FOR APPs & PRIMARY CARE CLINICIANS · EKG REFERENCE

Recognizing AV block

Compare conduction delay, intermittent block, and complete block.

Heart block: EKG examples

P wave: the upper chambers’ electrical signal. QRS complex: the sharp spike from the lower chambers. PR interval: the time from the start of a P wave to the start of the QRS.

First-degree heart block

Delayed, but every signal gets through. Each P wave is followed by a QRS. The PR interval is longer than 0.20 seconds.

Second-degree: Mobitz I (Wenckebach)

The delay gets longer, then one signal is blocked. The PR interval progressively lengthens until a P wave has no QRS after it. The cycle then starts again.

Second-degree: Mobitz II

A signal is blocked without a gradually increasing delay. Conducted beats have the same PR interval. A P wave is suddenly not followed by a QRS.

Third-degree: complete heart block

The upper and lower chambers beat independently. P waves follow their own rhythm. A slower backup rhythm produces the QRS complexes, with no consistent relationship between the two. This example shows a wide QRS; some complete blocks have a narrow QRS.

Illustrative six-second rhythm strips for teaching, not patient recordings. Display size is not a calibrated printed EKG.

Reference: University of Utah ECG Learning Center: Conduction abnormalities