Overturn the tradition, look at the electrocardiogram cleverly: V1, V2, V3 leads are not just the chest leads

Time : 2023-05-30

If the V1, V2 and V3 leads are the frontal leads, most readers who have studied ECG should agree; Some readers will raise objections, after all, there is no such point of view in any ECG book.

Chest and frontal leads of ECG

The electrocardiogram commonly used clinically includes 12 conventional leads, which can be divided into two types according to the difference of the ECG vector, namely the horizontal lead and the frontal lead. Horizontal leads, also known as precordial leads, include leads V1, V2, V3, V4, V5, and V6; frontal leads, also known as limb leads, include leads I, II, III, aVL, aVR, and aVF. The two types of leads are clearly assigned and seem to have a clear boundary.


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Figure 1 Schematic diagram of commonly used ECG leads


Generally, the ECG is also printed according to the above two classifications, that is, the two columns on the left are the frontal leads, and the two columns on the right are the horizontal leads. Due to the simplicity of the application and the fixed mindset, it is also easy for us to look at the ECG according to the above classification. For example, when looking at the electrical axis, look for the limb leads, but when locating myocardial infarction, look directly for the chest leads. However, the joy of the EKG is that there is always new information to mine.

Can V1, V2 and V3 also be frontal leads?

According to textbooks, leads V1, V2, and V3 are precordial leads, and are often used as leads to judge anterior wall myocardial infarction. Why can they also be regarded as frontal leads? At this point, we should review the basic principles of the electrocardiogram again. The chest lead is a unipolar lead, and the other end is a zero potential point, that is, the limb lead and the chest lead formed when the electrode wires of the left upper limb, right upper limb and left lower limb are connected in one place. A common reference potential point, this potential reference point is called the Wilson central terminal.

And let's look at the specific positions of V1, V2, and V3 leads (as shown in the figure below), the chest leads are not completely "horizontal", so from a vector perspective, V1, V2, and V3 leads Also has a vector in the frontal direction.

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Figure 2 The location of the chest leads


Among the frontal leads, the pressurized limb leads (aVL, aVF, and aVR) are also unipolar leads, and like V1, V2, and V3, the other end is also the Wilson central terminal. Therefore, from the direction of the vector, lead V1 is similar to lead aVR, lead V2 is similar to lead aVL, and lead V3 is similar to lead aVF.


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Figure 3 How to understand that leads V1, V2, and V3 can be used as frontal plane leads


Understood in this way, it is not surprising that leads V1, V2, and V3 are considered as frontal plane leads.

How to use the V1, V2 and V3 leads of the "frontal plane" skillfully

The main function of the electrocardiogram is diagnosis. Having said so much, how to apply it is the most important. Let's look at a few practical cases.

1Look at V1 for ST-segment elevation in lead aVR

The previous view was that the aVR lead is a "solitary" lead, in the no-man's-land of the cardiac electrical axis. After reading this article, we can find that the aVR lead is not alone, because the V1 lead is similar to the aVR lead in the vector direction.

ST-segment elevation in lead aVR on the electrocardiogram is considered to be an extremely dangerous manifestation, which often indicates serious lesions in the left main or proximal anterior descending artery, and is a high-risk electrocardiographic manifestation of sudden cardiac death. However, ST-segment elevation in lead aVR alone is easily overlooked or disputed because it has no adjacent leads. Therefore, when the ST segment is elevated in lead aVR, if there is also ST segment elevation in lead V1, then, in all likelihood, it is acute myocardial infarction.


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Figure 4 Simultaneous ST-segment elevation in leads aVR and V1 indicates severe coronary artery disease


2. Left anterior branch conduction block, see V2

First look at an electrocardiogram:


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Figure 5


This ECG is a typical left anterior fascicular block with left axis deviation and a qR shape in lead aVL. It can be found that in addition to the aVL lead, the V2 lead also has a qR shape, but the adjacent V1 and V3 leads have no q wave performance, and the patient has no history of anterior wall or anteroseptal myocardial infarction, and echocardiography is also There were no signs of wall motion abnormalities. The qR-shaped appearance in lead V2 is associated with a left anterior fascicular block, and its morphology is similar to that in lead aVL.


3. Inferior wall acute myocardial infarction see V3

Here's another ECG:


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Figure 6


On this ECG, the ST-segment elevation of the inferior leads (II, III, and aVF) should be the first thing that catches the eye. There should be no problem in diagnosing acute inferior myocardial infarction. In addition, looking closely at the precordial leads, ST-segment elevation also appeared in lead V3. Does the patient have anterior wall myocardial infarction in addition to the inferior wall?

Attentive readers may have discovered that, except for V3, the other leads in the chest lead do not have ST-segment elevation, but ST-segment depression, which obviously does not meet the requirements of two or more adjacent leads. the rules. However, it is not difficult to understand after reading the above. The vector direction of lead V3 is close to that of lead aVF, so ST-segment elevation may also occur in inferior wall myocardial infarction. The next time you encounter a patient with inferior wall myocardial infarction, in addition to the inferior wall leads, don't forget to look at the V3 lead.

There are many similar ECG manifestations... From the next ECG, in addition to looking at V1, V2 and V3 of the frontal leads, try to look at V1, V2 and V3 from the perspective of the frontal leads, maybe there will be different harvest.