EFFECTS OF MAGNESIUM, SULFATE ON ATRIOVENTRICULAR-CONDUCTION TIMES AND SURFACE ELECTROCARDIOGRAM IN DOGS ANESTHETIZED WITH SEVOFLURANE

We have studied the effects of magnesium on atrioventricular (AV) cond uction times and surface electrocardiogram during both sinus rhythm an d 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) si gnificantly increased plasma magnesium concentrations from 1.3 (SEM 0. 1) to 15.3 (1.3) mg dl(-1). MgSO4 significantly prolonged A-H (AV noda l conduction time during sinus rhythm), St-H (intraatrial and AV nodal conduction time during atrial pacing) and H-S (total ventricular cond uction 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 g reater than or equal to 30 mg kg(-1) in a dose-related manner during b oth sinus rhythm and atrial pacing. QTc interval remained unchanged du ring sinus rhythm. The doses of MgSO4 used did not have deleterious ef fects on AV conduction times and surface electrocardiogram during 1 MB C of sevoflurane anaesthesia. This finding suggests that MgSO4 in high doses was safe and may be indicated for cardiac arrhythmia and hypert ension during sevoflurane anaesthesia. However, further study is requi red to apply these findings to clinical anaesthesia.