ECG RHYTHM LAB

Second-Degree AV Block · Mobitz I

PR intervals lengthen before a nonconducted P wave; the cycle then restarts.

Generated six-second Lead II example · 80 bpm target rate · not a patient recording.

Typical rate

Ventricular rate below atrial rate

Regularity

Grouped beating

P waves

Regular atrial activity

PR interval

Progressively lengthens, then drops

QRS

Usually narrow

What to look for

Follow successive P waves: longer PR, longer PR, then a missing QRS.

Show this rhythm

Sources and limitations