How to Tell the Difference Between Heart Blocks

Amanda Thomas May 31, 2024
Heart Blocks on red background

If you’ve ever been in a relationship, you’ll know that communication is key.

You can say the same for our hearts. To function properly, the electrical signals in our hearts need to communicate effectively with each other. 

However, sometimes, this communication can become disrupted, resulting in a heart block. A heart block happens when there’s an interruption or slowdown in electrical signals responsible for controlling our heartbeat. 

This can lead to various symptoms, including:

  • Dizziness
  • Fainting
  • Fatigue

There are several types of heart blocks, each with unique characteristics and treatment options. In this article, we’ll go over the types of heart blocks and how to tell them apart. So, if you need help spotting the differences between Mobitz 1 and 2 or figuring out what a Wenckebach rhythm is, read on.

Jump to Section


  1. Types of Heart Block
  2. How Can You Tell the Difference Between Each Type of Heart Block?

Types of Heart Block

There are four main types of heart blocks, each with unique characteristics and effects on the heart’s rhythm.

1st Degree

First-degree heart block is the mildest form, characterized by a prolonged PR interval of more than .20 seconds (>200 milliseconds) on the electrocardiogram (ECG) but without missed beats.

The delay occurs in the atrioventricular (AV) node, but all atrial impulses still reach the ventricles. Clients with 1st-degree heart block are usually asymptomatic and don’t require treatment.

2nd Degree Type 1 (Wenckebach, Mobitz I)

Second-degree AV Block Type 1, also known as Wenckebach or Mobitz I, involves progressive prolongation of the PR interval until it drops a beat.

Nurses can see this repeating cycle on the ECG due to an intermittent failure of the AV node to conduct impulses. Clients may be asymptomatic or experience mild symptoms like dizziness or palpitations.

2nd Degree Type 2 (Mobitz II)

Second-degree AV Block Type 2, or Mobitz II, is more serious and can lead to a complete heart block.

When comparing Mobitz 1 vs 2 (I vs II), Mobitz II doesn’t show progressive PR prolongation. Instead, the PR interval remains constant, but QRS complexes don’t follow some of the P waves.

This block usually occurs below the AV node, either at the bundle of His or one of its branches, and can cause significant symptoms such as:

3rd Degree

A 3rd degree AV heart block, also known as complete heart block, is the most deadly.

In this condition, there’s no conduction of atrial impulses to the ventricles. The atria and ventricles beat independently, which is evident on the ECG. On an ECG, the atrial rate (P waves) is usually faster than the ventricular rate (QRS complexes).

Clients often present with:

Third-degree heart block requires immediate treatment, often with a pacemaker.

How Can You Tell the Difference Between Each Type of Heart Block?

Though the symptoms may be similar, there are a few key differences between each type of heart block that can help distinguish between them.

These include the:

  • Block’s location
  • ECG pattern
  • Severity of symptoms

2nd Degree Type 1 (Wenckebach, Mobitz I) vs 2nd Degree Type 2 (Mobitz II)

Nurses can differentiate Mobitz 1 vs 2 by the pattern seen on the ECG.

In the Wenckebach rhythm (Mobitz I), the PR interval gradually lengthens until it drops a beat. In contrast, Mobitz II presents with consistent PR intervals but with sudden, unpredictable dropped beats.

Clinically, Mobitz II is more likely to cause symptoms and has a higher risk of progressing to complete heart block.

2nd Degree Type 2 (Mobitz II) vs 3rd Degree (Complete Heart Block)

Nurses can distinguish Mobitz type 2 vs complete heart block by the conduction of some atrial impulses to the ventricles in Mobitz II.

In 3rd-degree heart block, there’s no association between the P waves and QRS complexes. The atria and ventricles beat independently. Symptoms are generally more severe in 3rd-degree heart block, necessitating prompt intervention.

A good way to remember the differences between each type is with the heart block poem:

If the R is far from P,

Then you have 1st degree.

PR gets longer, longer, longer, drops,

Then you have a Wenckebach.

If some R’s don’t get through,

Then you have that Mobitz II.

If the P’s and Q’s don’t agree,

Then you have that 3rd degree.

Understanding these differences is critical for nurses and health care providers. Accurately identifying the type of heart block can significantly impact client management and outcomes. 

Join SimpleNursing for More Learning Resources

Ready to master more nursing concepts?

Join SimpleNursing to access a wealth of nursing school resources to help you succeed in your nursing education.

Want to ace Nursing School Exams & the NCLEX?

Make topics click with easy-to-understand videos & more. We've helped over 1,000,000 students & we can help you too.

JOIN FOR FREE

Nursing students trust SimpleNursing

Simplenursing student
I cannot express enough gratitude for Nurse Mike and this wonderful platform he has created. I had a subscription to SimpleNursing the entire 2 years of my nursing school career and it was the best resource I had available to me. The visuals, the explanations, the memory tricks, the songs, the study guides, and the test questions are brilliant.
read more
Simplenursing student
Before starting nursing school, I was a C-average student. I didn't think I'd be competent enough and make it through my second semester. I was told about SimpleNursing and purchased it immediately. Long story short, I graduated nursing school with honors and passed all of my classes with As and Bs only. I would have never been able to do that without the help of SimpleNursing. Nurse Mike teaches in the only way that I am able to learn and I cannot thank him enough.
read more