An automatic cardiac action potential duration meter

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Abstract
The duration of a cardiac action potential (AP) is measured from the beginning of its upstroke to the end of its asymptotic repolarization phase: the end being given by a point in proportion to the AP amplitude. If the resting potential, AP amplitude and duration are altered simultaneously, frequent accurate measurements can be extremely tedious. A fully automatic AP duration meter was constructed to measure within about 2% on a beat-to-beat basis. It is suitable either for brief sampling of AP durations when recording with microelec-rodes, which may impale cells intermittently, or for continuous monitoring, as with suction electrodes on intact beating hearts in situ. The device can track changes in duration during periods of regional myocardial ischemia in intact [animal and human] ventricles in situ while the AP alters its base line, upstroke velocity, amplitude and duration.