Objective: To investigate changes in atrial conduction induced by MgSO4 and glucose, insulin and potassium (GIK) during the first 12-h period of sinus rhythm after successful DC-conversion of chronic atrial fibrillation (CAF).
Methods: Signal-averaged P-wave duration, QRS-duration and PQ-time were recorded in 20 patients who were randomly assigned to control or intervention. Ten patients received no infusates (control group) and 10 patients received MgSO4 and GIK infusions (intervention group). P-wave duration was determined from the X-, Y- and Z-leads, which were further combined to obtain a spatial magnitude. P-wave morphology was studied by analysing global activation patterns and discrete components from the calculated spatial magnitude signal.
Results: No changes in the measured parameters were seen in the control group. The P-wave duration, QRS-duration and PQ-time increased from 139(13) [mean(SD)] to 149(15) (p < 0.01), 90(7) to 94(9) (p < 0.05) and 188(10) to 207(13) ms (p < 0.01). respectively, after bolus infusion of MgSO4. The time from the start of the P-wave to its 1st and 2nd max. locations increased by 6 ms (p < 0.01) in both cases after bolus infusion of MgSO4 and had reversed after 10 h of MgSO4 and GIK infusion. P-wave duration and PQ-time decreased after 10 h of MgSO4 and GIK infusion, from 149(34) (bolus) to 138(12) and from 207(13) to 195(27) ms (p < 0.05), respectively, in spite of an even higher serum Mg concentration at the end of this period.
Conclusion: Bolus infusion of MgSO4 2 h after DC-conversion of CAF produced an intra-atrial conduction delay that could be reversed by adding a GIK infusion, in spite of a concomitant increase in serum Mg concentration. No recovery of the intra-atrial conduction delay, seen after DC-conversion of CAF, was observed in either of the two groups during the 12-h study period.