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Ann Thorac Surg 2009;87:1072-1078. doi:10.1016/j.athoracsur.2009.01.022
© 2009 The Society of Thoracic Surgeons
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Right arrow Mechanical Circulatory Assistance

Original Articles: Adult Cardiac

Renal Function and Outcome After Continuous Flow Left Ventricular Assist Device Implantation

Sigrid E. Sandner, MDa,*, Daniel Zimpfer, MDa, Philipp Zruneka, Angela Rajek, MDb, Heinrich Schima, PhDa, Daniela Dunkler, PhDa, Michael Grimm, MDa, Ernst Wolner, MDa, Georg M. Wieselthaler, MDa

a Department of Cardiothoracic Surgery, Medical University of Vienna, Vienna, Austria
b Department of Cardiothoracic Anesthesia, Medical University of Vienna, Vienna, Austria

Accepted for publication January 6, 2009.

* Address correspondence to Dr Sandner, Department of Cardiothoracic Surgery, Medical University of Vienna, Waehringer Guertel 18-20, A, Vienna, 1090, Austria (Email: sigrid.sandner{at}meduniwien.ac.at).


   Abstract
Top
 Abstract
Introduction
 Material and Methods
 Results
 Comment
 References
 
Background: Renal dysfunction as a risk factor with the use of left ventricular assist devices (LVAD) is controversial. We determined the effect of renal function on outcomes after continuous flow LVAD implantation.

Methods: Eighty-six patients with advanced heart failure undergoing continuous flow LVAD implantation as bridge to transplantation from November 1998 to July 2007 were retrospectively analyzed. Renal function was assessed using the Modification of Diet in Renal Disease study–derived glomerular filtration rates (GFR [mL · min–1 · 1.73 m–2]). Patients were categorized into two groups based on pre-LVAD GFR: those with normal renal function (GFR > 60, n = 46), and those with renal dysfunction (GFR < 60, n = 40).

Results: Post-LVAD survival at 1, 3, and 6 months for GFR greater than 60 was 91.3%, 79.9%, 72.6%, respectively, and for GFR less than 60, it was 92.5%, 66.5%, 47.9%, respectively (p = 0.038). Bridge-to-transplant rate was lower for GFR less than 60 than for GFR greater than 60 (40.0% versus 63.0%, p = 0.033). For GFR less than 60, GFR improved on LVAD support: implant to month 6, 41.7 ± 11.5 to 62.7 ± 25.0 (p = 0.021). Post-LVAD survival was improved in GFR less than 60 patients who after LVAD implantation recovered renal function to GFR greater than 60 (p < 0.001). Patients with post-LVAD renal failure had significantly lower post-LVAD survival regardless of pre-LVAD renal function (p < 0.001).

Conclusions: Patients with renal dysfunction have poorer outcomes after continuous flow LVAD implantation. However, renal function improves after LVAD implantation and is associated with improved survival. Our data underscore the importance of end-organ function in patient selection for LVAD therapy.


   Introduction
Top
 Abstract
 Introduction
Material and Methods
 Results
 Comment
 References
 
Left ventricular assist device (LVAD) implantation is an effective treatment option to bridge patients with end-stage heart failure to cardiac transplantation. Continuous flow devices that provide nonpulsatile mechanical circulatory support are increasingly used. Renal dysfunction is a risk factor for morbidity and mortality with the use of pulsatile LVADs [1–5]. However, no data exist on the clinical impact of preoperative renal dysfunction on patients undergoing continuous flow LVAD implantation. This study was designed to determine outcomes after continuous flow LVAD implantation in patients who have preoperative renal dysfunction compared with patients who have normal renal function.


   Material and Methods
Top
 Abstract
 Introduction
 Material and Methods
Results
 Comment
 References
 
Patient Population
The retrospective analysis included 86 consecutive patients with end-stage heart failure undergoing continuous flow LVAD implantation as bridge to transplantation from November 1998 to July 2007. Devices included the DeBakey VAD (n = 75 [MicroMed, Houston, TX]), HVAD (n = 6 [HeartWare, Miramar, FL]), and DuraHeart LVAD (n = 5 [Terumo Corp, Ann Arbor, MI]) and have been described previously [6–9].

