Action Potential Graph

Lead 1

Left to Right

Lead 2

Downwards to the right

Lead 3

Downward to the left

Lead aVF

Top to bottom

Lead aVR

Towards the right arm

Lead aVL

Towards the left arm

Einthoven's Triangle

The sum of all the leads will be zero

Precordial Leads

V1, V2, V3, V4, V5, and V6

Placed from near the sternum, around the heart, to under the left armpit.

Leads and "Planes"

The limb leads cannot measure front and back (they only measure coronal plane)

The precordial leads cannot measure head to toe (they only measure transverse plane)

P-wave

Marks atrial depolarization.

QRS Complex

Marks ventricular depolarization

T-wave

Marks ventricular repolarization.

PR Interval

Marks atrial depolarization and transmission through the AV node

QT Interval

Starts at the beginning of ventricular depolarization, includes ventricular contraction (mechanical not electrical), and to the end of ventricular repolarization.

The 5-step approach to analyzing ECGs.

1. Rate

2. Rhythym

3. P-waves

4. PR interval

5. QRS

Rate on ECG

Calculated by dividing 300 by the number of big squares between beats.

Normal is 60-100, bradycardia is <60, and tachycardia is >100.

Rhythm on ECGs

There are four types of rhythm:

1. Regular

2. Irregular with a pattern

3. Irregular with no pattern

4. Regular with miss or extra

P-Waves on ECGs

Ask yourself...

1. Are P-waves present?

2. Are they the same shape and size?

3. Are there more or fewer P-waves than QRS complexes?

4. Do the P-waves create QRS complexes?

PR Interval on ECGs

Ask yourself...

**1. Is the PR interval short, normal, or long? **

**Short **is defined as **less than 3 little squares**, **normal **is **3-5 little squares**, and **long **is **more than 5 little squares**.

**2. Does the PR interval change or is it constant?**

QRS Complex on ECGs

**Ask yourself if the width of the QRS complex is narrow (normal) or wide?**

**Normal QRS is less than 3 little squares**