Intravenous MgSO4 alone and in combination with glucose, insulin and potassium (GIK) prolong the atrial cycle length in chronic atrial fibrillation.

AIMS To investigate the effects of parenteral administration of MgSO4, and glucose, insulin, and potassium (GIK), on the dominant atrial cycle length during chronic atrial fibrillation (CAF). METHODS AND RESULTS The length of the dominant atrial cycle (DACL) in the power-frequency spectrum of the QRST-suppressed lead V1 ECG was identified before and after intravenous administration of MgSO4 alone and after 5 and 10 h of MgSO4 and GIK infusion, in 13 patients with CAF. The changes in DACL were compared with changes in heart rate (HR), blood pressure and blood parameters. MgSO4 alone increased the DACL from 146(13) (mean(SD)) (control) to 153(14) ms (P < 0.01) and decreased the HR from 102(22) to 95(18) beats x min(-1) (P < 0.05). After 5 h of MgSO4 and GIK infusion the DACL was increased compared with control, from 146(13) to 152(11) ms (P < 0.01), but unchanged compared with that after the bolus infusion of MgSO4. HR was decreased compared with control (102(22)) and the bolus infusion of MgSO4 (95(18)) to 87(15) beats x min(-1) after 5 h of intervention. The DACL was further increased after 10 h of MgSO4 and GIK infusion compared with both control (from 146(13) to 157(11) ms), (P < 0.01) and the 5h infusion (152(11) to 157(11) ms), (P < 0.05). No further changes were seen in HR after 10 h (87(17)) of intervention. There were indications of an inverse relationship between total changes in HR (deltaHR) and DACL (deltaDACL) during the interventions (P < 0.05). CONCLUSION Bolus infusion of MgSO4 prolongs the DACL and decreases HR in CAF. A further prolongation of DACL was seen after 10 h of MgSO4 and GIK infusion compared with control and with 5 h of intervention. Changes in DACL and HR during the entire intervention period showed an inverse relationship. The antiarrhythmic properties of MgSO4 and the GIK solution in CAF clearly require further attention.