Microprocessor application for numerical ECG encoding and transmission

Over the past few years a number of hospitals have established computer facilities for routine ECG interpretation. The combined workload of several hospitals could be processed by a "regional ECG interpretation center," if ECG data could be conveniently and efficiently transmitted to this center. ECG transmission over the public telephone network is common practice today, using FM techniques. However, because of the limited bandwidth of the telephone network and of occasionally severe noise, the signal quality achieved is only marginally adequate for computer interpretation. Transmission of binary-coded ECG's could overcome this problem but the data rates required greatly exceed the available channel capacity of telephone lines. Digital transmission may still be possible if ECG are preprocessed in order to eliminate redundant information and thereby lower the data rate. In this paper the operational characteristics of digital ECG communication are discussed in the context of computer-aided interpretation. Encoding methods proposed by other authors are briefly reviewed, and finally, a prototype system based on an 8-bit microprocessor is described. This system provides real-time transmission of 3 encoded ECG leads, sampled at a rate of 300 per second per lead and digitized with a resolution of 8 bits, using a 2400-Bd synchronous MODEM on standard (unconditioned) telephone lines. Some preliminary results are shown.