16 Oct

Antithrombotic Therapy in Mechanical and Biological Prosthetic Heart Valves and Saphenous Vein Bypass Grafts: Thromboemboli

Only rarely have reports been published of patients with ball valves who were untreated with either anticoagulants or antiplatelet agents (Table 1). With cloth-covered Starr-Edwards aortic valves, a nonrandomized comparative (level III) study of patients who either never received anticoagulants or in whom anticoagulants were discontinued after 1 year showed acceptable rates of thromboembolism compared with the rates observed in a small group of patients who received anticoagulants, but there is contrary (level IV and V) evidence based on nonrandomized historical comparisons,* and a devastating experience in a case series without controls.
Regarding the Lillehei-Kaster valve, in a (level V) case series without controls, the incidence of thromboembolism in untreated patients (no anticoagulants or antiplatelet agents) with valves in the aortic position was impressive (7%), but in patients with valves in the mitral position, the incidence of thromboemboli was devastating (33%) (Table 3). In patients treated with anticoagulants, the incidence of thromboembolic episodes in case series analyses (level V) was higher with valves in the mitral position than in the aortic position. Some, however, have shown the incidence of thromboembolism in patients with valves in the aortic position to be comparable to that reported by others for valves in the mitral position. Here

Regarding the Bjork-Shiley valve, in a level IV study that employed nonrandomized historical cohort comparisons, aspirin, 1 g/day, in combination with dipyridamole, 100 mg/day, was no better than no treatment for the prevention of thromboembolism (Table 4). Treatment with anticoagulants gave better results. Further nonrandomized evaluations, which included additional patients treated with anticoagulants, compared with these former patients supported the impression that anticoagulants provided better protection than a combination of aspirin and dipyridamole (Table 4). A more recent case series without controls in children, most of whom received only aspirin, showed no postoperative thromboembolic events over an average of 3 years (level V study).
Table 3—Thromboemboli with UUehei-Kaster Valves

Treatment No. Pts ValvePosition* ProthrombinTime ThromboembolicEpisodes/100 pts/yr Thromboemboli% EvidenceLevel Reference
None 70 Ao 7 in 33 most V Christo et al, 19801®
12 M 33 in 47 mos
Warfarin or dicoumarol
81 Ao 15-25s§ 2.6 V Zwart et al, 19791®
108 M 5.0
45 Ao 0 in 4 years V Starek et al, 1976“
48 M 10 in 4 years||
97 Ao 6.11 V Dale et al, 1977″

Table 4—Thromboemboli with Bjork-Skttey Valves

Treatment No. Patients ValvePosition Prothrombin Time, % Thromboemboli Episodes/ 100 pts/yr EvidenceLevel Reference
None 27 Ao 23 IV Bjork and Henze, 1975“
Warfarin or dicoumarol 73 Ao 5-16f 0.7 Bjork and Henze, 197923
193 M 4.2 IV
109 Ao + M 2.2
99 Ao 5-15* 5.6§ V Dale et al, 19775
ASA 1 g + 64 Ao 23 IV Bjork and Henze, 19752*
Dipyridamole 100 mg
ASA 6 mg/kg 51|| Ao 0 in 3 yr V Verrier et al, 1986**
± (children)
25 mg<12 yr age
50 mg>12 yr age

Categories: Antithrombotic Therapy
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