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Related Experiment Videos

Sympathetic modulation of the relation between ventricular repolarization and cycle length.

A Zaza1, G Malfatto, P J Schwartz

  • 1Centro di Fisiologia Clinica e Ipertensione, Università degli Studi di Milano, Italy.

Circulation Research
|May 1, 1991
PubMed
Summary

Sympathetic nerves asymmetrically control heart repolarization. Right stellectomy shortens action potential duration (APD) and speeds adaptation, while left stellectomy prolongs it, revealing complex sympathetic modulation of cardiac electrophysiology.

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Area of Science:

  • Cardiovascular Physiology
  • Autonomic Nervous System
  • Cardiac Electrophysiology

Background:

  • Sympathetic nervous system influence on ventricular repolarization is crucial for understanding cardiac arrhythmogenesis.
  • Previous research has not fully elucidated the specific mechanisms of sympathetic control over repolarization dynamics.

Purpose of the Study:

  • To investigate the role of sympathetic innervation in modulating ventricular repolarization, specifically action potential duration (APD) and QT interval.
  • To analyze the effects of unilateral and bilateral stellectomy, as well as beta-blockade, on the steady-state APD/cycle length (CL) relationship and adaptation kinetics.

Main Methods:

  • Conducted experiments on 24 anesthetized cats, measuring endocardial monophasic action potential duration (APD) and QT interval.

Related Experiment Videos

  • Performed right and left stellectomies, followed by bilateral stellectomy or beta-blockade (propranolol).
  • Assessed steady-state APD/CL and QT/CL relations and evaluated APD adaptation kinetics to sudden changes in pacing CL.

    • Main Results:

    • Right stellectomy reduced APDmax and CL50, accelerating APD adaptation (shortened tau slow), effects reversed by left stellectomy or beta-blockade.
    • Left stellectomy prolonged APDmax and CL50, slowing APD adaptation (prolonged tau slow).
    • Bilateral stellectomy further increased APDmax, CL50, and tau slow in both groups, indicating a dominant role of remaining sympathetic input.

    Conclusions:

    • Sympathetic innervation significantly modulates both the steady-state dependence of ventricular repolarization on heart rate and the kinetics of adaptation to rate changes.
    • The sympathetic control of ventricular repolarization exhibits significant asymmetry, with distinct effects from right versus left stellate ganglia.
    • Findings suggest that right stellectomy's effects are mediated by a reflex increase in left-sided sympathetic outflow, highlighting the complex interplay within the autonomic nervous system's control of cardiac function.