Effects of magnesium sulfate and lidocaine on cisapride-induced ventricular proarrhythmia in canine heart

Background: Cisapride, a widely used gastrointestinal prokinetic agent, was known to prolong ventricular repolarization and induce torsades de pointes. Magnesium sulfate (MgSO₄) or lidocaine was frequently used to treatment torsades de pointes. However, knowledge was limited about the electrophysiological effects of magnesium sulfate or lidocaine on cisapride-induced ventricular arrhythmia. Method: Cisapride (6 mg/kg) was administrated in dogs with complete AV block. The monophasic action potential, QT interval and amplitudes of early afterdepolarization (EAD) were measured before and after MgSO₄ (100 mg/kg) or lidocaine (1 mg/kg) administration, respectively. Result: Lidocaine decreased QT interval, biventricular 90% of action potential duration (APD₉₀), amplitudes of EADs, and interventricular difference of APD₉₀. MgSO₄ decreased cisapride-induced EADs and interventricular difference of APD₉₀, but did not change QT interval or bilateral ventricular APD90. Moreover, MgSO₄ was more effective than lidocaine in suppressing the amplitude of right ventricular EADs (19 ± 11 % versus 8± 4 %, p < 0.05) and the amplitude of left ventricular EADs (25± 12 % versus 10± 5 %, p < 0.01). Conclusion: Through different electrophysiological mechanisms, MgSO₄ and lidocaine were effective drugs in treating cisapride-induced proarrhythmia.