Modification of intrinsic AV-nodal properties by magnesium in combination with glucose, insulin, and potassium (GIK) during chronic atrial fibrillation.

OBJECTIVE: To explore the effects of MgSO4 in combination with glucose, insulin, and potassium (GIK) on intrinsic AV-nodal properties during chronic atrial fibrillation.

METHODS: The study included two patient groups--(a) control and intervention and (b) intervention--with different infusion times and concentrations of MgSO4. Ambulatory electrocardiographic recordings were analyzed using modified heart-rate stratified histogram (HRSH) analysis allowing detailed observation of the RR distribution at different average heart rate levels. The two RR-interval populations observed in most patients were characterized by analyzing the relationship between the summits of the peaks of the bimodal histograms.

RESULTS: A bimodal RR distribution with a shorter and a longer RR-interval population was observed in 9 of 11 (control), 9 of 11 (intervention) in group (a), and 11 of 13 in group (b) patients. No significant changes in the two RR populations were seen in the control registration (group a). There were, however, indications of a conduction delay in the longer RR intervals in group (a), which received a low concentration of MgSO4, when control was compared with intervention recordings. In group (b), receiving a high MgSO4 concentration, a conduction delay was seen in both the shorter and longer RR populations, being most pronounced for the longer RR population.

CONCLUSION: High MgSO4 levels caused a delay in both the shorter and longer RR intervals. The conduction delay in the longer RR population was most pronounced, indicating that MgSO4 differently affected the two corresponding AV-nodal pathways.