Pure Monophasic Action Potentials and Their Employment in Studies of Ventricular Surface Negativity

Abstract

Recent interpretations of monophasic action potentials led from an injured and uninjured spot on the ventricular surface hold (1) that the entire deflection is dominated by electrical potential alterations at the uninjured spot, 1 (2) that it is essentially influenced by potential variations at the injured spot, 2 or even more specifically, (3) that the initial rise may be governed by electrical variations at the injured region, whereas its rapid offset is determined by the discontinuance of negativity at the normal region. 3 Further experimentation makes it apparent that correct interpretations have been hampered by registration of impure monophasic waves, i. e., curves that exhibit oscillations or notches either before the rise or somewhere on the ascending limb, or which give evidence of auricular and other extraneous activity. Previous investigators have been obliged to apologize for inescapable extrinsic effects and to devise explanations to account for them. By recording from a discrete spot of injury, as produced by a new type of suction Ag-AgCl₂ electrode devised by the author, and another Ag-AgCl₂ wick electrode in apposition with the epicardial surface, it proved possible to record consistently monophasic curves that rise acutely from a straight base line and which exhibit no vibrations on the upstroke. An example is displayed in Fig. 1.

The first purpose of this preliminary communication is to present some evidence that such perfect curves are not influenced by potential changes of the injured area, whereas the so-called extrinsic effects, which appear in the form of notches on the ascending limbs of impure curves are mainly caused by such alterations.

If monophasic curves from an injured-uninjured region are recorded on paper travelling 100–150 mm./sec. in relation to the waves of a Lead II standard E.C.G., and immediately thereafter monophasic records are taken from the same injured spot and a leg, after the manner of Wilson et al.,∗ then the incidence of the rise of 2 such curves should coincide in all cases regardless of the location of the injured spot, as shown in diagram I of Fig. 2