Impact of Drug-Eluting Versus Bare-Metal Stents on Mortality in Patients With Anemia
Mehdi H. Shishehbor, DO, MPH*,*,
Steven J. Filby, MD*,
Adnan K. Chhatriwalla, MD*,
Ryan D. Christofferson, MD*,
Anil Jain, MD , ,
Samir R. Kapadia, MD*,
A. Michael Lincoff, MD*,
Deepak L. Bhatt, MD*,
Stephen G. Ellis, MD*
* Department of Cardiovascular Medicine, Cleveland Clinic, Cleveland, Ohio
Department of Internal Medicine, Cleveland Clinic, Cleveland, Ohio
Information Technology Division, Cleveland Clinic, Cleveland, Ohio
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Abstract
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Objectives: Our aim was to assess the incidence of all-cause mortality in patients with anemia undergoing percutaneous coronary intervention (PCI) receiving drug-eluting stents (DES) or bare-metal stents (BMS).
Background: Anemia has been associated with poor clinical outcomes in patients undergoing PCI. However, it is unknown whether stent selection (DES or BMS) has a differential outcome in this high-risk group.
Methods: Anemia was defined as a hematocrit below 36% for female subjects and below 40% for male subjects as defined by the World Health Organization. All patients undergoing PCI with DES or BMS alone from March 2003 to June 2007 were included. The primary end point was all-cause mortality. Anemia was further characterized using mean corpuscular volume as microcytic, normocytic, or macrocytic.
Results: A total 11,181 patients underwent PCI over a 4.5-year interval; of these, 2,172 met our inclusion criteria. There were a total of 429 deaths. The majority of patients had normocytic anemia (n = 1,931). Of the 3 anemia subtypes, macrocytic anemia (DES 26%, BMS 44%) had the highest mortality followed by normocytic (DES 17%, BMS 25%) and microcytic (DES 13%, BMS 18%) anemia, respectively. All-cause mortality was significantly lower with DES in unadjusted and multivariable adjusted Cox proportional models (adjusted hazard ratio: 0.66, 95% confidence interval: 0.54 to 0.82; p < 0.001).
Conclusions: In an adjusted analysis, the use of DES as compared with the use of BMS was associated with decreased mortality in patients with anemia. Additionally, among anemia subtypes, macrocytic anemia had the highest mortality.
Key Words: anemia • drug-eluting stents • bare-metal stents • all-cause mortality
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Abbreviations and Acronyms
| | BMS = bare-metal stent(s) | | CI = confidence interval | | DES = drug-eluting stent(s) | | HCT = hematocrit | | HR = hazard ratio | | MCV = mean corpuscular volume | | MI = myocardial infarction | | PCI = percutaneous coronary intervention | | SES = socioeconomic status | | TVR = target vessel revascularization |
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Anemia has been characterized as an independent cardiovascular risk factor; its presence portends poor outcomes in patients with coronary artery disease. It is associated with higher rates of in-hospital mortality in patients with congestive heart failure and myocardial infarction (MI), and patients with pre-operative anemia have higher mortality after coronary artery bypass surgery (1–5). Importantly, several studies have also shown a strong association between anemia and adverse clinical events in patients undergoing percutaneous coronary intervention (PCI) (6–8).
Due to reports of increased incidence of stent thrombosis with drug-eluting stents (DES), a 1-year course of dual antiplatelet therapy with aspirin and a thienopyridine agent is currently recommended in DES-treated patients (9). The presence of low hemoglobin is of particular concern in these patients as they may be at increased risk of bleeding during this treatment period; and for this reason, operators often choose to place bare-metal stents (BMS) in anemic patients. Still, there are no available data regarding the impact of stent selection (DES vs. BMS) in anemic patients to guide decision making during PCI. We, thus, examined the incidence of all-cause mortality in patients with anemia undergoing PCI who received DES versus BMS. Furthermore, we examined the interaction between anemia subtype and mortality in each stent group.
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Methods
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Study population.
