliability. It also underscores the need for additional safety measures, such as a 24-hour hotline with technical support. Training has been continuously improved, but the risk of operator error can never be completely eliminated. Even in the one uncertain case of the amyloidosis patient found dead at home with his battery disconnected, adherence to the clinical protocol with constant presence of a family member potentially could have prevented his death.

In conclusion, our experience has shown the Jarvik 2000 Heart to be a reliable and durable ventricular assist device. Since an active lifestyle outside the hospital can lead to damage of external device components, it is important for all external parts to be rugged and exchangeable. Implant reliability and exchangeability of external components enhance the success of long-term circulatory support, and initial results with the Jarvik 2000 Heart are promising.


   Discussion
Top
 Abstract
 Introduction
 Patients and Methods
 Results
 Comment
 Discussion
Acknowledgments
 References
 
DR FRAZIER: In April of 1986 Jarvik showed me this pump at the annual contractors conference. I told him that the main problem with all these devices is the inlet cannula. The Jarvik pump, however, doesn't need an inlet cannula because it's small enough so that you can put it in the ventricle. The left ventricular cavity pressure is the pressure seen by the pump. This will result in higher flows at a given RPM. An extracardiac position of the pump would necessitate an inlet cannula, thereby introducing a resistor effect thus lowering the inlet pump pressure. This would affect pump efficiency. The intracardiac positioning also simplifies pump placement allowing it to be implanted without cardiopulmonary bypass in the majority of patients. Jarvik, as a machinist, personally made the first devices, and I implanted them in Houston. The initial pumps were implanted in calves in 1989. By 1992, the bearing problem seemed to be resolved by Dr Jarvik. No bearing problems were encountered experimentally or clinically after that time. The pump ran continuously in animals for more than 8 months without complications.

There have been no pump or bearing failures to date. The English patient referred to in this presentation is approaching 5 years with a continuously functioning pump and remains a NYHA class I patient. It is a remarkably problem-free device. I think the axial flow pumpsoffer a great future for meaningful long term benefit for the terminal heart failure patient.

DR SIEGENTHALER: Thank you.

DR PAUL KURLANSKY (Miami, FL): Very interesting presentation. As I understand it, the external driver here is related to the power supply. Because it generates nonpulsatile flow, the device doesn't need any venting like the pulsatile devices. How far are we away from a transcutaneous power supply for this apparatus so that there might be no external components directly connected to the device? The other question is a clinical one: what is the anticoagulation regimen recommend for these patients and what is the incidence of infection and thromboembolism?

DR SIEGENTHALER: There are systems on the market, for example the LionHeart, that use transcutaneous power supply. I think the technology hasn't quite matured because you still need to implant a large battery-type device, and patients can go without the transcutaneous coil only for about 20 to 30 minutes. However, I think this is a really promising technology for the future.

In terms of infection, we noted a very low incidence. This is probably due to absent motion at the drive-line exit site. In addition, drivelines of axial flow pumps don't need a vent line and are therefore much smaller than those of pulsatile devices. There were a total of four infections in abdominal drive line patients and three in destination therapy patients, which gives you an incidence per patient day which is about 10 times lower than the currently described literature with various large pneumatic or electric vented pulsatile devices.

Anticoagulation in our center in Europe has been the Achilles' heel of this technology, but our group was hit harder with this problem than anybody else. We currently give Coumadin and aim for an INR of 3 to 3.5. In addition, we give aspirin and we monitor thrombocyte function to make sure they have sufficient thrombocyte inhibition at all times.

DR ROBERT L. KORMOS (Pittsburgh, PA): I enjoyed this presentation very much. I just have a couple of questions. One relates to some limitation that you alluded to with respect to providing adequate flow perhaps in patients when they reach a certain body size, and I would like you to comment perhaps on what those limitations might be.

I was going to ask a similar question about external cables, but we will leave that go. And finally, we found with the use of these rotary pumps that removing pulse often raises diastolic blood pressure, and I was interested to know what was the incidence of hypertension in this series of patients that you treated? Thank you.

