Testing

Essential ECG Signal Requirements* - recommendations for the standardization and interpretation of the electrocardiogram (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

Essential ECG Testing – based on ISO 60601-2-25

Essential performance requirements are as follows:

1. Defibrillation Protection: -Within 5 s after exposure to the defibrillation voltage, the ECG shall resume normal operation in the previous operating mode, without loss of any operator settings or stored data, and shall continue to perform its intended function -Two defibrillation tests need to be done, Common mode and Differential mode

2. Essential Performance and Accuracy of ECG machine *only needed if automated measurements are provided by the machine

a) Requirements for amplitude measurements – refer to Table GG.1 on pg.63

• Exclude the two biggest differences in the amplitude measurements. The difference for each remaining amplitude measurement shall not deviate from the reference value by more than ±25 μV for reference values ≤500 μV, or by more than 5 % or ±40 μV (whichever is greater) for reference values >500 μV.

b) Requirements for absolute interval measurements – refer to Table GG.1 on pg 63

c) Requirements for biological interval measurements – refer to Table GG.2 on pg. 64

3. Filters (including line frequency interference filters) -Filters for line frequency interference suppression shall not introduce on the ECG report more than 50 μV peak-to-valley distortion of the signal in any lead when tested with the test ECG ANE20000 (on pg. 63 of Table GG.1).

4. Electrostatic Discharge -The machine shall resume normal operation in the previous operation mode without loss of operator settings or stored data within 10 s of a discharge (temporary degradation is allowable for up to 10 s).

5. Electrical fast transients and bursts -When exposed to electrical fast transients and bursts (via the power cord supply), the machine shall resume normal operation in the previous operation mode without loss of operator settings or stored data within 10 s. The machine shall comply with the requirements of amplitude measurements when the signal CAL20110 of Table GG.1 is applied.

6. Conducted Disturbances -When exposed to a conducted radio frequency voltage, via the power cord supply, the machine shall continue to perform its intended function. The machine shall comply with the requirements of amplitude measurements when the signal CAL20110 of Table GG.1 is applied. The difference for each amplitude measurement shall not deviate from the reference value by more than ± 50 μV for reference values ≤ 500 μV, or by more than 5% or ±100 μV (whichever is greater) for reference values > 500 μV.

7. Electrosurgery interference -When the machine is used together with high frequency surgical equipment, it shall return to previous operating mode within 10 s after exposure to the field produced by the high frequency surgical equipment, without loss of any stored data.