Mobitz I

Question 1

What is another name for Mobitz I?

Answer 1

Wenckebach or 2nd-degree AV block type I.

Question 2

What is the hallmark ECG feature of Mobitz I?

Answer 2

Progressive lengthening of the PR interval until a QRS complex is dropped.

Question 3

Where does Mobitz I usually occur in the conduction system?

Answer 3

At the AV node.

Question 4

How does the rhythm appear in Mobitz I?

Answer 4

Atrial rhythm regular; ventricular rhythm irregular due to dropped beats.

Question 5

What happens to the PR interval after a dropped QRS in Mobitz I?

Answer 5

It resets to normal and begins to lengthen again.

Question 6

How do the P waves look in Mobitz I?

Answer 6

Normal in appearance; always present.

Question 7

Is the QRS complex typically narrow or wide in Mobitz I?

Answer 7

Narrow (<0.12s) unless there is pre-existing bundle branch block.

Question 8

What common causes can trigger Mobitz I?

Answer 8

Myocardial infarction (esp. inferior), ischaemia, medications (beta-blockers, calcium channel blockers, digoxin).

Question 9

How do you clinically remember Mobitz I versus Mobitz II?

Answer 9

“Mobitz I = PR gets longer, longer, drop. Mobitz II = PR constant, sudden drop.”

Question 10

What symptoms might a patient with Mobitz I present with?

Answer 10

Often asymptomatic; if symptomatic → dizziness, syncope, palpitations.

Question 11

How serious is Mobitz I compared to Mobitz II?

Answer 11

Mobitz I is usually benign; Mobitz II carries higher risk of complete block.

Question 12

What treatment is usually required for Mobitz I if asymptomatic?

Answer 12

No treatment, just monitoring.

Question 13

What is the first step if Mobitz I causes symptomatic bradycardia with low cardiac output?

Answer 13

Atropine administration.

Question 14

What may be required if Mobitz I does not respond to atropine and symptoms persist?

Answer 14

Temporary pacing.

Question 15

What happens to Mobitz I during exercise or sympathetic stimulation?

Answer 15

It may improve because conduction through the AV node speeds up.