Anticoagulation and mechanical heart valves: fewest strokes and bleeds occurred when INR is 2.5-4.9.

Clinical bottom line (level 4)

  1. Patients with mechanical heart valves on warfarin, had the lowest risk of a thromboembolic event or major bleed when their INR was between 2.5 and 4.9 (NNF = 50 for 4 years) .
Cannegieter et al: New England Journal of Medicine 1995; 333 (1): 11-17
Expires June 2003

The study

Inception cohort study with objective outcomes, not adjusted for confounding factors, not validated in an independent set of patients.

Setting: four anticoagulation clinics, Holland

1608 patients (aged ?, ?% male) mechanical heart valves and on oral anticoagulation

Excluded if
  • not residents
  • seen for <one month


    • Patients received acenocoumarol, phenprocoumon- INR titrated to 3.6 to 4.8.

    100% followed for mean 4 years
    Outcomes studied:
  • thromboembolic events cerebral infarct (confirmed on CT), systemic embolism (confirmed by angiography, surgery or autopsy)
  • major bleeds patient admitted to hospital, required surgery or intracranial bleed

    • The evidence

    outcome time to outcome number of patients/total number %
    (95% CI)
    thromboembolic events mean 4 years 45/1608 2.80%
    (1.99% to 3.60%)
    major bleeds mean 4 years 164/1608 10.2%
    (8.72% to 11.7%)

    • Events per 100 patient years (95% CI):
      • INR level 1.0-1.4: 27 (3.4 to 99). NNF (per patient year): 4 (1 to 29)
      • INR level 2.0-2.4: 7.5 (3.6 to 13). NNF: 13 (8 to28)
      • INR level 2.5-4.9: 2.0 (1.0 to 3.8). NNF: 50 (26 to 100)
      • INR level 5.0-5.5: 4.8 (2.6 to 7.7). NNF: 21 (13 to 38)
      • INR level = 6.5: 75 (54 to 100). NNF: 1 (1 to 2)

    Comments

    1. No adjustment made for potential risk factors.

    Citation

    1. Cannegieter SC, Rosendaal FR, Wintzen AR, et al: Optimal oral anticoagulant therapy in patients with mechanical heart valves. New England Journal of Medicine 1995; 333 (1): 11-17
    Search Terms: atrial fibr* in Cochrane
    Contributor: Chris Ball and Clare Wotton, June 2000
    Reviewer:

    Clinical Question.
    Patient mechanical heart valves
    Intervention or Exposure oral anticoagulation
    Outcome thromboembolic events