A method for the on-line automatic beat-to-beat digital display of cardiac action potential duration.

Abstract

A system which permits the on-line automatic beat-to-beat measurement of action potential duration (a.p.d.) is described. A voltage comparator is set to sample a given voltage on phase 3 of an action potential. When phase 0 of the action potential passes through the preset voltage threshold, the comparator initiates a square wave which is terminated when an identical value is reached on phase 3. The duration of the square wave is equivalent to a.p.d. The comparator could be set to sample any value up to 99% of the full repolarisation voltage. Once the comparator level is set, it tracks identical voltage values on a beat basis, thus providing a continuous comparison of a.p.d. In order to provide a useful display of a.p.d., the square-wave output from the comparator was displayed in three ways: (i) the duration was displayed in milliseconds on the panel meter of a standard interval counter; (ii) by using light-emitting diodes which were included in the photographic field of a camera mounted on an oscilloscope, the derived digital values were automatically recorded on film; (iii) using a standard integrating circuit, a.p.d. could be displayed as a vertical analogue signal. The system is highly accurate, providing instantaneous values for a.p.d. which are reproducible to within less than ±0·5 ms (error of less than 0·5%).