Warfarin Use and the Risk for Stroke and Bleeding in Patients With Atrial Fibrillation Undergoing Dialysis

Warfarin Use and Risk of Stroke in Patients With Atrial Fibrillation Undergoing Hemodialysis: A Meta-Analysis

In spite of the substantial burden of atrial fibrillation and associated elevated ischemic stroke risk in patients undergoing hemodialysis, the role of warfarin in these high-risk patients remains uncertain. Our objective was to clarify the association between warfarin use and risk of stroke for patients with atrial fibrillation undergoing dialysis.PubMed and Embase from January 1966 to January 2015 were searched to identify relevant studies. Inclusion criteria were cohort studies, patients with atrial fibrillation undergoing hemodialysis, and reported quantitative estimates of the multivariate adjusted relative risk (RR) and 95% confidence interval (CI) for future stroke associated with warfarin use. We identified 8 studies, with a total of 9539 participants and 706 stroke events. Three studies reported total stroke as primary endpoint and other studies reported ischemic stroke as primary endpoint. Pooling the results showed that warfarin use was associated with higher risk of any stroke (RR 1.50, 95% CI: 1.13-1.99). By stroke type, warfarin was not significantly linked to risk of ischemic stroke (RR 1.01, 95% CI: 0.65-1.57, P = 0.97), but was related to greater hemorrhagic stroke risk (RR 2.30, 95% CI: 1.62-3.27). Warfarin heightened overall bleeding risk (RR 1.27, 95% CI: 1.03-1.56), but not death (RR 0.67, 95% CI: 0.37-1.21).Among patients with atrial fibrillation undergoing hemodialysis, use of warfarin is associated with a higher risk of hemorrhagic stroke, but did not increase overall mortality.

The Quandary of Oral Anticoagulation in Patients With Atrial Fibrillation and Chronic Kidney Disease

Compared to patients with normal renal function, the prevalence of atrial fibrillation (AF) in chronic kidney disease (CKD) is increased, as is consequently the stroke prevalence in these patients. This increased risk of stroke in patients with CKD is caused not only by the increased prevalence of AF, but also by associated co-morbidities, and inherent platelet and vascular dysfunction. Paradoxically, imbalance in the same factors also increases the bleeding risk, imposing a dilemma as to whether anticoagulation should be prescribed or deferred, particularly in patients with end-stage renal disease (ESRD), in whom the bleeding diathesis and thromboembolic predisposition are most recalcitrant. Unfortunately, it is in this vulnerable population, in whom therapeutic options are most limited, that evidence-based studies relating to stroke prophylaxis are scarce, discordant and based only on registry observations. Pending randomized controlled studies on this issue, we will review important epidemiologic data and major recent registry-based studies that the clinician has to weigh when making the best decision on the issue of the prophylactic use of warfarin in patients with CKD with AF, focusing on patients with end-stage renal disease.

The 2014 Atrial Fibrillation Guidelines Companion: A Practical Approach to the Use of the Canadian Cardiovascular Society Guidelines

The Canadian Cardiovascular Society (CCS) Atrial Fibrillation Guidelines Program has generated a comprehensive series of documents regarding the management of atrial fibrillation (AF) between 2010 and 2014. The guidelines provide evidence-based consensus management recommendations in a broad range of areas. These guidelines have proven useful in informing clinical practice, but often lack detail in specifications related to practical application, particularly for areas in which the evidence base is limited or conflicting. Based on feedback from the community, the CCS Atrial Fibrillation Guidelines Committee has identified a number of areas that require clarification to address commonly asked practical questions related to guidelines application. In the present article a number of such questions are presented and suggestions about how they can be answered are suggested. Among the issues considered are: (1) What duration of AF is clinically significant? (2) How are the risk factors in the CCS Algorithm for selecting anticoagulation therapy derived and defined? (3) How is valvular heart disease defined and how do different forms of valve disease affect the choice of anticoagulant therapy for AF patients? (4) How should we quantify renal dysfunction and how does it affect therapeutic choices? The response to these questions and the underlying logic are provided, along with an indication of future research needed where no specific approach can presently be recommended based on the literature.

