Effects of lidocaine and droxicainide on myocardial necrosis: a comparative study

Anti-inflammatory properties of local anesthetics and their present and potential clinical implications

Development of new local anesthetic agents has been focused on the potency of their nerve-blocking effects, duration of action and safety and has resulted in a substantial number of agents in clinical use. It is well established and well documented that the nerve blocking effects of local anesthetics are secondary to their interaction with the Na+ channels thereby blocking nerve membrane excitability and the generation of action potentials. Accumulating data suggest however that local anesthetics also possess a wide range of anti-inflammatory actions through their effects on cells of the immune system, as well as on other cells, e.g. microorganisms, thrombocytes and erythrocytes. The potent anti-inflammatory properties of local anesthetics, superior in several aspects to traditional anti-inflammatory agents of the NSAID and steroid groups and with fewer side-effects, has prompted clinicians to introduce them in the treatment of various inflammation-related conditions and diseases. They have proved successful in the treatment of burn injuries, interstitial cystitis, ulcerative proctitis, arthritis and herpes simplex infections. The detailed mechanisms of action are not fully understood but seem to involve a reversible interaction with membrane proteins and lipids thus regulating cell metabolic activity, migration, exocytosis and phagocytosis.

Reduction of myocardial infarct size in rabbits and inhibition of activation of rabbit and human neutrophils by lidocaine

Myocardial reperfusion is associated with increased influx of activated neutrophils and intracellular accumulation of sodium in the ischemic zone. Lidocaine is a sodium channel blocker that also inhibits several neutrophil functions. We investigated the effect of lidocaine on infarct size in rabbits undergoing 30 minutes of ischemia and 48 hours of reperfusion. Animals randomly received lidocaine (10 mg/kg, n = 11) or saline (n = 11) during occlusion. The area of necrosis (AN) was measured histologically and expressed as a percentage of the area at risk (AR). Myocardial oxygen consumption and the perfusion bed at risk were similar in the two groups. Lidocaine reduced infarct size compared with control (AN/AR = 30% +/- 4% vs 61% +/- 5%, respectively; p = 0.0001). This reduction was associated with a significant decrease in neutrophil infiltration and in the degree of hemorrhage in the reperfused myocardium. Lidocaine also significantly inhibited superoxide anion production by rabbit and human neutrophils in whole blood. Therefore, lidocaine treatment results in a significant reduction in infarct size in the rabbit model, partly through reduction of neutrophil-mediated injury to viable cells, suggesting that lidocaine may be useful to enhance myocardial salvage in patients undergoing pharmacologic or mechanical reperfusion.

Role of endothelin in a rabbit model of acute myocardial infarction: effects of receptor antagonists

The role of endothelin (ET) in acute myocardial infarction and proarrhythmic potential was investigated in a rabbit model. One group of rabbits underwent 30 min of circumflex occlusion and 3 h of reperfusion with measurements of myocardial blood flow and myocardial levels of ET-1 messenger RNA (mRNA). In a second group, the systemic and coronary effects of exogenous ET were studied in animals pretreated with either saline, FR139317, an ETA-receptor antagonist, or PD145065, an ETA-and ETB-receptor antagonist. In a third study, animals undergoing 30 min of circumflex occlusion followed by 48 h of reperfusion were treated with exogenous ET-1, FR139317, PD145065, or saline. Arrhythmias were recorded and infarct size measured at 48 h. These studies revealed that ischemia and reperfusion was followed by a progressive microcirculatory failure ("no-reflow phenomenon") in rabbits. This was associated with a 2.6-fold elevation in levels of myocardial ET-1 mRNA in the ischemic zone in comparison to the nonischemic zone (p = 0.04). Exogenous ET-1 caused elevation in coronary and systemic vascular resistance that was significantly blocked by antagonism of the ETA receptor. In rabbits subjected to myocardial ischemia and reperfusion, ET-1 infusion led to a higher incidence of ventricular arrhythmias, whereas ET-receptor antagonism with PD145065 significantly reduced ventricular arrhythmias. Exogenous ET-1 and FR139317 failed to alter infarct size (AN) of the area at risk (AR) compared with control [AN/AR(%) was 46 +/- 8, 55 +/- 9, and 47 +/- 7, respectively]. However, PD145065 significantly decreased AN/AR (22 +/- 7; p < or = 0.02). The increased production of ET-1, resulting from increased levels of mRNA after reperfusion, may contribute to the no-reflow phenomenon. Although the vasoconstrictor effects of ET-1 can be blocked by ETA-receptor antagonism alone, only blockade of both the ETA and ETB receptors significantly reduced infarct size. These data suggest that production of ET increases in the heart during ischemia and is deleterious to the reperfused myocardium.

Combined adenosine and lidocaine administration limits myocardial reperfusion injury

