cardiolab logocardiolab

1st Degree AV Block

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

1st Degree AV Block

Every atrial impulse conducts to the ventricles, but conduction through the AV node is delayed. Not a true "block" — rather, prolonged AV conduction.

Mechanism

Every atrial impulse conducts to the ventricles, but conduction through the AV node is delayed. Not a true "block" — rather, prolonged AV conduction.

Findings· 4
  • Regular rhythm.
  • PR interval >200 ms (>1 large box).
  • Every P wave is followed by a QRS.
  • Otherwise normal morphology.
Clinical Impact

Usually benign and asymptomatic. Common with increased vagal tone, medications (beta-blockers, digoxin), or as a normal variant. No treatment required in isolation.

Differential· 1
Mobitz Type I

1st degree conducts all beats with fixed prolonged PR. Mobitz I has progressive PR lengthening with dropped beats.