Copyright © 1991 by the European Society of Cardiology.
© 1991 The European Society of Cardiology
Alternans of epicardial repolarization as a localized phenomenon in man
Department of Physiology, University College & Middlesex School of Medicine London
*Departments of Cardiology, The Middlesex Hospital London
Department of Physiology, Charing Cross & Westminster School of Medicine London, U. K.
Departments of Anaesthesia, The Middlesex Hospital London
Departments of Cardiothoracic Surgery The Middlesex Hospital London
Received 2 January 1990; revised 30 March 1990; .
Address for correspondence: Dr P. M. I. Sutton, Department of Physiology, University College & Middlesex School of Medicine, Gower Street, London WCIE 6BT, U. K.
Abstract
Electrophysiological alternans (beat-to-beat alternation of the configuration of the action potential and/or electrocardiogram) may be important in the causation of ventricular arrhythmias.
We recorded monophasic action potentials from the left ventricular epicardium in patients undergoing routine cardiac surgery. We set out to determine: (a) whether a small increase in atrial pacing rate could elicit electrophysiological alternans; (b) whether different phases of the operation influence the incidence and; (c) whether electrical alternans was a localized phenomenon.
Thirty-six patients were studied, and alternans of action potential duration was observed in 14 (39%). The difference between alternate long and short action potential durations ranged from 4 to 112 ms. The mean differences during each stage of the protocol were: pacing before bypass 33.3 ± 22.7 ms (three of 17 patients); pacing after bypass 46.7 ± 37.8 ms (nine of 36 patients); pacing during transient graft occlusion 28.0 ± 23.1 ms (five of 17 patients); pacing following release of the grafts 29.6 ± 30.0 ms (five of 17 patients). None of the patients showed any evidence of alternans in the electrocardiogram or mechanical alternans in radial artery pressure. In seven of the 14 patients showing alternans, recordings were made in closely adjacent (approximately 1 cm) areas showing that alternans could be a localized phenomenon.
The findings indicate that electrical alternans was a frequent occurrence in this study (39% of patients) and may be a localized phenomenon.
Key Words: electrophysiology • monophasic action potential • electrical alternans • cardiac arrhythmias • cardiac surgery
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