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Premature Atrial Contractions


Premature atrial contractions (PACs) are premature beats which are stimulated in a different part of of the atria causing interruption in the sinoatrial node (SA) beat. SA node is the pacemaker of the heart where heartbeats are naturally generated.


In the management of patients with PACs, it is important to know the clinical history particularly about cardiac disorders or structural heart disease. History of medication including proarrhythmic drugs, sympathomimetics or drugs which increase the risk of altered serum potassium or magnesium concentration may assist in determining the etiology of premature atrial contractions.

Symptoms that are important in the management are those which can predict some of the underlying clinical conditions such as ischemic heart disease (which may present with chest pain or the anginal equivalent) or hemodynamic compromise (which may manifest as syncope) [5].

Observable symptoms may be absent in many patients [6]. However, some patients may report feelings of a 'stop' or 'skip' heartbeat. Exercise can cause either an increase or decrease the frequency of PACs.

Cannon A waves due to increase in contraction following a PAC can result in palpitations, neck and/or chest discomfort. Repeated PACs or bigeminy may cause syncope due to low stroke volume or inadequate cardiac output. After several PACs, hypotension may occur.

Heart Disease
  • PACs are commonly observed in elderly patients and may be a result of degenerative disorders such as congestive heart disease, angina pectoris and coronary heart disease.[symptoma.com]
  • In most cases, premature atrial contractions aren’t a sign of heart disease and just happen naturally.[webmd.com]
  • Some of the underlying conditions that can cause PACs are Heart disease – This illness can include genetic defects, infection, and blocked or narrow blood vessels. Heart disease can describe many different problems with the heart.[justanswer.com]
  • […] healthy individuals without any evidence of heart disease.[cardiachealth.org]
  • Patients with PACs complain of palpitations and "a sense of the heart 'skipping a beat.' " PACs mostly occur in healthy individuals without heart disease.[sites.google.com]
  • You will be cared for by regional and world leaders in the treatment of heart arrhythmias such as atrial fibrillation, atrial flutter, ventricular tachycardia, Wolff-Parkinson-White syndrome, atrioventricular re-entrant tachycardia, and other heart rhythm[uabmedicine.org]
  • Although most PACs are benign, they may change into atrial flutter, atrial fibrillation, or supraventricular tachycardia.[sites.google.com]
  • A non-compensatory pause should be noted following the PAC; blocked premature atrial contractions may mimic AV block (atrial rate ventricular rate) but, unlike PACs, AV blocks maintain consistent intervals between atrial events 4. fetal tachycardia blocked[radiopaedia.org]
Irregular Heart Rhythm
  • Atrial fibrillation (AF) is one of the most common abnormal or irregular heart rhythms ( arrhythmias ) in the world today.[selfgrowth.com]
  • Up to the time of admission, the patient never experienced paroxysmal tachycardia, and his principal complaint was the irregular heart rhythm refractory to all types of antiarrhytmic drug therapy.[degruyter.com]
  • Atrial fibrillation is an irregular heart rhythm characterized by a rapid onset, spontaneous irregular heartbeat. This abnormal heart rhythm could be stimulated by PACs.[symptoma.com]
  • If this is not possible and frequent, intolerable palpitations are present, drugs to control irregular heart rhythms are helpful. If the extra heartbeat happens often, it can — but does not always — set off atrial fibrillation.[cedars-sinai.edu]
  • A commonly used heart monitor may be a simple tool for predicting the risk of atrial fibrillation, the most frequently diagnosed type of irregular heart rhythm, according to researchers at UC San Francisco.[ucsf.edu]
Systolic Murmur
  • Heart examination found a grade I/IV systolic murmur best at the mid-left sternal border without radiation that changed with position and respiration. There were no bruits or jugulovenous distention and he had normal femoral pulses.[pediatriceducation.org]


When PACs are suspected in a patient during auscultation, it is important to determine their frequency using ECG [7]. Increased PACs may occur during exercise, therefore, radiotelemetric measurement of the ECG during or immediately after the exercise is not inconclusive. Radiotelemetry may be important in determining whether frequent PACs can affect individuals engaging in active physical activities (e.g. athletes). PACs that occur during rest or recovery period may not have direct implication on the physical activity of an individual.

