13 Oct

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

Antithrombotic Therapy in Mechanical and Biological Prosthetic Heart Valves and Saphenous Vein Bypass GraftsMechanical Bioprosthetic Valves
Mechanical prosthetic heart valves are well-recognized sources of thromboemboli, and the medical literature suggests that the risk of thromboembolism with all mechanical valves is sufficiently high to warrant lifetime anticoagulant therapy. In view of the hemorrhage risks of lifelong anticoagulant therapy, the question of clinical relevance at this time is whether the dose of warfarin can be effectively reduced or whether antiplatelet agents can safely be substituted or used in combination with lower doses of warfarin.
Definitive answers to these questions are not available in the literature. The adequacy of published reports for providing valid information on the risk of thromboembolism after valvular heart operations has recently been questioned. In spite of a serious lack of complete data, clinical decisions must be made, and, therefore, recommendations must be made on the basis of incomplete information. read more

Experience with ball valves, particularly various models of the Starr-Edwards valve, is summarized in Tables 1 and 2. Regarding antiplatelet agents, the use of either dipyridamole alone or aspirin alone has been sparse, and none of the studies have been randomized. Among only 7 patients, (level III study) in a nonrandomized historical comparison, the incidence of thromboembolism with dipyridamole alone was not improved relative to the incidence of thromboembolism in untreated patients.2 Clearly, this experience is too sparse to be definitive. Among 70 patients treated with aspirin alone (1.3 g/day) (level III), it seemed that fewer thromboemboli occurred than in patients who received no prophylaxis, but the difference was not statistically significant2 (Table 2). Others, by means of a nonrandomized historical cohort comparison (level IV), investigated the effects of aspirin alone (1 g/day). They observed fewer thromboemboli than in patients treated with anticoagulants alone, provided the patients were in sinus rhythm. Aspirin alone, however, in patients with Starr-Edwards valves who were in AF, was less effective in the prevention of systemic thromboembolism than anticoagulants alone. More recently, aspirin plus dipyridamole, administered to children, most of whom had Starr-Edwards valves, was shown to give an incidence of thromboemboli (2.3/100 patient years) that did not differ from the incidence with warfarin (level III evidence).
Table 1—ThromboetnboU with Starr-Edwards BaU Valves

Treatment ValveType Pt No. ValvePosition ProthrombinTime Thromboemboli Episodes/ 100 pts/yr Thromboemboli EvidenceLevel Reference
None Cloth-covered 58 Ao, M 4 III Moggio et al. 1978*
Metal struts 37 Ao 41% in 24 mo III Duvoisin et al. 196713
Metal struts ? M 75 III Yeh et al, 1967u
Cloth-covered 40 Ao 3% in 6-24 mo III Vidne et al, 1974“
Metal struts 5210 AoM 56% in 20 mof 30% in 20 mo III Akbarian et al. 1968u
Partially cloth-covered 29 Ao 69% in 12 mol V Stein et al, 197617
Warfarin or dicoumarol § 65 Ao, M 20% in 23 mo I Altman et al, 1976®
Metal struts Cloth-covered 216 Ao 5-15% 7 V Dale, 1976“
Metal struts Cloth-covered 73 Ao 10% 9.3 I Dale et al, 1977®
Metal struts ? M 25-30 s|| 1.8 III Yeh et al, 1967**
Metal struts 177 Ao ^1.5 x control 4% in 24 mo III Duvoisin et al, 1967“
Cloth-covered 48 Ao, M ? 1.2 III Moggio et al, 1978*
? 50 Ao, M 20-30% 18% in 14 mol I Sullivan et al, 19694
Metal struts 5015 AoM 8% in 20 mol 27% in 20 mol III Akbarian et al, 1968“
? 83 Ao, M ? 2.3 III Makhlouf et al, 19873*
Metal struts Cloth-covered 132170 MAo 1.5 x control 6.46.5 V FUster et al, 198217A
Partiallycloth-covered

Table 2—ThromboemboH with Starr-Edwards Ball Valves

Treatment ValveType Pt No. ValvePosition ProthrombinTime Thromboemboli Episodes/ 100 pts/yr Thromboemboli EvidenceLevel Reference
ASA 1 g/day Cloth-covered Metal strutf 77 Ao 14.5 IV Dale and Myhre, 198F
ASA 1.3 %/day Cloth-covered Metal strutf 70 Ao, M 2.6 III Moggio et al, 1978*
Dipyridamole 400 mg/day Cloth-covered Metal strutt 7 Ao, M 10.0 III Moggio et al, 1978*
ASA 20 m/kg + dipyridamole 5 mg/kg ?(Mostly ball valve) 150 Ao, M 2.3 III Makhlouf et al, 19873*
Warfarin + ASA 0.5 g/day ?t 57 Ao, M 5% in 25 mo I Altman et al, 1976®
Warfarin + ASA 1 g/day Cloth-covered Metal strut 75 Ao 10%§ 1.8 I Dale et al, 1977*
Warfarin + dipyridamole 400 mg/day ? 42 Ao, M 20-30% 2% in 13 mo# I Sullivan et al, 1969*
Inadequatewarfarin Metal strut 140 Ao <1.5 x control 26% in 24 mo III Duvoisin et al, 196713
Metal strut ? M <20 s|| 10.5 III Yeh et al, 1967“
Metal strut 3117 Ao1lM 19% in 20 mo# 24% in 20 mo# III Akbarian et al, 1968w
Metal strut ? Ao < 1.5 x control 8.5 V F\ister et al, 1982,7A
Cloth-covered ? M 14.2

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