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Ann Thorac Surg 2007;83:1082-1088
© 2007 The Society of Thoracic Surgeons
a Division of Cardiology, University of Maryland Medical Center, Baltimore, Maryland
b Division of Clinical Engineering, University of Maryland Medical Center, Baltimore, Maryland
c Division of Cardiac Surgery, University of Maryland Medical Center, Baltimore, Maryland
Accepted for publication October 16, 2006.
* Address correspondence to Dr Feller, Division of Cardiology, University of Maryland Medical Center, 22 S Greene St, S3B08, Baltimore, MD 21201 (Email: efeller{at}medicine.umaryland.edu).
Presented at the Poster Session of the Forty-second Annual Meeting of The Society of Thoracic Surgeons, Chicago, IL, Jan 30Feb 1, 2006.
| Abstract |
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Methods: We retrospectively compared common pre-LVAD clinical characteristics and indicators of heart failure severity between 13 pulsatile and 14 nonpulsatile LVAD recipients. The outcomes analyzed were either heart transplantation, if the LVAD was intended as a bridge to transplantation, or hospital discharge if the intention was destination therapy.
Results: There was no significant difference between groups in pre-LVAD disease severity indicators. Nonpulsatile LVAD recipients had a significantly smaller body surface area (1.9 ± 0.2 m2 versus 2.1 ± 0.2 m2, p = 0.04) and cardiopulmonary bypass time was also significantly shorter (61 ± 34 minutes versus 110 ± 49 minutes, p = 0.01). Aside from duration of initial intensive care unit stay (nonpulsatile, 10 ± 16 days; pulsatile, 14 ± 11 days; p = 0.02), there was no difference in post-LVAD outcomes: 10 of 14 nonpulsatile and 8 of 13 pulsatile LVAD patients achieved the combined end point (p = 0.69).
Conclusions: Similarly ill congestive heart failure patients benefited equally well from either a nonpulsatile or a pulsatile LVAD. This may support an expanded role for nonpulsatile LVADs in the treatment of severe heart failure.
| Introduction |
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Smaller, nonpulsatile devices have been developed to circumvent these issues [1113]. Although they may offer easier implantation and accommodate smaller patients, they typically deliver less maximum output [12]. However, it has yet to be shown that these lower flow capabilities compromise peripheral perfusion and that this adversely affects clinical outcomes.
Despite a lack of definitive evidence, concerns persist about the adequacy of support provided by continuous-flow LVADs [14, 15]. We hypothesized that implantation of a second-generation nonpulsatile LVAD would result in comparable outcomes to those of similarly ill patients implanted with first-generation implantable pulsatile LVADs. The purpose of this study was to compare clinical indicators of disease severity and the achievement of a predetermined end point between the two groups.
| Patients and Methods |
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The Novacor and Jarvik devices were both available as a bridge to transplantation at our institution during this time period. The Jarvik was implanted under the auspices of a clinical trial [16]. In July 2004, we began enrollment in the WorldHeart Randomized Evaluation of the Novacor LVAS In A Non-Transplant Population (RELIANT) destination therapy trial [17], which randomizes participants to the Novacor or HeartMate. Inclusion and exclusion criteria for the trials are given in Table 1. Patients implanted for acute myocardial infarction or postcardiotomy shock were excluded, as were patients who required a right VAD or whose care was transferred to an outside institution.
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Of the Jarvik patients, 9 were enrolled in the feasibility trial (open from September 2002 to January 2005), 3 received the device under emergency use provisions during the period between the feasibility and pivotal trials (February to August 2005), and 2 were enrolled in the pivotal trial (August 2005 to the present). The rationale for device selection for each patient is given in Table 2.
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In contrast, the Jarvik 2000 has no inflow conduit and is implanted directly into the left ventricular apex [18]. The outflow conduit is typically anastomosed to the descending aorta through a left thoracotomy. In 1 patient, who required a single-vessel bypass graft, implant was through a median sternotomy, with outflow anastomosis to the ascending aorta. The Jarvik speed was adjusted between 8000 and 12,000 revolutions per minute to maintain the aortic valve opening as far as possible while providing adequate flow for end-organ perfusion and exercise tolerance.