Periodically, PACs may be detected during the heart rate recovery period after exercise, especially after sub-maximal graded exercise. Sometimes, it can be challenging when determining whether the early beats with a feature of marginally different P wave shape are due to PACs or a normal variation associated with sinus arrhythmia and wandering atrial pacemaker. 

24-hour Holter monitoring is very effective in the diagnosis of the condition, because PACs may not occur during a standard ECG test [8].

When PACs occur more frequently (e.g. 3 times per minute on an average), it may be suggestive of an underlying atrial disease. Proper clinical examination should be done with specific focus on AV regurgitation, even without any obvious signs or symptoms relating to PACs. Echocardiography could be used to determine the presence and severity of heart diseases. Most often, there may be no obvious underlying pathological condition. When this is confirmed, a possible cause of the arrhythmia may be atrial myocarditis and viral antibody serology and hematological investigations may be requested. Biochemistry can be done if the suspected underlying condition is a systemic disease or serum electrolyte imbalance.

Inverted P Wave
  • P wave suggests atrial source near AV junction Nearly normal P waves suggest focus near SA node P' wave, P'R' intervals, coupling interval usually constant Suggests single focus PR interval normal, shorter, or prolonged R-R interval shorter than normal[fprmed.com]
  • PACS arising close to the AV node (“low atrial” ectopics) activate the atria retrogradely, producing an inverted P wave with a relatively short PR interval 120 ms (PR interval 120 ms is classified as a PJC).[lifeinthefastlane.com]


Patients with no underlying heart-related problems with little or no symptoms and a lower risk of PACs can be counseled about their condition, while those with more obvious clinical features may require further assessment, counseling or treatment.

Treatment options include:

  • Beta-blockers (e.g. atenolol, metoprolol).
  • Use of radio frequency catheter ablation of the ectopic focus when necessary [9].
  • Dietary adjustment advice may be given to patients when the stimulation is caused by high intake of caffeine, alcohol or other stimulants [10].


In normal healthy subjects, early atrial contractions occur commonly and are normal findings among this population without any particular underlying health risk. Rarely PACs can stimulate a serious arrhythmia like atrial flutter or atrial fibrillation among patients with structural heart problems [4]. 


The sinoatrial node (sinus node) is a group of cells located in the right atrium of the heart. It controls the rate of the heartbeat through autonomous electrical signals. Sometimes, electrical signals can arise from other regions of the heart causing premature atrial contractions (PACs) or premature ventricular contractions (PVCs).

The primary cause of a premature heartbeat is frequently unknown and most patients with PACs do not have underlying heart-related diseases. Factors that may contribute to premature heart beats and sometimes aid in diagnosis of the disease include:


PACs are common in healthy people without cardiac disorders and [3] and more than 60% of the adult population are diagnosed with the condition in a 24-hour Holter monitoring test.

The disorder may occur due to an increased atrial pressure, particularly in patients with cardiac failure or mitral incompetence. PACs may also occur before the onset of atrial fibrillation. This may be further complicated by alcohol and caffeine intake.

Sex distribution
Age distribution


Features of premature atrial contractions on electrocardiography include:

  • Electrical signals arise from the atrial region.
  • The rate of heart beat is variable, but the underlying rate appears normal.
  • The rhythm is irregular due to interruption by a premature beat.
  • Each QRS complex shows a P waves. The P wave of a PAC may be obstructed by the previous T wave and appears differently from the sinus P waves.
  • PRI value is between 0.12–0.20 seconds, but may be longer or shorter for the PAC.
  • QRS complex appears normal.

PACs can be triggered by stimulants such as alcohol, tobacco or adrenergic drugs. 


Benign premature beats can be prevented by avoiding stimulants such as marijuana, tobacco and caffeine. Also, regular cardiovascular exercise is helpful. Stress management is also important and if necessary, anxiolytic agent may be advised. Patient history is very important so as to avoid drugs that can increase PACs.


Premature atrial contractions (PACs) can cause heart palpitations or noticeable abnormal heartbeats. Palpitations are feelings of having an abnormal increase, decrease or irregularly timed heart beat. PACs occur when a region of the atria depolarizes before the sinoatrial (SA) node, causing a premature beat. This can cause abnormal premature beats of both atrial and ventricles (conducted PAC) or the beat is not conducted into the ventricles causing a blocked PAC. Both conducted and blocked PACs can result into arrhythmia or dysrhythmia. Generally, PACs can affect any age group. Treatment of PACs is usually not necessary, however, in severe condition, patients may require medications.