Modulation of stroke risk in chronic kidney disease

Stroke is the second most common cause of death and the leading cause of neurological disability worldwide, with huge economic costs and tragic human consequences. Both chronic kidney disease (CKD) and end-stage kidney disease are associated with a significantly increased risk of stroke. However, to date this has generated far less interest compared with the better-recognized links between cardiac and renal disease. Common risk factors for stroke, such as hypertension, hypercholesterolaemia, smoking and atrial fibrillation, are shared with the general population but are more prevalent in renal patients. In addition, factors unique to these patients, such as disorders of mineral and bone metabolism, anaemia and its treatments as well as the process of dialysis itself, are all also postulated to further increase the risk of stroke. In the general population, advances in medical therapies mean that effective primary and secondary prevention therapies are available for many patients. The development of specialist stroke clinics and acute stroke units has also improved outcomes after a stroke. Emerging therapies such as thrombolysis and thrombectomy are showing increasingly beneficial results. However, patients with CKD and on dialysis have different risk profiles that must be taken into account when considering the potential benefits and risks of these treatments. Unfortunately, these patients are either not recruited or formally excluded from major clinical trials. There is still much work to be done to harness effective stroke treatments with an acceptable safety profile for patients with CKD and those on dialysis.

Risks of Death and Stroke in Patients Undergoing Hemodialysis With New-Onset Atrial Fibrillation: A Competing-Risk Analysis of a Nationwide Cohort

BACKGROUND

Whether oral anticoagulant use should be considered in patients undergoing hemodialysis with atrial fibrillation (AF) remains controversial because of the uncertainty regarding risk-benefit assessments. The purpose of this study was to investigate the risk of ischemic stroke in patients undergoing hemodialysis with new-onset AF, in comparison with those without arrhythmia.

METHODS AND RESULTS

This nationwide, population-based, propensity score-matched cohort study used data from Taiwan's National Health Insurance Research Database during 1998 to 2011 for patients on hemodialysis with new-onset nonvalvular AF and matched subjects without arrhythmia. The clinical end points were ischemic stroke (fatal or nonfatal), all-cause death, and other serious adverse cardiovascular events. In comparison with the matched cohort, patients with AF (n=6772) had higher risks of ischemic stroke (adjusted hazard ratio [aHR], 1.27; 95% confidence interval [CI], 1.13-1.43), all-cause death (aHR, 1.59; 95% CI, 1.52-1.67), in-hospital cardiovascular death (aHR, 1.83; 95% CI, 1.71-1.94), myocardial infarction (aHR, 1.33; 95% CI, 1.17-1.51), and hospitalization for heart failure (aHR, 1.90; 95% CI, 1.76-2.05). After considering in-hospital death as a competing risk, AF significantly increased the risk of heart failure (HR, 1.56; 95% CI, 1.45-1.68), but not those of ischemic stroke and myocardial infarction. Additionally, the predictive value of the CHA2DS2-VASc score for ischemic stroke was diminished in the competing-risk model.

CONCLUSIONS

The risk of stroke was only modestly higher in patients undergoing hemodialysis with new-onset AF than in those without AF, and it became insignificant when accounting for the competing risk of in-hospital death.

Effectiveness and Safety of Warfarin in Dialysis Patients With Atrial Fibrillation: A Meta-Analysis of Observational Studies

In routine practice, warfarin is widely used in dialysis patients with atrial fibrillation (AF) for stroke prevention though the ratio of risks to benefits remains unclear. Recent cohort studies investigating the association between warfarin use and the risks of stroke and bleeding in dialysis patients with AF present conflicting results. The objective of this study was to assess the effectiveness and safety of warfarin use in patients with AF undergoing dialysis. Three databases PubMed, EMBASE, and OVID were searched from their inception to August 2015. Observational studies which assessed the ischemic stroke or bleeding risk of warfarin use in dialysis patients with AF were included. Two reviewers independently extracted data and assessed methodological quality based on the Newcastle-Ottawa Scale score. Combined hazard ratios (HRs) and 95% confidence intervals (CIs) were calculated using the random-effects model and heterogeneity was assessed based on the Cochrane Q-statistic test and the I statistic. Metaregression analyses were performed to explore the source of heterogeneity. A total of 11 eligible studies with 25,407 patients were included in the analysis. Warfarin use, in comparison with no-warfarin use, was not associated with a lower risk for ischemic stroke (HR 0.95, 95% CI 0.66-1.35). Sensitivity analyses found results to be robust. Metaregression analysis showed that demographic feature, clinical characteristics, or study-level variable had no impact of warfarin use on stroke risk. In addition, warfarin use was associated with a 27% higher risk for bleeding (95% CI 1.04-1.54). Overall, warfarin use did not have a significant association with reduced mortality (95% CI 0.96-1.11). It appears that warfarin use is not beneficial in reducing stroke risk, but with a high risk for bleeding in dialysis patients with AF. Randomized trials are needed to determine the risk-benefit ratio of warfarin in dialysis patients with AF.

