Effects of magnesium, sulphate on atrioventricular conduction times and surface electrocardiogram in dogs anaesthetized with sevoflurane

We have studied the effects of magnesium on atrioventricular (AV) conduction times and surface electrocardiogram during both sinus rhythm and atrial pacing in seven dogs anaesthetized with 1 MAC of sevoflurane. A bolus dose of magnesium sulphate (MgSO4) 30, 60 and 90 mg kg(-1) significantly increased plasma magnesium concentrations from 1.3 (SEM 0.1) to 15.3 (1.3) mg dl(-1). MgSO4 significantly prolonged A-H (AV nodal conduction time during sinus rhythm), St-H (intraatrial and AV nodal conduction time during atrial pacing) and H-S (total ventricular conduction time) intervals at doses greater than or equal to 30 mg kg(-1); H-V interval (His-Purkinje conduction time) at doses greater than or equal to 60 mg kg(-1); RR and PR intervals and QRS duration at doses greater than or equal to 30 mg kg(-1) in a dose-related manner during both sinus rhythm and atrial pacing. QTc interval remained unchanged during sinus rhythm. The doses of MgSO4 used did not have deleterious effects on AV conduction times and surface electrocardiogram during 1 MBC of sevoflurane anaesthesia. This finding suggests that MgSO4 in high doses was safe and may be indicated for cardiac arrhythmia and hypertension during sevoflurane anaesthesia. However, further study is required to apply these findings to clinical anaesthesia.