Renal function was assessed by calculated glomerular filtration rates (GFR) using the equation derived by the Modification of Diet in Renal Disease (MDRD) study group [10] (abbreviated): GFR = 186 x (serum creatinine, mg/dL)–1.154 x (age)–0.203 x 0.742 (if female). The GFR cutoff points were determined as specified by the National Kidney Disease Foundation Outcomes Quality Initiative (NKF-K/DOQI) guidelines [11]. Among patients with chronic kidney disease, the stage is defined by the level of GFR, with higher stages representing lower GFR levels. A GFR cutoff of less than 60 mL · min–1 · 1.73 m–2 is commonly used to distinguish patients with chronic kidney disease [11]. Here, patients were categorized into two groups according to pre-LVAD renal function. Patients with GFR greater than 60 mL · min–1 · 1.73 m–2 were defined as having normal renal function (n = 46, 53.5%), and patients with GFR less than 60 mL · min–1 · 1.73 m–2 were defined as having renal dysfunction (n = 40, 46.5%). Groups were then compared with regard to patient demographic data, comorbidities, hemodynamic variables, serum laboratory values, and pre-LVAD status. Outcome measures included the composite endpoint of heart transplantation or ongoing mechanical support at 180 days; early mortality (< 30 days); overall post-LVAD survival; bridge to transplantation rate; frequency of adverse events; and assessment of renal function. All 86 patients were followed for at least 180 days or until either transplantation or death.

The need for individual patient consent for this study was waived by the Ethics Committee owing to the strict adherence to the data protection regulations of Austria.

Statistical Analysis
Continuous variables are represented as mean ± SD, and categorical variables are represented as proportions. Continuous variables were compared using the independent-samples t test, and categorical variables were compared using the {chi}2 test. Univariate and multivariable Cox regression analyses were used to determine predictors of post-LVAD mortality. The multivariable Cox regression analysis was adjusted for the following factors previously identified as risk factors for outcome on LVAD: age, sex, hematologic abnormalities (hemoglobin), nutritional status (serum albumin), and inotropic support [12, 13]. Kaplan-Meier estimates of survival were compared using the log-rank test. A p value less than 0.05 was considered statistically significant. Analyses were performed using SPSS version 14.0 for Windows (SPSS, Chicago, IL) and SAS System software version 9.1 (SAS Institute, Cary, NC).


   Results
Top
 Abstract
 Introduction
 Material and Methods
 Results
Comment
 References
 
Baseline Characteristics
Baseline characteristics of the patients are given in Table 1. Patients with renal dysfunction were older (58.4 ± 7.0 versus 47.6 ± 12.5 years, p < 0.001) and had a higher rate of ischemic heart disease as cause of heart failure (60.0% versus 28.3%, p = 0.003) than did patients with normal renal function. The incidence of hypertension was also higher among patients with renal dysfunction (42.5% versus 21.7%, p = 0.039), whereas the incidence of diabetes mellitus was comparable in both groups. Patients with renal dysfunction had significantly elevated serum creatinine (1.6 ± 0.4 versus 1.0 ± 0.1 mg/dL, p < 0.001) and blood urea nitrogen levels (43.5 ± 20.4 versus 21.0 ± 7.1 mg/dL, p < 0.001); serum albumin and serum total bilirubin levels were comparable in both groups.


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  		Table 1 Baseline Patient Characteristics
 
Post-LVAD Outcomes and Adverse Events
Thirty-five patients (76.1%) with normal renal function and 22 (55.0%) with renal dysfunction reached the composite endpoint of heart transplantation or survival at 180 days with ongoing mechanical support (p = 0.039; Table 2). Overall actuarial survival was 91.3% at 1 month, 79.9% at 3 months, and 72.6% at 6 months for patients with normal renal function, compared with 92.5%, 66.5%, and 47.9% for patients with renal dysfunction (p = 0.038; Fig 1). Bridge-to-transplant rate was significantly lower among patients with renal dysfunction than among patients with normal renal function (40.0% versus 63.0%, p = 0.033; Table 2). Early mortality less than 30 days after LVAD implantation was not significantly different between the groups. For patients with normal renal function and renal dysfunction, respectively, the median duration of support was 129 days and 113 days, with a mean of 159.5 ± 117 days and 138.8 ± 126 days (p = 0.431) during a cumulative follow-up of 20.1 and 15.2 patient-years; the median time to transplantation was 130 days and 124 days, respectively, with a mean of 166 ± 96 days and 142 ± 74 days (p = 0.389).


