Little Secrets on the ECG Recording Paper

Time : 2023-05-29

The common ECG recording paper contains so much "unknown" information (take Nippon Kohden's 1250P model as an example) let's find out together.


1. Paper speed and sensitivity

Paper speed includes 10mm/s, 25mm/s and 50mm/s etc. Sensitivity includes 5mm/mv, 10mm/mv and 20mm/mv. Everyone must be familiar with the above content, so I won’t repeat it here.

2. Frequency response range

For some manufacturers of ECG machines, the frequency response range will be displayed on the ECG recording paper. As shown in the red line in Figure 1, 2, 3, and 4 in the small picture. The 1250P model of Nippon Kohden does not display the frequency response range on the ECG recording paper, but when the EMG filter is turned off, the upper limit of the set frequency response range (high frequency filter) value can be displayed on the ECG recording paper. The frequency filter value can be selected in the user setting-waveform setting-high frequency filter of the electrocardiograph: 75Hz, 100Hz, 150Hz.

In addition, some ECG workstations (such as MedEx, etc.) use high-pass filtering and or low-pass filtering to display the frequency response range on the ECG recording (paper) interface. The so-called high-pass means that electrical signals higher than the set frequency (such as 0.05Hz) can pass through the filter. The set frequency can be understood as the lower limit of the frequency response range. Low-pass means that electrical signals lower than the set frequency (such as 150Hz) can pass through the filter, and the set frequency can be understood as the upper limit of the frequency response range.

(1) What is frequency response?

The human body's ECG signal consists of a series of components of different frequencies. The frequency response of the electrocardiograph, referred to as frequency response, refers to the change of the amplitude of the output waveform of the electrocardiograph as the frequency of the (ECG) input signal changes, also known as the frequency response. For example, the current frequency of the atrial muscle is about 0.1-8Hz, so the P wave amplitude recorded by the electrocardiograph is low, while the current frequency of the ventricular muscle is about 8-30Hz, and the QRS amplitude recorded by the electrocardiograph is relatively high.

(2) Significance of different frequency response ranges

The electrocardiograph allows useful signals within the frequency response range to pass through the filter without attenuation, while effectively filtering out electrical signals at frequencies outside the frequency response range. Compared with the wide frequency response range of 0.05-150Hz, a narrower frequency response range such as 0.05-40Hz filters out the ECG signal in the frequency range of 40-150Hz, and the amplitude of the QRS complex is reduced on the ECG (with the real value compared to). Most of the information of the adult QRS wave is below 100Hz, a few are above 100Hz, and the frequency of the infant QRS wave group is as high as 250Hz. 250Hz.

Generally speaking, the wider the value of the frequency response range, the more it can truly reflect the characteristics of the individual's ECG. A narrower frequency response range will not only reduce the amplitude of the QRS wave, but also reduce the amplitude of the P wave, ORS wave, and T wave. Insufficient high-frequency response of older ECG machines or a narrow frequency range due to improper machine setup may result in small amplitude measurements for diagnostic triage. In adults, when the pathological q wave is small, the ECG information may be lost due to the insufficient upper limit of the frequency response, resulting in missed diagnosis. Of course, when the upper limit of the frequency response is high, the "interference wave" cannot be effectively filtered out, which is manifested as a rough baseline. When the frequency range is lower, the baseline is smoother.

Regardless of children or adults, the wider the frequency response range, the closer the QRS amplitude is to the real ECG characteristics of the individual; this change is more obvious in children, and the narrower frequency response range will cause a decrease in QRS amplitude.

3. Baseline drift suppression

Baseline drift is generally caused by human breathing or movement, electrode movement, etc., and is generally less than 1 Hz. In the 1250P model, the information of baseline drift suppression is represented by D, d or blank. D or d should be the first letter of "drift" in English. D represents strong baseline drift suppression, d represents weak baseline drift suppression, and blank represents baseline drift suppression is off. Its related parameters are set as: strong 0.1Hz (-34dB), weak 0.1Hz (-20dB); the decibel here is the unit of common mode rejection ratio, indicating the ability to suppress baseline drift.

Since the frequency of baseline drift is close to the frequency of ST segment ECG signals (maximum about 0.6-0.7 Hz), when there is no baseline drift, the baseline drift suppression should be set to OFF to avoid insufficient acquisition of ST segment ECG signals, causing The ST segment is severely distorted. In addition, in the Nippon Kohden 9020P model, the baseline drift suppression setting is strong, and when the heart rate is

When baseline drift occurs on the ECG, the key points of inspection are as follows: ① Are the electrodes and lead wires fully connected? ②Are the limb electrodes and chest electrodes loose? ③Are the electrodes and skin clean? ④Is the ointment applied properly? ⑤ Is it related to patient movement or breathing? When none of the above reasons exists, the baseline drift suppression function can be turned on.

4. AC, filter

Also known as power frequency filtering, it is expressed as AC50 or H50 in the ECG in Figure 1 (presumably H should mean hum), where 50 means 50Hz. In addition, there are two states of 60Hz and OFF. AC interference is shown in Figure 5 on the ECG: a signal of constant amplitude and constant period is repeated in the baseline. When it occurs, it should be clarified whether there are the following reasons:

① Poor grounding of the instrument; ② Poor grounding of the metal bed; ③ The patient is in contact with the metal parts of the surrounding wall or hospital bed; ④ Other personnel are in contact with the patient; ⑤ The electrodes or lead wires are not placed or connected; ⑦The patient or doctor touches the electrode during printing; ⑧Interference from nearby electrical appliances, lighting equipment, dark wires in the wall or the ground; ⑨Electrical interface poor grounding

5. Myoelectricity, filtering

Myoelectric interference is caused by the patient's tension, cold stimulation, etc., and its frequency is between 0.5-10KHz. The electromyographic interference pattern is shown in Figure 6: signals with irregular amplitude and period are repeated in the baseline. Myoelectric filtering includes three states: 25Hz, 35Hz and OFF. The "filter" key on the panel of the electrocardiograph represents EMG filtering. On the ECG recording paper, it is: 25Hz or 35Hz, Filter Off or MF:OFF, etc.

When myoelectric interference occurs, the following possibilities should be ruled out, and the myoelectric filter can be turned on if necessary: ① Is the room a bit cold; ② Is the patient tense or not relaxed, or shivering; ; ④ The electrode clips of the extremities are too tight, etc.

For the 1250P model, when the EMG filter is turned on, it can be shown in Figure 7. When the myoelectric filter is turned off, the high frequency filter value (75Hz, 100Hz and 150Hz three states) will be displayed on the original myoelectric filter display.

There is a lot of knowledge contained in a small ECG drawing! Through this article, I hope everyone has a deeper understanding of the information on the ECG recording paper. Of course, due to differences in machine manufacturers and models, the contents on the ECG drawings may be different from those described by Dou Dae. If necessary, you can refer to the relevant model manuals for further clarification.

In addition, it is worth noting that regardless of the model, it is recommended not to turn on the filter function (AC, EMG, baseline drift suppression) routinely, because it may cause distortion of the ECG waveform, such as reduced QRS wave amplitude and abnormal ST segment. etc., affecting the judgment of ECG.