EBM EBM ------Journal ReadingJournal Reading

: : 2005/10/26

Clinical scenario• 65 y/o male• Brief history

– Controlled HTN– 6 months atrial fibrillation, resistant to

cardioversion– No evidence for valvular or coronary heart

disease

• long-term anticoagulants: – Benefit (reduce embolic stroke) v.s risk

(hemorrhage)

The PICO

• P: non valvular atrial fibrillation• I: warfarin• C: warfarin and control treatment• O: risk of embolism and complications of

anticoagulation

The Search• GRATEFUL MED• MeSH:

– Atrial fibrillation, warfarin, Stroke(explode cerebrovascular disorders

• Limit– English language, randomized controlled trial

• 9 articles– 3: editorials, commentaries– 1: prognosis– 1: quality of life�The most recent of the 4�Warfarin in the prevention of stroke associated with

nonrheumatic atrial fibrillation, NEJM. 1992

What were the results ?• How large was the treatment effect?

– Absolute risk reduction– Relative risk – Relative risk reduction(RRR)

• How precise was the estimate of treatment effect?– Point estimate– 95% confidence interval: true 95% of the time

When is the sample size big enough?

• The larger the sample size, the greater of our confidence

• Positive study� lower boundary of the CI, still clinically significant?

• Negative study� upper boundary of the CI, be important

• Other criteria for CI

What can the clinician do if the CI around the RRR is not reported in the article

• P-value– 0.05: lower bound of 95% CI for RRR= 0

• Cannot exclude� treatment had no effect

– <0.05: lower bound of 95% CI >0

• +/- standard error*2• Calculate CI yourself or someone else

Will the results help me in caring for my patients ?

• Can the results be applied to my patient care?– Inclusion/exclusion criteria– Whether there is some compelling reason why the

results should “not” be applied to the p’t– Believable subgroup data: if difference is

• Large• Very unlikely to occur by chance• Results from analysis specified as a hypothesis before the

study began• One of only a very few subgroup analyses that were carried

out• Replicated in other studies

• Were all clinically important outcomes considered?– Treatment improve outcomes that are

“important” to patients– Substituted end point v.s important outcome

• Antiarrhythmic agent: abnormal ventricular depolarization� v.s life-threatening arrhythmia�

– No deleterious effects on other outcomes• Surgical trial� immediate and early mortality

• Are the likely treatment benefits worth the potential harm and costs?– Number needed to treat (NNT)

�before deciding on treatment, we must consider our patient’s risk of the adverse event if left untreated

Resolution of the scenario

(0.26-0.45)

Conclusion

• Define the problem clearly

• Search: best available evidence

• Assess the quality of evidence

• Result • Important Outcome• Benefit/risk/cost

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