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  		Table 2 Outcomes and Adverse Events
 

Figure 1
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  		Fig 1. Kaplan-Meier analysis of survival after left ventricular assist device implantation for patients with Modification of Diet in Renal Disease (MDRD) study–derived glomerular filtration rate (GFR) greater than 60 mL · min–1 · 1.73 m–2 (solid line) and MDRD-GFR less than 60 mL · min–1 · 1.73 m–2 (dashed line).

 
Adverse events included reoperation for bleeding, sepsis, and right-side heart failure; these were comparable in both groups (Table 2). Four patients (8.7%) with normal renal function and 5 patients (12.5%) with renal dysfunction had an ischemic stroke (p = 0.565); and 2 patients (4.3%) with normal renal function and 8 patients (20.0%) with renal dysfunction had a hemorrhagic stroke (p = 0.024). The incidence of post-LVAD renal failure requiring continuous venovenous hemodialysis (CVVHD) was higher in patients with renal dysfunction than in patients with normal renal function (42.5% versus 28.3%); however, this was not statistically significant.

The most common causes of death in the first 180 days after LVAD implantation included sepsis (GFR > 60, n = 6; GFR < 60, n = 7; p = 0.565), and hemorrhagic stroke (GFR > 60, n = 2; GFR < 60, n = 6; p = 0.090). Other causes of death included multiorgan failure (n = 5), ischemic stroke (n = 1), and unknown cause of death (n = 1).

Renal Function as Predictor of Post-LVAD Mortality
Pre-LVAD GFR less than 60 mL · min–1 · 1.73 m–2 was identified as a significant predictor of post-LVAD mortality by univariate analysis (odds ratio [OR] 2.0, 95% confidence interval [CI]: 1.1 to 4.1, p = 0.047); however, GFR was not an independent predictor in the multivariable model (OR 1.2, 95% CI: 0.5 to 2.5, p = 0.676) (Table 3).


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  		Table 3 Predictors of Post-LVAD Mortality
 
Post-LVAD Recovery of Renal Function
Figure 2 shows changes in renal function after continuous flow LVAD implantation. Paired samples analysis was performed on patients with renal function measurements at consecutive time intervals after LVAD implantation. Among patients with renal dysfunction an overall improvement of GFR (mL · min–1 · 1.73 m–2) was observed: implant to month 1, 44.6 ± 13.6 to 80.7 ± 32.6 (p < 0.001); implant to month 3, 40.8 ± 10.3 to 70.9 ± 21.9 (p < 0.001); implant to month 6, 41.7 ± 11.5 to 62.7 ± 25.0 (p = 0.021). Among patients with normal renal function, only an early improvement of GFR was observed: implant to month 1, 76.7 ± 12.5 to 93.7 ± 36.5 (p = 0.002).


Figure 2
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  		Fig 2. Improvement of renal function after left ventricular assist device implantation in patients with Modification of Diet in Renal Disease (MDRD) study–derived glomerular filtration rate (GFR) greater than 60 mL · min–1 · 1.73 m–2 (solid line) and MDRD-GFR less than 60 mL · min–1 · 1.73 m–2 (dashed line).

 
Patients with renal dysfunction were then stratified by whether or not, at 1 month after LVAD implantation, they recovered renal function and improved GFR to greater than 60 mL · min–1 · 1.73 m–2. Twenty-six patients (65.3%) recovered renal function; in these patients, GFR increased from 46.3 ± 14.8 to 84.0 ± 20.3 mL/min/m2 (p < 0.001). Patients who recovered renal function had significantly improved survival compared with patients whose GFR remained less than 60 mL · min–1 · 1.73 m–2 (actuarial 6-month survival 65.9% versus 11.5%, p < 0.001).

Patients who recovered renal function had a significantly lower incidence of diabetes than patients whose GFR remained less than 60 mL · min–1 · 1.73 m–2 (22.2% versus 61.5%, p = 0.015). A higher proportion of patients who recovered renal function received intravenous inotropic support before LVAD implant (55.6% versus 30.8%); however, this was not statistically significant. Absence of diabetes was the only variable that reached statistical significance when predictors of recovery of renal function were analyzed in a regression model (OR 0.2, 95% CI: 0.04 to 0.8, p = 0.022).

