Eur J Cardiothorac Surg 2008;34:275-280. doi:10.1016/j.ejcts.2008.02.019
Copyright © 2008, European Association for Cardio-thoracic Surgery. Published by Elsevier. All rights reserved.
Clinical outcome and bridge to transplant rate of left ventricular assist device recipient patients: comparison between continuous-flow and pulsatile-flow devices
Andrea Garattia,*,
Giuseppe Bruschib,
Tiziano Colombob,
Claudio Russob,
Marco Lanfranconib,
Filippo Milazzo,
Maria Frigeriob,
Ettore Vitalib
a Department of Cardiovascular Disease ‘E. Malan’, Cardiac Surgery Unit, Policlinico S. Donato Hospital, Via Morandi 30, S. Donato Milanese, Milan, Italy
b Departments of Cardiology and Cardiac Surgery ‘A. DeGasperis’, Niguarda Ca’Granda Hospital, Milan, Italy
Received 18 September 2007;
received in revised form 14 February 2008;
accepted 15 February 2008.
* Corresponding author. Tel.: +39 02 52774393. (Email: agaratti{at}tiscali.it).
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Abstract
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Background: Long-term implantable continuous axial-flow pumps are increasingly used in bridging heart failure patients to heart transplant. Compared to pulsatile left ventricular assist devices (LVADs), they offer smaller dimensions, less surgical trauma and less thromboembolisms. However concerns still remain about the long-term effects of continuous-flow on patients’ outcome. The aim of this study was to review our mechanical bridge to transplant experience to compare pre- and post-transplant outcomes between pulsatile and continuous-flow LVAD recipients. Methods: Thirty-six patients with a continuous-flow device (Micromed DeBakey, Houston, TX or InCor Berlin Heart, Berlin, Germany – group A) were compared with 41 patients supported with a pulsatile device (Novacor®, WorldHeart, Oakland, CA – group B). Results: Mean age (48.6 ± 12.4 vs 47.2 ± 12.5) and LVAD duration (119.3 ± 115.4 vs 128.3 ± 198.3) were similar in the two groups. Group A recipients were smaller compared to group B (mean body surface area = 1.77 ± 0.18 vs 1.93 ± 0.16; p
< 0.001). Idiopathic dilated cardiomyopathy was not significantly greater between the two groups (78% vs 58.3%; p
= 0.085). Successful bridging to transplantation was similar in group A compared to group B (52.8% vs 63.4%; p
= non significant). On-VAD mortality was similar between the two groups (A vs B = 33.3% vs 36.6%; p
= non significant). Thirty-day mortality after HTx in group A was 10.5% compared to 7.7% in group B (p
= non significant). First year post-transplant incidence of treated rejections (36.8% vs 46%; p
= non significant) as the mean number of rejection/patient (0.38 ± 0.5 vs 0.53 ± 0.83; p
= non significant) were similar in group A compared to group B. Conclusions: In our experience, when compared to pulsatile LVAD, continuous-flow pumps are similarly effective in transplant rate and post-transplant outcome.
Key Words: Left ventricular assist devices • Heart transplantation • Chronic post-transplant rejection • Multi-organ failure syndrome
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1. Introduction
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Chronic heart failure (HF) is a leading cause of death in developed countries and affects almost five million Americans, with annual costs of up to $40 billion [1]. HF is the most frequent cause of hospitalization due to a chronic condition among elderly Americans, with >700,000 admissions/year. Even in the European community, chronic HF has an important economic impact, representing approximately 1% of the total public health expenditure [2]. Over the last two decades, the involvement of mechanical circulatory support (MCS) devices has steadily evolved in the clinical management of end-stage HF, and use of these devices has emerged as standard care for treating acute and chronic HF refractory to conventional medical therapy [3]. The largest experience worldwide has been obtained with the intracorporeal pulsatile device Novacor® LVAD (World Heart Corp, Oakland, CA) and the HeartMate VE LVAD (Thoratec Corp, Pleasanton, CA). So far, more than 1700 patients have been supported with the Novacor® LVAD (Novacor Registry, June 2005), while the HeartMate system has been implanted in around 5000 patients. Implantation of these devices is difficult and lengthy, however, often requiring the creation of a pump pocket, which imposes an added risk of perioperative morbidity and mortality [4]. Furthermore, the size and the weight of these devices, as the presence of compliance chambers, preclude implantation of these devices in patients with body surface area (BSA) of less than 1.5 m2. In recent years, smaller, non-pulsatile devices (cLVAD) have become clinically available [5,6]. Compared to pulsatile left ventricular assist devices (pLVAD), they offer smaller dimensions, less surgical trauma and less thromboembolisms. Anyway, concerns still remain about the long-term effects of continuous-flow on peripheral organs function and patients’ outcome. Bridge to transplantation rates have been found to be comparable between patients supported with pLVAD and cLVAD. However, disagreement exists regarding post-transplant outcomes, as recent evidence suggests that the risk of severe rejection seems to be increased in transplanted patients previously supported with non-pulsatile LVADs [7]. The aim of this study was to review our mechanical bridge to transplant experience to compare pre- and post-transplant outcomes between pulsatile and continuous-flow LVAD recipients.
