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Ann Thorac Surg 2007;84:515-520
© 2007 The Society of Thoracic Surgeons
a Division of Cardiothoracic Surgery, Washington University School of Medicine, Barnes-Jewish Hospital, St. Louis, Missouri
b Division of Cardiology, Washington University School of Medicine, Barnes-Jewish Hospital, St. Louis, Missouri
Accepted for publication March 27, 2007.
* Address correspondence to Dr Moazami, Division of Cardiothoracic Surgery, Washington University School of Medicine, 660 S Euclid Ave, Campus Box 8234, St. Louis, MO 62236 (Email: moazamin{at}wustl.edu).
| Abstract |
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Methods: Between 1996 and 2005, 73 patients were implanted with the Novacor (World Heart Corp, Ottawa, Ontario, Canada; n = 35) or the HeartMate (Thoratec Corp, Pleasanton, CA; n = 38) as either bridge to transplantation (n = 44) or destination therapy (n = 29). Our analysis focused on patients with late-onset infection (
30 days) of the driveline exit site with prior clinical healing of all incisions.
Results: Late driveline infections developed in 17 patients (23%) at a median of 158 days (intraquartile range [IQR]: 68 to 213 days) after implantation. The median duration of support in this subgroup was 400 days (IQR, 283 to 849 days). Despite an aggressive treatment algorithm, repeat surgical revision was needed in 12 patients, up to six times in 2 individuals. In 6 patients, the infection progressed to pump pocket infections that led to urgent heart transplantation (n = 4) or explantation (n = 2). The individual risk that a driveline infection would develop dramatically increased with the duration of support, reaching 94% at 1 year. Multivariate analysis identified duration of support (p < 0.001) and documented trauma at the driveline exit site (p < 0.001) as independent predictors of infection. Number and duration of readmissions to the hospital significantly increased (p < 0.001), and long-term follow-up for survival (4.4 ± 2.2 years, 100% complete) showed a trend towards impaired outcome after driveline infection (5-year survival: 41% versus 70%, p = 0.10).
Conclusions: Long-term LVAD support in the current series was jeopardized by late-onset driveline infections, which occurred in all patients with support duration longer than 1 year. Once driveline infections developed, they were difficult to control and significantly increased morbidity.
| Introduction |
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Mechanical circulatory support, primarily in the form of left ventricular assist devices (LVAD), has become an attractive treatment option for many patients with severe congestive heart failure. The successful clinical introduction of LVAD has resulted in a shift in the management of end-stage heart failure, one that will undoubtedly affect and include a vast proportion of future patients. The use of implantable LVADs is also associated with possible complications, however, such as hemorrhage, thromboembolism, device failure, arrhythmias, organ system failure, and infection [4–6]. New technology used in LVAD successfully addressed some of the previous clinical problems, and the development of portable, vented, electric LVADs facilitated the transfer of patient care into the outpatient setting [7–9].
Owing to the shortage of available hearts for transplantation and the technical improvements in the currently available devices, centers have looked to LVAD as long-term therapy to entirely bypass cardiac transplantation [5]. The use of LVAD as a long-term or even permanent therapy demands that the risk of device-related complications, including infection, be reduced such that a reasonable patient self-care protocol is possible.
Late-onset driveline infections may be a particularly difficult obstacle to overcome. The mechanisms by which these infections typically occur have previously been described by our unit [10]. However, despite a brief mention in the Randomized Evaluation Of Mechanical Assistance Therapy As An Alternative In Congestive Heart Failure (REMATCH) trial [11], the true impact of late-onset driveline infections and its implication on the anticipated application of LVAD as permanent therapy remain ill defined. Therefore, the purpose of the current investigation was to address this specific issue by evaluating its incidence, cause, and clinical course during a 10-year period at our institution.
| Material and Methods |
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There were 47 men (64%) and 26 women (36%) with a mean age of 49 ± 13 years at the time of implantation. Among other important clinical characteristics, traumatic events to the driveline exit site were prospectively collected in our LVAD database from each patient during routine follow-up visits and whenever patients presented at our institution with device-related complications. Patient demographics are summarized in Table 1. Smoking history, chronic obstructive pulmonary disease (COPD), diabetes mellitus, chronic renal insufficiency, and peripheral vascular disease were the most common preoperative comorbidities. All patients undergoing LVAD insertion received a standardized antimicrobial prophylaxis consisting of intravenous vancomycin, aztreonam, and fluconazole, which was initiated during the operation and continued for 3 days after the procedure.
