Rapid Review·Cardiovascular
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Arrhythmias: Supraventricular
T1Must knowPremature Atrial Complexes
Focus on
An early narrow beat with an abnormally shaped P wave in front of it and a pause that is less than fully compensatory. Benign in a normal heart: cut the caffeine, alcohol and nicotine, fix the potassium, beta blocker if it still bothers the patient.
Key takeaways
What it is and what causes it
Premature atrial complex (PAC)
also called an atrial premature beat, an ectopic atrial focus that fires a little early.The ECG signature
a narrow QRS with a preceding, abnormally shaped P wave; a premature ventricular complex is the opposite (wide QRS, no P wave).Triggers
smoking, alcohol, coffee, stress; hypokalemia.Clinical features and diagnosis
Usually benign and asymptomatic
some feel palpitations or an irregular pulse.
What this shows
Electrocardiogram (ECG)
several premature narrow complexes, each preceded by a deformed P wave, with a pause that is not fully compensatory, as in the Premature atrial contraction ECG.- Three clues: the P wave has a different shape (it starts elsewhere in the atria), the beat comes early, and a short pause follows.
Compensatory pause
the R-R interval around the premature beat equals twice the normal R-R; when it is less than twice, the beat is atrial.Management
Rule out
structural heart disease and electrolyte abnormalities.No treatment unless symptomatic
avoid the triggers.Persistent palpitations
a beta blocker.Refractory
electrophysiology study with ablation.A coffee-drinking smoker feels occasional skipped beats. The ECG shows early narrow complexes, each preceded by an oddly shaped P wave, with a pause shorter than twice the normal R-R. What are they and what is the management?
Premature atrial complexes. Rule out structural heart disease and electrolyte problems (hypokalemia), then avoid the triggers (coffee, smoking, alcohol); a beta blocker only for persistent palpitations.
How it's tested
A 30-year-old with occasional "skipped beats" after espresso; the ECG shows early narrow beats with a strange P wave and a short pause: premature atrial complexes — reassure, reduce caffeine.
Which feature distinguishes it from a PVC: the narrow QRS with a preceding abnormal P wave and a non-compensatory pause.
Same patient still symptomatic after trigger removal: low-dose beta blocker.
Frequent PACs in a 72-year-old with hypertension and a dilated left atrium: monitor for atrial fibrillation.
Go deeper
Related Step 2 pages: Approach to Tachyarrhythmias, Premature Ventricular Complexes, Atrial Fibrillation, AV Nodal Reentrant Tachycardia
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