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2. Material and methods
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Between January 1988 and March 2007, 77 patients underwent long-term implantable LVAD support as bridge to transplant at our institution. Thirty-six patients (group A; 46.8%) were supported with a continuous-flow axial pump LVAD (28 Micromed DeBakey, Micromed Technology Inc., Houston TX, USA; 8 Berlin Heart Incor, Berlin Heart AG, Berlin). In 41 patients (group B; 53.2%) a pulsatile LVAD (Novacor®, WorldHeart, Ottawa, Canada) was implanted. Preoperative, intraoperative and postoperative variables (age, sex, etiology, BSA, hemodynamic and laboratory data, total blood transfusion, LVAD duration) were retrospectively collected by chart review, as well as in-hospital and on-VAD mortality causes. Transplant data and post-transplant mortality causes were as well reviewed. First year post-transplant incidence of cellular rejection greater than International Society of Heart and Lung Transplantation (ISHLT) grade IB, was retrospectively assessed by Heart Transplant Ambulatory chart review, and compared between the two groups. Implantation technique of these devices has been extensively described in literature as well in our previous reports [8], and no significant differences in apical and aortic anastomosis exist in our opinion between pLVAD and cLVAD. The important surgical difference is that cLVADs lie completely inside the pericardium, along the diaphragmatic margin of the heart; consequently a huge LVAD pocket is avoided in cLVADs, thus minimizing surgical trauma and intra-operative blood loss. Anticoagulation management was generally identical in the two groups. Anticoagulation treatment is based on the protocol proposed by the group at the ‘La Pitiè – Salpetriere’ Hospital in Paris [9]: during the first 24 h postoperatively, the patients usually receive no anticoagulation. Thereafter, intravenous heparin therapy is started according to thromboelastography (TEG) modified with heparinase. Long-term anticoagulation consists of sodium warfarin (dosage according to international normalized ratio of prothrombin time 2.0–2.5 times normal value) and enoxaparin (4000–8000 IU/day). This protocol is very careful with regard to platelet activity by including dypiridamol (800 mg/day intravenously intraoperatively and thereafter 800 mg/day orally) and aspirin (100 mg daily). When thrombocytosis or platelet-related hypercoagulability is discovered, ticlopidine (250 mg/day) is added to the regimen. Antiaggregation therapy is monitored with platelet aggregation study and the therapeutic goal is suppression of ADP-, epinephrine-, and arachidonic acid-induced platelet aggregation to 50–75% below the lower limit of preserved proaggregatory response to collagen in platelet aggregation studies. Pentoxifylline (400 mg/day intravenously initially and thereafter 800 mg/day orally) is used to further improve hemorheology as it is recognized to possess significant anti-inflammatory properties along with the capability to stabilize red blood cells and lower fibrinogen levels. The Niguarda Ca’ Granda Hospital ethical committee approved collection of these data without informed consent.