Clinical characteristics of hemodialysis patients with atrial fibrillation: The RAKUEN (Registry of atrial fibrillation in chronic kidney disease under hemodialysis from Niigata) study

BACKGROUND

Clinical characteristics, management, and outcomes in hemodialysis patients with atrial fibrillation (AF) remain unclear.

METHODS AND RESULTS

We studied 423 Japanese patients undergoing maintenance hemodialysis (age 65.2±12.4 years, male 70%, mean duration of hemodialysis 139±124 months). AF was present in 19% (n=82) and was independently related to increased age (odds ratio 1.070, 95% confidence interval 1.043-1.098), longer hemodialysis duration (odds ratio 1.006, 95% confidence interval 1.004-1.008), and congestive heart failure (odds ratio 2.749, 95% confidence interval 1.546-4.891). During observations lasting a mean of 36 months, the incidences of all-cause death, cardiovascular death, and major bleeding, in particular gastrointestinal bleeding, were significantly higher in the AF (n=82) than the non-AF (n=341) patients (p<0.001, p=0.004, p=0.002, p=0.027, respectively), but the incidence of ischemic stroke/systemic embolism was similar in the AF and non-AF patients. AF was independently associated with all-cause death (hazard ratio 1.728, 95% confidence interval 1.123-2.660) and major bleeding (hazard ratio 1.984, 95% confidence interval 1.010-3.896). Warfarin was prescribed in 33% of the AF patients, but the rates of all-cause death, ischemic stroke, and major bleeding during the study period were not significantly different between warfarin (n=27) and non-warfarin (n=55) groups.

CONCLUSIONS

In our hemodialysis patients, AF was a common comorbidity and was independently associated with all-cause death and major bleeding, but not with increased risk of ischemic stroke.

Comparison of novel oral anticoagulants versus vitamin K antagonists in patients with chronic kidney disease

PURPOSE OF REVIEW

Novel oral anticoagulants (NOACs) including apixaban, dabigatran and rivaroxaban have been approved by international regulatory agencies to prevent venous thromboembolism as well as treat atrial fibrillation and venous thromboembolism in individuals with chronic kidney disease (CKD). However, alterations in their metabolism in the setting of CKD may impact their efficacy and lead to an increased risk of bleeding. This review summarizes the current literature on the efficacy and safety of these agents in individuals with moderate CKD.

RECENT FINDINGS

In clinical trials, the use of the NOACs in patients with moderate CKD has demonstrated efficacy and safety similar to those seen with vitamin K antagonists. However, no universal reversal agent for the anticoagulant effect of the NOACs exists in the setting of bleeding. Limited data have demonstrated that hemodialysis has been effectively used to aid in reversing the effects of dabigatran, and the use of prothrombin complex concentrate has also been used for serious and major adverse bleeding events with some success.

SUMMARY

As the use of the NOACs in patients with CKD increases, it will be important to monitor their safety, and clinicians who prescribe them should carefully monitor kidney function and recognize the potential for adverse effects.

Atrial fibrillation and chronic kidney disease: focus on rivaroxaban

Renal insufficiency increases the risk of stroke and bleeding in atrial fibrillation patients. Although vitamin K antagonists reduce the risk of stroke in patients with moderate renal dysfunction, this observation is less clear in patients with renal impairment. Moreover, the risk of bleeding with vitamin K antagonists increases as renal function worsens. Maintaining international normalized ratio values within therapeutic targets is more difficult in patients with renal dysfunction, and those agents may cause warfarin-related nephropathy and vascular calcification. Rivaroxaban is the only nonvitamin K oral anticoagulant with a dose specifically tested in patients with moderate renal insufficiency. Rivaroxaban is effective for the prevention of stroke in atrial fibrillation patients with moderate renal dysfunction, with a lower risk of intracranial and fatal bleeding.

