Automatic recording of ventricular fibrillation

The authors describe a data acquisition system which has been developed to record ventricular fibrillation (VF) from a coronary care unit (CCU). Data acquisition is triggered by a simple VF detector. The trigger is activated when the root mean square signal in the 3-6 Hz band exceeds 75% of the total for more than 2 s. The hardware trigger was designed to trigger easily so as to miss as few VF events as possible. Computer software constantly updates a circular buffer containing 1 minute of data recorded at 250 Hz from all 10 CCU beds. When triggered, 4 minutes of post-trigger data are acquired and then both pre- and post-trigger data are written to a hard disk. In 13 months of operation, a total of 816 triggers were recorded. Most of these were VF-like events and artifacts. 47 were genuine VF events. The nursing staff reported a further 12 VF events, but documentary evidence was available for only 4