Anticoagulation for atrial fibrillation in patients on dialysis: are the benefits worth the risks?

Thromboembolic Events in the Hemodialysis Setting: Understanding Risk Profiles and Cumulative Incidences to Inform Clinical Trial Design

BACKGROUND

People with kidney failure have a high risk of cardiovascular morbidity/death, including thromboembolic events. Factor XIa inhibitors are a new class of anticoagulants in development that may offer antithrombotic benefits with a lower risk of incremental bleeding events than traditional therapies. We investigated major adverse vascular events (MAVEs), a relevant composite outcome for testing novel antithrombotic agents, in a large cohort of patients on hemodialysis, to better understand the key requirements to adequately design a phase 3 trial.

METHODS AND RESULTS

We included 25 211 patients on hemodialysis for >90 days in phases 4 to 7 (2009-2021) of the DOPPS (Dialysis Outcomes and Practice Patterns Study). Atherosclerotic cardiovascular disease (ASCVD) was defined as history/presence of coronary, peripheral, or cerebrovascular disease. We estimated MAVE rates and cumulative incidence, overall and by ASCVD. Over half (52%) of the cohort met the ASCVD criteria. The MAVE hospitalization/death composite rate (per 100 patient-years) was 6.0 in the overall cohort and 8.7 in the ASCVD subset. Three-year cumulative incidence of MAVE was 13% in the overall cohort and 18% in the ASCVD subset. The estimated sample size to be randomized in a hypothetical trial in the ASCVD population was ≈7000 patients.

CONCLUSIONS

Even in the enriched ASCVD group, the observed MAVE incidence combined with a high competing risk, regulatory requirements (α=0.01), and limited recruitment pool makes feasibility of a potential randomized trial targeting MAVE reduction challenging. These results highlight key considerations and challenges for developers of novel therapies targeting systemic thromboembolic events in patients on hemodialysis.

Deciphering the Dilemma: Anticoagulation for Heart Failure With Preserved Ejection Fraction (HFpEF)

Impairment in ventricular relaxation and preserved left ventricular ejection fraction are the two main features of heart failure with preserved ejection fraction (HFpEF) a difficult clinical condition. Therapeutic choices for HFpEF patients are still scarce despite its rising frequency and negative effects on morbidity and mortality, necessitating creative methods to enhance results. The increased thromboembolic risk seen in these individuals raises questions about the relevance of anticoagulation in the therapy of HFpEF. Although anticoagulation has been shown to be beneficial in heart failure with decreased ejection fraction (HFrEF) and other high-risk cardiovascular disorders, its efficacy and safety in HFpEF present a challenging therapeutic challenge. Anticoagulants have been the subject of clinical trials in HFpEF, but the results have been conflicting, giving clinicians only a little information with which to make decisions. The decision-making process is made more difficult by worries about potential bleeding hazards, particularly in susceptible elderly HFpEF patients with other comorbidities. The link between heart failure and anticoagulant medication in HFpEF is thoroughly analyzed in this narrative review. In HFpEF, cardiac fibrosis and endothelial dysfunction create a prothrombotic milieu, as is highlighted in this passage. Also covered are recent developments in innovative biomarker research and cutting-edge imaging techniques, which may provide ways to spot HFpEF patients who might benefit from anticoagulation. This therapeutic conundrum may be resolved by using precision medicine strategies based on risk classification and individualized therapy choices. This review emphasizes the need for more research to establish the best use of anticoagulation in HFpEF within the framework of personalized therapy and shared decision-making. To successfully manage thromboembolic risk and reduce bleeding consequences in HFpEF patients, it is essential to perform well-designed clinical studies and advance our understanding of the pathophysiology of HFpEF. These developments may ultimately improve the prognosis and quality of life for people who suffer from this difficult and mysterious ailment.