Risk Factors of Ischemic Stroke and Subsequent Outcome in Patients Receiving Hemodialysis

Background and Purpose—

End-stage renal disease (ESRD) requiring hemodialysis carries up to a 10-fold greater risk of stroke than normal renal function. Knowledge on risk factors and management strategies derived from the general population may not be applicable to those with ESRD. We studied a large ESRD population to identify risk factors and outcomes for stroke.

Methods—

All adult patients receiving hemodialysis for ESRD from January 1, 2007, to December 31, 2012, were extracted from the electronic patient record. Variables associated with stroke were identified by survival analysis; demographic, clinical, imaging, and dialysis-related variables were assessed, and case-fatality was determined. Follow-up was until December 31, 2013.

Results—

A total of 1382 patients were identified (mean age, 60.5 years; 58.5% men). The prevalence of atrial fibrillation was 21.2%, and 59.4% were incident hemodialysis patients. One hundred and sixty patients (11.6%) experienced a stroke during 3471 patient-years of follow-up (95% ischemic). Stroke incidence was 41.5/1000 patient-years in prevalent and 50.1/1000 patient-years in incident hemodialysis patients. Factors associated with stroke on regression analysis were prior stroke, diabetes mellitus, and age at starting renal replacement therapy. Atrial fibrillation was not significantly associated with stroke, and warfarin did not affect stroke risk in warfarin-treated patients. Fatality was 18.8% at 7 days, 26.9% at 28 days, and 56.3% at 365 days after stroke.

Conclusions—

Incidence of stroke is high in patients with ESRD on hemodialysis with high case-fatality. Incident hemodialysis patients had the highest stroke incidence. Many, but not all, important risk factors commonly associated with stroke in the general population were not associated with stroke in patients receiving hemodialysis.

Warfarin use and the risks of stroke and bleeding in hemodialysis patients with atrial fibrillation: A systematic review and a meta-analysis

BACKGROUND AND AIM

The efficacy and safety of warfarin therapy in hemodialysis (HD) patients with atrial fibrillation (AF) remains controversial. Thus, we performed, up to date, the first meta-analysis on the risks of stroke and bleeding in warfarin treatment in these populations.

METHODS AND RESULTS

The relevant literature was searched using the following electronic databases without any language restrictions: the Cochrane Library Database, PubMed, ISI, Ovid, and Chinese Biomedical Database from the establishment of the database to October 2014. The studies were included if (a) studies described the risk of stroke or bleeding with or without warfarin in dialysis patients with AF, (b) studies provided information about hazard ratio (HR) and 95% confidence interval (CI) of stroke or bleeding, and (c) the study design was a clinical cohort. The inverse variance method was used to obtain overall HRs and 95% CIs. Sensitivity analyses and publication bias were also performed. We identified six eligible studies with a total of 9816 patients. Combined HRs showed that warfarin cannot prevent strokes in HD patients with AF (HR = 1.23, 95% CI 0.80-1.87; P = 0.347), but its use was associated with a higher risk of bleeding (HR = 1.20, 95% CI 1.03-1.39; P = 0.019).

CONCLUSION

This meta-analysis suggested that warfarin should not be recommended for the routine treatment of HD patients with AF.

Outcomes After Warfarin Initiation in a Cohort of Hemodialysis Patients With Newly Diagnosed Atrial Fibrillation

BACKGROUND

Although warfarin is indicated to prevent ischemic strokes in most patients with atrial fibrillation (AF), evidence supporting its use in hemodialysis patients is limited. Our aim was to examine outcomes after warfarin therapy initiation, relative to no warfarin use, following incident AF in a large cohort of hemodialysis patients who had comprehensive prescription drug coverage through Medicare Part D.

STUDY DESIGN

Retrospective observational cohort study.

