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European Heart Journal 1986 7(4):341-352;
Copyright © 1986 by the European Society of Cardiology.
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© 1986 The European Society of Cardiology

On the mechanisms by which hypoxia eliminates digitalis-induced tachyarrhythmias

M. DI GENNARO, M. VASSALLE*, G. IACONO, M. PAHOR, R. BERNABEI and P. U. CARBONIN

Istituto di Clinica Medica, Università Cattolica del S. Cuore, Policlinico ‘A. Gemelli’ Largo A. Gemelli8, 00168 Rome, Italy

Received 14 August 1985; revised 20 November 1985; .

Address for correspondence: Dr. P. U. Carbonin, Istituto di Clinica Medica, Universita Cattolica del S. Cuore, Policlinico ‘A. Gemelli’, Largo A. Gemelli 8,00168 Rome, Italy

Abstract

The mechanism by which hypoxia abolishes the tachyarrhythmias induced by cardiac steroids was studied in cardiac Purkinje and ventricular muscle fibres. In muscle fibres, hypoxia reduces excitability markedly, reduces the size and increases the time to peak of the oscillatory potentials (Vos) and of the after contractions induced by cardiac steroids, thereby abolishing the tachyarrhythmias. In Purkinje fibres, hypoxia also decreases Vos and excitability but abolishes the tachyarrhythmias only if repeated or prolonged. In Purkinje-muscle preparations, hypoxia blocks impulse conduction from the fast discharging Purkinje fibres to the myocardial fibres when the latter are still little intoxicated.

It is concluded that hypoxia affects promptly ventricular muscle fibres and (depending on the experimental conditions) Purkinje fibres also, and readily blocks impulse transmission to muscle fibres. Hypoxia abolishes arrhythmias by decreasing Vos size (probably through an impaired calcium uptake into the sarcoplasmic reticulum), by causing a conduction block at the Purkinje-muscle junction (probably through an increase in cytoplasmic calcium) and by reducing excitability.

Key Words: oscillatory potential • Purkinje-muscle junction • Purkinje fibres • ventricular muscle fibres • guinea-pig • dog


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