In a prospective, randomized, open label, positive-controlled study² in 254 patients, the thromboembolic-free interval was found to be significantly greater in patients with mechanical prosthetic heart valves treated with warfarin alone compared with dipyridamole- aspirin (p < 0.005) and pentoxifylline-aspirin (p < 0.05) treated patients. Rates of thromboembolic events in these groups were 2.2, 8.6, and 7.9/100 patient years, respectively. Major bleeding rates were 2.5, 0.0, and 0.9/100 patient years, respectively.

In a prospective, open label, clinical trial comparing moderate (INR 2.65) vs. high intensity (INR 9.0) warfarin therapies in 258 patients with mechanical prosthetic heart valves, thromboembolism occurred with similar frequency in the two groups (4.0 and 3.7 events/100 patient years, respectively). Major bleeding was more common in the high intensity group (2.1 events/100 patient years) vs. 0.95 events/100 patient years in the moderate intensity group.³

In a randomized trial in 210 patients comparing two intensities of warfarin therapy (INR 2.0 - 2.25 vs. INR 2.5 - 4.0) for a three- month period following tissue heart valve replacement, thromboembolism occurred with similar frequency in the two groups (major embolic events 2.0% vs. 1.9%, respectively and minor embolic events 10.8% vs.10.2%, respectively). Major bleeding complications were more frequent with the higher intensity (major hemorrhages 4.6%) vs. none in the lower intensity.⁴

REFERENCES

1. Hurlen M, Abdelnoor M, Smith P, Erikssen J, Arnesen H. Warfarin, aspirin, or both after myocardial infarction. N Engl J Med. 2002;347:969-974.

2. Mok CK, Boey J, Wang R, et al. Warfarin versus dipyridamole-aspirin and pentoxifylline-aspirin for prevention of prosthetic valve thromboembolism: a prospective randomized clinical trial. Circ. 1985;72:1059-1063.

3. Saour JN, Sieck JO, Mamo LA, Gallus AS. Trial of different intensities of anticoagulation in patients with prosthetic heart valves. N Engl J Med. 1990;322:428-432.

4. Turpie AG, Hirsh J, Gunstensen J, Nelson H, Gent M. Randomized comparison to two intensities of oral anticoagulant therapy after tissue heart valve replacement. Lancet. 1988;331:1242-1245.

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