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Immobilization of the percutaneous lead of the LVAD occurred immediately after device placement and before the patient was transferred from the cardiothoracic operating room. Initially the lead was secured by using a Hollister Drain/Tube Attachment Device (Hollister Global, Melbourne, Australia). If the implanted device used a filter attachment, the drain/tube attachment device was placed distal to this attachment. When it was determined that the patient was hemodynamically stable and turning could be tolerated in the immediate postoperative phase, an abdominal binder was then applied.
Hospital staff and the supported LVAD recipient were aggressively taught about the importance of wearing both the abdominal binder and drain/tube attachment device at all times and to ensure proper placement. During in-hospital treatment, all driveline exit sites underwent daily antiseptic cleaning with hydrogen peroxide and povidone-iodine (Betadine, Purdue Pharma, Stanford, CT) solutions and were dressed with sterile gauze according to our standardized protocol.
Data Analysis
Our analysis focused on patients with late-onset infection of the driveline exit site and their comparison with patients who did not present with this complication. Late onset driveline infections (
30 days after LVAD implantation with prior clinical healing of all incisions) were defined as erythema, drainage, or purulence at the driveline exit site in the presence of a positive culture result.
Operative mortality included any death that occurred during the initial hospitalization or within 30 days after operation for discharged patients. Cumulative survival rates were calculated using Kaplan-Meier analysis, and survival curves were compared using the log-rank test. Mean follow up was 4.2 ± 2.2 years and was 100% complete.
The cumulative risk of developing a driveline infection was calculated using hazard analysis. Continuous data are reported as mean ± one standard deviation (SD), or median with intraquartile range (IQR), if appropriate, and compared using the Student t test. Categoric variables were analyzed using the
2 test or the Fisher exact tests, as appropriate. Odds ratios (OR) are reported with 95% confidence intervals (CI).
Multivariate analysis (stepwise backward regression) was used to determine risk factors that were significant, independent predictors of late onset driveline infections (SigmaStat 2.03, SPSS Inc, Chicago, IL). The 21 variables analyzed were age, gender, body mass index (BMI), history of tobacco use, COPD, diabetes mellitus, chronic renal insufficiency, peripheral vascular disease, ischemic etiology of heart failure, previous cardiac surgery, preoperative intraaortic balloon pump (IAPB), indication for LVAD placement, length of hospital stay immediately before LVAD placement, year of implant, type of LVAD implanted (Novacor versus HeartMate), reexploration for bleeding, postoperative hemodialysis, length of mechanical ventilation, length of stay at the intensive care unit (ICU), length of LVAD support, and history of documented trauma to the driveline exit site.
These variables were initially screened by performing univariate logistic regression on all possible explanatory variables with the dependent variable of late onset driveline infection. This was screened to include any variable with a value of p < 0.20 for further examination. The variables that remained were then subjected to a cross-tab analysis to look for any strong correlations between pairs of variables, and none were found. These variables were then forced into a logistic regression model and this model was bootstrapped with 1000 repetitions. The resulting bootstrap regression models were aggregated by counting the number of models in which each potential explanatory variable was found to be significant with a p < 0.05.
| Results |
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Multivariate analysis identified duration of support (p < 0.001) and documented trauma at the driveline exit site (p < 0.001) as the only independent predictors of late infection. The cumulative hazard of developing a driveline infection dramatically increased with the duration of support (Fig 1). Within 1 year of mechanical support, the individual risk of a late driveline infection developing was 94%.
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Excisional débridement and wide drainage were necessary in 14 patients. The surgical goal was to excise the exit site back to a place on the driveline where the tissues were clearly adherent circumferentially. Despite this aggressive approach, repeat revision was needed in 12 of the 14 patients, up to six times in 2 individuals. Despite surgical débridement, the infection progressed to the pump pocket in 6 patients, which led to urgent heart transplantation in 4 or explantation in 2. Permanent healing of the infected exit site could only be achieved in 3 patients.
This complicated clinical course is also reflected in a significant increase in the number of readmissions to the hospital and length of stay (p < 0.001 versus group A; Table 2). The presence of late driveline infections did not influence the frequency of subsequent heart transplantation. In group B, 53% (9/17) underwent cardiac transplantation compared with 63% of patients (35/56) in group A (p = 0.58).
There was a trend for overall long-term survival (Fig 2) and survival after subsequent heart transplantation (Fig 3) to be diminished with late onset infections. Late driveline infections during this 10-year period in our series were equally distributed, without significant improvement in more recent years (Fig 4).
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| Comment |
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With these advances in the field, some of the problems with early infections were successfully addressed. The achieved improvement was confirmed by our data, which showed that only 15% of local infections (3/20) occurred within the first 30 days after device implantation.
