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Intrathoracic Impedance Preceding Ventricular Tachyarrhythmia Episodes

Authors

  • HANS J. MOORE M.D.,

    1. Washington Veterans Affairs Medical Center, Washington, DC
    2. Georgetown University School of Medicine, Washington, DC
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  • MATTHEW N. PETERS B.S.,

    1. Washington Veterans Affairs Medical Center, Washington, DC
    2. University of Maryland School of Medicine, Baltimore, MD
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  • MICHAEL R. FRANZ M.D., Ph.D.,

    1. Washington Veterans Affairs Medical Center, Washington, DC
    2. Georgetown University School of Medicine, Washington, DC
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  • PAMELA E. KARASIK M.D.,

    1. Washington Veterans Affairs Medical Center, Washington, DC
    2. Georgetown University School of Medicine, Washington, DC
    3. George Washington University School of Medicine, Washington, DC
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  • STEVEN N. SINGH M.D.,

    1. Washington Veterans Affairs Medical Center, Washington, DC
    2. Georgetown University School of Medicine, Washington, DC
    3. Howard University School of Medicine, Washington, DC
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  • ROSS D. FLETCHER M.D.

    1. Washington Veterans Affairs Medical Center, Washington, DC
    2. Georgetown University School of Medicine, Washington, DC
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  • Funding sources: None.

  • Financial disclosures: Dr. Moore owns stock and has received compensation for talks from Medtronic. Dr. Karasik owns Medtronic stock. Mr. Peters, Dr. Franz, Dr. Singh, and Dr. Fletcher have nothing to disclose.

Address for reprints: Hans J. Moore, M.D., Cardiology, 4A107, Veterans Affairs Medical Center, 50 Irving St, NW, Washington, DC 20422. Fax: 202-745-8172; e-mail: Hans.Moore@VA.Gov

Abstract

Background: Heart failure is associated with ventricular tachyarrhythmias (VT/VF). Fluid accumulation during worsened heart failure may trigger VT/VF. Increased intrathoracic impedance has been correlated with fluid accumulation during heart failure. Implanted defibrillators capable of daily measures of intrathoracic impedance allow correlation of impedance with occurrence of VT/VF. We hypothesized that VT/VF episodes are preceded by decreases in intrathoracic impedance. The goal was to identify the relationship of intrathoracic impedance measured by implanted cardioverter defibrillators to the occurrence of VT/VF.

Method: Implanted defibrillator follow-up data were obtained retrospectively. Those with Medtronic OptiVol (Medtronic Inc., Minneapolis, MN, USA), storing averaged daily and reference impedance values, were reviewed for VT/VF episodes. Impedance changes in the week leading up to VT/VF were analyzed.

Results: A total of 317 VT/VF episodes in a cohort of 121 patients’ follow-up data were evaluated. Averaged daily intrathoracic impedance declined preceding 64% of VT/VF episodes, with an average decline of 0.46 ± 0.35 Ohms from the day before the VT/VF episodes. However, the mean values of the averaged daily and reference impedance did not change significantly. A novel measure, ΔTI, the sum of the daily differences between the averaged daily and reference impedance, was negative preceding 66% of VT/VF episodes (P < 0.001). The mean ΔTI was −4.0 ± 1.3 Ohms, which was significantly lower than the theoretically expected value of zero Ohms (P < 0.01).

Conclusion: (1) Averaged daily impedance declined preceding 64% of VT/VF episodes, but the overall decline was of small magnitude; (2) a novel measure, ΔTI, was negative preceding 66% of VT/VF episodes, and significantly below zero. (PACE 2010; 33:960–966)

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