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Cardiac Electrical Alternans and Ventricular Fibrillation During Hypothermia in Non-Hibernating Versus Hibernating Animals: Role of Propagation Velocity and Dispersion of Repolarization

  • Alexey V. Glukhov
  • Yuriy V. Egorov
  • Igor R. Efimov
  • Leonid V. Rosenshtraukh
Chapter

Abstract

The heart of hibernating species is resistant to lethal ventricular fibrillation (VF) induced by hypothermia. Spatially discordant cardiac alternans (SDA) is a promising predictor of VF, yet its role in the mechanism of hypothermic arrhythmogenesis in both non-hibernating and hibernating mammals remains unclear. We optically mapped the posterior epicardial surface of Langendorff-perfused hearts of summer active (SA, n = 6), winter hibernating (WH, n = 7), ground squirrels (GS) Spermophilus undulatus, and rabbits (n = 5). Action potential duration (APD) and conduction velocity (CV) dynamic restitution as well as APD/CV alternans were measured at baseline (37°C) and during hypothermia (27–17°C). In rabbits, hypothermia significantly increased the magnitude of SDA which enhanced the ventricular repolarization gradient, caused conduction delays, conduction block, and the onset of VF (0% at 37°C vs. 60% at 17°C, p < 0.01). In contrast, no arrhythmia was observed in both SA and WH hearts at any temperature. No difference in APD dispersion was observed between animals. In rabbits, hypothermia caused a heterogeneous CV slowing which significantly exaggerated conduction anisotropy (from 2.0 ± 0.1 at 37°C to 2.8 ± 0.1 at 17°C, p < 0.01). A steeper slope in the CV restitution curve and bigger amplitude in CV alternans was observed in rabbit hearts compared with GS. The amplitude of SDA well correlated with the amplitude of CV alternans. In conclusion, the mechanism underlying SDA formation during hypothermia is shown to be associated with anisotropic CV alternans conditioned by an enhanced dispersion of repolarization. Increased conduction anisotropy formed functional barriers which facilitated development of SDA between cells with different ionic properties through the electrotonic uncoupling of neighboring regions of myocardium. The factors of hibernating species responsible for their resistance to SDA and VF can be accredited to their safe and dynamically stable conduction anisotropy along with a low dispersion of repolarization.

Keywords

Ventricular Fibrillation Ground Squirrel Action Potential Duration Rabbit Heart Diastolic Interval 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Abbreviations

VF

Ventricular fibrillation

GS

Ground squirrel

SA

Summer active

WH

Winter hibernating

SCA and SDA

Spatially concordant and discordant alternans

APD

Action potential duration

CV

Conduction velocity

DI

Diastolic interval

SR

Sarcoplasmic reticulum

Notes

Acknowledgments

This work was supported by the Stanley and Lucy Lopata Endowment (for IRE), Russian Foundation for Basic Research Grant 05-04-48311, and Russian President Foundation for Scientific School Grant SS-6211.2006.7 (for LVR).

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Copyright information

© Springer-Verlag Berlin Heidelberg 2012

Authors and Affiliations

  • Alexey V. Glukhov
    • 1
    • 2
  • Yuriy V. Egorov
    • 1
  • Igor R. Efimov
    • 2
  • Leonid V. Rosenshtraukh
    • 1
  1. 1.Laboratory of Heart ElectrophysiologyCardiology Research CenterMoscowRussia
  2. 2.Department of Biomedical EngineeringWashington UniversitySt. LouisUSA

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