SETTING & PARTICIPANTS

Patients in the US Renal Data System undergoing maintenance hemodialysis who had AF newly diagnosed in 2007 to 2011, with Medicare Part D coverage, who had no recorded history of warfarin use.

PREDICTOR

Warfarin therapy initiation, identified by a filled prescription within 30 days of the AF event.

OUTCOMES

Death, ischemic stroke, hemorrhagic stroke, severe gastrointestinal bleeding, and composite outcomes.

MEASUREMENTS

HRs estimated by applying Cox regression to an inverse probability of treatment and censoring-weighted cohort.

RESULTS

Of 12,284 patients with newly diagnosed AF, 1,838 (15%) initiated warfarin therapy within 30 days; however, ∼70% discontinued its use within 1 year. In intention-to-treat analyses, warfarin use was marginally associated with a reduced risk of ischemic stroke (HR, 0.68; 95% CI, 0.47-0.99), but not with the other outcomes. In as-treated analyses, warfarin use was associated with reduced mortality (HR, 0.84; 95% CI, 0.73-0.97).

LIMITATIONS

Short observation period, limited number of nonfatal events, limited generalizability of results to more affluent patients.

CONCLUSIONS

In hemodialysis patients with incident AF, warfarin use was marginally associated with reduced risk of ischemic stroke, and there was a signal toward reduced mortality in as-treated analyses. These results support clinical equipoise regarding the use of warfarin in hemodialysis patients and underscore the need for randomized trials to fill this evidence gap.

Risk of Ischemic Stroke and Stroke Prevention in Patients with Atrial Fibrillation and Renal Dysfunction

Chronic kidney disease (CKD) has been identified as an important risk factor for new-onset atrial fibrillation (AF) and would significantly increase the risk of AF-related strokes. Stroke prevention in AF patients with CKD is a big challenge, especially for patients with end-stage renal disease (ESRD) undergoing long-term dialysis. In addition to an increase risk of stroke, renal dysfunction was also associated with a higher risk of hemorrhage due to dysregulation of coagulation and uremia-mediated platelet dysfunction. Therefore, the net clinical benefit balancing stroke risk reduction and increased risk of bleeding should be weighed carefully before initiating oral anti-coagulants for ESRD patients. Several studies investigating whether warfarin should be used for stroke prevention in AF patients with ESRD have been published and showed inconsistent results. Since none of these studies was a prospective and randomized trial, the best strategy for stroke prevention in AF patients with ESRD undergoing dialysis remained unknown and more data are necessary to answer this issue.

Considerations for Systemic Anticoagulation in ESRD

In the setting of end-stage kidney disease, the incidence and risk for thrombotic events are increased and use of anticoagulants is common. The incidence of bleeding, however, is also a frequent issue and creates additional challenges in the management of anticoagulation therapy. Patients with end-stage renal disease are typically excluded from large clinical trials exploring the use of anticoagulants, which limits our knowledge of optimal management approaches. Furthermore, varying degrees of renal failure in addition to conditions that alter the pharmacokinetics of various anticoagulants or pharmacodynamic response may warrant alternative approaches to dosing. This review will explore systemic chronic anticoagulation therapy in the setting of chronic kidney disease where hemodialysis is required. Agents discussed include vitamin K antagonists, low-molecular-weight heparins, fondaparinux, oral factor Xa antagonists, and direct thrombin inhibitors. Clinical challenges, approaches to dosing regimens, and tools for measuring responses and reversal will be explored.

The association between kidney function and major bleeding in older adults with atrial fibrillation starting warfarin treatment: population based observational study

OBJECTIVE

To determine rates of major bleeding by level of kidney function for older adults with atrial fibrillation starting warfarin.

DESIGN

Retrospective cohort study.

SETTING

Community based, using province wide laboratory and administrative data in Alberta, Canada.

PARTICIPANTS

12,403 adults aged 66 years or more, with atrial fibrillation who started warfarin treatment between 1 May 2003 and 31 March 2010 and had a measure of kidney function at baseline. Kidney function was estimated using the Chronic Kidney Disease Epidemiology Collaboration equation and participants were categorised based on estimated glomerular filtration rate (eGFR): ≥ 90, 60-89, 45-59, 30-44, 15-29, <15 mL/min/1.73 m(2). We excluded participants with end stage renal disease (dialysis or renal transplant) at baseline.

