Signal quality in a three-channel ambulatory electrocardiographic monitoring system.
BACKGROUND: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.