20 Oct

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

Aspirin in various doses has been evaluated in patients with bioprosthetic valves in nonrandomized (level III and IV) studies. Among patients in normal sinus rhythm, even though the risk of thromboembolism is low, aspirin may offer additional protection against thromboemboli. Even among patients with AF, the frequency of thromboemboli with aspirin alone was very low (Tables 6, 7).
Regarding the use of warfarin in patients with bioprosthetic valves, it has been suggested that warfarin might diminish calcification which frequently occurs in such valves. Synthesis of the calcium-binding amino acid, gamma-carboxyglutamic acid, is a vitamin K-dependent enzymatic process. Warfarin inhibits gamma-carboxyglutamic acid synthesis, and, therefore, might diminish the calcification of porcine bioprosthetic valves through this mechanism. It is also possible that warfarin inhibits the formation of microthrombi, which may serve as a nidus for calcification. The evidence at the moment is incomplete, but it is possible that warfarin may have a secondary benefit in regard to the prevention of calcification. so

Saphenous Vein Bypass Grafts
Several prospective randomized trials have now been performed in which antiplatelet agents or anticoagulants have been administered with the hope of reducing the incidence of occlusion of saphenous vein bypass grafts (Table 8). In a level II study, aspirin in small doses (100 mg/day) was shown to be associated with greater graft patency at 4 months than in untreated patients. Only 68% of grafts (36 of 53) in controls were patent compared with 90% (36 of 40) in patients treated with aspirin (p= .012). Larger doses of aspirin (600 mg/day or 975 mg/day) have also been employed. These level II studies that employed larger doses of aspirin also started treatment later (35 days after operation rather than one day after operation). No significant improvement of graft patency compared with controls, was shown in these studies after 1-2 years.
Table 8—Saphenous Vein Graft Potency

Drug/ Daily Dose Graft Patency Treated(») Graft Patency Untreated(%) StudyDuration(mo) TreatmentOnset(DaysPostop) EvidenceLevel P Reference
Aspirin
_ 100 mg 36 of 40(90) 36 of 53(68) 4 1 IV .012 Lorenz et al, 19844*
325 mg 347 of 371(94) 327 of 384(85) <2 -1 I <.01 Goldman et al, 1988**
600 mg 65 of 81(80) 54 of 74(72) 24 3-4 II NS McEnany et al, 198247
975 mg 313 of 339(92) 327 of 384(85) <2 -1 I <.05 Goldman et al, 1988**
975 mg 87 of 111(78) 76 of 95(80) 12 3-5 II NS Sharma et al, 1983*
975 mg 101 of 115(88) 116 of 147(79) 12 3-5 II NS Brown et al, 1981*
Aspirin + dipyridamole
1,300 mg +100 mg 69 of 75(92) 72 of 93(77) 3-6 1 I <.02 Mayer et al, 198153
975 mg + 225 mg 425 of 478(89) 364 of 486(75) 12 — 2*, 0 I <.05 Chesebro et al, 198480
975 mg+ 225 mg 27 of 33(82) 50 of 61(82) 6 3 II NS Panteley et al, 197951
975 mg + 225 mg 113 of 135(84) 116 of 147(79) 12 3-5 II NS Brown et al, 1981*
975 mg+ 225 mg 61 of 74(83) 76 of 95(80) 12 3-5 II NS Sharma et al, 1983*
990 mg+ 225 mg 87 of 95(92) 88 of 118(75) 6 -1 I <.01 Rajah etal, 1985s2
975 mg+225 mg 330 of 359(92) 327 of 384(85) <2 — 2, -1 I <.05 Goldman et al, 1988**
990 mg+ 225 mg 100 of 133(75) 91 of 133(68) 12 2 or 3 I NS Brooks et al, 198551*
Sulfinpyrazone
800mg 204 of 212(96) 199 of 219(91) <1 1 I <.025 Bauret al, 1982*
800 mg 296 of 328(90) 327 of 384(85) <2 -2 I NS Goldman et al, 1988**
Warfarin
55 of 65(84) 54 of 74(72) 24 3-4 II NS McEnany et al, 198247
29 of 37(78) 50 of 61(82) 6 3 II NS Panteley et al, 197951
t 227 of 251(90) 199 of 238(84) 2 4-7 I <.015 Gohlke et al, 198188

Categories: Antithrombotic Therapy
Tags: , , ,

© 2008 HIV/AIDS News & Information