Anticoagulation use and the risk of stroke and major bleeding in patients on hemodialysis: From the VIVALDI, a population-based prospective cohort study

BACKGROUND

Evidence supporting the use of anticoagulation for the prevention of stroke and thromboembolism in patients with kidney failure on hemodialysis (HD) and atrial fibrillation (AF) is limited. We prospectively assessed the incidences of stroke and major bleeding, as well as anticoagulation strategies in patients on HD with AF.

METHODS

We recruited 625 prevalent HD patients into a population-based observational cohort study. The primary prospective outcomes were thromboembolic events (stroke, transient ischemic attack, systemic embolism) and major bleeding. Secondary outcomes included a composite of thromboembolic events, major bleeding, and cardiovascular death to determine net clinical harm.

RESULTS

A total of 238 patients (38.1%) had AF, 165 (26.4%) already at baseline and 73 (15.9%) developed AF during a median follow up of 870 days. Forty (6.4%) thromboembolic events and 89 (14.2%) major bleedings occurred. Overall, 256 patients died (41.0%). In AF patients, use of vitamin K antagonists (VKAs) in 61 patients (25.6%) was not significantly associated with reduced risk of the primary thromboembolic outcome (subdistribution hazard ratio [SHR] 1.41 adjusted for age, sex, congestive heart failure, hypertension, stroke/transient ischemic attack/thromboembolism, vascular disease, and diabetes history score and antiplatelet co-medication (95% CI, 0.49-4.07), but with increased risk of major bleeding (SHR: 2.28; 95% CI, 1.09-4.79) compared with AF patients without anticoagulation (N = 139, 58.4%). Use of VKAs was associated with net clinical harm (adjusted SHR: 2.07; 95% CI, 1.25-3.42).

CONCLUSIONS

Although the nonrandomized nature of the study is prone to bias, anticoagulation with VKAs was not associated with decreased thromboembolic risk, but rather with increased risk of major bleeding and may be net harmful to patients with AF on HD.

Warfarin use and the risk of stroke, bleeding, and mortality in older adults on dialysis with incident atrial fibrillation

AIM

There is conflicting evidence regarding the safety and effectiveness of warfarin for atrial fibrillation (AF) treatment among older end-stage renal disease (ESRD) patients, and differences among subgroups are unclear.

METHODS

Older dialysis patients who were newly diagnosed with AF (7/2007-12/2011) were identified in the United States Renal Data System. The adjusted hazard ratios (HR) of the outcomes (any stroke, ischaemic stroke, major bleeding, severe gastrointestinal bleeding, and death) by time-varying warfarin use were estimated using Cox regression accounting for the inverse probability of treatment weight.

RESULTS

Among 5765 older dialysis patients with incident AF, warfarin was associated with significantly increased risk of major bleeding (HR = 1.50, 95% CI 1.33-1.68), but was not statistically associated with any stroke (HR = 0.92, 95% CI 0.75-1.12), ischaemic stroke (HR = 0.88, 95%CI 0.70-1.11) or gastrointestinal bleeding (HR = 1.03, 95% CI 0.80-1.32). Warfarin use was associated with a reduced risk of mortality (HR = 0.72, 95%CI 0.65-0.80). The association between warfarin and major bleeding differed by sex (male: HR = 1.29; 95%CI 1.08-1.55; female: HR = 1.67; 95%CI 1.44-1.93; P-value for interaction = 0.03).

CONCLUSION

Older ESRD patients with AF who were treated with warfarin had a no difference in stroke risk, lower mortality risk, but increased major bleeding risk. The bleeding risk associated with warfarin was greater among women than men. The risk/benefit ratio of warfarin may be less favourable among older women.

Clotting-Factor Concentrations 5 Days After Discontinuation of Warfarin

BACKGROUND

The American Society of Regional Anesthesia and Pain Medicine guidelines recommend discontinuation of warfarin and an international normalized ratio (INR) of 1.2 or less before a neuraxial injection. The European and Scandinavian guidelines accept an INR of 1.4 or less. We evaluated INR and levels of clotting factors (CFs) II, VII, IX, and X 5 days after discontinuation of warfarin.

