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Premature Atrial Contractions

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

Atrial Bigeminy

A repeating pattern where every other beat is a premature atrial contraction. The ectopic atrial focus fires with a fixed coupling interval after each sinus beat, producing a strictly alternating normal-PAC pattern.

Mechanism

A repeating pattern where every other beat is a premature atrial contraction. The ectopic atrial focus fires with a fixed coupling interval after each sinus beat, producing a strictly alternating normal-PAC pattern.

Findings· 3
  • Alternating pattern: one normal sinus beat (upright P, narrow QRS) followed by one PAC (abnormal P, narrow QRS).
  • Fixed coupling interval.
  • Non-compensatory pause after each PAC.
Clinical Impact

May be benign or indicate atrial irritability from stimulants, hypoxia, or electrolyte imbalance. Frequent PAC burden can trigger atrial fibrillation in susceptible patients.

Differential· 2
PVC

Both premature beats. PVCs have wide bizarre QRS without preceding P wave.

Atrial Fibrillation

Frequent PACs can trigger AFib. Irregularly irregular rhythm with no P waves distinguishes AFib.