Mobitz type I, also known as the Wenckebach block, is a subtype of second-degree atrioventricular (AV) block.

Mobitz type I is a type of conduction disorder, which happens when the electrical signals that tell the heart to beat become disrupted.

The heart has four chambers. Doctors refer to the upper two chambers as the atria and the bottom chambers as the ventricles. To pump blood around the body, the heart muscle contracts. Electrical signals control these contractions.

An electrical signal begins in the sinoatrial node, which generates electrical signals at regular intervals. The signal then moves to the AV node, which conducts the electrical signals into the ventricles.

An AV block occurs when this electrical signal is blocked or delayed between the AV nodes and the ventricles.

This article reviews a Mobitz type I block, its symptoms, causes, treatment options, and more.

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An AV block occurs when the electrical signal is delayed or intermittent. Mobitz type I, also called Wenckebach, is a subtype of a second-degree heart block. In this type of heart block, the signals progressively slow down, causing the heart to drop a beat.

There are three degrees of AV block, which include:

  • First-degree heart block: This is when the signals slow down. It is unlikely to cause symptoms or require treatment.
  • Second-degree heart block: This is when the signals are intermittent. There are two types of second-degree heart block — Mobitz type I and Mobitz type II.
  • Third-degree heart block: This stage involves a blockage of the electrical signals. This is a medical emergency and can be life threatening.

Is it serious?

Mobitz type I is often benign, and most people do not experience symptoms. A doctor may only discover the condition during a routine exam or when checking for other conditions using an ECG. Those who do not experience symptoms may require monitoring on an outpatient basis.

If people do experience symptoms, they may require treatment.

Mobitz type I and II are both second-degree AV heart blocks.

According to a 2022 article, Mobitz type I is generally benign and occurs at the AV node. The electrical signals become slower, and the heart may skip a beat. Most people will not develop symptoms.

Mobitz type II occurs just beyond the AV node. The electrical signals reach the ventricles intermittently, which can result in symptoms including:

  • fainting
  • dizziness
  • chest pain
  • shortness of breath
  • nausea
  • fatigue
  • the sensation of the heart skipping a beat

Mobitz type I is unlikely to require treatment. However, those with Mobitz type II heart block may require a pacemaker. It also has a higher chance of progressing to third-degree heart block, which can cause a heart attack.

Learn more about Mobitz type 2 heart block.

In most cases, Mobitz type I does not cause any symptoms. If symptoms do occur, they may include one or more of the following:

  • fainting
  • lightheadedness
  • dizziness

Mobitz type I heart block can develop following cardiac surgery. It can also develop as a result of the following medical conditions:

  • inferior myocardial ischemia, which is when there is a blockage affecting the blood flow to the heart
  • hyperkalemia, which is when a person’s potassium levels in the blood are too high
  • cardiomyopathy, which refers to the thickening of the heart wall
  • Lyme disease

Medications can also cause Mobitz type I heart block. These include:

Fingolimod, which is an immunosuppressant agent to treat multiple sclerosis, can also cause AV heart block.

Treatment for Mobitz type I is not usually necessary. If a person is not experiencing symptoms, a doctor may recommend regular monitoring to ensure that the heart block is not progressing.

If symptoms are present, a doctor may prescribe a medication called atropine.

If medications are causing Mobitz type I, the condition is often reversible once a person stops taking the medication.

It is important for a doctor to determine which degree of heart block a person has. This is because the outlook and treatment options can differ.

To diagnose a heart block, a doctor may order an ECG.

Mobitz type I causes a progressive prolongation of the PR interval, which eventually builds to a non-conducting P wave. The PR interval and P wave are parts of an ECG used by doctors, nurses, and other medical professionals to monitor the heartbeat and rhythm.

They may also ask about a person’s medical history and about any medications they are taking.

A person may not be able to prevent Mobitz type I from developing. However, they can take steps to take care of their heart to help prevent other heart diseases.

The American Heart Association recommends:

  • eating a nutritious, well-balanced diet
  • taking regular exercise
  • learning the warning signs of a heart attack
  • avoiding smoking and secondhand smoke
  • getting regular checkups
  • keeping stress under control
  • understanding family history and possible risk factors
  • regulating blood sugar levels
  • achieving and maintaining a suitable BMI

These tips may not prevent an AV block, but they can help prevent heart disease and keep a person’s heart in good shape for longer.

Mobitz type 1 heart block may not cause any symptoms. A doctor may only discover the condition during a routine exam or when checking for other conditions using an ECG.

However, if a person feels lightheaded, dizzy, or faints, they should contact a doctor.

Mobitz type 1 is a subtype of second-degree heart block. The electrical signals that control a person’s heartbeat get progressively slower until the heart skips a beat.

A person is unlikely to experience symptoms. However, if they do, they may notice that they feel lightheaded, dizzy, or faint.

It is typically a benign condition. However, it has a chance of progressing to more serious types of AV block. As a result, a person may require regular monitoring to ensure that the heart block is not progressing.