METHODS

Patients who discontinued warfarin for 5 days and had an INR of 1.4 or less had activities of factors II, VII, IX, and X measured. The primary outcome was the frequency of subjects with CF activities of less than 40%.

RESULTS

Twenty-three patients were studied; 21 (91%) had an INR of 1.2 or less. In these 21 patients, the median (interquartile range) activities of factors II, VII, IX, and X were 66% (52%-80%), 114% (95%-132%), 101% (84%-121%), and 55% (46%-63%), respectively. Ninety-five percent (99% confidence interval, 69%-99%) had CF activities of greater than 40%. The patient who did not CF activities greater than 40% had end-stage renal disease. Two subjects had an INR of greater than 1.2; the activities of factor II, VII, IX, and X were 37% and 46%, 89% and 105%, 66% and 78%, and 20% and 36%, respectively. Neither patient had CF activities of greater than 40%.

CONCLUSIONS

Based on 40% activity of CFs, patients with INRs of 1.2 or less can be considered to have adequate CFs to undergo neuraxial injections. The number of patients with an INR of 1.3 and 1.4 is too small to make conclusions.

Long-term prognostic impact of anticoagulation on patients with atrial fibrillation undergoing hemodialysis

INTRODUCTION AND OBJECTIVES

Evidence for the efficacy and safety of oral anticoagulation with dicumarines in patients with atrial fibrillation (AF) on hemodialysis is controversial. The aim of our study is to evaluate the long-term prognostic implications of anticoagulation with dicumarines in a cohort of patients with non-valvular AF on a hemodialysis program due to end-stage renal disease.

METHODS

Retrospective, observational study with consecutive inclusion of 74 patients with AF on hemodialysis. The inclusion period was from January 2005 to October 2016. The primary variables were all-cause mortality, non-scheduled readmissions and bleeding during follow-up.

RESULTS

Mean age was 75±10 years; 66.2% were men and 43 patients (58.1%) received acenocoumarol. During a median follow-up of 2.40 years (IQR=0.88-4.15), acenocoumarol showed no survival benefit [HR=0.76, 95% CI (0.35-1.66), p=0.494]. However, anticoagulated patients were at increased risk of recurrent cardiovascular hospitalizations [IRR=3.94, 95% CI (1.06-14.69), p=0.041]. There was a trend towards an increase in repeated hospitalizations of ischemic cause in anticoagulated patients [IRR=5.80, 95% CI (0.86-39.0), p=0.071]. There was a statistical trend towards a higher risk of recurrent total bleeding in patients treated with acenocoumarol [IRR=4.43, 95% CI (0.94-20.81), p=0.059].

CONCLUSIONS

In this study, oral anticoagulation with acenocoumarol in patients with AF on hemodialysis did not increase survival. However, it was associated with an increased risk of hospitalizations of cardiovascular causes and a tendency to an increased risk of total bleeding.

2017 Scientific Sessions Sol Sherry Distinguished Lecture in Thrombosis: Factor XI as a Target for New Anticoagulants

The goal of anticoagulant therapy is to attenuate thrombosis without compromising hemostasis. Although the direct oral anticoagulants are associated with less intracranial hemorrhage than vitamin K antagonists, bleeding remains their major side effect. Factor XI has emerged as a promising target for anticoagulants that may be safer than those currently available. The focus on factor XI stems from epidemiological evidence of its role in thrombosis, the observation of attenuated thrombosis in factor XI-deficient mice, identification of novel activators, and the fact that factor XI deficiency is associated with only a mild bleeding diathesis. Proof-of-concept comes from the demonstration that compared with enoxaparin, factor XI knockdown reduces venous thromboembolism without increasing bleeding after elective knee arthroplasty. This article rationalizes the selection of factor XI as a target for new anticoagulants, reviews the agents under development, and outlines a potential path forward for their development.

