cardiolab logocardiolab

2nd Degree AV Block

caution
Lead II
25 mm/s10 mm/mV
Heart rate
72bpm
RR
833ms
QT
358ms
Type

2nd Degree AV Block

Progressive fatigue of AV nodal conduction. Each successive impulse takes longer to traverse the AV node until one impulse fails completely, then the cycle restarts.

Mechanism

Progressive fatigue of AV nodal conduction. Each successive impulse takes longer to traverse the AV node until one impulse fails completely, then the cycle restarts.

Findings· 3
  • Grouped beating pattern.
  • PR interval progressively lengthens over 3–4 beats, then a P wave occurs without a QRS (dropped beat).
  • RR intervals shorten before the pause.
Clinical Impact

Generally benign, especially when occurring at the level of the AV node. Common during sleep or in athletes. Rarely requires pacing unless symptomatic.

Differential· 2
Mobitz Type II

Both drop QRS complexes. Mobitz I has progressive PR lengthening; Mobitz II has constant PR.

1st Degree AV Block

Prolonged PR may be confused. 1st degree conducts all beats; Mobitz I periodically drops QRS.