Module title = Tutorial: ACS Plus

Lesson title = The J Point

The ST Segment occurs between the QRS complex and the T wave:


The electrical event that occurs during the ST segment is the flat portion of the action potential (phase 2):


During this time, the ventricular muscle is contracting (or fully contracted) and the voltages within the ventricles are relatively unchanged (which is why the normal ST segment is isoelectric and flat). This is the interval between ventricular depolarization and repolarization.

The junction between the QRS complex and the ST segment is called the J point:


The J point is important because it is the start of the ST segment. The J point must be assessed for:

• absolute position: it can be elevated or depressed
• shape: it can be notched or slurred

This image shows J point elevation in lead III:


This image shows J point depression in lead V3:


These above 2 examples came from the same ECG, but in 2 different leads. It is possible to have J point depression and elevation at the same time.

Sometimes the J point is easy to identify, as is seen in the above images. Sometimes, the J point is more diffuse and less obvious to identify, as in the following examples.

In the first example, the 2 arrows define a "range" of the J point. Even though it is diffuse, it should be clear that there is J point elevation in this first example.


This example (which is V6) shows a diffuse J point and J point depression. It also shows a wide QRS and an inverted T wave.


After identification of the J point, you should describe the J point as depressed or elevated. Usually the ST segment is dictated by the J point, so if you have J point elevation, you will also have ST segment elevation and conversely, J point depression will produce ST segment depression.


After determining if the J point is elevated or depressed, analyze the shape of the J point. Here is an example of J point notching indicated by the blue arrow in lead II:


In the same patient, same ECG, we also see notching in V5:


Because these notches occur at the J point, they are sometimes also called J waves.

J point slurring is when the terminal portion of the QRS complex has a "less steep" slope and becomes slightly "wider". Here is an example of slurring and notching. Note that V5 shows both slurring and notching while V6 shows slurring only.


There are important diagnoses that can cause J point slurring and notching and these diagnoses will be discussed in the upcoming lessons. Spoiler alert: they are early repolarization (which is common) and Brugada syndrome (which is not common).

Here is one more case of slurring and notching. The following 3 ECG's were all from the same patient, but in different leads:





Summary:

Analyze the J point for:

• absolute position: it can be elevated or depressed
• shape: it can be notched or slurred