Treatment of atrial fibrillation with warfarin among older adults with end stage renal disease

BACKGROUND

There is increasing evidence questioning the use of warfarin for atrial fibrillation (AF) among older adults with end stage renal disease (ESRD). We assessed the patterns and determinants of warfarin utilization among these patients in the US.

METHODS

We assembled a cohort of older adults (age ≥65) undergoing dialysis with incident AF from July 2007 to November 2011 from the US Renal Data System (USRDS). We used descriptive statistics to characterize warfarin utilization within 30 days of AF discharge, and logistic regression to quantify patient characteristics associated with warfarin initiation.

RESULTS

Among 5730 older adults undergoing dialysis with incident AF, 15.5% initiated warfarin. Among 2906 patients with high risk of bleeding, 12.7% initiated warfarin; whereas 14.9% initiated warfarin among 4824 patients with high risk of stroke. After adjustment for patient characteristics, warfarin initiation was lower among patients who were older [odds ratio (OR) = 0.74 per 10-year increase, 95% confidence interval (CI) 0.66-0.83] and those with a history of diabetes (OR = 0.75, 95% CI 0.63-0.90), myocardial infarction (OR = 0.64, 95% CI 0.50-0.80), or bleeding (OR = 0.63, 95% CI 0.50-0.80). There was no association between sex, race, or dialysis modality and warfarin initiation. Among patients who initiated warfarin, 46.8% discontinued warfarin use after a median treatment length of 8.6 months.

CONCLUSION

Despite the unclear benefit and increased bleeding risk of warfarin treatment in patients with ESRD, 1 in 8 older adults undergoing dialysis with incident AF in the US who had high risk of bleeding used warfarin. Changes to warfarin therapy due to discontinuation were common after initiation.

Safety Outcomes of Apixaban Compared With Warfarin in Patients With End-Stage Renal Disease

Background: Current guidelines make no specific recommendations on the selection of direct oral anticoagulants for the prevention and treatment of venous thromboembolism in patients with end-stage renal disease (ESRD) receiving hemodialysis. Based on these guidelines, warfarin remains the anticoagulant of choice in these patients. Objective: To compare bleeding rates in patients receiving apixaban or warfarin with ESRD undergoing chronic hemodialysis. Methods: This was a single-center, retrospective, institutional review board–approved cohort analysis. Patients with ESRD undergoing chronic hemodialysis and receiving anticoagulation therapy with either apixaban or warfarin were included in this study. All data were collected from paper charts and electronic medical records and included documentation of bleeding events and related interventions. The primary outcome of this study was clinically relevant major bleeding events. Secondary outcomes included clinically relevant nonmajor bleeding events and minor bleeding events. Results: A total of 160 patients were included in this study (warfarin group, n = 120; apixaban group, n = 40). There were 7 major bleeding events in the warfarin group compared with zero in the apixaban group ( P = 0.34). There were similar rates of clinically relevant nonmajor bleeding events (12.5% vs 5.8%, P = 0.17) and minor bleeding (2.5% vs 2.5%, P = 0.74) events in patients receiving apixaban and warfarin. Conclusions: There were no observed differences in bleeding rates in patients receiving apixaban compared with those receiving warfarin. Apixaban may be a cautious consideration in hemodialysis patients until there is further insight into the effect of subsequent, multiple doses on drug accumulation and clinical outcomes.

