Skip to Main Content

We have a new app!

Take the Access library with you wherever you go—easy access to books, videos, images, podcasts, personalized features, and more.

Download the Access App here: iOS and Android

23-15: Type 1 Second-Degree AV Block (Mobitz I, Wenckebach)

Maite A. Huis in ‘t Veld; Amal Mattu; R. Jason Thurman

ECG Findings

  • Progressive PR-interval prolongation throughout the cardiac cycle until a P wave occurs without a QRS complex (“dropped” beat).

  • After the dropped QRS complex, the cycle continues again with the PR interval of the 1st beat in the cycle always shorter than the PR interval of the last beat in the previous cycle.

  • P wave may be hidden by the preceding T wave.

Pearls

  1. The number of P-QRS complexes prior to the “dropped” beat may vary.

  2. A clue to the diagnosis of Mobitz type I AV block can be found in the appearance of grouped QRS complexes.

  3. This type of block is often asymptomatic and may be seen in athletes or others with high vagal tone.

  4. These patients have low risk of progression to complete heart block and usually do not require a pacemaker. However, Mobitz type I heart block may be caused by inferior MI or drugs (digoxin, amiodarone, β-blockers, calcium channel blockers).

FIGURE 23.15A

Second-Degree AV Block (Mobitz I, Wenckebach). (ECG contributor: James Paul Brewer, MD.)

An E C G tracing with 12 leads from a patient with second-degree A V block.
View Full Size||Download Slide (.ppt)
FIGURE 23.15B

The PR interval gradually increases (double arrows) until a P wave is not followed by a QRS and a beat is “dropped” (brackets). The process then recurs. P waves occur at regular intervals, although they may be hidden by T waves.

An E C G tracing with one lead consists of a sharp dip, a wide, curved peak, and a small, curved peak. Double-headed arrows are between the curved peak and the beginning of the dip. A pair of square brackets encloses a region near the flatline.
View Full Size||Download Slide (.ppt)

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.

This site uses cookies to provide, maintain and improve your experience. MH Privacy Center Close