MAIN OUTCOME MEASURES

Admission to hospital or visit to an emergency department for major bleeding (intracranial, upper and lower gastrointestinal, or other).

RESULTS

Of 12,403 participants, 45% had an eGFR <60 mL/min/1.73 m(2). Overall, 1443 (11.6%) experienced a major bleeding episode over a median follow-up of 2.1 (interquartile range: 1.0-3.8) years. During the first 30 days of warfarin treatment, unadjusted and adjusted rates of major bleeding were higher at lower eGFR (P for trend <0.001 and 0.001, respectively). Adjusted bleeding rates per 100 person years were 63.4 (95% confidence interval 24.9 to 161.6) in participants with eGFR <15 mL/min/1.73 m(2) compared with 6.1 (1.9 to 19.4) among those with eGFR >90 mL/min/1.73 m(2) (adjusted incidence rate ratio 10.3, 95% confidence interval 2.3 to 45.5). Similar associations were observed at more than 30 days after starting warfarin, although the magnitude of the increase in rates across eGFR categories was attenuated. Across all eGFR categories, adjusted rates of major bleeding were consistently higher during the first 30 days of warfarin treatment compared with the remainder of follow-up. Increases in major bleeding rates were largely due to gastrointestinal bleeding (3.5-fold greater in eGFR <15 mL/min/1.73 m(2) compared with ≥ 90 mL/min/1.73 m(2)). Intracranial bleeding was not increased with worsening kidney function.

CONCLUSIONS

Reduced kidney function was associated with an increased risk of major bleeding among older adults with atrial fibrillation starting warfarin; excess risks from reduced eGFR were most pronounced during the first 30 days of treatment. Our results support the need for careful consideration of the bleeding risk relative to kidney function when assessing the risk-benefit ratio of warfarin treatment in people with chronic kidney disease and atrial fibrillation, particularly in the first 30 days of treatment.

The target-specific oral anticoagulants: practical considerations

More than 4 years have passed since the first approval of a target-specific oral anticoagulant (TSOAC) in the United States, and the number of clinicians who have prescribed (or considered prescribing) one or more of these medications is increasing. Although these agents may, in properly selected patients, offer advantages over more traditional therapies, their lack of familiarity can be intimidating. Clinicians who are prescribing the TSOACs face a number of management questions not definitively answered by the registration trials. This chapter reviews some of these situations, including updated information on the periprocedural management of TSOACs and the latest evidence about how to best measure TSOAC effect. The lack of an antidote and other considerations that may be relevant when deciding between newer and more traditional anticoagulant medications are also discussed.

Balancing ischaemia and bleeding risks with novel oral anticoagulants

Vitamin K antagonists (VKAs) have long been the standard of care for treatment of venous thromboembolism (VTE), and thromboprophylaxis in atrial fibrillation (AF). Despite their efficacy, their use requires frequent monitoring and is complicated by drug-drug interactions and the need to maintain a narrow therapeutic window. Since 2009, novel oral anticoagulants (NOACs), including the direct thrombin inhibitor dabigatran and the direct factor Xa inhibitors apixaban, edoxaban, and rivaroxaban, have become alternative options to VKAs owing to their predictable and safe pharmacological profiles. The overall clinical effect of these drugs, which is a balance between ischaemic benefit and bleeding harm, varies according to the clinical scenario. As adjunctive therapy to dual antiplatelet therapy in patients with acute coronary syndrome, NOACs are associated with incremental bleeding risks and modest benefits. For treatment of VTE, NOACs have a safer profile than VKAs and a similar efficacy. In thromboprophylaxis in AF, NOACs are associated with the greatest benefits by reducing both ischaemic events and haemorrhagic complications and might reduce mortality compared with VKAs. The role of NOACs continues to evolve as these drugs are evaluated in different patient populations, including those with renal impairment or with AF and undergoing percutaneous coronary intervention.

