ECG TELEMETRY EXPERIMENTS FOR EARLY
CARDIAC EMERGENCY TREATMENT

Chr. Zywietz, Medical School Hannover/Germany
D. Assanelli, University Hospital Brescia/Italy
C. Malossi, Elettronica Trentina, Cavareno/Italy

Long term morbidity and mortality of infarcted patients may be reduced if early treatment of acute or hyper-acute infarction can be provided. Preparation of such treatment in an emergency department is supported if the 12 lead electrocardiogram of patients with an acute event/pain can be monitored during transportation to the hospital.

A pre-requisite for this monitoring is the possibility of real time digital transmission of the standard 12 lead ECG from the ambulance car during transportation via telephone line, satellite or radio frequency.

Within two European research and development projects - Standard Communications Protocol for Computerised Electrocardiography (SCP-ECG, AIM 1015) and Open European Data Interchange for Processing of Electrocardiograms (OEDIPE, AIM 2026) of the European Advanced Informatics in Medicine program a methodology for high compression of ECGs with defined (restricted) error tolerances has been developed. Typically a standard 12 lead ECG record for computerised evaluation consists of 10 sec of data resulting in 8 KB/sec of data. During the SCP ECG project transmission protocols and compression methods have been investigated extensively. As a result a compression a scheme was developed which requires the transmission of 4 to 7 KB of data per 10 s record. This allows the reconstruction of the original ECG with an RMS error of £ 10 µV RMS and a peak error of not larger than 100 µV.

The error restriction ensures that clinically important detail information (e.g. atrial fibrillation versus atrial flutter) is maintained. The practical applicability of the SCP-ECG protocol has been demonstrated within the OEDIPE project.

Compressed 12 lead ECGs can be transmitted in real time at transmission speeds of 9.6 Kbit/sec. After the SCP ECG project and during the OEDIPE project a computer electrocardiograph has been developed which is capable of direct interconnection (dialling + modem communication) via the telephone network to a host computer within the emergence department. There the transmitted ECG is reconstructed and can be monitored.

Various transmission experiments from a resting and moving ambulance car have been performed in Brescia and in Hannover to analyse the practicability of this approach. The experiments have shown that a transmission speed of 9600 bits/sec can not always be reached during the major business hours within the analogue telephone network. Establishment of connection and a transmission with reasonable low error frequency requires sometimes the reduction of the transmission speed to 2400 bit/sec. There is on the other hand no problem with transmission speed if ISDN connections can be used. In summary: a data compression method and a communications protocol for real time telephone transmission of standard electrocardiograms have been developed which allow a real time monitoring via telephone line if a transmission speed of at least 9600 bit/sec can be provided. A real-time telemonitoring of the full standard ECG provides the basis for improved cardiac emergency care with earliest treatment of acute infarctions.