Cost-Effectiveness of Cardiac Radiosurgery for Atrial Fibrillation: Implications for Reducing Health Care Morbidity, Utilization, and Costs

In the United States (U.S.), atrial fibrillation (AF) is the second-most common cardiovascular condition after hypertension, affecting four million Americans each year. Individuals with AF are three times more likely to be hospitalized over the span of a year when compared to medically matched control groups. The considerably large clinical population of individuals with AF mandates that the cost-effectiveness and efficacy of current treatment regimens for AF have egregious implications for health care spending and public health. Unfortunately, catheter ablation for AF treatment has been shown to make only modest gains in quality-adjusted life years, has yet to demonstrate cost-utility advantages over conventional therapies for AF, and has a reported rate of recurrence for AF that is notably high. Thus, there is a major unmet clinical need for a therapeutic option to treat AF that produces more consistent and efficacious results that are cost-effective. Cardiac radiosurgery as a therapy for AF has the potential to be remarkably cost-effective and produce robust patient outcomes. CyberHeart Inc. has developed the world's first-ever cardiac radiosurgery (CRS) system designed to ablate the heart non-invasively. Procedures that ablate the heart utilizing the Cyberheart CRS system are anticipated to allow higher efficacy and more consistent results than current techniques such as catheter ablation. The aim of this study is to present the current healthcare utilization and expenditures in AF treatment, report the cost-effectiveness of catheter ablation for AF, and project the potential cost-effectiveness of cardiac radiosurgery for the treatment of AF.

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.

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.

Understanding and Managing Atrial Fibrillation in Patients with Kidney Disease

Chronic kidney disease (CKD) is on the rise due to the increased rate of related comorbidities such as diabetes and hypertension. Patients with CKD are at higher risk of cardiovascular events and atrial fibrillation is more common in this patient population. It is estimated that the prevalence of chronic atrial fibrillation in patients with CKD is two to three times higher than general population. Furthermore, patients with CKD are less likely to stay in sinus rhythm. Atrial fibrillation presents a major burden in this population due to difficult treatment decisions in the setting of a lack of evidence from randomized clinical trials. Patients with CKD have higher risk of stroke with more than half having a CHADS2 score ≥ 2. Anticoagulation have been shown to significantly decrease embolic stroke risk, however bleeding complications such as hemorrhagic stroke is twofold higher with warfarin. Although newer novel anticoagulation drugs have shown promise with lower intracranial hemorrhage risk in comparison to warfarin, lack clinical trial data in CKD and the unavailability of an antidote remains an issue. In this review, we discuss the treatment options available including anticoagulation and the evidence behind them in patients with chronic kidney disease suffering from atrial fibrillation.

Anticoagulation in Chronic Hemodialysis: Progress Toward an Optimal Approach

Appropriate anticoagulation for hemodialysis (HD) requires a subtle balance between under- and over-heparinization to prevent extracorporeal circuit (ECC) clotting and bleeding, respectively. We discuss five key issues relating to anticoagulation therapy for chronic HD in adults following a review of relevant literature published since 2002: (i) options for standardization of anticoagulation in HD settings. The major nephrology societies have issued low evidence level recommendations on this subject. Interventional studies have generally investigated novel low-molecular weight heparins and provided data on safety of dosing regimens that cannot readily be extrapolated to clinical practice; (ii) identification of clinical and biological parameters to aid individualization of anticoagulation treatment. We find that use of clinical and biological monitoring of anticoagulation during HD sessions is currently not clearly defined in routine clinical practice; (iii) role of ECC elements (dialysis membrane and blood lines), dialysis modalities, and blood flow in clotting development; (iv) options to reduce or suppress systemic heparinization during HD sessions. Alternative strategies have been investigated, especially when the routine mode of anticoagulation was not suitable in patients at high risk of bleeding or was contraindicated; (v) optimization of anticoagulation therapy for the individual patient. We conclude by proposing a standardized approach to deliver anticoagulation treatment for HD based on an individualized prescription prepared according to the patient's profile and needs.

Influence of kidney function on risk of supratherapeutic international normalized ratio-related hemorrhage in warfarin users: a prospective cohort study

BACKGROUND

Anticoagulation management is difficult in chronic kidney disease, with frequent supratherapeutic international normalized ratios (INRs ≥ 4) increasing hemorrhagic risk. We evaluated whether the interaction of INR and lower estimated glomerular filtration rate (eGFR) increases hemorrhage risk and whether patients with lower eGFRs experience slower anticoagulation reversal.