Chronic kidney disease and stroke

Chronic kidney disease (CKD) is associated with an increased risk of both ischemic and hemorrhagic stroke. In addition to shared risk factors, this higher cerebrovascular risk is mediated by several CKD-associated mechanisms including platelet dysfunction, coagulation disorders, endothelial dysfunction, inflammation, and increased risk of atrial fibrillation. CKD can also modify the effect of treatments used in acute stroke and in secondary stroke prevention. We review the epidemiology and pathophysiology that link CKD and stroke and the impact of CKD on stroke outcomes. Interdisciplinary collaboration between nephrologists, pharmacists, hematologists, nutrition therapists, primary care physicians, and neurologists in providing care to these subjects may potentially improve outcomes.

Correlates and outcomes of warfarin initiation in kidney transplant recipients newly diagnosed with atrial fibrillation

In the kidney transplant population with atrial fibrillation (AF), evidence regarding the effectiveness and safety of warfarin treatment is lacking. We used fee-for-service Medicare claims to identify kidney transplant recipients with newly diagnosed AF from the United States Renal Data System. Warfarin use within 30 days of AF diagnosis was ascertained from Medicare Part D prescription claims (2007-11) or using a validated algorithm (1997-2011). The study end points were (i) the composite of death, stroke or gastrointestinal bleed, (ii) death and (iii) death-censored graft failure. Warfarin user and non-user groups were balanced using inverse probability of treatment weighting and hazard ratios were (HRs) estimated using Cox regression. Among 718 subjects with an indication for anticoagulation, 24% initiated warfarin treatment within 30 days of AF diagnosis. Age was the only independent correlate of warfarin use [odds ratio = 1.02 per year; 95% confidence interval (95% CI) 1.01-1.04]. In the larger cohort of 6492 patients with AF, warfarin use [(23.5%) versus non-use (76.5%)] was associated with small and non-significant reductions in the composite of death, stroke or gastrointestinal bleed (HR = 0.92; 95% CI 0.83-1.02), death (HR = 0.92; 95% CI 0.82-1.02) and death-censored graft failure (HR = 0.90; 95% CI 0.76-1.08). Our study suggests the need for clinical trials of warfarin use in the kidney transplant population with AF.

Effect of experimental kidney disease on the functional expression of hepatic reductases

Chronic kidney disease (CKD) affects the nonrenal clearance of drugs by modulating the functional expression of hepatic drug-metabolizing enzymes and transporters. The impact of CKD on oxidative and conjugative metabolism has been extensively studied. However, its effect on hepatic drug reduction, an important phase I drug-metabolism pathway, has not been investigated. We aimed to assess the effect of experimental CKD on hepatic reduction using warfarin as a pharmacological probe substrate. Cytosolic and microsomal cellular fractions were isolated from liver tissue harvested from five-sixths-nephrectomized and control rats (n = 10 per group). The enzyme kinetics for warfarin reduction were evaluated in both fractions, and formation of warfarin alcohols was used as an indicator of hepatic reductase activity. Selective inhibitors were employed to identify reductases involved in warfarin reduction. Gene and protein expression of reductases were determined using quantitative real-time polymerase chain reaction and Western blotting, respectively. Formation of RS/SR-warfarin alcohol was decreased by 39% (P < 0.001) and 43% (P < 0.01) in cytosol and microsomes, respectively, in CKD rats versus controls. However, RR/SS-warfarin alcohol formation was unchanged in the cytosol, and a trend toward its decreased production was observed in microsomes. Gene and protein expression of cytosolic carbonyl reductase 1 and aldo-keto reductase 1C3/18, and microsomal 11β-hydroxysteroid dehydrogenase type 1 were significantly reduced by >30% (P < 0.05) in CKD rats compared with controls. Collectively, these results suggest that the functional expression of hepatic reductases is selectively decreased in kidney disease. Our findings may explain one mechanism for altered nonrenal clearance, exposure, and response of drugs in CKD patients.

