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| {{SK}} PAC, PACs, premature atrial contractions, premature atrial complex, premature atrial complexes, APC, APCs, atrial premature contraction, atrial premature contractions, atrial premature complex, atrial premature complexes, APB, atrial premature beat, atrial premature beats, extrasystole, premature atrial beat, premature atrial beats, premature supraventricular beat, premature supraventricular beats | | {{SK}} PAC, PACs, premature atrial contractions, premature atrial complex, premature atrial complexes, APC, APCs, atrial premature contraction, atrial premature contractions, atrial premature complex, atrial premature complexes, APB, atrial premature beat, atrial premature beats, extrasystole, premature atrial beat, premature atrial beats, premature supraventricular beat, premature supraventricular beats |
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| ==Overview==
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| Premature atrial contractions is a benign type of premature heart beat which originates in one of the upper two chambers of the heart (the [[Atrium (heart)|atria]]). PACs occur frequently in subjects with normal heart, however patients with [[structural heart disease]] and [[coronary heart disease]] are at increased risk. PACs usually reflect one of the conditions listed in the differential diagnosis of underlying causes below, and the treatment involves removing or treating the underlying cause. PACs are to be distinguished from [[premature ventricular contractions]] ([[PVCs]]) that originate in one of the lower pumping chambers (the ventricles).
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| ==Prognosis==
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| In general the prognosis of PACs is good, and their occurrence and prognosis is determined by the underlying condition that triggered the PACs. In rare cases, a PAC can, like a PVC, trigger a more serious arrhythmia such as [[atrial flutter]] or [[atrial fibrillation]]. Unlike PVC's, PAC's generally do not cause hemodynamic compromise because the conduction throughout the [[AV node]] and ventricles is normal, and the filling and contraction of the heart is therefore normal.
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| ==Diagnosis==
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| ===Symptoms===
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| There may be a sense of "a skipped beat" or "a thump in the chest" or neck. In many cases, the person feels nothing.
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| ===Physical Examination===
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| ====Pulse====
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| The pulse may feel irregular in a patient who actively has frequent PACs.
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| ===Laboratory Findings===
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| * Consider checking [[Thyroid Function Test]]s to rule out [[hyperthyroidism]]
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| * Consider checking hemoglobin and [[hematocrit]] to rule out [[anemia]]
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| ===Electrocardiogram===
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| The presence of PACs is diagnosed based upon either an [[Electrocardiogram|EKG]], Holter, or Cardiac Event Monitor.
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| # By definition the [[P wave]]s are premature
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| # Morphology of the P' wave is different than the [[P wave]] in [[normal sinus rhythm]]. If its origin is close to that of the sinus node, then the P' morphology is hard to distinguish from the native sinus P wave.
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| # A PAC differs from a [[Premature Junctional Contraction]] (PJC) in that the [[PR interval]] is > 0.12 second in a PAC.
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| # The PR interval may be shorter than that in [[Normal Sinus Rhythm]] ([[NSR]]) if it is located closer to the AV node.
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| # The PR interval tends to lengthen when the coupling time to the PAC is short.
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| # A PAC may not be conducted to the ventricles and this is called a blocked PAC.
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| #* The differential diagnosis in this scenario includes second degree [[AV block]]. In second degree AV block, the PP intervals remain constant.
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| # Usually the QRS is of normal duration, but occasionally there is aberrant conduction, most frequently of [[Right Bundle Branch Block]] (RBBB) morphology.
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| #* Aberrancy is more likely to occur when the coupling time is shorter.
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| # Usually there is no compensatory pause. The PAC resets the [[sinus node]].
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| # Most of these patients do not have organic heart disease.
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| #* 64% of healthy subjects will have PACs on 24 hour [[Holter monitoring]].
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| #* Frequency higher in the elderly
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| # The QRS complex is normal
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| # There is normal [[T wave]] repolarization (not inverted to the other T waves)
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| {{#ev:youtube|KPN1Jgf7hfM}}
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| ===EKG Examples===
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| ----
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| Shown below is an example of an EKG showing sinus rhythm with atrial premature beats in trigemini.
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| [[Image:Rhythm_premature.png|center|500px]]
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| Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/File:Rhythm_premature.png
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| ----
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| Shown below is an example of an EKG showing premature atrial contractions with evident negative p-wave.
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| [[Image:Bes.png|center|800px]]
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| Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/File:Bes.png
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| ----
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| Shown below is an example of a 12 lead EKG showing premature atrial contractions in a patient with [[RBBB]] + [[LAFB]]
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| [[Image:Bifascicular1.jpg|center|800px]]
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| Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/Main_Page
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| ----
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| Shown below is an EKG showing [[sinus rhythm]] with atrial premature beats in trigemini.
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| [[File:PrematureatrialbeatstrigeminiEKG.jpg|center|800px]]
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| Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/File:E287.jpg
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| ----
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| Shown below is an EKG showing sinus rhythm with premature atrial complexes. The P' wave can be seen deforming the T wave in the lead II rhythm strip. Note also that the atrial premature complexes reset the sinus node and hence there is no compensatory pause before the next sinus P wave. The QRS is deformed with a rsR' in V1 and a broad S in I with a duration of > 120 ms. diagnostic of aberrance with a right bundle branch morphology. The S1 Q3 and the right ward axis of the aberrant complexes suggest an additional [[left posterior fasicular block]].
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| [[File:Premature atrial complexes1.jpg|center|800px]]
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| Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/File:E000746.jpg
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| ----
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| Shown below is an EKG showing an atrial premature beat (3rd beat). In fact note the QT interval of the second beat is short and in fact this was an artifact from a paper jam in the EKG recorder. The EKG also shows a first degree A/V block and abnormal Q waves in the inferior and anterior leads consistent with inferior and anterior myocardial infarctions which are probably old.
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| [[File:Premature atrial complexes2.jpg|center|800px]]
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| Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/File:E281.jpg
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| ----
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| ==Treatment==
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| Removal or treatment of the underlying cause of PACs listed in the differential diagnosis is generally sufficient. [[Beta-blockers]] may be helpful if the patient remains symptomatic.
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| ==References== | | ==References== |