2.1 Device description
2.1.1 Worldheart Novacor® (WorldHeart, Ottawa, Canada)
WorldHeart's Novacor® LVAD is an implanted, wearable system which has been extensively described in literature since its first application at Stanford University in 1984. Briefly the device incorporates a dual pusher-plate, 70 ml stroke volume, sac-type blood pump coupled to a pulsed-solenoid energy converter drive. Modular porcine-valved conduits are attached to the blood pump with keyed inflow and outflow screw fittings. Novacor® LVAD has been implanted in more than 1700 patients, and is the first mechanical circulatory support device to support a single patient for more than 6 years [10].
2.1.2 Micromed DeBakey LVAD (Micromed Technology Inc., Houston TX, USA)
The electromagnetically actuated MicroMed DeBakey LVAD is a miniaturized, fully implantable titanium axial-flow blood pump. A titanium inflow cannula connects the pump to the apex of the left ventricle, and a Vascutek Gelweave vascular graft (Vascutek, Renfrewshire, Scotland) as an outflow conduit connects the pump to the ascending aorta. An ultrasonic flow probe is placed around the outflow conduit to provide exact measurement of pump flow. The pump is designed to achieve 5 l/min against 100 mmHg pressure, with a rotor speed of 10,000 rotations per minute and a power input of less than 15 W.
2.1.3 Berlin Heart Incor (Berlin Heart AG, Berlin AG, Germany)
The Incor (Berlin Heart AG, Berlin) is a new axial-flow pump that differs considerably from other available systems. The impeller is held by a magnetic bearing and has no physical contact with other parts, and can rotate at speeds of up to 10,000 rpm. This corresponds to a potential blood flow of 7 l/min (against 150 mmHg). Silicone inflow and outflow cannulas are attached to the pump chamber with connector systems that are easy to re-open. The driveline of the device is connected trans-cutaneously to an externally wearable controller and to two battery packs.
2.2 Statistics
Results are presented as mean values ± standard deviation. Student's t-test was used for comparison of continuous variables. A Wilcoxon two sample test was used for comparison of continuous variables where the examined samples were small in numbers with unknown distributions. Fisher's exact test (two-tailed) was used for categorical variables. A p value less than 0.05 was considered statistically significant. Confidence intervals (CI) for the most important variables were calculated. The confidence level set for CI was 95%.
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3. Results
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Baseline characteristics of the two groups are summarized in Table 1
. Mean age was similar between the two groups (48.6 ± 12.4 years (CI: 44.5–52.65) vs 47.2 ± 12.5 years (CI: 43.37–51.03); p
= non significant). All patients in group B were males, while eight recipients (22,2%) in group A were females. Group A recipients were smaller compared to group B (mean BSA = 1.77 ± 0.18 m2 (CI: 1.71–1.83) vs 1.93 ± 0.16 m2 (CI: 1.88–1.98); p
< 0.001). Idiopathic dilated cardiomyopathy was not significantly greater among the two groups (pulsatile 78% (CI: 65.3–90.6%) vs continuous 58.3% (41.8–74.2%); p
= 0.085). Hemodynamic data (ejection fraction, cardiac index, pulmonary capillary wedge pressure) as well as biochemical values (serum BUN, serum creatinine, serum bilirubin) were statistically identical. Overall blood product transfusions were greater in group B compared to group A (blood products transfusions (red blood cells + fresh frozen plasma) were 14 ± 4 (CI: 12.78–15.22) vs 8 ± 2 (CI: 7.35–8.65) units/patient in group B and group A respectively (p
< 0.05); platelet transfusions were 6 ± 2 (CI: 5.39–6.61) vs 3 ± 1 (CI: 2.67–3.33) units/patient in group B and group A respectively (p
< 0.05)). On-VAD mortality was 33.3% (n
= 12; CI: 17.64–48.36) in group A and 36.6% (n
= 15; CI: 22.2–51.78) in group B (p
= non significant). Mean support duration in patients who died before transplantation was 89.9 ± 86.9 days (CI: 40.73–139.07) in group A versus 62.3 ± 87.5 days (CI: 18.02–106.58) in group B (p
