The little secret on ECG recording paper

I read an article about the electrocardiograph a few days ago, which made me interested in the electrocardiogram recording paper, which is the “accessory equipment” of the electrocardiograph. Unexpectedly, there is so much information on the ECG recording paper (take Nippon Kohden’s 1250P model as an example).

 

1.) Paper speed and sensitivity

 

Paper speeds include 10mm/s, 25mm/s and 50mm/s. Sensitivity includes 5mm/mv, 10mm/mv and 20mm/mv. Everyone is familiar with the above content, so I won’t go into details here.

 

2.) Frequency Response Range

 

For some manufacturers’ ECG machines, the frequency response range will be displayed on the ECG recording paper. As shown in the red lines in small figures 1, 2, 3, and 4 in Figure 1. The 1250P model of Nippon Electric does not display the frequency response range on the ECG recording paper, but when the EMG filter is turned off, the upper limit (high frequency filter) value of the set frequency response range can be displayed on the ECG recording paper (specifically See Figure 8), the high-frequency filter value can be selected in the ECG machine’s user settings – waveform settings – high frequency filter: 75Hz, 100Hz, 150Hz.

 

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

 

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

 

(2) The meaning 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 with 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 is shown as a decrease in the amplitude of the QRS complex on the ECG because the ECG signal in the frequency range of 40-150Hz is filtered out (compared with the actual value). compared to). Most of the adult QRS complex information is below 100Hz, a few are above 100Hz, and the infant QRS complex frequency is as high as 250Hz. Therefore, the current domestic and foreign guidelines or consensus stipulate that the upper limit of the frequency response range of the electrocardiograph is 150Hz for adults and 150Hz for infants. 250Hz.

 

Generally speaking, the wider the value of the frequency response range, the more truly reflect the ECG characteristics of the individual. 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. Older ECG machines have a narrow frequency response range due to insufficient high frequency response or improper machine settings, which may result in smaller amplitude measurements for diagnostic classification. 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, thereby causing missed diagnosis. Of course, when the upper limit of the frequency response is high, the “interference wave” cannot be effectively filtered out, and the baseline is rough. When the frequency response range is low, the baseline is smoother.

 

Regardless of whether 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 a narrower frequency response range will cause the QRS amplitude to decrease.

 

3.) Baseline drift suppression

 

Baseline drift is generally caused by human respiration or movement, electrode movement, etc., which is generally less than 1 Hz. In the 1250P model, information on baseline drift suppression is indicated by D, d, or blank. D or d should be the first letter of the English “drift”. D represents strong baseline drift suppression, d represents weak baseline drift suppression, and blank represents baseline drift suppression is turned off (OFF). The relevant parameters are set as: strong 0.1Hz (-34dB), weak 0.1Hz (-20dB); the dB (decibel) here is the unit of the common mode rejection ratio, indicating the ability to suppress the baseline drift.

 

Since the frequency of baseline drift is close to the frequency of ST segment ECG signal (maximum about 0.6-0.7Hz), when there is no baseline drift, the baseline drift suppression should be set to OFF state to avoid insufficient acquisition of ST segment ECG signal, causing The ST segment is severely distorted. In addition, in the Nihon Kohden 9020P model, the baseline drift suppression is set to strong, and when the heart rate is less than 50 beats/min, the ST segment will deform as the heart rate slows down. Therefore, it is recommended to set the baseline drift suppression for bradycardia. Weak or OFF state.

 

When there is a baseline drift on the ECG, check the following points: ① Are the electrodes and lead wires fully connected? ②Are the limb electrodes and chest electrodes loose? ③ Are 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 exist, the baseline drift suppression function can be turned on.

 

4.) Alternating current (AC) filtering

 

Also known as power frequency filtering, it is represented 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: 60Hz and OFF. Alternating current disturbances appear on the ECG: a constant amplitude, constant period signal repeats in the baseline. When it occurs, it should be clear whether there are any of the following reasons:

 

① The instrument is poorly grounded; ② The metal bed is poorly grounded; ③ The patient touches the surrounding walls or metal parts of the hospital bed; ④ Other personnel touch the patient; ⑤ The electrodes or lead wires are not placed or connected well; Contamination or corrosion; ⑦The patient or physician touches the electrodes during printing; ⑧Dark wire interference from nearby electrical appliances, lighting equipment, walls or ground; ⑨The electrical interface is poorly grounded

 

5.) Electromyography (EMG) filtering

 

The EMG interference is caused by the patient’s nervousness and cold stimulation, and its frequency is between 0.5-10KHz. The EMG interference graph is shown in Figure 6: the signal with irregular amplitude and cycle repeats in the baseline. The EMG filter includes three states: 25Hz, 35Hz and OFF. The “Filter” key on the ECG panel represents the EMG filter. On the ECG recording paper, it is: 25Hz or 35Hz, Filter Off or MF:OFF, etc.

 

When EMG interference occurs, the following possibilities should be excluded, and EMG filter can be turned on if necessary: ​​①Whether the room is a little cold; ②Whether the patient is tense or unrelaxed, or has chills; ③Whether the hospital bed is too narrow or too short to relax the limbs; ④ Too tight electrode clamps on the limbs, etc.

 

For the 1250P model, when the EMG filter is turned off, the high frequency filter value (75Hz, 100Hz and 150Hz three states) will be displayed on the original EMG filter display.

 

There is a lot of knowledge on the small ECG chart! Through this article, I hope you have a better understanding of the information on the ECG recording paper. Of course, due to the different manufacturers and models of the machine, the content on the ECG drawing may be different from the description. If necessary, you can refer to the manual of the relevant model for further clarification.

 

In addition, it is worth noting that no matter what kind of model, the filter function (AC, EMG, baseline drift suppression) is not recommended to be turned on routinely, because it may cause ECG waveform distortion, such as QRS wave amplitude reduction, ST segment abnormality etc., affect the judgment of the electrocardiogram. If you are looking for ECG Medical Paper supplier, Suzhou Guanhua is your best choice.