Testing

Essential ECG Signal Requirements* - recommendations for the standardization of ECG (Circulation)

1. Low frequency filtering -a cut-off of 0.5 Hz was widely used in traditional analog filtering, which reduced baseline drift due to the generally lower frequency of respiratory movement. However, this can lead to marked phase distortions in areas where frequency content and wave amplitude changes abruptly, particularly at the ST segment (after the QRS complex), leading to possible artefactual ST-segment deviation. Lowing the frequency cutoff to as low as 0.05 Hz as per the 1975 guidelines (and has since remained the current recommendation) will sequester the distortions of the repolarization waves but at the same time increase the level of baseline drift. -digital filtering allows for methods of increasing the low frequency cutoff (to avoid respiratory noise interference) without the introduction of phase distortion, such as using a flat step response filter that results in zero phase shift. The low frequency cutoff for linear digital filters with zero phase distortion is relaxed to 0.67 Hz (or below).

2. High frequency filtering -High frequency is needed to accurately define the most rapidly changing parts of the ECG signal, namely the QRS complex, where detecting R amplitude and Q waves is essential diagnostic information. -Data being sampled at 500 per second with a high frequency digital filter cutoff of 150 Hz is required to reduce amplitude error measurements ~ 1% in adults. Greater bandwidth of up to 250 Hz may be required for infants. Suboptimal frequencies such as 40 Hz that are used to reduce noise can potentially miss critical diagnostic information

Steps to ensuring safety of ECGs – based on Design and development of a validation framework for ECG device stabilisation

1. Insulate users from voltage fluctuations or electrical shocks
2. ECG must detect signals of the heart only, and reject signals from other sources
3. Defibrillation/voltage surge protection
4. Preservation of ECG signal without interference from noise
5. Protection against environmental emissions
6. Able to detect all (7) types of arrhythmias
7. Able to detect pacemaker pulses (by oversampling)
8. Able to reject tall T wave signals beyond a limit to prevent heart beat duplication