ALI R. RAHIMI, BOBBY WRIGHTS, MD, HOSSEIN AKHONDI, MD & CHRISTIAN M. RICHARD, MSC

Clinical Correlation Between Effective Anticoagulants & Risk of Stroke: Are We Using Evidence-Based Strategies

Trina LaPharmD. CandidateOct 20th, 2011

Southern Medical Journal 2004;97: 924-931

Introduction

Atrial fibrillation (AF) can predispose patients to blood clots that can cause stroke

If untreated, one in three people with nonvalvular AF will suffer a stroke

The importance & efficacy of anticoagulation therapy in preventing a stroke is a common knowledge & has become the standard of care

Introduction

Warfarin was reported to be substantially more efficacious than aspirin

Anticoagulant prophylaxis is effective as INR of 2 to 3, and is associated with a lower risk of bleeding

However, despite extensive evidence & recommendations for its use, anticoagulant prophylaxis is underused in the management of AF

Study’s Objective

Primary endpoint: To define correlation between effective anticoagulant prophylaxis and risk of thromboembolic stroke

Secondary endpoint: To observe & investigate the role of other factors, such as practice patterns in different settings

Study Design

Patients with a diagnosis of AF requiring anticoagulation therapy & who were admitted between years 1997 & 2000 to community-based teaching hospital in Southeast Georgia were identified through a retrospective chart review

The sample consisted of 297 patients 91 patients who suffered a stroke at any point during

the study period 206 patients who did not suffer a stroke by the end of

year 2000

Study design

Patients demographics, clinical diagnoses, findings & treating physicians were extracted from admission records

History of AF, duration of the disease, treatment modalities, indicators for anticoagulation therapy, & risk factors for comorbid diseases were obtained from hospital charts

Study design

Two study groups Warfarin: 124 patients No Warfarin: 166 patients No record of anticoagulation therapy: 7 patients

INR Between 2.0 & 3.0 as therapeutic

Prescribing physician specialties Neurologists Cardiologists General internists Others

InclusionInclusion ExclusionExclusion

A diagnosis of AF requiring anticoagulation therapy

Hypercoagulable state

Hemorrhagic strokeCarotid stenosisPeripheral vascular

diseaseDilated

cardiomyopathy

Inclusion & Exclusion

Variables collectedVariables collected Data AnalysisData Analysis

AgeINRGenderRaceCo-morbiditiesManaging Physician

Specialty

Normal probability plots & the Shapiro-Wilks test to assess the normality assumption

Chi-square test of independence to compare patients prescribed/not prescribed warfarin for each indicator variables

The risk of stroke associated with anticoagulation tx was assessed using 2x2 contingency table & stratified Mantel-Haenszel analysis

Nature of the variables collected

ResultsVariables Warfarin

(n=124)Non-Warfarin(n=166)

Statistical test P value

Age 72.95 ± 10.60 74.23 ± 11.92 0.232

Gender Male Female

46.8%53.2%

44.8%55.2%

0.754

INR 2.51 ± 2.03 1.19 ± 0.45 <0.001

Comorbidities CVA CHF CAD HTN Diabetes

24.2%29.8%22.6%54.8%25.0%

13.3%27.1%18.1%58.4%25.9%

0.0170.6100.3420.5410.861

Managing physicianSpecialty Cardiology Neurology Internal Med Other

30.6%13.7%33.1%22.6%

16.9%10.8%39.2%33.1%

0.02

Stroke 19.4% 37.3% <0.001

Results

Higher warfarin dosages Larger values in INR (r=+0.395) Fewer strokes (r=-0.372) Prescribed by cardiologists (0.289)

Greater occurrences of strokes are present in those patients under the care of neurologist (r=+0.394)

Average dosage of warfarin prescribed Cardiologists: 2.94 mg Neurologists: 1.76 mg

Odds of Warfarin Prescription

Patients who were more likely to be prescribed warfarin when History of AF & stroke (P=0.013) Care management by a cardiologists (P=0.035)

Elderly patients were more likely to have additional comorbidities that influenced the prescription of warfarin

Neurologists (P=0.308) & internists(P=0.77) have similar patterns of prescribing warfarin when compared with cardiologists

Odds of Stroke

Patients who are not prescribed warfarin have significantly higher risk of suffering a stroke

Patients with diagnosis of CHF in addition to AF were 6.8 times less likely to suffer a stroke when compared with AF patients without CHF

NNT: 50

Author’s comment

Treatment of AF & anticoagulant prophylaxis are complex & time consuming clinical undertakings that requires long-term commitments

This study’s result with regard to the risk of stroke in patients with AF are consistent & in line with previously published studies

The elderly patients and the presence of co-morbid diseases play a significant role in the decision making process

Limitations & Conclusion

Limitations Many patients’ records revealed the presence of

internist in addition to other specialists There were some overlaps between the primary

providers in ordering warfarin dosagesConclusions

Despite extensive evidence supporting anticoagulation therapy, both physicians & patients are less inclined to more aggressive stroke prevention measures

Cost, fear of bleeding complications, drug interactions, & time are the factors influencing decision making

educational opportunities & an aggressive public awareness might be needed

Comments

I think this is a very important study because it showed the correlation between effective anticoagulant on stroke prevention, and it raised the awareness of not fully use evidence-based strategies per physicians

However, the study did not document some essential information History of compliance with warfarin When patients started taking warfarin How the physician adjust warfarin dosing Record of all medications, including AF medications due to

potential drug interaction History of adverse drug events and complications

Level of evidence