Relation of digoxin use in atrial fibrillation and the risk of all-cause mortality in patients ≥65 years of age with versus without heart failure

Previous studies on digoxin use in patients with atrial fibrillation (AF) and the risk of all-cause mortality found conflicting results. We conducted a population-based, retrospective, cohort study of patients aged ≥65 years admitted to a hospital with a primary or secondary diagnosis of AF, in Quebec province, Canada, from 1998 to 2012. The AF cohort was grouped into patients with and without heart failure (HF) and into digoxin and no-digoxin users according to the first prescription filled for digoxin within 30 days after AF hospital discharge. We derived propensity score-matched digoxin and no-digoxin treatment groups for the groups of patients with and without HF, respectively, and conducted multivariable Cox proportional hazards regression analyses to determine association between digoxin use and all-cause mortality. The AF propensity score-matched cohorts of patients with and without HF were well balanced on baseline characteristics. In the propensity score-matched HF group, digoxin use was associated with a 14% greater risk of all-cause mortality (adjusted hazard ratio 1.14, 95% confidence interval 1.10 to 1.17). In the propensity score-matched no-HF group, digoxin use was associated with a 17% greater risk of all-cause mortality (adjusted hazard ratio 1.17, 95% confidence interval 1.14 to 1.19). In conclusion, our retrospective analyses found that digoxin use was associated with a greater risk for all-cause mortality in patients aged ≥65 years with AF regardless of concomitant HF. Large, multicenter, randomized controlled trials or prospective cohort studies are required to clarify this issue.

Evidence for the prevention and treatment of stroke in dialysis patients

The risks of both ischemic and hemorrhagic stroke are particularly high in dialysis patients of any age and outcomes are poor. It is therefore important to identify strategies that safely minimize stroke risk in this population. Observational studies have been unable to clarify the relative importance of traditional stroke risk factors such as blood pressure and cholesterol in those on dialysis, and are affected by biases that usually make them an inappropriate source of data on which to base therapeutic decisions. Well-conducted randomized trials are not susceptible to such biases and can reliably investigate the causal nature of the association between a potential risk factor and the outcome of interest. However, dialysis patients have been under-represented in the cardiovascular trials which have proven net benefit of commonly used preventative treatments (e.g., antihypertensive treatments, low-dose aspirin, carotid revascularization, and thromboprophylaxis for atrial fibrillation), and there remains uncertainty about safety and efficacy of many of these treatments in this high-risk population. Moreover, the efficacy of renal-specific therapies that might reduce cardiovascular risk, such as modulators of mineral and bone disorder, online hemodiafiltration, and daily (nocturnal) hemodialysis, have not been tested in adequately powered trials. Recent trials have also demonstrated how widespread current practices could be causing stroke. Therefore, it is important that reliable information on the prevention and treatment of stroke (and other cardiovascular disease) in dialysis patients is generated by performing large-scale randomized trials of many current and future treatments.

Incidence and prediction of ischemic stroke among atrial fibrillation patients with end-stage renal disease requiring dialysis

BACKGROUND

Renal dysfunction is a significant risk factor for ischemic stroke in atrial fibrillation (AF). However, the incidence of ischemic stroke and how to predict its occurrence among AF patients with end-stage renal disease (ESRD) are unclear.

OBJECTIVE

The purpose of this study was to compare the CHADS2 and CHA2DS2-VASc scores for stroke risk stratification in AF patients with ESRD.

METHODS

A total of 10,999 AF patients with ESRD undergoing renal replacement therapy who were not receiving oral anticoagulants or antiplatelet agents were identified from Taiwan's National Health Insurance Research Database. The study end-point was occurrence of ischemic stroke.

RESULTS

The median (interquartile) CHADS2 and CHA2DS2-VASc scores for the study cohort were 3 (2-5) and 5 (4-7), respectively. During follow-up, 1217 patients (11.7%) experienced ischemic stroke, with an incidence rate of 6.9 per 100 person-years. In Cox regression models, the CHADS2 and CHA2DS2-VASc scores both were significant predictors of ischemic stroke. C-indexes for CHADS2 and CHA2DS2-VASc were 0.608 and 0.682, respectively (P < .001). CHA2DS2-VASc improved the net reclassification index by 4.8% compared with CHADS2 (P < .0001). Among 1409 patients with a CHADS2 score of 0 or 1, the CHA2DS2-VASc score ranged from 1 to 4, with event rates ranging from 2.1 to 4.7 per 100 person-years.

CONCLUSION

The CHA2DS2-VASc score was useful in predicting ischemic stroke in AF patients with ESRD undergoing dialysis and was superior to the CHADS2 score. The net clinical benefit balancing stroke reduction against major bleeding with anticoagulation in these high-risk patients remains to be defined.