How to Read an EKG Strip in 5 Steps

An electrocardiograph (EKG or ECG) records the electrical signals from a heart and captures them on a computer monitor or printer. For instance, Cardiologists often run this test to decide whether a heart is healthy. They are also often used to check for different heart conditions. On this strip, the heart’s activity is translated into line tracings, where the dips and spikes in an EKG cycle are called waves that represent different phases of the heart’s activity. This method is primarily for reading Non-Interpretive EKG Machines.

Understanding the EKG Grid and Measurement

To start, each EKG is made up of large boxes that contain small boxes. Both sets of boxes measure time and distance. A 12-lead ECG records a 10 second rhythm strip. To read the results accurately, one must understand the following time values:

• A large box, commonly referred to as a ‘big box’ (5mm), represents 0.20 seconds.
• A small box (1mm) represents 0.04 seconds.

Key Components of the Wave

To read an EKG, it’s important to understand the components of the wave. Each cycle consists of specific segments:

• The P-Wave: Records the electrical activity through the upper heart chambers and represents atrial depolarization, or contraction.
• The PR interval: Spans from the beginning of atrial depolarization (P-Wave) to the beginning of ventricular depolarization (QRS Complex). The duration period of this interval can determine heart health and help diagnose diseases.
• The QRS complex: Records the electrical activity through the lower heart chambers, which represents ventricular depolarization, or contraction. It consists of the Q Wave (first downstroke), R Wave (first upward deflection), and S Wave (first downward deflection).
• The T-Wave: Like the P-Wave, the T-Wave records upper heart chamber activity; however, T-Waves represent atrial repolarization, or relaxation.

Step-by-Step EKG Analysis

1. Analyze the P-Wave

The P-Wave, located at the beginning of the ECG cycle, should be present and upright. A P-Wave that is absent or inverted is abnormal. The P-wave should also not be more than 1 large box tall and 1 large box wide. Normal duration is typically between 0.06 – 0.12 seconds.

2. Measure the PR Interval

The next step is to measure the PR interval. To do this, count the number of small boxes in between the beginning of the P-Wave and the peak of the QRS complex. Then, multiply that number by 0.04 seconds. Normal interval length should be between 0.12 – 0.20 seconds.

3. Measure the QRS Complex

To measure the QRS complex, count the number of small boxes from the beginning to the end of the QRS complex, then divide by 0.04 seconds. Our normal target range is 0.06 – 0.12 seconds.

4. Identify the Heart Rhythm

To identify the rhythm, measure the distance between the R waves and determine if they are consistent throughout the strip. If the distances are consistent, then the rhythm is regular. If not, the rhythm is irregular. There are 3 main categories of rhythms:

• Regular: Constant R to R interval.
• Regularly Irregular: Variable R to R interval w/ a pattern.
• Irregularly Irregular: Variable R to R interval w/ no pattern.

5. Determine the Heart Rate

Note that the normal range at rest is between 60 BPM and 100 BPM per minute. Depending on whether the rhythm is regular or irregular, there are various methods that are widely used to accurately measure heart rate:

• The Big Box Method: If the heart rhythm is regular, you can use the Big Box Method. To do this, divide 300 by the number of large boxes in between the R waves. For example, if there are 5 large boxes in between a set of R’s, the heart rate would be 60 BPM.
• The 6 Second Method: If the heart rhythm is irregular and you’re working with a 6-second strip, the 6 second method is an easy and viable option. First, start by counting the # of R waves from beginning to the end of the 6 second strip.

EKG Measurement Summary

• Small Box: 0.04 seconds
• Large (Big) Box: 0.20 seconds
• Normal P-Wave Duration: 0.06 – 0.12 seconds
• Normal PR Interval: 0.12 – 0.20 seconds
• Normal QRS Complex: 0.06 – 0.12 seconds
• Normal Resting Heart Rate: 60 – 100 BPM