Mastering EKG Rhythm Analysis: A Quick Guide

Understanding EKGs can feel very overwhelming when you first begin to climb the learning curve. There are so many different types of rhythms and you are expected to understand the many characteristics behind each one to correctly identify them. In this article, you will learn the concise approach that will make you fast and accurate when reading EKG rhythms. Additionally included is our free EKG study guide that details each rhythm to tailor the approach we describe here. You will find the free pdf download at the bottom of this article. 

Step 1: Understand the meaning of PQRST

If you first focus on understanding what the PQRST stands for, you will not have to rely strictly on memorization. If you understand the PQRST, then you will understand the electrical cycle of the heart and its impact on the mechanical function of the heart.

- P wave = atrial depolarization (contraction)

-QRS complex = ventricular depolarization (contraction)

-T wave = ventricular repolarization (relaxation)

Step 2: Start with Heart Rate

Determine the heart rate to establish the rhythm's nature. Unless otherwise stated, calculate the heart rate using the number of R waves within a 6-second strip and multiply by 10. This can condense the rhythm down by simply understanding the rate. For example, if the heart rate is less than 100bpm, you can eliminate all the tachycardia rhythms.

Step 3: Rule out Ventricular

Remember what represents ventricular contraction? The QRS Complex! We like to suggest to first rule out or rule in ventricular rhythms by putting the focus on the QRS first, rather than the traditional P wave to improve your speed and approach.

How do you know if it is a ventricular rhythm? Answer this one question- Is the complex wide (>0.12 seconds or 3 small boxes) or is it normal (less than 3 small boxes)?

If the complex is wide, immediately narrow your rhythm selections to ventricular rhythms and bundle branch blocks.  If not, then move on to the next step.

Step 4: Identify P Waves

If Ventricular rhythm is ruled out, now move to the P wave. Answer the two questions below to potentially identify a rhythm.

-Are there identifiable P waves? If no, think Atrial fibrillation or Junctional Rhythms.

-Are the P waves consistent or irregular? If irregular, think heart blocks or premature atrial contractions (PACs)

Step 5: Measure PR Interval

After determining the P wave characteristics, measure its relationship with the QRS complex. The PR interval is simply the distance between the P wave (Atrial Contraction) and the QRS Complex (Ventricular contraction). What does that mean? It means we are seeing how long it takes the SA node to communicate to the Purkinje fibers to initiate a ventricular contraction. If it is delayed or blocked, then we will see a slow conduction which shows up as a long PR interval on the EKG. What does the PR interval tell us specifically about the rhythms? It is your direct tool to identify heart blocks and is the only thing you need to identify heart blocks correctly. Do not look at other factors when determining if there is a heart block or which type of heart block. The PR interval will tell you everything. You simply just need to know the PR interval length and the PR interval consistency between each PQRS complex.

A prolonged PR interval is considered to be >.20 seconds or 5 small boxes.

Quick Rules:

-PR interval measures the same before each QRS complex, but it is > 5 small boxes. = First Degree Heart Block

-PR interval measures inconsistent and has the marking characteristic as getting longer and longer with each PQRS complex and eventually misses a QRS complex = 2^nd degree type II Heart Block.

-PR interval measures the same before each QRS complex, but it has mixed P waves with no QRS complexes paired. = 2^nd Degree Type II Heart Block

-PR interval measures inconsistent before each QRS complex, and has mixed P waves with no QRS complex paired = 3^rd degree Heart Block

Many struggle determining between 2^nd degree type II versus 3^rd degree heart block because they both have P waves that don’t pair with QRS complexes occasionally or frequently. DON’T TRY TO DETERMINE THEM BY LOOKING AT THE MISPAIRS. It is much simpler than you think if you just strictly look at the PR interval.  Is the PR interval always the same before a QRS complex (eg- 4 small boxes)? Then it is automatically 2^nd degree type II. Is the PR interval inconsistent compared to other PR intervals that pair with QRS complexes (eg- 4 small boxes with one PQRS versus the next PQRS is 7 boxes)? Then it is automatically 3^rd degree heart block.

Step 6: Analyze ST Segment and T Wave

Don’t forget to look at the ST segment for elevation or depression. Elevated or depressed ST segments and inverted or peaked T waves can hint at myocardial ischemia, injury, or electrolyte imbalances.

Step 7: Test yourself with live strips

The best way to apply your understanding is through testing yourself with live strips. Fun EKG games can help ease the boredom of studying this material if that is your struggle. Here is the link to an EKG interpretation game we like: https://skillstat.com/tools/ecg-simulator/

Repetition is also key. Continue to review the materials on this study guide provided below, then immediately after, go test yourself on the live simulator game. Even if you are doing poor at first, you will soon learn the major characteristics of each rhythm. The simulator will also improve your ability to interpret quickly and accurately, making the standstill strips you will be tested on much easier.

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