Design of a measurement system for electrophysiological cardiac surgery

The treatment of cardiac arrhythmias by surgical removal of abnormal electrical pathways across the atrio-ventricular ring or re-entrant circuits within the myocardium is dependent on the ability to accurately locate the abnormality by measuring and displaying the activation front of muscle depolarisation as it spreads across the surface of the heart. The localisation of the aberration requires induction of the arrhythmia, simultaneous measurement of activity from many (100-200) sites over the surface of the heart, attachment of fiducial markers to this data, and display of the activation sequence in the form of an isochronous map. An instrument has been built at Green Lane Hospital to provide the necessary measurement, control, and analysis facilities required by this procedure. The purpose built measurement system is a multiprocessor unit which incorporates up to 512 programmable intracardiac amplifiers, two multifunction cardiac pacing stimulators, a versatile real time data display, a patient safety isolation system, and digital storage for eight seconds of electrocardiographic data. Signals are acquired from a mesh of bipolar electrodes attached to either a 'sock' or a 'band' which is placed on the heart during open heart surgery. The analysis of data is carried out on a personal computer, connected to the measurement system via a serial command link and a high speed parallel data link. Corrective surgery is now being carried out on a routine basis for some types of arrhythmias.