The Current of Injury in Acute Myocardial Ischaemia
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The use of the term ‘current of injury’ may give rise to some misunder-standing. In classical studies on cardiac electrophysiology, part of the heart was deliberately injured by, e.g. locally applying heat, mechanical injury or chemical irritants, and recordings were made between an electrode placed on the injured part and one on the intact cardiac surface (Burdon-Sanderson and Page, 1879). Because of the potential difference between the injured part (equivalent to the intracellular compartment) and the intact surface (the extracellular space), a ‘current of injury’ would flow through a resistor connecting both parts. The effect on the recorded action potential was described by Burdon-Sanderson and Page as follows: ‘… if either of the leading-off contacts is injured … the initial phase is followed by an electrical condition in which the injured surface is more positive, or less negative relatively to the uninjured surface consequently the equilibrium which normally exists between all parts of the surface during the “isoelectric interval” is destroyed.’ In other words, instead of an extracellular electrogram, characterized by a QRS complex, an isoelectric ST segment and a T wave, one would record a ‘monophasic’ potential resembling a transmembrane action potential as recorded with a microelectrode. In the early part of this century, recordings of such ‘injury potentials’ or ‘monophasic potentials’ yielded a great many data on cardiac electrophysiology (see, for example, Schutz, 1931).
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