Improvement of renal function was observed for all device types from LVAD implantation to 1 month post-LVAD: DeBakey VAD (67 paired samples), 61.8 ± 20.9 to 86.5 mL · min–1 · 1.73 m–2 (p < 0.001); HVAD (5 paired samples), 71.9 + 19.9 to 96.5 ± 30.0 mL · min–1 · 1.73 m–2 (p = 0.011); and DuraHeart VAD (5 paired samples), 56.8 ± 18.2 to 95.9 ± 31.6 mL · min–1 · 1.73 m–2 (p = 0.007).

Post-LVAD Renal Failure
Thirty patients (34.9%) had post-LVAD renal failure requiring CVVHD. These patients had greatly increased overall mortality regardless of pre-LVAD renal function. Post-LVAD survival was 83.3% at 1 month, 49.4% at 3 months, and 29.0% at 6 months for patients with post-LVAD renal failure requiring CVVHD, compared with 96.4%, 87.1%, and 78.4% for patients without renal failure (p < 0.001; Fig 3). The 30-day mortality rate was 16.7% for patients with post-LVAD renal failure requiring CVVHD and 3.6% for patients without renal failure (p = 0.034). A significantly higher number of patients who had post-LVAD renal failure requiring CVVHD (n = 12, 40%) died from sepsis than did patients who did not have renal failure (n = 1, 1.8%; p < 0.001). The bridge-to-transplant rate was significantly lower among patients with post-LVAD renal failure requiring CVVHD (20.0% versus 69.6%, p < 0.001).


Figure 3
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  		Fig 3. Kaplan-Meier analysis of survival for patients with (dashed line) and without (solid line) renal failure requiring continuous venovenous hemodialysis after left ventricular assist device implantation.

 
Patients who had post-LVAD renal failure requiring CVVHD were older than patients who did not have renal failure (57.2 ± 9.2 versus 50.1 ± 12.0 years, p = 0.006) and had lower pre-LVAD hemoglobin levels (11.7 ± 1.4 versus 12.6 ± 1.7 g/dL, p = 0.030). Blood urea nitrogen levels were higher in patients with post-LVAD renal failure requiring CVVHD (36.7 ± 20.9 versus 28.5 ± 16.6 g/dL), and MDRD-derived GFR was lower (57.1 ± 18.9 versus 65.2 ± 20.8 mL/min/m2); however, this was not statistically significant.

Twenty-eight patients receiving a DeBakey VAD (37.3%) and 2 patients receiving an HVAD had post-LVAD renal failure requiring CVVHD. There was no case of post-LVAD renal failure requiring CVVHD among patients receiving a DuraHeart VAD (p = 0.237).


   Comment
Top
 Abstract
 Introduction
 Material and Methods
 Results
 Comment
References
 
Renal dysfunction is associated with heightened risk of mortality and morbidity for patients with congestive heart failure [14] and for patients undergoing cardiac surgery [15]. However, renal dysfunction as a risk factor with the use of LVADs is controversial. Butler and colleagues [5] showed that patients with the worst renal function (by Cockcroft-Gault calculated creatinine clearance) before Novacor LVAD implant had the highest mortality risk after LVAD placement. Oz and associates [16] found that renal function (by urine output) in the immediate preoperative hours was the most important predictor of mortality in 56 HeartMate VE patients. However, the revised risk factor summation score that included 130 consecutive patients did not find an effect of preoperative renal insufficiency [17]. Similarly, Khot and colleagues [18] showed that in patients with severe renal dysfunction, complicating cardiogenic shock clinical outcomes were comparable to those in patients without renal dysfunction.

