INTRACORONARY MAGNESIUM IS NOT PROTECTIVE AGAINST ACUTE REPERFUSION INJURY IN THE REGIONAL ISCHEMIC-REPERFUSED DOG HEART

Intravenous magnesium lowers mortality in patients with suspected myoc ardial infarction. We tested the hypothesis that the protective effect may be due to a direct, local influence of magnesium on myocardial re perfusion injury in a dog model of ischaemia/reperfusion. Ten anaesthe tized open chest dogs underwent Ih of left anterior descending artery (LAD) occlusion and 6 h of reperfusion. The animals received intracoro nary (i.c.) magnesium aspartate (Mg, n = 5) or vehicle infusion (n = 5 ) for the first hour of reperfusion. Mg infusion was adapted to actual LAD flow (ultrasonic flow probe) to increase regional plasma concentr ation by 4 mmol L(-1). Regional myocardial function was measured as pe rcent systolic wall thickening (sWTh, sonomicrometry). Intracoronary M g increased LAD flow during application (at 15 min reperfusion; Mg, 19 4+/-44 (mean+/-SD); control, 116+/-41 mL min(-1) 100 g(-1), P < 0.01). sWTh decreased during coronary occlusion from 14.3+/-7.1% to -4.7+/-2 .7% in the control group and from 14.8+/-2.5% to -4.1+/-3.1% in the Mg group. Throughout the reperfusion period wall function remained depre ssed in both groups to a similar degree (control, -3.5+/-1.8%; Mg, -3. 0+/-1.9% at 6 h reperfusion). Global haemodynamics were not different. Infarct size after 6 h reperfusion (TTC staining) was similar in both groups (Mg, 20.6+/-5.0; control, 24.4+/-8.7% of area at risk). Region al magnesium application (i.c.) to post-ischaemic reperfused myocardiu m had no influence on infarct size or postischaemic regional wall func tion in this model. The beneficial action of systemic Mg in patients w ith myocardial infarction is probably not due to an early direct prote ctive effect on ischaemic-reperfused myocardium.