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Related Experiment Videos

Norepinephrine release by ventricular stimulation: effect on fibrillation thresholds

D E Euler

    The American Journal of Physiology
    |March 1, 1980
    PubMed
    Summary
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    Stimulating the heart with a train of pulses, rather than a single pulse, significantly lowers ventricular fibrillation thresholds in dogs. This effect is amplified by beta-adrenergic blockade and cardiac denervation, suggesting local norepinephrine release influences fibrillation.

    Area of Science:

    • Cardiovascular Physiology
    • Electrophysiology
    • Anesthesiology

    Background:

    • Determining ventricular fibrillation thresholds is crucial for understanding cardiac arrhythmogenesis.
    • The method of electrical stimulation can influence fibrillation threshold measurements.
    • Autonomic nervous system activity, particularly norepinephrine release, may play a role in cardiac excitability.

    Purpose of the Study:

    • To compare ventricular fibrillation thresholds using single stimuli versus trains of stimuli in anesthetized dogs.
    • To investigate the influence of beta-adrenergic blockade and cardiac denervation on these thresholds.
    • To elucidate the role of locally released norepinephrine in modulating fibrillation thresholds.

    Main Methods:

    • Ventricular fibrillation thresholds were measured in pentobarbital-anesthetized dogs using either a single 10-ms stimulus or a train of 14 pulses (4 ms, 100 Hz).

    Related Experiment Videos

  • Studies were conducted before and after beta-adrenergic blockade with propranolol.
  • Fibrillation thresholds were also assessed in dogs with chronic cardiac denervation compared to sham-thoracotomized controls.

    • Main Results:

    • Train stimulation resulted in significantly lower fibrillation thresholds compared to single-pulse stimulation (P < 0.01).
    • Beta-adrenergic blockade and cardiac denervation significantly increased train stimulation thresholds.
    • Train thresholds in catecholamine-depleted hearts were comparable to those in beta-blocked innervated hearts, and trains augmented local myocardial contractility.

    Conclusions:

    • Locally released norepinephrine significantly influences the current required to induce ventricular fibrillation during threshold determination.
    • Train stimulation protocols may be more sensitive to the effects of endogenous catecholamines on cardiac excitability.
    • These findings have implications for understanding electrophysiological testing and the role of sympathetic activity in cardiac arrhythmias.