Most studies that have sought to identify risk factors associated with post-LVAD survival included patients receiving pulsatile flow LVADs. However, LVAD systems that provide continuous low-pulsatile circulatory support are increasingly used and have been shown to safely bridge patients to transplantation [19]. In the present study, outcomes after continuous flow LVAD implantation were determined in a group of patients who had preoperative renal dysfunction and compared with a group of patients who had normal renal function. We employed the GFR formula derived by the MDRD equation [10] for estimation of renal function. The GFR is accepted as the best overall measure of renal function [20]. Two recent studies have reported that the MDRD equation adequately predicts GFR in advanced heart failure, with higher accuracy than the Cockcroft-Gault equation [21, 22]. In our cohort of 86 consecutive continuous flow LVAD recipients, patients who had renal dysfunction had significantly increased overall mortality when compared with patients who had normal renal function. In addition, patients with renal dysfunction had significantly lower bridge-to-transplant rates. However, GFR was not an independent predictor in the multivariable model. These data are comparable with the results of Lietz and associates [13], who showed that although markers of end-organ dysfunction were among the most important determinants of in-hospital mortality after LVAD implantation, GFR itself was not predictive in the multivariable model.

We observed a stroke rate of 32.5% among patients with renal dysfunction, and a significantly higher incidence of hemorrhagic stroke among these patients when compared with patients who had normal renal function. The overall stroke rate in the present study was 22.1% and is comparable to recently reported data [23]. Stroke rates (including hemorrhagic stroke) as high as 45% have been reported for the DeBakey VAD [24]. Lower thromboembolic risks have been reported for patients with the HeartMate XVE and HeartMate II LVADs [25–27]. The heterogeneity of patient populations, recent improvements in patient selection and medical management, and differences in thrombogenicity among pump designs have been suggested as reasons for this variability in cerebrovascular accident incidence [25].

Several authors have reported risk factors for cerebrovascular accident, among them older age, diabetes, hypertension, and impaired renal function [28, 29]. In the present study, patients with renal dysfunction were older, and had a higher incidence of hypertension and ischemic heart disease. This suggests that patients with renal dysfunction represent a cohort of patients with more prevalent vascular pathologies and comorbid conditions, putting them at risk of vascular disease–related events. Few studies have reported on the association of GFR with risk of stroke, and they showed a small and nonsignificant increase in stroke risk with decreasing GFR [30, 31]. Bos and associates [32] recently found a strong inverse association between GFR and risk of hemorrhagic stroke that was independent from other vascular risk factors. Decreased GFR is often attributable to small-vessel disease in the kidney that may correlate with small-vessel disease in the brain predisposing to hemorrhagic stroke [32, 33]. However, chronic kidney disease has numerous effects that may harm the cardiovascular system, including inhibition of erythropoiesis and platelet function [34]. That is of particular relevance for VAD patients, in whom coagulation abnormalities are frequently observed [35] and have been shown to be associated with cerebrovascular accident [23].

We used a standardized anticoagulation protocol for all patients receiving continuous flow devices [36]. Briefly, patients receive unfractionated heparin or, alternatively, low molecular weight heparin, in the immediate postoperative period and are then switched to a vitamin K-antagonist for long-term anticoagulation therapy with a target international normalized ratio of 2.5 to 3.5. All patients receive adjunctive antiplatelet therapy starting on postoperative day 3, consisting of aspirin or clopidogrel and dipyridamole. Treatment for hypertension includes angiotensin-converting enzyme inhibitors, angiotensin-receptor blockers, and beta-blockers as firstline therapy; if blood pressure control is deemed insufficient, alpha-1 antagonists are added to the regimen. At our center, diuretic agents are used sparingly in blood pressure management to avoid hypovolemia and insufficient LVAD flow rates.

We, among others, have shown that end-organ perfusion in patients with advanced heart failure can be improved with LVAD implantation [5, 37–39]. We found using both the MDRD formula and Cockcroft-Gault–calculated creatinine clearance for estimation of GFR that renal function after LVAD implantation is comparable between pulsatile and continuous flow devices [39]. Recovery of renal function was observed in both device types to a similar extent. In addition, incidence of renal failure was comparable between the device types. In the present study, improvement of renal function was most evident in patients with renal dysfunction. Sixty-five percent of patients with GFR less than 60 mL/min/min2 improved renal function to GFR greater than 60 mL/min/m2 at 1 month after LVAD implantation. The greatest improvement in renal function was observed at 1 to 2 months after implant in both groups. That corresponds to the time when patients are discharged from the hospital having received optimal medical management, in particular, fluid balance management. Therefore, the lesser extent of improvement observed when renal function at later times after LVAD implantation as compared with baseline renal function may in part be due to inadequate patient self-management with increasing duration of device support.

