Premature Atrial Contractions
normalLead II
25 mm/s10 mm/mV
Heart rate
72bpm
RR
833ms
QT
358ms
RR
833ms
PR
162ms
QRS
105ms
QT
358ms
QTc
380ms
Type
Premature Atrial Contractions
An ectopic focus in the atria fires before the next expected sinus beat. The premature impulse depolarizes the atria abnormally and usually conducts through the AV node to produce a normal QRS.
Recognition· 4
- Early beat (comes before expected)
- Abnormal P wave (different shape/inverted)
- Narrow QRS (looks normal)
- May have non-compensatory pause after
Mechanism
Ectopic focus in atria fires early — impulse conducts normally to ventricles
An irritable spot in the atria fires before the SA node's next scheduled beat. This premature impulse creates an abnormal P wave. The impulse usually conducts normally through the AV node and His-Purkinje system, producing a narrow QRS complex.
Findings· 2
- Early beat with an abnormal (often inverted or morphologically different) P wave followed by a narrow QRS.
- May be followed by a non-compensatory pause.
Clinical Impact
Can trigger atrial fibrillation in susceptible patients
↓Palpitations (patient feels 'skipped beat')
↓Rarely significant unless very frequentRISK
Usually benign — most people have occasional PACs
Management· 3
1
Primary Treatment
Usually no treatment needed.
2
If highly symptomatic
reduce caffeine, stress management, beta-blockers.
3
Long-term Management
Frequent PACs may warrant holter monitoring to assess A-fib risk.
Differential· 2