[Electrophysiological effects of lidocaine on the QRS and ST segment during acute myocardial infarct. Evaluation with thoracic electromaps]

Abstract

We have evaluated the effects of lidocaine on the main haemodynamic parameters, the QTc interval, the ST segment elevation (sigma ST) and the R wave sum (Max sigma pos), studied by automatic recording of thoracic maps, in 9 patients with acute anterior myocardial infarction, admitted to the CCU within 6 hours from pain onset. Lidocaine has been given at the dosage of 2 mg/kg as an i.v. bolus, followed by continuous infusion at 2 mg/min. Haemodynamic parameters, QTc interval and ECG maps have been recorded before and after 5, 15 and 30 min from the beginning of the therapy. Heart rate, systolic and diastolic arterial pressure and cardiac output have not been significantly affected by Lidocaine. The QTc interval has showed a significant reduction of the control ECG from 0.364 +/- 0.059 sec to 0.352 +/- 0.051 at 5 min, 0.353 +/- 0.053 at 15 min and 0.0355 +/- 0.058 sec and 30 min (P less than 0.05). The sigma ST segment decreased significantly after Lidocaine at 5 and 15 min. (from 126 +/- 26 mV to 109 +/- 23 mV and to 112 +/- 23 mV; P less than 0.01 and, respectively, P less than 0.025), whereas at 30 min. sigma ST was not different from control value. There were no significant changes of max sigma pos. Lidocaine did not significantly modify the main haemodynamic determinants of oxygen consumption. We therefore believe that the observed reduction of ST segment elevation was not caused by a decrease of the ischemic damage but was probably due to a primary electrophysiological effect. This drugs, which affects in a different way the action potentials of normal and ischemic cells, could abolish their differences, thus reducing the systolic current of injury.