Improvement of GFR was associated with significantly improved survival. Strikingly, patients who improved their GFR to greater than 60 mL · min–1 · 1.73 m–2 had post-LVAD survival comparable to that of patients with normal renal function. Possible explanations for improved renal function on LVAD include improved cardiac output with increased perfusion of the kidneys, and correction of neurohormonal dysregulation associated with congestive heart failure [40]. It will be essential to determine which patients will most likely improve renal function on LVAD, and thus ultimately derive the most benefit from this form of therapy. In our cohort, patients who did or did not recover renal function differed significantly with respect to the incidence of diabetes. In addition, absence of diabetes was the only variable that reached statistical significance when predictors of recovery of renal function were analyzed in a regression model. This finding suggests that patients without structural kidney disease, namely, chronic renal dysfunction secondary to atherosclerosis or nephrosclerosis, may be more likely to improve renal function on LVAD. This speculation is supported by data from Butler and colleagues [5] who showed that absence of diabetes was among the variables that showed a trend toward an association with improved renal function and survival after pulsatile Novacor LVAD implantation.

The capability of continuous flow devices to provide adequate left ventricular decompression and end-organ perfusion has been widely shown in the literature [41–43]. Garcia and coworkers [44] recently demonstrated in patients with HeartMate XVE and HeartMate II VADs, respectively, that continuous flow LVADs are as effective as pulsatile-flow LVADs with regard to degree of left ventricular unloading. Butler and coworkers [5] showed that in patients with pulsatile Novacor pumps, renal function improves substantially and rapidly in post-LVAD survivors and is associated with improved outcomes. Radovancevic and colleagues [38] showed that creatinine clearance either improved or stayed the same for as long as 15 months after continuous flow LVAD implantation. In a prospective, multicenter clinical trial to determine the efficacy and safety of a third-generation LVAD, the VentrAssist, for a BTT cohort Esmore and colleagues [45] showed that the generated LVAD pump flow index was sufficient to maintain an adequate circulation and significantly improve end-organ function. Taken together, these data suggest that continuous flow LVADs provide adequate flow to maintain end-organ function during mechanical circulatory support [38].

Patients with post-LVAD renal failure requiring CVVHD had greatly increased overall mortality regardless of pre-LVAD renal function. Incidences of renal failure in LVAD recipients as high as 56% have been reported [46], with 6-month mortality rates as high as 93% [47, 48]. Here, the 6-month mortality rate was 71%, with the majority of deaths due to sepsis. Topkara and colleagues [48] have suggested that patients in whom renal failure develops after LVAD implantation are sicker at baseline. We have made a similar observation in the present study. Patients who had post-LVAD renal failure requiring CVVHD were older than patients without renal failure and had lower pre-LVAD hemoglobin levels. We have recently found age to independently predict survival after LVAD implantation (Sandner and coworkers, unpublished data). Although our analysis revealed significantly lower survival among LVAD patients over 60 years of age, their posttransplant outcome was excellent. We therefore do not consider age alone to be an absolute exclusion criterion for LVAD implantation among bridge-to-transplantation candidates. The indication for VAD implantation in the majority of our patients was fixed pulmonary hypertension that precluded primary heart transplantation. We have previously shown that LVADs decrease fixed pulmonary hypertension in heart transplant candidates and allow patients to overcome a contraindication for heart transplantation [49]. These patients, although considered transplant candidates, were not yet actively on the waiting list for transplantation at the time of LVAD implantation and in the immediate postoperative period when renal failure occurred.

Limitations of this study include those related to any retrospective analyses. Renal function was assessed using calculated estimates of GFR; other renal variables such as urine output and additional diagnostic measures such as renal histology or ultrasonography were not routinely available. Our data represent the experience with three continuous flow devices; we do not know whether similar outcomes can be expected with other devices.

Here, we demonstrate that patients with renal dysfunction have worse outcomes after continuous flow LVAD implantation. However, renal function improves after LVAD implantation and is associated with improved survival. Taken together, our data show that careful and individual consideration of age-related comorbidities and end-organ function when selecting patients for bridge-to-transplant therapy appears imperative.


   References
Top
 Abstract
 Introduction
 Material and Methods
 Results
 Comment
 References
 

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