Premature Atrial Contractions (PAC)

Table Of Contents

Was sind Vorhofextrasystolen?
EKG-Merkmale
Formen von Vorhofextrasystolen (PAC)
EKGs
Ursachen
Symptome
Klinische Bedeutung
Diagnostik
Therapie

Premature atrial contractions (PAC) – Simply explained: definition, ECG features and clinical significance

What are premature atrial contractions?

Premature atrial contractions (Premature Atrial Contractions, PAC) are early heartbeats that originate not from the sinus node but from an ectopic focus in the atrium. This produces a heartbeat earlier than expected, usually followed by a non-completely compensatory pause.

PACs are among the most common supraventricular arrhythmias and can occur in people with structurally normal hearts as well as in patients with structural heart disease.

ECG features

Premature occurring heartbeat
Abnormal P wave (shape differs from the sinus P wave)
P wave usually visible before the QRS complex
Narrow QRS complex (< 120 ms), unless a bundle branch block is present
Usually a non-completely compensatory pause after the extrasystole
Occasionally the PAC is blocked in the AV node and produces no QRS complex (blocked PAC)

Forms of premature atrial contractions (PAC)

Premature atrial contractions can occur in different patterns:

Single PACs – isolated extrasystoles
Atrial bigeminy – a PAC follows each sinus beat (1:1 pattern)
Atrial trigeminy – a PAC follows two sinus beats (2:1 pattern)
Atrial quadrigeminy – a PAC follows three sinus beats (3:1 pattern)
PAC pairs (couplets) – two consecutive premature atrial contractions
Runs (atrial runs) – three or more consecutive PACs; short episodes of atrial tachycardia
Blocked PAC – the premature atrial contraction is not conducted to the ventricles; on the ECG there is a premature P wave without a subsequent QRS complex.

The higher the PAC burden, the greater the risk for supraventricular arrhythmias.

ECGs

PAC

EKG 1

Causes

PACs can occur, among other causes, with:

Stress or lack of sleep
Caffeine, alcohol, or nicotine
Electrolyte disturbances (e.g., hypokalemia, hypomagnesemia)
Hyperthyroidism
Fever or infections
Structural heart disease
Myocardial ischemia
After cardiac procedures (e.g., coronary angiography or heart surgery)

Symptoms

Many patients are asymptomatic.

Possible symptoms:

Skipped beats
Palpitations
Brief pause in the heartbeat
Restlessness
Dizziness (rare)

Clinical significance

Single PACs are usually benign and often require no specific therapy.

However, a high PAC burden can be associated with an increased risk for the following conditions:

Atrial fibrillation
Supraventricular tachycardias
Rarely, tachycardia-induced cardiomyopathy

Diagnostics

12-lead ECG
Long-term ECG (24–72 hours)
Laboratory (electrolytes, TSH, inflammatory markers)
Echocardiography if structural heart disease is suspected

Treatment

Treatment depends on the cause and symptoms.

Asymptomatic PACs

Usually no therapy required
Education and reassurance

Symptomatic PACs

Treat underlying triggers
Reduction of caffeine, alcohol and nicotine
Correction of electrolyte disturbances
Treatment of hyperthyroidism or infection
In pronounced symptoms, possibly beta-blockers

Catheter ablation is only necessary in selected cases with a high symptomatic PAC burden.