PACs are usually harmless but rarely, they may occur due to a life-threatening heart disease such as arrhythmias. PACs are commonly observed in elderly patients and may be a result of degenerative disorders such as congestive heart disease, angina pectoris and coronary heart disease. Furthermore, arrhythmias are a major cause of falls, physical disability and frequent hospitalization among the aged patient [1].

Premature atrial contractions may either be:

  • Unifocal: PACs emerges from a single focal point with identical features.
  • Multifocal: PACs arise from two or more foci and appear with multiple P-wave structures.

Patient Information

Premature atrial contractions (PAC) are caused by stimulation of the atria by an electrical signal generated from a different part of atrial chamber, before the normal heartbeat occurs. 


PACs are early heartbeats which are generated by premature electrical impulses which arise from anywhere within atrium, other than the sinus node. Although, they often occur in healthy people, other heart diseases or injury may be implicated.

In most patient, premature atrial contraction effects are not severe. However, this condition may have significant health implications if it is related with atrial fibrillation. Atrial fibrillation is an irregular heart rhythm characterized by a rapid onset, spontaneous irregular heartbeat. This abnormal heart rhythm could be stimulated by PACs.


Premature atrial contractions usually do not produce significant symptoms, sometimes, the patient may have feelings of skipped, rapid or fluttering heartbeats.

Other associated symptoms that include:


The doctor may ask to know about the medical history of the patient. This history may include questions about their social habit (alcohol, recreational drug or caffeine consumption), symptoms observed and other important information from the patient.

Clinical conditions which usually cause heart related diseases such as diabetes, high blood pressure, obesity etc. may require proper management even in the absence of PACs.

The doctor based on the symptoms may:

  • Physically examine the patient to detect possible underlying clinical problems.
  • Examine the state of the patient heart by monitoring the heart rate.
  • Request for laboratory investigations such as hematological, serological and biochemical analysis of blood.
  • Ask for electrocardiogram (ECG) examination. This is done to detect cause of irregular heartbeat pattern.
  • Instruct the patient to wear Holter monitoring device for 24-48 hours. This is used to measure heart rhythm.


Most PACs are benign and self limiting. Treatment depends on the underlying cause and is usually based on the observed symptoms. Drugs such as beta or calcium blockers are sometimes prescribed for treatment with proper monitoring. Generally, in the absence of any severe underlying heart conditions, most patients can benefit from proper counseling and reassurance by the healthcare provider.



  1. Abrams D, Perkin M, Skinner J. Long QT syndrome. BMJ. 2010 Jan 8; 340:b4815.
  2. Berman ND. Ventricular tachycardia initiated by both normally and aberrantly conducted atrial premature beats. Pacing Clin Electrophysiol. 1980; 3:519.
  3. Conen D, Adam M, Roche F, et al. Premature atrial contractions in the general population: frequency and risk factors. Circulation. 2012 Nov 6; 126(19):2302-8.
  4. Ettinger PO, Wu CF, De La Cruz C Jr, et al. Arrhythmias and the "Holiday Heart": alcohol-associated cardiac rhythm disorders. Am Heart J. 1978; 95:555.
  5. Folarin VA, Fitzsimmons PJ, Kruyer WB. Holter monitor findings in asymptomatic male military aviators without structural heart disease. Aviat Space Environ Med. 2001; 72:836.
  6. Goodacre S, McLeod K. ABC of clinical electrocardiography: Paediatric electrocardiography. BMJ. 2002 Jan 8; 324(7350):1382-5.
  7. Kaye GC. Percutaneous interventional electrophysiology. BMJ. 2003 Aug 2; 327(7409):280-3.
  8. O'Mahony D, Foote C. Prospective evaluation of unexplained syncope, dizziness, and falls among community-dwelling elderly adults. J Gerontol. 1998; 53:M435-40.
  9. Yamada T, Murakami Y, Okada T, et al. Electroanatomic mapping in the catheter ablation of premature atrial contractions Europace. November. 2008; 10(11):1320-4.
  10. Vincenti A, Brambilla R, Fumagalli MG, et al. Onset mechanism of paroxysmal atrial fibrillation detected by ambulatory Holter monitoring. Europace. 2006; 8:204.

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Last updated: 2019-07-11 20:15