12 Lead EKG Interpretation Part #3

EKG LEADS PLACEMENT

BIPOLAR LEADS:

Bipolar leads are so named because they require a positive pole and a negative pole. Just like a a battery that have positive an begative poles. The positive electrode is the one that actually “sees” the current coming. The lead that sees the current makes the wave. The direction the current is coming from determines if the wave will face upwards of downwards. Sounds like Greek in England? I apologize but I will try to make it as simple as possible.
Lets review that small paragraph:

• That bipolar leads have positive and negative poles = CHECK
• The positive lead is the one that sees the current = CHECK
• The direction the current is coming from determines the direction of wave deflection = CHECK

So which are these bipolar leads that have positive and negative poles with the positive lead seeing the current? There are 3 bipolar leads in a 12 lead EKG: –

• Lead I. Measures the current traveling between the right and left arms. The right arm is negative pole and the left arm is positive pole. So, the lead on the left arm is the one that sees the current travelling from the right arm = CHECK
• Lead II. Measures the current traveling between the right arm and the left leg. The right arm is negative pole and the left leg is positive pole. So, the lead on the left leg sees the current coming from the right arm. = CHECK
• Lead III. Measures the current traveling between the left arm and the left leg. The left arm is the negative pole and the left leg is the positive pole. Likewise, the lead on theleft leg sees the current coming from the left larm. =CHECK

You’ll notice that in the bipolar leads the right arm is always negative and the left leg is always positive. Also note that the left arm can be positive or negative depending on which lead it is a part of. If you join leads I, II, and III at the middle, you get the triaxial diagram

AUGMENTED LEADS:

· aVR. Measures the current traveling toward the right arm. This is a positive electrode. The electrode is on the right arm.
· aVL. Measures the current traveling toward the left arm. This is a positive electrode. The electrode is on the left arm.
· aVF. Measures the current traveling toward the left foot (or leg). This is a positive electrode. The electrode is on the left leg.

These are called augmented leads because they generate such small waveforms on the EKG paper that the EKG machine must augment (increase) the size of the waveforms so they’ll show up on the EKG paper. These leads are also unipolar, meaning they require only one electrode to make the leads. In order for the EKG machine to augment the leads, it uses a midway point between the other two limbs as a negative reference point
Both the bipolar and augmented leads are also called frontal leads because they look at the heart from only the front of the body.

PRECORDIAL (CHEST) LEADS

These leads are located on the chest. They are also unipolar leads, and each one is a positive electrode. The precordial leads see a wraparound view of the heart from the horizontal plane. These leads are named V1, V2, V3, V4, V5, and V6.

 FACTS ABOUT EKG

· An impulse traveling toward (or parallel to) a positive electrode writes a positive complex on the EKG paper.
· An impulse traveling away from a positive electrode writes a negative complex.
· An impulse traveling perpendicularly to the positive electrode writes an isoelectric complex (one that is as much positive as it is negative).
· If there is no impulse at all, there will be no complex¾just a flat line.

NORMAL QRS DEFLECTIONS

How should the QRS complexes in the normal EKG look? Let’s look at the frontal leads:

• Lead I Should be positive.
• Lead II Should be positive.
• Lead III Should be small but mostly positive.
• aVR Should be negative.
• aVL Should be positive.
• aVF Should be positive.

Now that this might need a day or two to digest, I will stop at this point. Next, we will re-visit this same topic with descriptive diagrams to show you how the current travel and the expected EKG wave deflection.