= non significant). Causes of mortality were comparable between the two groups, with multiorgan failure syndrome (MOFS) and cerebrovascular accident (CVA) as the two principal cause of on-VAD mortality (Fig. 1
). In group B age was significantly higher in patients who died during LVAD support (54 ± 9.5 years (CI: 49.19–58.81) vs 43 ± 12.4 years (CI: 38.23–47.7); p
< 0.05), while this difference was not observed in group A (50 ± 12.9 years (CI: 42.7–57.3) vs 48 ± 12.3 years (CI: 43–52.9); p
= non significant). In group A, 19 patients (52.8%) could be transplanted, four patients (11.1%) are still on support, and one patient (2.8%) could be weaned from the device after 195 days of support. In group B, 26 patients (63.4%) could be transplanted. LVAD duration before transplantation was similar in the two groups (119.3 ± 115.4 days (CI: 73.13–165.47) vs 128.3 ± 198.3 days (CI: 52.08–204.52) in groups A and B respectively). The two groups did not show significant differences in respect to donor characteristics (donor age, donor–recipient matching and donor troponin T levels). Total ischemic time was similar in the two groups (195.6 ± 63.7 h (CI: 170.1–221.09) vs 174.3 ± 69.3 h (CI: 147.6–200.94) in groups A and B respectively). Thirty-day mortality after HTx in group A was 10.5% (two patients) compared to 7.7% (two patients) in group B (p
= non significant). Late post-transplant mortality was greater in pulsatile group compared to continuous-flow group (12.5% vs 5.9%, respectively; p
< 0.05). As the pulsatile VAD at our institution were implanted since 1992 and the continuous-flow LVAD were implanted since 2000, mean post-HTx follow-up was significantly longer in group B compared to group A (108 ± 42 vs 56 ± 24 months respectively; p
< 0.001). Overall post-transplant mortality, anyway, was similar between the two groups (15.8% (CI: 1.33–30.67) vs 19.2% (CI: 3.92–34.08) in groups A and B respectively; non significant) (Table 2
). Furthermore there was no difference in long-term survival after transplantation between both LVAD groups, as shown in the Kaplan–Meier survival analysis (Fig. 2
). One, 3 and 5 year survival was 89.47 ± 7.04%, 83.88 ± 8.54%, 83.88 ± 8.54% and 88.46 ± 6.27%, 88.46% ± 6.27%, 88.46% ± 6.27% in groups A and B respectively. The overall post-transplant immunosuppressive protocol was the same throughout the whole study period. It consisted of triple therapy with steroids, azathioprine, and cyclosporine. Induction immunosuppression was obtained using rabbit anti-thymocyte globulins (ATG-Fresenius, Bad Homburg, Germany) 2.5 mg/kg intraoperatively and 1–2 mg/kg daily for 4 days. Methylprednisolone was administered during surgery (500 mg) and then 250 mg intravenously every 12 h for three doses postoperatively; followed by prednisone 0.8 mg/kg daily and progressively tapered to 0.2 mg/kg daily within the 11th postoperative day. Azathioprine was administered intravenously at time of surgery (3 mg/kg) and maintained at 1.5 mg/kg daily postoperatively according to peripheral leukocytes count. Cyclosporine was started soon after surgery (6–12 hafter HTx) and gradually increased to obtain trough whole blood levels of 350–450 ng/ml. First year post-transplant incidence of rejections greater than International Society of Heart and Lung Transplantation (ISHLT) grade IB (36.8% (CI: 14.42–57.58) vs 46% (CI: 26.84–65.16); p
= non significant) as the mean number of rejection/patient (0.38 ± 0.5 (CI: 0.16–0.6) vs 0.53 ± 0.83 (CI: 0.21–0.85); p
= non significant) were similar in group A compared to group B respectively. All rejections could be treated successfully.
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Fig. 1. On-VAD causes of mortality. Group A: continuous-flow LVAD; group B: pulsatile-flow LVAD. MOFS: multiorgan failure syndrome; CVA: cerebrovascular accident; RHF: right heart failure.
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Fig. 2. Post heart transplant Kaplan–Meier survival analysis. Previous pulsatile-flow LVAD (– – –); previous continuous-flow LVAD (- - -).
