Impaired Lignocaine metabolism in patients with myocardial infarction and cardiac failure

Plasma concentrations of lignocaine were measured during and after infusion of lignocaine at 1.4 mg/min for 36-46 hours in 12 patients with myocardial infarction and one patient with cardiac failure due to uncontrolled ventricular tachycardia. In six patients without cardiac failure the plasma concentrations of lignocaine rose progressively during the infusion and the mean lignocaine half life was 4.3 hours compared with 1.4 hours in healthy subjects. Mean plasma lignocaine concentrations were significantly higher in seven patients with cardiac failure, and concentrations also rose during the infusion and the half life was considerably prolonged to 10.2 hours. Lignocaine concentrations rose rapidly to toxic levels when cardiogenic shock developed in one patient and did not fall when the infusion was stopped. The mean plasma antipyrine half life was moderately prolonged (19.4 hours) in a larger group of patients with myocardial infarction and cardiac failure but returned to normal during convalescence (13.2 hours). The metabolism of lignocaine is grossly abnormal in patients with cardiac failure and cardiogenic shock after myocardial infarction.