Leads & Morphology
Leads
Leads are the term we use to describe the "electrical cameras" that are placed on the patient. As mentioned before, the heart is capable of generating electricity. This electricity can be seen and recorded on graph paper. We use a combination of electrodes, wires, and devices to "see" into the heart. But the actual lead is in reference to the location of the electrode.
EKG Device
The EKG device has a number of pieces. But the main piece that we want to focus on are the wires which are referred to as leads.
(1) The lead wires are often referred to this as the electrical camera, but its a combination of both the electrodes and the leads as well as the device that captures the image of the heart.
(2) The electrodes are the sticky patches that are attached to the patient. They act as little camera mounts that the camera sits on to take the picture.
Depending on where the electrodes are placed will determine the angle of the 'camera' perspective. Let's discuss this.
CAMERA/LEADS
The leads (electrodes) are like tiny cameras that are placed around the heart. Just like a literal camera that you place in a location and point the lens to capture the image, the electrodes work the same way. For example, if the electrodes are placed under the ventricles (bottom left of your chest) the electrode will be taking a picture of the bottom part of your heart.
If the electrodes are placed at the top of your chest, they will be taking a picture that reflects more of the characteristics of the top part of the heart.
Lead II
It is important to note that the electrical camera often uses two electrodes to create a line or angle to take its picture. This line can be drawn as an arrow pointing out how the camera sees the electrical current. For any lead that has a negative and positive pole, the positive pole is the one taking the picture.
In the case of Lead II, the patient has two electrodes placed on their body. One electrode is placed on their right arm, the other is placed on their left leg. The arrow pointing down on Figure 1, is showing the current or flow of the electricity through the heart. Remember that the electrical camera is similar to a regular camera, it takes a picture from the location of the lens.
Now that we understand that a lead/electrode is an electrical camera, let's discuss one of the best camera angles you can get on the heart. Lead II (2) is the best perspective for reading the electrical signal of the heart. Lead II displays an upright P wave, Upright QRS complex, and an upright T wave.
(See Figures Below)
Lead II Perspective
Lead II should display an upright P wave, Upright R wave, and Upright T wave. This is the best angle/perspective to view an ECG.
Morphology
Morphology is the study of forms of things. Basically it is the study of the structure. When we are referring to morphology in ECG, we are talking about the variations that occur within the shapes of the waves, in particular the shape of the QRS complex. Let's look at some shapes or complexes that we may encounter when we see a ECG scan.
QS Wave or S Wave
R Wave
QR Wave
RS Wave
The configurations listed above are some of the morphologies that you may see on an ECG scan. Note that the waves reflect the deflections you normally would see for a normal QRS complex minus any wave that isn't present. For example, to make a RS Wave, simply remove the Q wave from a QRS complex. The main thing to know is that the QRS configuration can come in different ways. Ultimately, they all represent the same electrical event in the heart, that is the depolarization of the ventricles.
Notes
- The leads/electrodes are tiny cameras that take pictures of the movement of the electricity through the heart.
- Lead II is the best perspective to view the heart. It displays an upright P wave, Upright QRS complex, and Upright T Wave.
- When we are referring to morphology in ECG, we are talking about the variations that occur within the shapes of the waves, in particular the shape of the QRS complex.
- There is a lot of variation within the QRS shapes.