Effect of low-intensity warfarin anticoagulation on level of activity of the hemostatic system in patients with atrial fibrillation. BAATAF Investigators.
OBJECTIVE
The Boston Area Anticoagulation Trial for Atrial Fibrillation (BAATAF) demonstrated that low-intensity warfarin anticoagulation can, with safety, sharply reduce the rate of stroke in patients with nonvalvular atrial fibrillation. The beneficial effect of warfarin was presumably related to a decrease in clot formation in the cardiac atria and subsequent embolization.


METHODS
To assess the effect of warfarin therapy on in vivo clotting in patients in the BAATAF, we measured the plasma level of prothrombin activation fragment F1+2. One sample was obtained from 125 patients from the BAATAF; 62 were taking warfarin and 63 were not taking warfarin (control group).


RESULTS
The warfarin group had a 71% lower mean F1+2 level than the control group (mean F1+2 of 1.57 nmol/L in the control group compared with a mean of 0.46 nmol/L in the warfarin group; P < .001). F1+2 levels were higher in older subjects but were consistently lower in the warfarin group at all ages. Fifty-two percent of patients in the control group were taking chronic aspirin therapy at the time their F1+2 level was measured. Control patients taking aspirin had F1+2 levels very similar to control patients not taking aspirin (mean of 1.52 nmol/L for control patients on aspirin compared with 1.64 nmol/L for control patients off aspirin; P > .1).


CONCLUSIONS
We conclude that prothrombin activation was significantly suppressed in vivo by warfarin but not aspirin among patients in the BAATAF. These findings correlate with the marked reduction in ischemic stroke noted among patients in the warfarin treatment group observed in the BAATAF.
Kistler
J P
JP
Neurology/Stroke Service, Massachusetts General Hospital, Boston 02114.
Singer
D E
DE
Millenson
M M
MM
Bauer
K A
KA
Gress
D R
DR
Barzegar
S
S
Hughes
R A
RA
Sheehan
M A
MA
Maraventano
S W
SW
Oertel
L B
LB
D000368:Aged; D000369:Aged, 80 and over; D001241:Aspirin / Q000627:therapeutic use; D001281:Atrial Fibrillation / Q000097:blood / Q000150:complications*; D002561:Cerebrovascular Disorders / Q000097:blood / Q000209:etiology / Q000517:prevention & control*; D005260:Female; D006487:Hemostasis; D006801:Humans; D002542:Intracranial Embolism and Thrombosis / Q000150:complications / Q000209:etiology / Q000517:prevention & control*; D008297:Male; D008875:Middle Aged; D010446:Peptide Fragments / Q000032:analysis; D011516:Prothrombin / Q000032:analysis; D014859:Warfarin / Q000627:therapeutic use*
D010446:Peptide Fragments; C045879:prothrombin fragment 1.2; D014859:Warfarin; D011516:Prothrombin; D001241:Aspirin