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4. Discussion
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Continuous-flow devices have been recently introduced, but their use is rapidly increasing. Miniaturization of mechanical support technology has resulted in the development of a generation of pumps that expands the potential pool of patients who can be supported and simplifies the implanting operation. The advantages of these pumps are smaller dimension, fewer moving parts with more mechanical reliability, limited blood-contacting surface and less thromboembolic events. We could demonstrate that in our experience continuous axial-flow devices have similar pre-transplant and post-transplant early- and long-term outcomes compared to implantable pulsatile devices. In particular in our study the combined end-point of transplantation, recovery and on-going support in cLVAD group resulted in 66.7%. This result favorably compared to published experiences of patients supported with axial-flow pump as a bridge to transplantation. In the worldwide experience of 150 patients supported with the Micromed DeBakey as a BTT, Goldstein [11] reported a 45% on-VAD mortality, with a combined end-point of HTx and on-going support successfully reached in 55% of patients after a mean support time of 75 days. In the recently published series of 133 patients supported with the HeartMate II axial-flow pump, Miller for the HeartMate II clinical investigators study group [12] reported a combined end-point of transplantation, recovery and on-going support in 75% of patients. Outcome after LVAD support is well-studied in pulsatile devices, with comparable outcome rates in patients with and without prior LVAD support [13]. However, few reports in literature compared pre- and post-transplant outcomes in pLVAD and cLVAD. Feller and colleagues [14] and Radovancevic and co-workers [15] separately compared end-organ function, pre- and post-transplant outcomes in two groups of patients supported with a Jarvik 2000 LVAD and a TCI HeartMate LVAD, failing to find worse outcomes in cLVAD patients compared to pLVAD recipients. These similar outcomes uncover a promising role for continuous-flow devices, particularly expanding the possibility of receiving an implantable long-term pump for smaller or female patients. Pre-transplant causes of death were similar between the two groups, with multi-organ failure and cerebrovascular accidents accounting for the majority of death. cLVAD seem to show a lower incidence of thromboembolisms and CVA compared to pLVAD, even if not statistically significant. Detailed comparison of end-organ function, LVAD related complications and coagulation management between the two groups is behind the scope of this report, and is going to be the subject of a future publication. In the biggest reported experience comparing pLVAD with cLVAD, Klotz and co-workers [7] recently suggested that the risk of severe rejection after HTx has increased threefold after continuous-flow LVAD support, compared with pulsatile LVAD support. The authors stated that the reasons for this high rate of severe rejection in continuous-flow LVAD recipients were not completely understood and warranted further studies to better elucidate post-LVAD immunology. However in our experience we failed to demonstrate an increased risk of post-transplant rejection in axial pump recipients compared to pulsatile device recipients. We did not measure directly pre-transplant sensitization, as we were unable to retrospectively collect the HLA values in both groups for comparison. Anyway in our whole LVAD experience only two patients during LVAD support developed pre-transplant major allo-sensitization (defined as PRA > 20%) thus requiring pre-transplant plasmapheresis and i.v. immunoglobulin, and they were excluded from this analysis. In order to avoid any confounding effect, we analyzed the most important donor and transplant variables, which are normally considered to be important determinants of post HTx rejection. The two groups did not show any significant differences in respect to donor characteristics (donor age, donor–recipient matching and donor troponin T levels) and, most importantly the ischemic time, which is one of the major determinants of post-transplant outcomes, was comparable among the two groups (Table 2). Multiple transfusions are common after LVAD implantation, as a consequence of surgical trauma (especially wide pump pocket in pulsatile devices), blood–biomaterial interaction and anticoagulation therapy. Extensive use of blood products, especially platelet transfusions, has been previously reported as the primary risk factor for the development of HLA antibodies [16] and consequently post HTx rejections. In our experience blood transfusions were significantly less in cLVAD group compared to pLVAD group. This is mostly due to the small dimensions of the axial pumps compared to the pulsatile devices, which avoid the creation of a huge pump pocket, thus limiting surgical trauma, blood loss and infections. Furthermore, in recent years we have implemented in our LVAD anticoagulation protocol the use of the aggregometry, especially to monitor axial-flow induced shear stress related platelet damage [17]. This monitoring allowed us to manage platelet dysfunction better thus limiting unnecessary platelet transfusions. Furthermore throughout our whole LVAD experience we have used only leukoreduced blood components and pooled platelets. This is consistent with the experience of Drakos and colleagues [18], who have recently showed that leukocyte-filtered cellular blood product transfusions may be associated with lessened alloimmunization and may mitigate the sensitization seen in 71 recipients of the HeartMate left ventricular assist device as a bridge to transplantation.
