The design of a real-time computer system for examining the electrical activity of the heart

Abstract

This report considers the design of a computer system for measuring cardiac electrical signals while simultaneously controlling heart rate and rhythm. The system is used for investigations ranging from ECG measurements from patients to the electrical study of isolated strands of animal hearts in a tissue bath. The system comprises five basic tasks: (1) synchronizing the system with events occurring in the heart (cueing); (2) recording heart signals in digital form and immediately displaying their wave forms; (3) controlling heart rate and rhythm by appropriately timed stimuli; (4) continuously displaying the status of the computer and the experiment; and (5) receiving, checking, and executing commands from the investigator. The system's hardware is controlled by a single dedicated laboratory computer and includes: (1) two A-D converters with independent channel sequencing and direct asynchronous memory access; (2) a high-speed graphic display for cardiac wave forms and a separate alphanumeric display for status information; and (3) multiple programmable real-time clocks. Essential software features include: (1) programs organized around multiple concurrent asynchronous processes; (2) disk I O overlapped with all A-D converter operations; and (3) protection against human errors by means of extensive checking of the investigator's commands. This system makes possible the examination of those cardiac phenomena which occur under such complicated circumstances or which produce such a large amount of information over a short period of time that their experimental investigation requires automatic devices, e.g., epicardial and body surface potential distributions measured during normal and abnormal sequences of cardiac excitation and repolarization.