Anticoagulation management was generally identical in both groups. Systemic anticoagulation was with heparin (partial thromboplastin time, 40 to 50 seconds) and warfarin (international normalized ratio, 2.0 to 3.0). Platelet inhibition was achieved with aspirin, dipyridamole, and clopidogrel, which was titrated by the maximum amplitude of the thrombelastogram. Use of systemic anticoagulation in HeartMate XVE recipients was at the discretion of the implanting surgeon.
Study data were obtained by retrospective chart review. We analyzed pre-LVAD clinical indicators of heart failure severity, including levels of serum sodium, serum creatinine, total bilirubin, and serum albumin; left ventricular ejection fraction, cardiac index, blood pressure, pulmonary artery pressures, pulmonary capillary wedge pressure, and need for inotropic drugs or intraaortic balloon pump, or both. Disease severity was based on comparisons of these variables between the pulsatile and nonpulsatile groups.
Because bridge-to-transplantation and destination therapy patients have different therapeutic goals, we defined an outcomes end point based on original intention-to-treat. For bridge-to-transplantation patients, this goal was survival to transplantation, defined as survival to induction of anesthesia at the time of transplantation. Bridge-to-transplantation patients who died before transplantation or who became ineligible for transplantation after LVAD insertion were treatment failures. For destination therapy patients, the goal was survival to hospital discharge, and those who died before discharge were treatment failures.
Additional perioperative outcomes studied were cardiopulmonary bypass time for LVAD implantation and length of stay in the intensive care unit after implantation. Postimplantation outcomes included length of hospital stay before the initial discharge, total intensive care unit and hospital days during the entire period of LVAD support, duration of post-LVAD inotrope use, and LVAD-related readmission rates.
Major postoperative complications were also compared. These included major bleeding requiring reoperation or major intervention, bloodstream infection, cerebrovascular accident (defined as neurologic deficit lasting >24 hours), renal failure requiring hemodialysis, and device failure requiring replacement or urgent status 1A listing for transplantation.
Comparisons of continuous variables between the groups were done with the Student t test for normally distributed variables and a Mann-Whitney U test for non-normally distributed variables. For categoric variables, the Fisher exact test was used for binomial comparisons. A value of p < 0.05 was considered significant.
| Results |
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The groups fared similarly in achieving the combined end point of survival to transplantation for bridge-to-transplantation patients or to hospital discharge for destination therapy patients (Fig 1). Ten of 14 patients in the nonpulsatile group and 8 of 13 patients in the pulsatile group reached the end point (p = 0.69 comparing proportion of patients reaching end point; log-rank p = 0.79 comparing survival time to the combined end point). Bridge-to-transplantation patients who died before induction of anesthesia for transplantation, who became transplantation-ineligible, or who continue to await heart transplantation are censored. Destination therapy patients who died before discharge or who continue to await discharge are also censored.
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Mean duration of support was significantly longer for the pulsatile group than for the nonpulsatile group at 223 ± 162 days (range, 43 to 542 days) versus 79 ± 68 days (range, 10 to 256 days, p = 0.01). In the pulsatile group, 7 patients are either initially or currently not listed for transplantation, compared with none in the nonpulsatile group. A nonsignificant trend (p = 0.10) was noted toward longer inotrope use in the pulsatile group.
Table 6. lists major postoperative complications by device type. The incidence of major bleeding and bloodstream infection was similar in each group. Three times as many pulsatile as nonpulsatile LVAD recipients experienced cerebrovascular accidents, and twice as many nonpulsatile LVAD patients had postoperative renal failure. One patient in the nonpulsatile and none in the pulsatile group experienced device failure during the study period. Three patients in each group had three or more major complications, and 2 in each group had none. No statistically significant differences were observed.
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| Comment |
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Although the Randomized Evaluation of Mechanical Assistance for the Treatment of Congestive Heart Failure (REMATCH) trial demonstrated that patients receiving LVADs lived longer and had a better quality of life than similarly ill patients receiving optimal medical therapy, the morbidity and mortality of the LVAD cohort in REMATCH was substantial [19]. Modifications in both the clinical and technologic arenas have improved the morbidity of LVAD patients [20, 21]. However, significant mortality in both the bridge-to-transplantation and destination therapy populations lingers, and many of the clinical goals of successful LVAD therapy remain largely unmet [22, 23].
