Premature atrial contraction
Encyclopedia
Premature atrial contractions (PACs), also known as atrial premature complexes (APC) or atrial premature beats (APB), are a common cardiac arrhythmia 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. PACs are often completely asymptomatic
and may be noted only with Holter monitor
ing, but occasionally they cause a sensation of palpitations. In most cases, no treatment other than reassurance is needed for PACs, although medications such as beta blocker
s can reduce the frequency of symptomatic PACs.
, Holter monitor
, or cardiac event monitor
.
or atrial fibrillation
.
, 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.
Atria
Atria may refer to:*Atrium , an anatomical structure of the heart*Atrium , a large open space within a building*Atria or Alpha Trianguli Australis, a star in the constellation Triangulum Australe...
. While the sinoatrial node
Sinoatrial node
The sinoatrial node is the impulse-generating tissue located in the right atrium of the heart, and thus the generator of normal sinus rhythm. It is a group of cells positioned on the wall of the right atrium, near the entrance of the superior vena cava...
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. PACs are often completely asymptomatic
Asymptomatic
In medicine, a disease is considered asymptomatic if a patient is a carrier for a disease or infection but experiences no symptoms. A condition might be asymptomatic if it fails to show the noticeable symptoms with which it is usually associated. Asymptomatic infections are also called subclinical...
and may be noted only with Holter monitor
Holter monitor
In medicine, a Holter monitor is a portable device for continuously monitoring various electrical activity of the cardiovascular system for at least 24 hours...
ing, but occasionally they cause a sensation of palpitations. In most cases, no treatment other than reassurance is needed for PACs, although medications such as beta blocker
Beta blocker
Beta blockers or beta-adrenergic blocking agents, beta-adrenergic antagonists, beta-adrenoreceptor antagonists or beta antagonists, are a class of drugs used for various indications. They are particularly for the management of cardiac arrhythmias, cardioprotection after myocardial infarction ,...
s can reduce the frequency of symptomatic PACs.
Diagnosis
Premature atrial contractions are typically diagnosed with an electrocardiogramElectrocardiogram
Electrocardiography is a transthoracic interpretation of the electrical activity of the heart over a period of time, as detected by electrodes attached to the outer surface of the skin and recorded by a device external to the body...
, Holter monitor
Holter monitor
In medicine, a Holter monitor is a portable device for continuously monitoring various electrical activity of the cardiovascular system for at least 24 hours...
, or cardiac event monitor
Cardiac event monitor
A cardiac event monitor is a device used to monitor patients with transient cardiac symptoms.There are two broad classifications for cardiac event monitors: manual and automatic. Automatic ECG event monitors such have the ability to monitor the patient's ECG and make recordings of abnormal events...
.
Prognosis
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 flutterAtrial flutter
Atrial flutter is an abnormal heart rhythm that occurs in the atria of the heart. When it first occurs, it is usually associated with a fast heart rate or tachycardia , and falls into the category of supra-ventricular tachycardias. While this rhythm occurs most often in individuals with...
or atrial fibrillation
Atrial fibrillation
Atrial fibrillation is the most common cardiac arrhythmia . It is a common cause of irregular heart beat, identified clinically by taking a pulse. Chaotic electrical activity in the two upper chambers of the heart result in the muscle fibrillating , instead of achieving coordinated contraction...
.
Electrocardiogram
On an electrocardiogram (EKG), PACs are characterized by an abnormally shaped P wave. Since the premature beat initiates outside the sinoatrial nodeSinoatrial node
The sinoatrial node is the impulse-generating tissue located in the right atrium of the heart, and thus the generator of normal sinus rhythm. It is a group of cells positioned on the wall of the right atrium, near the entrance of the superior vena cava...
, the associated P wave appears different from those seen in normal sinus rhythm. Typically, the atrial impulse propagates normally through the atrioventricular node
Atrioventricular node
The atrioventricular node is a part of the electrical control system of the heart that coordinates heart rate. It electrically connects atrial and ventricular chambers...
and into the cardiac ventricles, resulting in a normal, narrow QRS complex
QRS complex
The QRS complex is a name for the combination of three of the graphical deflections seen on a typical electrocardiogram . It is usually the central and most visually obvious part of the tracing. It corresponds to the depolarization of the right and left ventricles of the human heart...
. 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.