Patients who underwent PCI between March 2003 to June 2007 at a single institution and received only DES or a BMS were identified through a query of the institutional PCI registry. Briefly, baseline characteristics, cardiac history, risk factors, medications, angiographic and procedural data were prospectively obtained and recorded. We also accounted for variables that may be important in selecting a DES or BMS. These included depression, malignancy, and socioeconomic status (SES). SES was obtained from U.S. census data using a validated score (10,11). The primary end point was all-cause mortality, which was assessed by querying the Social Security Death Index. The institutional review board waived requirements for informed consent for the institutional PCI registry. Angiographic data were collected on all patients undergoing PCI and recorded in the cardiovascular information registry.
Definition of anemia.
Blood studies were routinely obtained on all patients before PCI including white blood cell count, serum hemoglobin, hematocrit (HCT), and creatinine. Baseline anemia was defined as an HCT <36% for female subjects and as an HCT <40% for all male subjects, in accordance with World Health Organization definition (12). We further categorized patients into the following tiers based on degree of anemia: HCT  28, HCT 29 to 35, and HCT >35. In order to further delineate the impact of stent selection in different subtypes of anemia, we used mean corpuscular volume (MCV) and divided the cohort into subgroups with microcytic (MCV <80), normocytic (MCV 80 to 100), and macrocytic anemia (>100) (13).
Statistical analysis.
Continuous variables are presented as mean ± SD. Differences in baseline and angiographic characteristics were compared using the Wilcoxon rank sum test for continuous variables and the chi-square test for categorical variables. We used Kaplan-Meier curves to present the unadjusted time-to-event data. Additionally, multivariable modeling was performed using Cox proportional hazards method to examine the association between the use of BMS and DES and all-cause mortality while accounting for the differences in baseline demographic features, angiographic variables, and other confounders shown in Tables 1 and 2. All statistical analyses were performed using SAS software, version 9.1 (SAS Inc., Cary, North Carolina) and S-plus 7.0 (Insightful, Inc., Seattle, Washington). All tests were 2-tailed; a p value of <0.05 was considered significant.
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Results
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Baseline characteristics.
A total of 2,172 patients met our study criteria; of these, 662 received only BMS and 1,510 underwent stenting with only DES (Tables 1 and 2). Patients presenting with acute coronary syndromes were more likely to receive BMS (Table 1). Alternatively, DES use was more common among patients with smaller mean stent diameters, longer mean stent length, and longer mean lesion length (Table 2). Additionally, patients undergoing intervention for chronic total occlusions, in-stent restenosis, and multivessel disease were more likely to receive DES. Prevalence of chronic conditions such as malignancy, kidney disease, chronic obstructive lung disease, and peripheral vascular disease was similar among patients receiving DES and BMS (Table 1).
Stent type and degree of anemia.
The majority of patients in our analysis had only mild anemia with 52% of those having HCT  35 and 95% having HCT 29. As shown in Figure 1, DES use was more prevalent than BMS at each HCT tier, and even those patients in our study with the lowest HCT levels were more likely to receive DES than BMS.
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Figure 1 Percent DES or BMS Use According to Hematocrit Cutpoints
Regardless of the hematocrit level, around 60% of the patients received a drug-eluting stent (DES) and 30% received a bare-metal stent (BMS).
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Association of anemia with mortality.
A total of 429 deaths occurred during the follow-up period. In a multivariable model despite adjusting for over 25 variables, HCT was significantly associated with all-cause mortality (adjusted hazard ratio [HR]: 0.93, 95% confidence interval [CI]: 0.91 to 0.96; chi-square = 27.4, p < 0.001). In the multivariable model, despite adjusting for HCT as a continuous variable and all confounders shown in Table 1, macrocytic (adjusted HR: 2.05, 95% CI: 1.15 to 3.69; chi-square = 5.9, p = 0.015) and normocytic anemia were significantly associated with all-cause mortality (adjusted HR: 1.59, 95% CI: 1.04 to 2.45; chi-square = 4.49, p = 0.034) as compared with microcytic anemia.
Univariate and multivariable analysis.