Protocols for patient selection, anticoagulation, inotropic and vasoactive therapy, and infection prevention have been developed but have yielded only modest gains in therapeutic success. Furthermore, device failure and its associated morbidities remain consistent problems in these devices, which have a highly variable lifespan ranging from months to years [2426].
The HeartMate and Novacor are pulsatile electromechanical devices. Both are implanted in subdiaphragmatic pockets, weigh approximately 1.5 to 2.0 kg, and have inflow and outflow cannulae incorporating one-way valves. Both devices have pusher-plates, complex bearing-dependent drive systems, and large air-venting subcutaneous drivelines. They are capable of supplying a maximum output of approximately 10 L/min but more commonly operate at 5 to 7 L/min.
In contrast, the Jarvik 2000 is a nonpulsatile, valveless device, whose only moving part is an impeller. It is directly inserted into the left ventricular apex with return cannulation to the aorta. This novel design is aimed at eliminating the thrombotic risk of an inflow cannula and the need for creation of a pump pocket. The Jarvik 2000 weighs 90 grams and can deliver a maximum output of approximately 7 L/min at physiologic afterload but is more typically run at 3 to 5 L/min. The impeller speed can be adjusted to maximize device output.
We assessed whether this small, nonpulsatile device would be capable of meeting predetermined therapeutic goals in similar fashion to the pulsatile devices. We compared common clinical predictors of heart failure severity in patients who received either a Novacor or HeartMate, or Jarvik 2000. There were no significant differences in clinical predictors of heart failure severity between the groups. All patients had severe, end-stage cardiomyopathy and were receiving optimum medical therapy. Our criteria for LVAD implantation were unchanged throughout the course of the investigation, so this finding was unsurprising. We did preferentially use the Jarvik device in smaller individuals who we believed would fare worse with implantation of the bulkier Novacor or HeartMate. This is evident in the statistically significant difference in body surface area between the groups.
We were interested primarily in assessing whether each device group was able to reach predefined therapeutic goals. All patients who received the Jarvik 2000 were implanted to bridge them to heart transplantation, and 10 of 14 reached that goal. In the Novacor/HeartMate cohort, 7 patients were transplantation-eligible and 6 were not. Together, 8 of these 13 patients successfully reached their predefined therapeutic goal. These similar outcomes uncover a promising role for nonpulsatile devices.
In our study, end-stage heart failure patients with equally severe cardiomyopathy fared equally well in reaching their end point with either a small, nonpulsatile LVAD or a larger, pulsatile LVAD. The augmentation afforded by the Jarvik 2000 appears to be adequate to support, stabilize, and improve circulation in end-stage congestive heart failure patients for weeks to months. Yet to be studied is whether the amount of augmentation to peripheral circulation and how it is delivered affects outcomes.
The Novacor/HeartMate patients achieve their end points as well, but at the expense of a significantly increased bypass time and intensive care unit stay. These patients also trended toward longer post-LVAD inotrope use. Further study with a larger patient population is warranted to clarify the cause of this difference and whether it ultimately affects overall outcome. The incidence of major postoperative complications was not different between the two groups, but our study may not have been adequately powered to detect these differences. It is possible that the reduced surgical morbidity of the simpler Jarvik implantation procedure leads to improved survival; however, we were not able to show a definitive advantage in this small study.
This study is small, observational, retrospective, and single-centered. Success of LVAD therapy was defined as survival to transplantation if the reason for the implant was for a bridge to transplantation and hospital discharge if the reason was destination therapy. This does not allow for direct intergroup comparison and represents a shortcoming of the analysis. Quality of life, long-term survival, and comorbidities were not included in the analysis and are beyond the scope of this report. However, these important topics need to be widely and systematically compared between devices, and the absence of that comparison is a weakness of this study.
To forward the clinical investigation of mechanical circulatory support devices, the focus of investigation must move beyond mandatory feasibility trials to interdevice comparisons of patient selection criteria, adverse events, and outcomes. If the ability of smaller devices to successfully treat the same patients who would conventionally receive an implantable pulsatile LVAD can be borne out with further experience, this supports a wider role for their use in severe heart failure.
| References |
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