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Differential Effects of Intravenous Magnesium on Atrioventricular Node Conduction in Supraventricular Tachycardia

  • Author Footnotes
    1 Dr. Stiles is supported by the National Heart Foundation of New Zealand and the Dawes Scholarship, Royal Adelaide Hospital, Adelaide, Australia.
    Martin K. Stiles
    Footnotes
    1 Dr. Stiles is supported by the National Heart Foundation of New Zealand and the Dawes Scholarship, Royal Adelaide Hospital, Adelaide, Australia.
    Affiliations
    Cardiovascular Research Centre, Department of Cardiology, Royal Adelaide Hospital, and the Disciplines of Medicine and Physiology, University of Adelaide, Adelaide, Australia.
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  • Author Footnotes
    2 Dr. Sanders is supported by the National Heart Foundation of Australia.
    Prashanthan Sanders
    Footnotes
    2 Dr. Sanders is supported by the National Heart Foundation of Australia.
    Affiliations
    Cardiovascular Research Centre, Department of Cardiology, Royal Adelaide Hospital, and the Disciplines of Medicine and Physiology, University of Adelaide, Adelaide, Australia.
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  • Patrick Disney
    Affiliations
    Cardiovascular Research Centre, Department of Cardiology, Royal Adelaide Hospital, and the Disciplines of Medicine and Physiology, University of Adelaide, Adelaide, Australia.
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  • Author Footnotes
    3 Dr. Brooks is supported by the Mary Overton Award from the Royal Adelaide Hospital, Adelaide, Australia.
    Anthony Brooks
    Footnotes
    3 Dr. Brooks is supported by the Mary Overton Award from the Royal Adelaide Hospital, Adelaide, Australia.
    Affiliations
    Cardiovascular Research Centre, Department of Cardiology, Royal Adelaide Hospital, and the Disciplines of Medicine and Physiology, University of Adelaide, Adelaide, Australia.
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  • Author Footnotes
    4 Dr. John is supported by the Biosense-Webster Electrophysiology Scholarship, University of Adelaide, Adelaide, Australia.
    Bobby John
    Footnotes
    4 Dr. John is supported by the Biosense-Webster Electrophysiology Scholarship, University of Adelaide, Adelaide, Australia.
    Affiliations
    Cardiovascular Research Centre, Department of Cardiology, Royal Adelaide Hospital, and the Disciplines of Medicine and Physiology, University of Adelaide, Adelaide, Australia.
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  • Author Footnotes
    5 Dr. Lau is supported by the Earl Bakken Electrophysiology Scholarship, University of Adelaide, Adelaide, Australia.
    Dennis H. Lau
    Footnotes
    5 Dr. Lau is supported by the Earl Bakken Electrophysiology Scholarship, University of Adelaide, Adelaide, Australia.
    Affiliations
    Cardiovascular Research Centre, Department of Cardiology, Royal Adelaide Hospital, and the Disciplines of Medicine and Physiology, University of Adelaide, Adelaide, Australia.
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  • Shashidhar
    Affiliations
    Cardiovascular Research Centre, Department of Cardiology, Royal Adelaide Hospital, and the Disciplines of Medicine and Physiology, University of Adelaide, Adelaide, Australia.
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  • Lauren Wilson
    Affiliations
    Cardiovascular Research Centre, Department of Cardiology, Royal Adelaide Hospital, and the Disciplines of Medicine and Physiology, University of Adelaide, Adelaide, Australia.
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  • Author Footnotes
    6 Dr. Mackenzie is supported by the Peter Doherty Fellowship, National Health and Medical Research Council of Australia.
    Lorraine Mackenzie
    Footnotes
    6 Dr. Mackenzie is supported by the Peter Doherty Fellowship, National Health and Medical Research Council of Australia.
    Affiliations
    Cardiovascular Research Centre, Department of Cardiology, Royal Adelaide Hospital, and the Disciplines of Medicine and Physiology, University of Adelaide, Adelaide, Australia.
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  • Glenn D. Young
    Correspondence
    Corresponding author: Tel: 61-8-8222-2723; fax: 61-8-8222-2722.
    Affiliations
    Cardiovascular Research Centre, Department of Cardiology, Royal Adelaide Hospital, and the Disciplines of Medicine and Physiology, University of Adelaide, Adelaide, Australia.
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  • Author Footnotes
    1 Dr. Stiles is supported by the National Heart Foundation of New Zealand and the Dawes Scholarship, Royal Adelaide Hospital, Adelaide, Australia.
    2 Dr. Sanders is supported by the National Heart Foundation of Australia.
    3 Dr. Brooks is supported by the Mary Overton Award from the Royal Adelaide Hospital, Adelaide, Australia.
    4 Dr. John is supported by the Biosense-Webster Electrophysiology Scholarship, University of Adelaide, Adelaide, Australia.
    5 Dr. Lau is supported by the Earl Bakken Electrophysiology Scholarship, University of Adelaide, Adelaide, Australia.
    6 Dr. Mackenzie is supported by the Peter Doherty Fellowship, National Health and Medical Research Council of Australia.
      Evidence from noninvasive studies suggests magnesium has a differential effect on atrioventricular nodal (AVN) pathways. To further explore the electrophysiologic effects of intravenous magnesium sulfate (MgSO4) on supraventricular tachycardia, with particular reference to AVN conduction pathways, we studied 23 patients with supraventricular tachycardia at the time of electrophysiologic study. Tachycardia cycle length; AH, HV, and VA intervals; anterograde and retrograde Wenckebach thresholds; slow and fast pathway effective refractory periods (ERPs); accessory pathway ERP; right atrial and ventricular ERPs; blood pressure; and serum magnesium were evaluated before and after administration of MgSO4 during sustained tachycardia. AVN reentry was induced in 14 patients and atrioventricular reentry was induced in 9; 1 of the latter had dual AVN physiology with tachycardia using the slow pathway. Serum magnesium level increased from 0.88 ± 0.11 to 1.79 ± 0.14 mmol/L (p <0.0001). Magnesium increased tachycardia cycle length to a greater extent in those with dual AVN physiology than those without: 340 ± 54 to 370 ± 57 ms versus 347 ± 29 to 350 ± 30 ms (p = 0.01). This was associated with greater increase in AH interval in those with dual AVN physiology than in those without: 241 ± 59 to 270 ± 60 ms versus 144 ± 16 to 140 ± 20 ms (p = 0.003). Presence of dual AVN physiology was more frequently associated with reversion to sinus rhythm: 5 of 15 versus 0 of 8 (p = 0.06). MgSO4 did not alter other measured parameters. In conclusion, magnesium increases tachycardia cycle length and AH interval in patients with dual AVN physiology through a dominant effect on the slow AVN pathway.
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