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Evidence Based Medicine

Evidence Based Medicine. And Atrial Fibrillation. Age and Prevalence of AF Atria Study. Go et al; JAMA; 2001. 1.9 million pts in HMO 17,974 pts with AF 45% > 75 years. Age and Projected Prevalence of AF Atria Study. Go et al; JAMA; 2001.

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Evidence Based Medicine

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  1. Evidence Based Medicine And Atrial Fibrillation

  2. Age and Prevalence of AF Atria Study Go et al; JAMA; 2001 1.9 million pts in HMO 17,974 pts with AF 45% > 75 years

  3. Age and Projected Prevalence of AF Atria Study Go et al; JAMA; 2001

  4. Atrial Fibrillation In The ElderlyAre Older Patients Different?

  5. Evidence based medicine • 80 year old male • Hypertension for 5 years; Atrial fib ? duration • Treated with diuretic and ACE: BP 150/87 mmHg • Electrocardiograph – within normal limits • Echocardiogram – EF 50% early diastolic relaxation abnormality • Creatinine 99 umol / l

  6. Atrial Fibrillation In The ElderlyThromboembolism • 5 year stroke risk is 15% • Aspirin risk by 20%; ARR 0.6; NNT 166 • Warfarin risk  x 70%; ARR 2.1: NNT 47.6 • Aspirin major risk 1% pa; warfarin 3% pa • P warfarin benefit 100 – (85) + 4.5 = 10.5% • P Aspirin benefit 100 – (85) + 12 = 3%

  7. Computer Decision support

  8. Current treatment N (%) Recommended Warfarin Antiplatelet Nil Both Placebo 5 (38.5) 8 (61.5) 0 0 Warfarin 11 (52.4) 7 (33.3) 3 (14.3) 0 Aspirin 46 (48.4) 41 (43.2) 7 (7.4) 1 (1.0) Comparison of Decision Model for patients > 75 only with clinical practice Proportion where current treatment = recommended treatment is 41.1% (53/129) 10% (13/129) on some medication when none recommended

  9. Evidence based medicine • Decision support can provide evidence based information to assist in clinical decision making • Clinicians believe that their decisions on OAC for atrial fibrillation are evidence based ? • However a computer decision support program did not agree that the majority of therapeutic decisions were likely to advantage the patient

  10. Evidence based medicineRisk benefit ? • Balancing the risks of stroke and upper GI tract bleeding in older patients with atrial fibrillation. Arch Intern Med 2002: 162(5) ; 541 - 50 • For 65-yr with average risks of stroke and upper GI tract bleeding, warfarin 12.0; aspirin 10.8 and no antithrombotic Rx, 10.1 QALYs per patient • For 80yr, baseline stroke risk 4.3% pa, warfarin, 7.44; aspirin, 7.39; and no treatment, 7.21 QALYs per patient

  11. Evidence based medicine • 80 year old male • Hypertension for 5 years; Atrial fib ? duration • Treated with diuretic and ACE: BP 150/87 mmHg • Electrocardiograph – within normal limits • Echocardiogram – EF 50% early diastolic relaxation abnormality • Creatinine 99 umol / l

  12. Calculation of Risk-Benefit Ratio Am Heart J.  2005; 149 (4): 650-656.

  13. Evidence based medicine

  14. Evidence based medicine • Warfarin reduces the risk of stroke by about two-thirds compared with placebo (ARR, 3.1% per year; NNT, 32) and by about a third compared with aspirin (ARR, 0.8% per year; NNT, 125), but causes at least twice as many intra-cranial and extra-cranial bleeds as aspirin

  15. Evidence based medicine

  16. Calculation of Risk-Benefit Ratio • Predicted event rate in population from calculator • Multiply by RRR (Relative risk reduction) • Gives the ARR (Absolute Risk Reduction) • 1 / ARR = NNT (Patient yr to prevent stroke) • NNH (numbers to harm) • 1 / Serious ADR

