Difference Between Mobitz 1 and 2

A delay in the passage of impulses into the ventricles via the AV node increases the duration of the PR interval seen in an ECG. This condition is known as a second-degree heart block. There are main two forms of second-degree heart block as mobitz 1 and 2. In mobitz 1 there is a progressive increase in the duration of PR interval until an impulse is completely blocked before reaching the ventricles whereas in mobitz 2 there is a prolonged PR interval whose duration remains constant and an occasional impulse is lost without reaching its destination. This is the key difference between mobitz 1 and 2.

CONTENTS

1. Overview and Key Difference
2. What is Second-Degree Heart Block
3. What is Mobitz 1
4. What is Mobitz 2
5. Similarities Between Mobitz 1 and 2
6. Side by Side Comparison – Mobitz 1 vs 2 in Tabular Form
7. Summary

What is Second-Degree Heart Block?

When there is a delay in the transmission of impulses through the AV node, there is a prolongation of the PR interval. In the presence of a PR interval whose duration is in between 0.25s – 0.45s, some of the action potentials wane off without passing on to the ventricles. In such instances, there will be a P wave which is not followed by a QRS-T wave. This condition is identified as a second-degree heart block. There are two main forms of second-degree heart blocks as mobitz 1 and mobitz 2.

  Clinical Features

• Syncope
• Lightheadedness
• Depending on the underlying cause there can be features such as chest pain.
• Hypotension
• Bradycardia

What is Mobitz 1?

In this form of second-degree heart block, there is a progressive increase in the duration of PR interval until an impulse is completely blocked before reaching the ventricles. Patients having mobitz 1 heart block mostly remain asymptomatic.

Management

• If the patient is on digoxin or beta blockers, they should be discontinued.
• When there is a suspicion of myocardial ischemia, it should be aptly treated.

What is Mobitz 2?

In mobitz 2 there is a prolonged PR interval whose duration remains constant. An occasional impulse is lost without being transmitted to the ventricles. Patients having mobitz 2 type heart block are at a higher risk of developing third-degree heart blocks and the chance of them becoming symptomatic is higher than those having mobitz 1 form of the disease.

Management

• In this form also, the use of digoxin and beta blockers should be discontinued, and the possibility of ischemic events in the myocardium should be excluded.
• Implantation of pacer device is usually considered to avoid the condition worsening into a complete heart block.

What is the Similarity Between Mobitz 1 and 2?

• In both conditions, there is a delay in the transmission of impulses into ventricles via the AV node.

What is the Difference Between Mobitz 1 and 2?

Summary – Mobitz 1 vs 2 

Mobitz 1 and 2 are the two forms of second-degree heart block. The difference between them is in mobitz 1 there is a gradual increase in the duration of PR interval until an impulse completely wanes off before reaching the ventricles but in mobitz 2 although the PR interval is prolonged it does not change with time.

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Reference:

1.Kumar, Vinay, Stanley Leonard Robbins, Ramzi S. Cotran, Abul K. Abbas, and Nelson Fausto. Robbins and Cotran pathologic basis of disease. 9th ed. Philadelphia, Pa: Elsevier Saunders, 2010. Print

Image Courtesy:

1.’Second degree heart block’By Npatchett – Own work, (CC BY-SA 4.0) via Commons Wikimedia