STUDY DESIGN

Prospective cohort study.

SETTING & PARTICIPANTS

Warfarin pharmacogenetics cohort (1,273 long-term warfarin users); warfarin reversal cohort (74 warfarin users admitted with INRs ≥ 4).

PREDICTOR

eGFR, INR as time-dependent covariate, and their interaction in the pharmacogenetics cohort; eGFR in the reversal cohort.

OUTCOMES & MEASUREMENTS

In the pharmacogenetics cohort, hemorrhagic (serious, life-threatening, and fatal bleeding) risk was assessed using proportional hazards regression. In the reversal cohort, anticoagulation reversal was assessed from changes in INR, warfarin and metabolite concentrations, clotting factors (II, VII, IX, and X), and PIVKA-II (protein induced by vitamin K absence or antagonist II) levels at presentation and after reversal, using linear regression and path analysis.

RESULTS

In the pharmacogenetics cohort, 454 (35.7%) had eGFRs < 60 mL/min/1.73 m(2). There were 137 hemorrhages in 119 patients over 1,802 person-years of follow-up (incidence rate, 7.6 [95% CI, 6.4-8.9]/100 person-years). Patients with lower eGFRs had a higher frequency of INR ≥ 4 (P<0.001). Risk of hemorrhage was affected significantly by eGFR-INR interaction. At INR<4, there was no difference in hemorrhage risk by eGFR (all P ≥ 0.4). At INR≥4, patients with eGFRs of 30 to 44 and < 30 mL/min/1.73 m(2) had 2.2-fold (95% CI, 0.8-6.1; P=0.1) and 5.8-fold (95% CI, 2.9-11.4; P<0.001) higher hemorrhage risks, respectively, versus those with eGFRs ≥ 60 mL/min/1.73 m(2). In the reversal cohort, 35 (47%) had eGFRs < 45 mL/min/1.73 m(2). Patients with eGFRs < 45 mL/min/1.73 m(2) experienced slower anticoagulation reversal as assessed by INR (P=0.04) and PIVKA-II level (P=0.008) than those with eGFRs ≥ 45 mL/min/1.73 m(2).

LIMITATIONS

Limited sample size in the reversal cohort, unavailability of antibiotic use and urine albumin data.

CONCLUSIONS

Patients with lower eGFRs have differentially higher hemorrhage risk at INR ≥ 4. Moreover, because the INR reversal rate is slower, hemorrhage risk is prolonged.

Effect of impaired renal function on the maintenance dose of warfarin in Japanese patients

BACKGROUND

Chronic kidney disease (CKD) alters dose-effect relationship not only of drugs eliminated by the kidney but also of some drugs metabolized by the liver and not renally excreted. It is not known whether impaired renal function alters dose-effect relationship of warfarin in Asian patients. It is also unknown whether the maintenance dose of warfarin can be predicted more accurately by incorporating renal function in Asians.

METHODS

This was a cross-sectional study of patients receiving constant doses of warfarin who had PT-INR within 1.5-3.0 for 3 months or longer.

RESULTS

In a total of 137 participants, the estimated creatinine clearance (eCrCl) was 62.5±25.5 [ml/min] and the warfarin dose was 3.21±1.46 [mg/day] (both mean±standard deviation). There was a significant correlation between warfarin dose and eCrCl (p<0.0001, r(2)=0.23). In a stepwise linear regression with the maintenance dose of warfarin as the dependent variable, eCrCl as well as age, body weight, intra-individual average prothrombin time/international normalized ratio (PT-INR), and genotype of VKORC1 -1639 G>A polymorphism were chosen as independent variables. The coefficient of determination (r(2)) of this formula was 0.47. A regression equation with all the same explanatory variables except for eCrCl had an r(2) of 0.41.

CONCLUSIONS

The maintenance warfarin dose was positively correlated with kidney function as represented by eCrCl in Japanese patients. Incorporating eCrCl improved accuracy of predicting warfarin maintenance dose in this population.