DR SIEGENTHALER: You are welcome. I will answer your second question first. We really did not observe much hypertension because in all of them we continue their heart failure medication and actually, we give them as much as possible. Since these pumps are very afterload dependent, it is crucial to lower the afterload as much as possible.

This gets us to your first question, the limitations of adequate flow-pump support. This is true cardiac assist device. It cannot replace the entire myocardial function of the left ventricle. Patients need some residual cardiac function and this can lead to problems if a patient reaches about 2.2 to 2.3 m2. We did implant only two patients with such a large body surface area and both had very limited, insufficient support. Therefore, we don't use it anymore in such large patients. However, the British patient with almost five years of support, who traveled to the United States, is a tall man with a body surface area of about 2.2 m2. He had enough myocardial recovery that he is doing perfectly fine. But I don't think there are any criteria to predict how much recovery patients ultimately will have.

DR FRAZIER: As a coauthor, I will answer that. In the 1970s, we could successfully power the devices transcutaneously. That was never the problem. The problem was the compliance chamber which required percutaneous venting. In the United States, we use a percutaneous exit site in the right subcostal area for the drive line. This exit site has been remarkably free of infections or other problems. The pump itself has never clotted. The anticoagulation, however, is necessary for the secondary effects such as aortic root stasis. This is why some pulsatility is desirable with the Jarvik pump.

DR R. MORTON BOLMAN III (Minneapolis, MN): Have there been any instances of recovery of the failing heart, where you have been able to remove this device? Does this unload the ventricle sufficiently to allow for myocardial recovery?

DR FRAZIER: In our initial clinical experience, ventricular improvement after device implantation seems more effective with this pump. This perhaps is related to the loss of any isometric contraction phase as unloading occurs throughout the cardiac cycle. More experience is necessary in a larger number of centers to better quantify this observation.


   Acknowledgments
Top
 Abstract
 Introduction
 Patients and Methods
 Results
 Comment
 Discussion
 Acknowledgments
References
 
We would like to thank Manfred Olschewski, MS, for the statistical advice with this manucript.


   References
Top
 Abstract
 Introduction
 Patients and Methods
 Results
 Comment
 Discussion
 Acknowledgments
 References
 

  1. Rose EA, Gelijns AC, Moskowitz AJ, et al. Long-term use of a left ventricular assist device for end-stage heart failure N Engl J Med 2001;345:1435-1443.[Abstract/Free Full Text]
  2. Dembitsky WP, Tector AJ, Park S, et al. Left ventricular assist device performance with long-term circulatory supportlessons from the REMATCH trial. Ann Thorac Surg 2004;78:2123-2130.[Abstract/Free Full Text]
  3. Westaby S, Banning AP, Jarvik R, et al. First permanent implant of the Jarvik 2000 Heart Lancet 2000;356:900-903.[Medline]
  4. Westaby S, Jarvik R, Freeland A, et al. Postauricular percutaneous power delivery for permanent mechanical circulatory support J Thorac Cardiovasc Surg 2002;123:977-983.[Abstract/Free Full Text]
  5. Siegenthaler MP, Westaby S, Frazier OH, et al. Advanced heart failurefeasibility study of long-term continuous axial flow pump support. Eur Heart J 2005;26:1031-1038.[Abstract/Free Full Text]
  6. Grunkemeier GL, Wu Y. Actual versus actuarial event-free percentages Ann Thorac Surg 2001;72:677-678.[Free Full Text]
  7. Grunkemeier GL, Anderson RP, Starr A. Actuarial and actual analysis of surgical resultsempirical validation. Ann Thorac Surg 2001;71:1885-1887.[Abstract/Free Full Text]
  8. Jin XY, Westaby S, Robson D, et al. Unique ECG finding in a patient with an axial blood flow pump Circulation 2001;104:970-971.[Free Full Text]



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