[Electrophysiological study of pro-arrhythmogenic effects of erythromycin]

Three cases of torsades de pointe induced by erythromycin have recently been reported. After observing a new case, the authors tried to demonstrate the possible mechanism of the arrhythmogenic action of this molecule. Twenty-two patients undergoing electrophysiological studies in the catheter laboratory to determine the cause of syncope were given an intravenous injection of 10 mg/Kg of erythromycin lactobionate. The drug was injected in 1 minute (bolus) in 11 patients (Group A). The other 11 patients (Group B) received the drug by slow intravenous infusion (20 minutes). Electrophysiological parameters were measured before and after erythromycin. A significant prolongation of the atrial refractory periods (+39 ms), ventricular refractory periods (+20 ms), QT (+20 ms) and QTC intervals (+42 ms) was observed in Group A. These electrophysiological effects could explain an arrhythmogenic action similar to that of antiarrhythmic drugs in Group I of Vaughan-Williams' classification. The slow intravenous infusion of erythromycin in Group B considerably reduced these undesirable secondary effects. This difference was directly related to serum concentrations of the molecule.