Quantifying a rare disease in administrative data: the example of calciphylaxis

BACKGROUND

Calciphylaxis, a rare disease seen in chronic dialysis patients, is associated with significant morbidity and mortality. As is the case with other rare diseases, the precise epidemiology of calciphylaxis remains unknown. Absence of a unique International Classification of Diseases (ICD) code impedes its identification in large administrative databases such as the United States Renal Data System (USRDS) and hinders patient-oriented research. This study was designed to develop an algorithm to accurately identify cases of calciphylaxis and to examine its incidence and mortality.

DESIGN, PARTICIPANTS, AND MAIN MEASURES

Along with many other diagnoses, calciphylaxis is included in ICD-9 code 275.49, Other Disorders of Calcium Metabolism. Since calciphylaxis is the only disorder listed under this code that requires a skin biopsy for diagnosis, we theorized that simultaneous application of code 275.49 and skin biopsy procedure codes would accurately identify calciphylaxis cases. This novel algorithm was developed using the Partners Research Patient Data Registry (RPDR) (n = 11,451 chronic hemodialysis patients over study period January 2002 to December 2011) using natural language processing and review of medical and pathology records (the gold-standard strategy). We then applied this algorithm to the USRDS to investigate calciphylaxis incidence and mortality.

KEY RESULTS

Comparison of our novel research strategy against the gold standard yielded: sensitivity 89.2%, specificity 99.9%, positive likelihood ratio 3,382.3, negative likelihood ratio 0.11, and area under the curve 0.96. Application of the algorithm to the USRDS identified 649 incident calciphylaxis cases over the study period. Although calciphylaxis is rare, its incidence has been increasing, with a major inflection point during 2006-2007, which corresponded with specific addition of calciphylaxis under code 275.49 in October 2006. Calciphylaxis incidence continued to rise even after limiting the study period to 2007 onwards (from 3.7 to 5.7 per 10,000 chronic hemodialysis patients; r = 0.91, p = 0.02). Mortality rates among calciphylaxis patients were noted to be 2.5-3 times higher than average mortality rates for chronic hemodialysis patients.

CONCLUSIONS

By developing and successfully applying a novel algorithm, we observed a significant increase in calciphylaxis incidence. Because calciphylaxis is associated with extremely high mortality, our study provides valuable information for future patient-oriented calciphylaxis research, and also serves as a template for investigating other rare diseases.

Outcomes after kidney transplantation of patients previously diagnosed with atrial fibrillation

Little is known about the prevalence and outcomes of patients with atrial fibrillation/flutter (AF) who receive a kidney transplant. We identified all patients who had >1 year of uninterrupted Medicare A+B coverage before receiving their first kidney transplant (1997-2009). The presence of pretransplant AF was ascertained from diagnosis codes in Medicare physician claims. We studied the posttransplant outcomes of death, all-cause graft failure, death-censored graft failure and stroke using multivariable Cox regression. Of 62 706 eligible first kidney transplant recipients studied, 3794 (6.4%) were diagnosed with AF prior to kidney transplant. Over a mean follow up of 4.9 years, 40.6% of AF patients and 24.9% without AF died. All-cause and death-censored graft failure were 46.8% and 16.5%, respectively, in the AF group and 36.4% and 19.5%, respectively, in those without AF. Ischemic stroke occurred in 2.8% of patients with and 1.6% of patients without AF. In patients with AF, multivariable-adjusted hazard ratios (95% confidence intervals) for death, graft failure, death-censored graft failure and ischemic stroke were 1.46 (1.38-1.54), 1.41 (1.34-1.48), 1.26 (1.15-1.37) and 1.36 (1.10-1.68), respectively. Pre-existing AF is associated with poor posttransplant outcomes. Special attention should be paid to AF in pretransplant evaluation, counseling and risk stratification of kidney transplant candidates.