Lidocaine is a well known antiarrhythmic agent. However, recent reports indicate that indocaine has myocardial protective effects on acute myocardial ischemia and reperfusion. The exact mechanism of myocardial protection of lidocaine is still not clearly understood. In this study we intended to assess the effects of lidocaine on high energy phosphate metabolism in cats subjected to myocardial ischemia-reperfusion by using³¹P MR spectroscopy. Effect of lidocaine on size of infarct will also be evaluated by 2, 3, 5-triphenyltetrazolium chloride(TTC) staining.

Twenty-seven cats were used for this study. The animals were divided into three groups : for group 1(n=10) and group 2(n=7), animals were subjected to a 90 min of LAD occlusion followed by a 90 min of reperfusion ; for group 3(n=10), a 20 min of occlusion followed by a 90 min of reperfusion. In group 2 and group 3, lidocaine(5mg/kg/hr) was infused continuously during the occlusion and reperfusion periods with an initial bolus injection(1mg/kg) before ligation of LAD. In-vivo MR spectroscopy was performed on a 4.7T Biospec System(Bruker, Switzerland). A home-made surface coil(diameter : 1.5cm) was used to receive³¹p signals from the myocardium underwent ischemic and reperfusion damage.

Decrease of PCr during ischemic period was not different between each groups : PCr showed less than 30% of the baseline value at L-30 in group 1 and group 2 and at L-20 in group 3. More than 90% recovery of PCr was achieved at R-30 in group 2 and group 3, whereas less than 50% of PCr was recovered in group 1. Decrease of ATP during ischemic period was less pronounced in group 2 than in group 1 : in group 2 ATP depleted down to 25% of the baseline at L-90, whereas in group 1 ATP decreased to 50% of the baseline. Recovery of ATP during reperfusion period was not signiflcant in all three groups. On TTC staining, evidence of infarct was seen in all cases of group 1 : the area of infarct was 12.3±2.7% of the left ventricular mass and 23.9±6.1% of the area at risk. On the contrary, there was no evidence of infact in any case of group 2 and group 3.

In this study, we found that lidocaine has myocardial protecitve effects on ischemia-reperfusion in cats. Lidocaine improves high energy phosphorous metabolism during ischemia and reperfusion as well as reduces infarct size.