Premature atrial contraction

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Premature atrial contraction
Two PACs as seen on a rhythm strip
Classification and external resources
Specialty cardiology
ICD-10 I49.1
ICD-9-CM 427.61
MeSH D018880

Premature atrial contractions (PACs), also known as atrial premature complexes (APC) or atrial premature beats (APB), are a common cardiac dysrhythmia characterized by premature heartbeats originating in the atria. While the sinoatrial node typically regulates the heartbeat during normal sinus rhythm, PACs occur when another region of the atria depolarizes before the sinoatrial node and thus triggers a premature heartbeat. The exact cause of PACs is unclear; while several predisposing conditions exist, PACs commonly occur in healthy young and elderly people without heart disease, and by themselves are not considered an abnormal finding.[1][2] PACs are often completely asymptomatic and may be noted only with Holter monitoring, but occasionally they can be perceived as a skipped beat or a jolt in the chest. In most cases, no treatment other than reassurance is needed for PACs, although medications such as beta blockers can reduce the frequency of symptomatic PACs.


Premature atrial contractions are typically diagnosed with an electrocardiogram, Holter monitor, or cardiac event monitor.


In otherwise healthy patients, occasional premature atrial contractions are a common and normal finding and do not indicate any particular health risk. Rarely, in patients with other underlying structural heart problems, PACs can trigger a more serious arrhythmia such as atrial flutter or atrial fibrillation.[citation needed] In otherwise healthy people PACs usually disappear with adolescence.


Premature atrial contractions are often benign, requiring no treatment. Occasionally, the patient having the PAC will find these symptoms bothersome, in which case the doctor may treat the PACs. Sometimes the PACs can indicate heart disease or an increased risk for other cardiac arrhythmias. In this case the underlying cause is treated. Often a beta blocker will be prescribed for symptomatic PACs.[3]


On an electrocardiogram (ECG), PACs are characterized by an abnormally shaped P wave. Since the premature beat initiates outside the sinoatrial node, the associated P wave appears different from those seen in normal sinus rhythm. Typically, the atrial impulse propagates normally through the atrioventricular node and into the cardiac ventricles, resulting in a normal, narrow QRS complex. However, if the atrial beat is premature enough, it may reach the atrioventricular node during its refractory period, in which case it will not be conducted to the ventricle and there will be no QRS complex following the P wave.

See also[edit]


  1. ^ Brodsky M, Wu D, Denes P, Kanakis C, Rosen KM (March 1977). "Arrhythmias documented by 24 hour continuous electrocardiographic monitoring in 50 male medical students without apparent heart disease". Am. J. Cardiol. 39 (3): 390–5. doi:10.1016/S0002-9149(77)80094-5. PMID 65912. 
  2. ^ Folarin VA, Fitzsimmons PJ, Kruyer WB (September 2001). "Holter monitor findings in asymptomatic male military aviators without structural heart disease". Aviat Space Environ Med. 72 (9): 836–8. PMID 11565820. 
  3. ^ Premature Atrial Contraction