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5. Study limitations
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One limitation of our study is that the Novacor LVADs were implanted from the year 1992 to the year 2003 while axial-flow pumps were implanted starting from the year 2000, and their implants increased rapidly in our institution to become our first LVAD choice. This is a problem other studies comparing pulsatile and continuous-flow LVAD in literature deal with, especially if they reported on retrospective analysis of their LVAD experience [7,15]. In designing the study we were aware of potentially introducing a time bias; otherwise the only overlapping time period is the three-year period between 2000 and 2003, when we implanted very few Novacor LVADs, and this makes any comparison useless. Regardless we think that this time bias has very little impact on our analysis for the following reasons: (1) our LVAD management, especially regarding anticoagulation management was unchanged during the study's period; (2) the learning-curve effect that can improve results over time was partially counteracted in our experience by the introduction of the axial-pumps, which required a new learning curve, as the two LVAD types (pulsatile vs continuous) are not completely identical in perioperative and postoperative management; (3) the peri-transplant and post-transplant management, especially regarding immunosuppressive therapy, was unchanged during the study's period; and (4) even if the post-transplant long-term follow-up between the two groups was different, as pLVADs were implanted in the early part of our LVAD experience, the Kaplan–Meier analysis of post-transplant survival shows that, independently from the period of implantation, the 5- and 10-year survival rates are statistically identical between the two groups, as assessed by the log-rank comparison of survival. A second limitation of the study is the small numbers of the study population, especially concerning the post-transplant survival analysis and the incidence of rejections. We are aware of the fact that the lack of significant differences between the outcomes we measured in the study could be related to the limited number of observations. Trying to overcome this limitation we computed the confidence intervals for the most important clinical variables in the study. The analysis of the confidence intervals seem to confirm that no differences exist between the two groups in term of pre-transplant and post-transplant mortality, and of post-transplant rejection incidence. Anyway further multi-institutional studies are required to increase the statistical power of analysis.
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6. Conclusions
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The new generation of continuous-flow assist devices is almost exiting the pioneering era to establish itself as a validated alternative to implantable pulsatile devices. Mechanical reliability of axial pumps is clinically evident, as is their ability to support end-organ function and restore hemodynamics adequately. Comparable pre- and post-transplant outcomes between pulsatile devices and axial pumps, will probably contribute to expand the potential pool of candidates to mechanical support in the next future, given that cLVADs can be implanted in smaller recipients, with less surgical trauma and a lesser risk of infection and thromboembolisms. Larger clinical investigations of inter-device comparisons of patient selection criteria, adverse events and outcomes are mandatory. If second or forthcoming third generation of pumps will continue to show successful results in supporting patients as bridge to transplant or as destination therapy, a wider role for mechanical support in severe heart failure patients is foreseeable in the next future.
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Appendix A
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Conference discussion
Dr C. Schlensak (Freiburg, Germany): I just want to give a short comment.
First, survival after implantation of LVADs strongly depends on patient characteristics (i.e. right heart function or liver and kidney function) rather than pulsatile or nonpulsatile blood flow.
Second, we have observed over the last 10 years that survival after cardiac transplantation proved to be excellent in patients after implantation of a cardiac assist device. This observation might be related to the beneficial effect of LVAD therapy on pulmonary vascular resistance and the improvement of patient functional status after LVAD implantation.
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Acknowledgments
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Dr Garatti wants to disclose the fact that during the revision process of the manuscript he stopped working in Niguarda Hospital (where the study was conducted) and started working in Policlinico San Donato Hospital (as reported in the affiliation). Dr Garatti wants to thank Dr Vitali (Niguarda's chief) and Professor Menicanti and Professor Frigiola (San Donato's chiefs), as well as the other co-authors, for allowing him to still produce the manuscript as the first author of the paper.
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Footnotes
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Presented at the 21st Annual Meeting of the European Association for Cardio-thoracic Surgery, Geneva, Switzerland, September 16–19, 2007.
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References
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Abstract
1. Introduction
