Premature atrial contraction overview

# Overview
Premature atrial contractions (PACs) also known as atrial premature complex (APC), premature atrial beat or  atrial premature beat (APB) is a benign type of premature heart beat which originates in one of the upper two chambers of the heart (the atria).  PACs are to be distinguished from premature ventricular contractions (PVCs) that originate in one of the lower pumping chambers (the ventricles).  PACs occur frequently in subjects with normal heart, however patients with structural heart disease and coronary heart disease are at increased risk.

# Pathophysiology
Mechanisms responsible for spontaneous premature atrial contraction are not clear but reentry within the atrium is the most probable mechanism.

# Causes
Premature atrial contraction occur frequently in subjects with normal heart, however patients with structural heart disease and coronary heart disease are at increased risk.  Alcohol and coffee are considered potential precipitants of PACs.  They may also be more common in other medical conditions such as chronic renal failure and chronic pulmonary disease.

# Differentiating Premature Atrial Contraction from other Diseases
Premature atrial contraction need to be differentiated from other supraventricular premature beat that can originate from the atrioventricular node (AV node) or bundle of His.  PACs also need to be distinguished from premature ventricular contractions (PVCs) that originate in one of the lower pumping chambers (the ventricles).

# Epidemiology and Demographics
Premature atrial contraction (PAC) can occur at any age and they should not be always considered as an abnormal finding.  The prevalence depends on the technique used for evaluation and the presence of heart disease.

# Risk Factors
Smoking, alcohol, and coffee are considered potential precipitants of premature atrial contraction.

# Natural History, Complications and Prognosis
Premature atrial contraction (PAC) is a common form of supraventricular arrhythmias and mostly the prognosis is good.  In rare cases, severe symptoms other than palpitation may occur.

# Diagnosis

## History and Symptoms
Most patients with premature atrial contraction are asymptomatic.  Rarely they present with palpitation and complications.

## Physical Examination
Premature atrial contraction patients will demonstrate either premature pulse waves or pauses upon palpation of their peripheral pulse.

## Laboratory Findings
Many cases of premature atrial contraction have no definite cause, it may be the result of various other problems.  If PAC patients present with symptoms, a generalized approach is done to find the precipitating factors.

## Electrocardiogram
Premature atrial contraction may have a variety of manifestations on the electrocardiogram.  The diagnosis of an PACs is made when a P wave with a morphology different from that of the sinus P wave (inverted or biphasic) occurs earlier than the anticipated sinus P wave.  It is always advisory to examine each lead as subtle differences in morphology may be present.

# Treatment

## Medical Therapy
No therapy is required for premature atrial contraction in asymptomatic individuals. If necessary, medical therapy should begin with a beta blocker.