Mortality was high in this cohort of patients with anemia undergoing PCI; however, patients treated with BMS had a significantly higher mortality compared with those treated with DES (26% vs. 17%, p < 0.001) for a median follow-up of 1.8 years (Fig. 2). In both univariate and multivariable Cox proportional hazard analysis, DES use was associated with a 33% relative risk reduction for all-cause mortality (adjusted HR: 0.66, 95% CI: 0.54 to 0.82; p < 0.001). Additional subgroup analysis of patients with HCT 28 (adjusted HR: 0.69, 95% CI: 0.52 to 0.91; p = 0.008); HCT 29 and <35 (adjusted HR: 0.58, 95% CI: 0.34 to 0.97; p = 0.04); and HCT 35 (adjusted HR: 0.64, 95% CI: 0.45 to 0.91; p = 0.01) yielded similar results (Fig. 3). Of anemia subtypes, normocytic anemia was most prevalent. Again, patients with normocytic anemia treated with DES had a lower mortality than those treated with BMS (p < 0.0001). Few patients had either microcytic or macrocytic anemia, though there was a trend favoring lower mortality in patients with macrocytic anemia treated with DES (Fig. 4).
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Figure 3 Mortality According to Hematocrit Cutpoints
In univariate analysis, DES use was associated with lower mortality among those with hematocrit 29. This trend persisted for those with a hematocrit 28 but did not reach statistical significance. Abbreviations as in Figure 1.
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Figure 4 Mortality According to Anemia Subclass
DES use was associated with lower mortality among those with macrocytic and normocytic anemia. However, no significant differences were noted among those with microcytic anemia. Abbreviations as in Figure 1.
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Discussion
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The principal finding of this study is that treatment with DES is associated with lower mortality than BMS in patients with anemia. This treatment effect was independent of baseline HCT, clinical and angiographic characteristics, white blood cell count, serum creatinine, SES, and presence of malignancy or depression. Reduced HCT was associated with increased mortality in both BMS and DES populations, and those with the most profound anemia had the highest mortality. Patients were more likely to receive DES than BMS irrespective of HCT stratum or anemia subtype. In subgroup analysis, DES continued to be associated with lower mortality among those with lower HCT values and across different anemia subtypes. The results of this analysis also indicate that, of the anemia subtypes, patients with macrocytic anemia have the highest mortality.
There have been several recent studies suggesting that patients with anemia undergoing PCI have poor cardiovascular outcomes and increased mortality. In a study by Nikolsky et al. (14) of 6,929 post-PCI patients, low baseline HCT was independently associated with substantially higher in-hospital and 1-year mortality rates. Another study by Lee et al. (7) found pre-procedural anemia to be an independent predictor of mortality that was associated with higher short-term major adverse cardiac events in 6,116 consecutive PCI patients. Taken together, these studies indicate that baseline anemia may be an independent marker for future cardiovascular events and increased mortality in patients undergoing PCI. Yet despite the reduction in rates of target vessel revascularization (TVR) with the use of DES as compared with BMS, some have raised concerns over the use of DES in at-risk populations such as those with anemia (15,16). Given the risk of bleeding with antiplatelet therapy and the recent recommendation for a prolonged course of dual antiplatelet therapy after DES implantation, these concerns take on even greater importance. However, to date the safety and efficacy of DES versus BMS in patients with anemia undergoing PCI has not been fully investigated.
To our knowledge, this is the first study to examine stent type and mortality in anemic patients. Surprisingly, DES use was more prevalent than BMS in all anemic subgroups in our analysis. One might have expected DES use to be lower in this population due to concerns of increased risk of bleeding, especially with the prolonged thienopyridine course currently recommended (9). Yet, as our study suggests, those patients treated with DES had lower mortality than those treated with BMS at every HCT stratum, thus underscoring the notion that DES may be used safely and advantageously in select anemic patients.
This mortality benefit of DES over BMS may seem surprising in light of recent concerns of a possible increased risk of death and MI from DES-related stent thrombosis (17–22), but, in fact, similar results of mortality reduction with DES have previously been reported in other populations. In a recent registry analysis, the use of DES was associated with significant reductions in mortality, particularly in high-risk patients (23,24). Consistent with these findings, recent studies have demonstrated that "off-label" use of DES versus BMS is associated with lower adverse cardiovascular outcomes and mortality (25–27). While no randomized clinical trials to date have demonstrated a mortality benefit with DES, these trials have largely focused on lower risk populations and have excluded patients with anemia. In contrast, our analysis, comprised entirely of patients with anemia, demonstrates that DES-treated patients are much more likely to have high-risk angiographic features. In addition, those who received DES were also more likely to be receiving PCI for "off-label" indications such as treatment of chronic total occlusions, in-stent restenosis, or multivessel disease. However, despite the potential mechanisms, selection bias and confounding may still play a significant role in our findings. In addition, our cohort has significant morbidity as shown in Table 1 and a higher mortality compared with other studies that have evaluated PCI in the setting of anemia. Therefore, the results of our analysis may not be generalizable to all patients with anemia.
