Myocardial Infarction
WARIS (The Warfarin Re-Infarction Study) was a double-blind, randomized study of 1,214 patients 2 to 4 weeks post-infarction treated with warfarin to a target INR of 2.8 to 4.8. [But note that a lower INR was achieved and increased bleeding was associated with INRs above 4.0; (see DOSAGE AND ADMINISTRATION)]. The primary endpoint was a combination of total mortality and recurrent infarction. A secondary endpoint of cerebrovascular events was assessed. Mean follow-up of the patients was 37 months. The results for each endpoint separately, including an analysis of vascular death, are provided in the following table:

TABLE 3: Event Warfarin
(N = 607) Placebo
(N = 607) RR
(95% CI) % Risk Reduction
(p-value)
Total Patient Yearsof Follow-up 2,018 1,944  
Total Mortality 94 (4.7/100py) 123 (6.3/100py) 0.76 (0.60, 0.97) 24 (p= 0.030)
Vascular Death 82 (4.1/100py) 105 (5.4/100py) 0.78 (0.60, 1.02) 22 (p= 0.068)
Recurrent MI 82 (4.1/100py) 124 (6.4/100py) 0.66 (0.51, 0.85) 34 (p= 0.001)
Cerebrovascular Event 20 (1/100py) 44 (2.3/100py) 0.46 (0.28, 0.75) 54 (p= 0.002)
RR = Relative risk; Risk reduction = (1 - RR); CI = Confidence interval; MI = Myocardial infarction; py = patient years 

WARIS II (The Warfarin, Aspirin, Re-Infarction Study) was an open-label randomized study of 3,630 patients hospitalized for acute myocardial infarction treated with warfarin target INR 2.8 to 4.2, aspirin 160 mg/day, or warfarin target INR 2.0 to 2.5 plus aspirin 75 mg/day prior to hospital discharge. There were approximately 4 times as many major bleeding episodes in the two groups receiving warfarin than in the group receiving aspirin alone. Major bleeding episodes were not more frequent among patients receiving aspirin plus warfarin than among those receiving warfarin alone, but the incidence of minor bleeding episodes was higher in the combined therapy group. The primary endpoint was a composite of death, nonfatal reinfarction, or thromboembolic stroke. The mean duration of observation was approximately 4 years. The results for WARIS II are provided in the following table.8

TABLE 4: WARIS II - Distribution of Separate Events According to Treatment Group *
CI denotes confidence interval.
†
The rate ratio is for aspirin plus warfarin as compared with aspirin.
‡
The rate ratio is for warfarin as compared with aspirin.
§
Major bleeding episodes were defined as nonfatal cerebral hemorrhage or bleeding necessitating surgical intervention or blood transfusion.
¶
Minor bleeding episodes were defined as non-cerebral hemorrhage not necessitating surgical intervention or blood transfusion.
Event Aspirin
(N = 1,206) Warfarin
(N = 1,216) Aspirin Plus Warfarin
(N = 1,208) Rate Ratio
(95% CI)* p-value
 No. of Events   
Reinfarction 117 90 69 0.56
(0.41 to 0.78)† < 0.001
    0.74
(0.55 to 0.98)‡ 0.03
Thromboem