Signal quality in a three-channel ambulatory electrocardiographic monitoring system

Ambulatory electrocardiographic recordings are not infrequently hampered by technical artefacts. Verification of good original signal level and an adequate number of ECG channels should enhance the quality.

Data from all three-channel (mV5, mV1, III) recordings in Peijas hospital during one-calendar year were prospectively collected. A total of 255 recordings (24 h n = 239, and 48 h n = 16) made for 247 patients were analysed. Relative signal strength number (integer scale 5-0) was registered during hook-up. Final quality of recordings were afterwards evaluated with a three-point semi-quantitative scale by an experienced physician.

The signal strength number was adequate (>or=3) in all 241 available cases. Distribution of signal strength did not significantly vary between ECG channels. The overall quality of recordings was 'good' in three-fourth of the cases and only were they seldom 'poor'. Signal strength and quality ratings were not significantly interrelated. The quality was, as expected, better in 24 h recording than in 48 recordings, and it was also better in channel III than in channel mV5.

The original signal strength level (impedance) is not a crucial fact in ambulatory electrocardiographic recordings as long as it is within (specified) acceptable limits. In terms of quality, a third (inferior) ECG channel is recommendable.