The mechanism of the mortality benefit of DES over BMS was not directly examined in the present study. One explanation for our findings is that DES use lowers mortality relative to BMS by preventing restenosis and lowering rates of TVR. While some have suggested there may be an increased risk of adverse events with DES from late stent thrombosis, restenosis after BMS implantation is a much more common clinical problem, occurring in approximately 20% to 30% of patients (28,29). Though often presumed to be a benign clinical entity, recent studies have indicated that restenosis is sometimes associated with acute MI (30–32). Furthermore, TVR due to restenosis is also associated with increased procedural complications such as death or MI (33). In this context, by preventing this common clinical problem and reducing the frequency of repeat intervention, DES treatment may result in a mortality reduction that offsets the potential risk of DES-related adverse events. The resulting net mortality benefit, however, may only be present in high-risk cohorts such as those with anemia and high-risk lesions. Additionally, it is possible that patients treated with DES received longer courses of clopidogrel than those treated with BMS. Prolonged treatment of clopidogrel after PCI has been associated with reduced incidence of cardiovascular death and MI particularly in high-risk patients and could also have accounted for some of the mortality benefit observed in this study (34).
To our knowledge, this is also the first study to examine the impact of different subtypes of anemia on mortality in patients undergoing PCI. Patients with a history of bleeding events are typically at highest risk of rebleeding with anticoagulation and antiplatelet therapy during and after coronary intervention. Blood loss can result in a normocytic anemia, reflecting acute loss of blood cells along with blood volume, or a microcytic anemia due to iron deficiency in patients with chronic blood loss. Both of these subtypes had better outcomes than those with macrocytic indexes in our study. However, normocytic and microcytic anemia have many etiologies other than acute blood loss, and given that acute bleeding is a contraindication to PCI, it is unlikely those in our study with normocytic or microcytic indexes had anemia from acute bleeding. While it is important to emphasize that DES use was associated with better outcomes than BMS in every anemia subtype and HCT strata, the results from the present study only apply to patients with stable pre-procedural anemia.
There are certain limitations of this study that should be noted. First, this was an observational analysis and stent type (BMS vs. DES) was not randomized. Unmeasured confounding variables may have accounted for some of the differences in outcomes, even though our analysis adjusted for multiple potential confounding factors. Second, we are unable to identify the exact etiology of anemia in each patient. Although we divided patients based on MCV, it is well known that there can be considerable overlap as to the etiology of anemia when using these cutoffs. In addition, some patients may have more than 1 type of co-existing anemia yielding a mixed red blood cell index. Third, we did not have data on the incidence of bleeding and stent thrombosis; therefore, we cannot comment on the risk of DES on these important end points. Fourth, we did not have data regarding long-term clopidogrel use; however, most operators in our institution recommend clopidogrel use for at least 1 year and in most cases indefinitely when DES is used. Finally, few patients within the present analysis had severe anemia, and, thus, the results of our study may only be applicable to patients with mild to moderately low HCT levels.
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Conclusions
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The use of DES as compared with BMS was independently associated with lower mortality in patients with mild-to-moderate, stable anemia undergoing PCI. While it is still advisable to treat patients at high risk for bleeding with BMS, the present study shows that the benefit of DES may outweigh the risk in select anemic patients. However, we remain cautious in advocating DES in all patients with anemia due to the risk of selection bias and confounding that are associated with observational registries.
* Reprint requests and correspondence: Dr. Mehdi H. Shishehbor, Department of Cardiovascular Medicine, Cleveland Clinic, 9500 Euclid Avenue, JJ40, Cleveland, Ohio 44195-0002. (Email: shishem{at}gmail.com).
Manuscript received July 15, 2008;
revised manuscript received November 18, 2008,
accepted November 23, 2008.
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Abstract
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