Do you make the ECG standard? Take a look at these details.

Electrocardiography (ECG or EKG) may be the most widely used examination in clinic, and has been used as a routine examination in most hospitals. Whether it is done by doctors or nurses, misjudgments caused by inappropriate ECG operation still occur from time to time. Today we're going to have an electroencephalograph to look at the correct way of doing electrocardiogram and the impact of the errors. Ltd.

The position of electrocardiogram leads has been well known to us.

Limb lead: yellow left arm, red right arm, Green left leg, black right leg;

Anterior thoracic lead: V1 is located in the fourth intercostal space of the right sternal margin, V2 is located in the fourth intercostal space of the left sternal margin, V3 is located at the midpoint of the connection between V2 and V4, V4 is located in the fifth intercostal space of the left clavicular midline, V5 is located at the same level with V4, V6 is located at the same level with V4.

Others do not often lead: V3R, V4R, V5R, V7, V8, V9, etc. Electroencephalograph

In fact, in 2007 and 2009, ACC/AHA/HRS issued the guidelines for standardized ECG operation in batches [1-2]. Today, we will explore the details that need to be paid attention to in combination with these guidelines and what we have seen in clinical practice.

Some details that need attention

1. Too close limb lead

There is a popular saying that as long as the limb leads are far away from the shoulder and hip, the position of the limb leads has little effect on ECG. Connecting the limb leads closer to the heart (such as the position near the elbow and knee joint) can reduce the resistance of the limb and make the ECG clearer.

However, some studies have found that the distances of limb leads can change the limb conduction voltage and Q wave duration. For example, in the improved Cornell criteria for left ventricular hypertrophy (LVH), RavL > 1.2 mV is diagnosed as LVH, which is affected by the distal and distal limb leads. The position of limb leads is still controversial, so it is suggested that the lead should be placed on the wrist and ankle.

2. Improper position of thoracic lead

In fact, for chest leads, the most important thing is the reproducibility of ECG, which is why we use various body surface markers to describe the location of chest leads. Earlier studies have shown that only half of men's electrocardiograms can be repeated (two leads within 1 cm) and fewer women. Now some studies advocate that V5 should be placed between V4 and V6 instead of the axillary front line, which can increase repeatability, and this method can be used in patients with uncertain axillary front line. Ltd.

Owing to the busy clinical practice or careless rib counting, operators often mistakenly place V1 and V2 leads between the 2nd and 3rd ribs. Some studies have shown that for every increase of rib space in V1 and V2 leads, the corresponding R wave will decrease by 0.1 mV, which may lead to poor increase of R wave and even misjudged as anterior wall myocardial infarction. Moreover, high V1 and V2 may cause rSr'waveform and T wave inversion, which may be misjudged as right bundle branch block (RBBB) by inexperienced clinicians.

Similarly, too high V3, V4 or too low V5, V6 placement can also lead to low voltage, similar to the performance of anterior wall myocardial infarction. In patients with diaphragm depression and chronic obstructive pulmonary disease, the relative high levels of V3 and V4 also cause this phenomenon. At the same time, the influence of too low V5 and V6 placement on voltage may interfere with the judgment of left ventricular hypertrophy by RV5 + SV1 standard.

The electrocardiogram of long-term hospitalized patients may lead to large deviations due to different doctors on duty. Therefore, it is recommended that the lead position be marked on the skin.

In some obese or female patients, larger breasts make it difficult to connect chest leads. For such patients, chest leads should be connected to the breast instead of the breast, which can reduce the huge electrical impedance of adipose tissue in the breast on the one hand, and on the other hand, allow multiple measurements to be fixed. However, some studies have shown that electrodes placed on the top of the breast can increase the repeatability of multiple electrocardiograms.

3. Limb movement

EMG during exercise can affect ECG measurements. Limb movements include not only visible movements to the naked eye, but also invisible fibrillation. In order to minimize such effects, we require patients to relax at room temperature above 18 degrees Celsius. If the patient is an infant or has a large EMG interference, Mason-Likar method can be used: the upper limb lead is placed inside the deltoid muscle of the subclavian fossa, and the lower limb lead is placed at the midpoint of the iliac spine and rib margin in the axillary front.

Mason-Likar method has been widely used in clinic for a long time, such as 24-hour ambulatory electrocardiogram. A large number of experiments have proved that Mason-Likar method can obtain more accurate ECG. But like the problem of distant and near limb leads above, this method can affect the measurement of limb lead voltage, but if we use it to observe the dynamic changes of electrocardiogram, the effect is small and not easily disturbed.

4. The influence of surrounding wires

Various operating guidelines do mention the impact of other wires on the electrocardiograph, so is it reasonable to stay away from wires? In fact, the fear of wires is the signal line of the electrocardiograph. Ltd.

In English, the word "power line interference" is used to describe the effect of wires on signal lines. There are also examples of this in our lives, such as the interference of wires to cable TV signals. This effect is mainly due to the magnetic field generated by the changing current in the wire and the inductive current formed in the signal line. If the signal current in the signal line is relatively small, it will be greatly disturbed.