More recently, there was a paradigm shift towards an outpatient setting, and late-onset infections came to the forefront of interest. In the current series, we therefore focused on late driveline infections, which turned out to be a major cause of morbidity. Furthermore, late driveline infections were associated with a trend towards diminished long-term survival. Their incidence significantly increased with the duration of support. Not a single patient had a support duration of more than one year without presenting with this complication. For the individual patient presenting with late driveline infections, the number of days readmitted to the hospital per month of mechanical circulatory support increased ninefold compared with patients from group A.
Despite recent technical and medical improvements, the initiating mechanism for these driveline infections was most frequently a rather simple mechanical problem: a documented trauma to the driveline exit site. We therefore propose that driveline trauma remains the most common initiator of late driveline exit site infections. In our experience, this trauma usually takes the form of a shearing traction or torsion injury, commonly initiated by events such as dropping the controller and battery pack, moving without picking up the controller and battery pack, or accidentally hooking the driveline on a passing object. Because the goal of placing these devices is to allow patient mobility and the chance to live as normal a life as possible, all such trauma to the driveline exit site can certainly not be avoided. Another important finding of our study was that 71% of patients from group B needed repeated surgical revisions, consistent with a very challenging clinical course.
The clinical course of LVAD related infections has been previously investigated by other authors. Argenziano and coworkers [18] reported that pump-pocket infections were best managed by device explantation or transplantation. Prendergast and associates [19] confirmed these findings by showing that transplantation in the face of LVAD infection was an effective treatment option. In their series, at 17 ± 9 months after cardiac transplantation, 80% of patients (8/10) without previous LAVD infection were alive compared with 88% of patients (7/8) who underwent transplantation in the setting of a device-related infection.
In contrast, current follow-up of patients undergoing subsequent heart transplantation in the presence of a late driveline infection did show a trend towards impaired outcome (5-year survival 36% versus 85%). Yet, the number of patients in group B was probably too small to show a statistical significance. In addition to important differences to the current series, Prendergast and colleagues [19] acknowledged in their report that patients with infections at time of transplantation often were in less stable condition postoperatively. We concur in that high-urgency heart transplantation and emergency device explantation are both extreme measures and can certainly not be considered a standard therapeutic approach to treat device-related infections.
Axial flow pumps have been introduced into clinical practice and have since gained increased interest and acceptance, at least for medium-term support. So far, more than 200 MicroMed DeBakey VADs (MicroMed Cardiovascular, Houston, TX) and more than 50 Jarvik 2000 axial flow pumps (Jarvik Heart Inc, New York, NY) have been implanted worldwide. Hetzer and colleagues [20] reported their initial clinical experience with a new magnetically suspended axial flow LVAD in 24 patients. The longest individual time of support was 12.6 months, which is shorter than the median duration of support in group B of our series. It is still impressive that there was not a single case of driveline infection.
These excellent results coincided well with the experience from Siegenthaler and associates with the Jarvik 2000 LVAD [21]. In this report the incidence of local infection was shown to be significantly lower when compared with the HeartMate LVAD. In a different report of 11 patients who received a DeBakey ventricular assist device axial flow pump for bridge to transplantation, no device, pocket, or driveline infections occurred [22]. Mean duration of support was again rather short (51 ± 49 days, range 11 days to 4.7 months).
Given these substantial differences in the time of support, we should not draw any final conclusions from these preliminary data. However, the incidence of infection in all these series was drastically lower than that observed with pulsatile pumps in the current series or in the REMATCH trial [10]. Potential advantages of axial flow pumps include the smaller diameter and the higher flexibility of the percutaneous driveline. Additional experiences with larger numbers of patients and longer duration of assist are warranted to judge the role of axial flow pumps not only as bridge to transplant but possibly destination therapy.
In summary, this investigation showed that duration of LVAD support could be limited by late-onset driveline infections most commonly initiated by traumatic events. The cumulative hazard of developing this complication dramatically increased over time and reached almost 100% at 1 year of circulatory support. Furthermore, current data suggest that once late-driveline infections occurred, they were extremely difficult to control, despite our ongoing attempts to precociously treat this complication. Consequently, during the last decade, our hospital staff and the supported LVAD recipients were aggressively taught about the importance of avoiding any activities that might expose the driveline to any abnormal mechanical stress.
From these data and the anticipated use of LVAD as permanent therapy, we also believe that it is imperative that we reinforce to manufacturers of available pulsatile assist devices the importance of continuously improving the design of extracorporal device accessories to minimize torsion and further protect the driveline.
| Acknowledgments |
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| References |
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P. Hendry Invited commentary Ann. Thorac. Surg., August 1, 2007; 84(2): 520 - 521. [Full Text] [PDF] |
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