Intravenous magnesium in experimental stent thrombosis in swine

We investigated the effects of magnesium on acute platelet-dependent stent thrombosis in an ex vivo porcine arteriovenous shunt model of high-shear bl ood flow. Control nitinol stents were expanded to 2 mm in diameter in a tub ular perfusion chamber interposed in the shunt and exposed to flowing arter ial blood at a shear rate of 2100 s(-1) for 20 minutes (n = 156 perfusion r uns in 10 swine). Animals were treated with intravenous heparin or MgSO4 al one (2 g bolus over 20 minutes, followed by 2 g/h infusion) and combined he parin plus MgSO4 in random fashion. Effects on thrombus weight (TW), platel et aggregation, bleeding time, activated clotting time, mean arterial blood pressure, and heart rate were quantified. Data points in the magnesium-tre ated animals were examined within 20 minutes after bolus (Mg-early) and >40 minutes after bolus (Mg-late). Stent TW (20+/-3 mg, pretreatment) was redu ced by 42+/-21%, 47+/-19%, 48+/-16%, 67+/-12%, and 86+/-8% in the groups tr eated with Mg-early alone, Mg-late alone, heparin alone, heparin+Mg-early, and heparin+Mg-late, respectively (all P<0.001 versus pretreatment, P<0.001 for heparin+Mg-early and Mg-late versus heparin or magnesium alone, and P< 0.05 for heparin+Mg-late versus heparin+Mg-early, ANOVA). Magnesium had no significant effect on platelet aggregation, activated clotting time, or ble eding time. There were no significant effects on heart rate or mean arteria l blood pressure. The serum magnesium level was inversely correlated with T W (r=-0.70, P=0.002). In conclusion, treatment with intravenous MgSO4 produ ced a time-dependent inhibition of acute stent thrombosis under high-shear flow conditions without any hemostatic or significant hemodynamic complicat ions. Thus, magnesium may be an effective agent for preventing stent thromb osis.