The endogenous compound adenosine may play a role in limiting myocardial ischemia-reperfusion injury through its ability to cause vasodilation, modulate cardiac adrenergic responses, inhibit neutrophil function, or modulate energy supply and demand of the myocardium. The local anesthetic lidocaine has been shown to be protective against myocardial ischemia-reperfusion injury, although its mechanism of action remains unresolved. We hypothesized that administration of exogenous adenosine during reperfusion would limit the size of the infarct that results from a period of ischemia and reperfusion only when the animals are treated with lidocaine. Male, mongrel dogs (13.0-20.0 kg) were anesthetized (30 mg/kg i.v. sodium pentobarbital), and a left thoracotomy was performed. The left circumflex coronary artery (LCx) was isolated and instrumented with an electromagnetic flow probe, a 25-gauge nonobstructing intracoronary catheter, and a critical stenosis. The dogs were allocated randomly to one of four groups: 1) control, n = 13, (saline), 2) adenosine, n = 13, (0.15 mg/kg/ml/min i.c. for the first hour of reperfusion), 3) lidocaine, n = 9, (2.0 mg/kg i.v. given immediately before coronary artery occlusion and just before reperfusion), or 4) adenosine plus lidocaine, n = 11. The LCx was occluded for 90 minutes and reperfused for 6 hours. Regional myocardial blood flow (RMBF) was determined (n = 6 per group) at 80 minutes of occlusion and at 45 minutes of reperfusion with radiolabeled microspheres. RMBF determinations revealed an increase in blood flow to the inner two thirds of the myocardium at 45 minutes of reperfusion only in the presence of the combined treatment. Adenosine treatment alone or lidocaine treatment alone did not affect RMBF. Quantification of infarct size (triphenyltetrazolium method) expressed as a percent of the area at risk revealed a significant limitation of infarct size only in the group treated with both adenosine and lidocaine: control, 47.8 +/- 6.6%; adenosine, 45.0 +/- 3.2%; lidocaine, 46.9 +/- 6.0%; and adenosine and lidocaine, 20.8 +/- 5.6%. Statistical analyses were performed with two-way analysis of variance to account for the two individual drug treatments. The findings show that intracoronary administration of exogenous adenosine, at the dose used, is only effective at limiting myocardial infarct size when administered to lidocaine-treated animals.

Dimethylthiourea, but not dimethylsulfoxide, reduces canine myocardial infarct size

We studied the effect of treatment with two diffusible, low molecular weight scavengers of toxic oxygen metabolites, dimethylthiourea (DMTU) and dimethylsulfoxide (DMSO), on canine infarcts caused by 90 min of ischemia and 3 h of reperfusion. Infarct size was determined by incubating ventricular slices with triphenyl tetrazolium chloride. Areas at risk were determined by autoradiography of 99Tc microspheres injected in vivo during ischemia and were similar (p greater than 0.05) in DMTU, DMSO, and saline treated dogs. However, the ratio of infarct size to area at risk was reduced (p less than 0.05) in dogs treated 30 min before reperfusion with 500 mg/kg DMTU (31.1 +/- 4.6%, n = 9) compared with saline treated dogs (53.4 +/- 4.6% n = 9). In contrast, the ratio of infarct size to area at risk was not significantly different (p greater than 0.05) in dogs treated with 2000 mg/kg DMSO 30 min before reperfusion (43.7 +/- 4.3%) compared to saline treated dogs. The serum concentration of DMTU (4.5 mM) was one-tenth that of DMSO (48 mM) in early reperfusion. Therefore, DMTU but not DMSO protected against post-ischemic cardiac reperfusion injury.

Comparative effects of nicardipine, a new calcium antagonist, on size of myocardial infarction after coronary artery occlusion in dogs

To examine whether nicardipine, a dihydropyridine derivative, limits size of myocardial infarction, and to compare the protective effects of nicardipine administered before and early and late after coronary artery occlusion, 99mTc-labeled albumin microspheres were injected into the left atrium during 5 min temporary coronary artery occlusion to determine the extent of the hypoperfused zone (the area at risk). The coronary arteries were then reperfused for 45 min before 6 hr permanent coronary artery occlusion. Fifteen minutes before permanent occlusion, dogs were randomly assigned to a control group (n = 11), a pretreatment group (n = 9), which received at this point 10 micrograms/kg of nicardipine as a loading dose followed by a continuous infusion of 8 micrograms/kg/hr for 6 hr, an early treatment group (n = 9), in which nicardipine treatment was initiated 15 min after occlusion, or a late treatment group (n = 8), in which nicardipine administration was delayed for 3 hr. Six hours after coronary artery occlusion, the hearts were excised and the left ventricle of each was cut into 3 mm thick slices and stained with triphenyltetrazolium chloride. The extent of myocardial necrosis was measured by planimetry of the unstained areas. Thereafter, the same slices were autoradiographed and the extent of the hypoperfused zone was measured by planimetry of the "cold spot." The extent of the hypoperfused zone was identical among the four groups. In the control group, the ratio of the extent of myocardial necrosis to the extent of the hypoperfused zone was 95.8 +/- 3.8% (mean +/- SEM). However, it was significantly smaller in the pretreatment group (59.9 +/- 13.3%, p less than .05) and the early treatment group (49.0 +/- 10.6%, p less than .01) than in the control group. In the late treatment group, this value was not different from that in the control group (86.5 +/- 7.1%). There was a close inverse correlation between reduction of infarct size and the extent of the hypoperfused zone in the pretreatment and early treatment groups. Thus, nicardipine administered before or early after coronary artery occlusion limited infarct size by 37% to 49%, whereas when administration was delayed for 3 hr infarct size was not reduced. Furthermore, nicardipine had more striking effects on the ischemic myocardium of dogs with small hypoperfused zones than on that of dogs with large hypoperfused zones.

Comparison of electrophysiological and mechanical effects of droxicainide and lidocaine on heart muscle isolated from rats

A new antiarrhythmic drug, droxicainide, was compared with lidocaine in order to evaluate droxicainide's effect on heart muscle. Dose-response curves for electrophysiological and mechanical effects of the two drugs on spontaneously beating atria, electrically stimulated atria and papillary muscles isolated from rats were obtained. After increasing doses of both droxicainide and lidocaine sinus node automaticity decreased, atrial and ventricular excitability and contractile force decreased and refractoriness increased. The effects of the two drugs on atrial and ventricular muscle were qualitatively and quantitatively the same, but droxicainide was less potent. The results fit well with the concept that droxicainide is a class 1 anti-arrhythmic drug.