Direct measurements of membrane time constant during defibrillation strength shocks

Vinod Sharma*, Fujian Qu, Vladimir P. Nikolski, Paul DeGroot, Igor R. Efimov

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


Background: Defibrillation shocks impose significant energy demand on implantable cardioverter-defibrillators (ICDs). Several modeling studies have been devoted to optimizing shock parameters, and a large number of these studies treat the heart as a simplified lumped network. The time constant of membrane polarization (τm) is a key variable for such modeling efforts. Objective: The purpose of this study was to perform direct measurements of transmembrane potential (Vm) during defibrillation strength shocks and estimate τm of membrane polarization. Methods: A portion of the left ventricular epicardial surface of Langendorff-perfused rabbit hearts was stimulated using uniform electric fields produced by two parallel line electrodes. The Vms were recorded from di-4-ANEPPS-stained hearts using a multisite optical mapping system. The hearts were paced with 20 S1 pulses from the apex, and shocks (S2: 5, 10, 20 V/cm) were applied via the line electrodes during the action potential of the 20th S1 at two different coupling intervals (S1S2: 120 and 180 ms). Residual responses were obtained by subtracting responses to the 19th S1 from the responses to the 20th S1S2 pair and used for time-constant analysis by fitting a monoexponential function. Results: τm exhibited a large variation and ranged from ∼1 to 30 ms. Furthermore, τm varied with electric field strength, S1S2 interval, position of the tissue from stimulating electrodes, and polarity of the response. To a large extent, the effects of all these factors were captured in a single parameter-the change in transmembrane voltage (ΔVm) in response to the applied field (E). τm showed a monotonically decreasing trend with ΔVm for all Es and S1S2s. Conclusion: Time constant of membrane polarization varies significantly during defibrillation strength shocks and shows a strong dependence on ΔVm.

Original languageEnglish (US)
Pages (from-to)478-486
Number of pages9
JournalHeart rhythm
Issue number4
StatePublished - Apr 2007


  • Membrane polarization
  • Optical mapping
  • Shock response
  • Voltage-sensitive dye

ASJC Scopus subject areas

  • Cardiology and Cardiovascular Medicine
  • Physiology (medical)


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