  17. Calculation of Risk-Benefit Ratio • Warfarin ( NNT – 32 : NNH – 80) • ARR = 100 / 30 = 3.13% • Assumed stroke risk – 3.13 / 0.7 = 4.46% • Bleed assumed rate 100 / 80 = 1.25% • Assuming risk rate unrelated to warfarin 0.8% • Total bleed rate 2.1%

  18. Calculation of Risk-Benefit Ratio • 80 yr old male, unCx Atrial fibrillation, BP 150/87 • Stroke risk – Framingham 5yr (8 points) – 11% • Stroke risk – CHADS2 (4% pa) – 20% • Bleeding risk – AFFIRM (2% pa + age 1.05) – 10.1% • Stroke risk is 3% and bleed risk 2%

  19. Calculation of Risk-Benefit Ratio • 80 yr old male, unCx Atrial fibrillation, BP 150/87 • Stroke risk – on Warfarin (3 – (0.7 * 3)) = 0.9 • Absolute risk reduction = 2.1 (NNT 47.6) • Bleeding risk = 2% pa (NNH 83) • Applying principle of risk equivalence – • ADR / Relative risk benefit (1.2 / 0.7 = 1.7) • Risk must > 1.7 for a favourable risk profile

  20. Evidence based medicineRisk benefit ? • HEMORR2HAGES National Register of Atr Fibrillation • Anti-thrombotic Rx on individual risks and benefits • Hospitalization for bleed / warfarin was 4.9 per 100 patient-yr, but depended on comorbidity (NNH 24.2) • High-risk patients haemorrhage rate (7.5-15.3) much greater than the low-risk patients (1.1-2.9) • Previous trial estimates - 2.4 per 100 yr (NNH 62.5)

  21. Evidence based medicine Am Heart J.  2006;151(3):713-719.

  22. Calculation of Risk-Benefit Ratio • 80 yr old male, unCx Atrial fibrillation, BP 150/87 • Stroke risk – on Warfarin (3 – (0.7 * 3)) = 0.9 • Absolute risk reduction = 2.1 (NNT 47.6) • Bleeding risk = 4.9% pa (NNH 24.4) • Applying principle of risk equivalence – • ADR / Relative risk benefit (4.1 / 0.7 = 5.9) • Risk must > 5.9 for a favourable risk profile

  23. Evidence based medicineHigh risk and warfarin? • CHAD2 SCORE > 3 - a stroke risk of 9 % • Stroke risk – on Warfarin (9 – (0.7 * 9)) = 2.7 • Absolute risk reduction = 6.3 (NNT 15.9) • The major bleed risk is 4.9% pa (NNH 20.4) • Risk equivalence (4.1 / 0.7) – stroke rate of 5.9% • Warfarin no difference 68.5% - ((100 – 45) + 13.5))

  24. Evidence based medicineIs aspirin a rational choice ? • Aged 80 yr (atrial fib) has a 5 yr stroke risk of 15% • Aspirin will reduce that risk by 20% • No event in 85% + 12 events not prevented • Aspirin will make no difference 97% of the time • Absolute risk reduction (ARR) – 0.6 (NNT 166.6) • The average bleed risk is 0.2% x 5 = 1%

  25. Evidence based medicinePatient preferences ? • Malcolm Man-Son-Hing, et al, Medical Decision Making2005: 25; 548-559 (Systemic review n = 8) • Fewer patients opt for warfarin compared with guidelines ( 5 / 8 studies) • Aspirin stroke rate of 1 %, opt for warfarin 50% • Aspirin stroke rate 2% ,opt for warfarin 66% • Aspirin stroke rate 2 – 6% in 3 to choose warfarin • Physicians balance patient preferences with Rx recommendations of clinical practice guidelines

  26. Evidence based medicine Anyone who believes that the same thing can be suited to everyone is a great fool, since medicine is practiced not on mankind in general but on every individual in particular Henry De Mondeville circa 1300

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