Hemostatic changes after early versus late intracoronary magnesium during acute myocardial infarction in swine

There has been some debate regarding the benefit of magnesium (Mg) in the treatment of acute myocardial infarction (AMI) because of conflicting results from recent clinical trials. Several different hypotheses have been advanced to explain the cardioprotective properties of Mg, including the influence of the timing of Mg administration during AMI. This experiment was designed to assess the effect of intracoronary Mg on certain hemostatic parameters that are known to change during an AMI. Yorkshire swine underwent thoracotomy and 50 min left anterior descending artety (LAD) occlusion, followed by 3 h of reperfusion. In the early group, 250 mg of MgSO₄ was delivered at the onset of reperfusion (n = 6, Mg-early group). In the second group, MgSO₄ was given after 1 h of reperfusion (n = 6, Mg-late group). Six animals received saline instead of Mg and served as controls. The dynamics of plasma antithrombin-III(AT-III), protein C, total protein S, fibronectin, endothelin-1 (ET-1), as well as the stable metabolites of thromboxane (TXB₂) and prostacyclin (6-keto-PGF(1a)) were determined at baseline, twice during occlusion, and three times during reperfusion. Mg given at reperfusion onset was associated with a diminished ET-1 (32.9%), decreased fibronectin level (21.7-25.2%), and increased protein C concentrations (31.9-52.3%) when compared with both the control and late Mg group. In summary, intracoronary Mg administered at the onset of reperfusion favorably influenced hemostasis in swine. The beneficial effects of early Mg supplementation in an expanding array of clinical conditions, including AMI, may be directly related to the improved hemostatic profile in such patients.