Diagnostic criteria

  The impulse arises from an ectopic atrial focus, not from the sinus node (sinoatrial node).

  Since the impulse arises from an ectopic atrial focus, P wave of the atrial premature contraction (APC)

      has a different shape than that of the sinus P wave.

  The PR interval of the APS may be shorter or longer when compared with the PR interval of the sinus beat.

      If ectopic atrial focus is closer to the AV node, then ectopic impulse will reach the AV node in a shorter time.

  The premature atrial beat is often conducted normally to the ventricles, creating a narrow QRS complex.

  Sometimes premature beats are conducted to the ventrciles with
aberration .

      In this case the resultant QRS complex is wide (>120ms) but still has a preceding P wave.

  Sometimes the very premature P wave cannot be conducted to the ventricles since it coincides with the

      refractory period of the atrioventricular node:
blocked APS (blocked APC) .

  Sometimes, an APC may briefly suppress the sinus node.




Clinical importance of APC

  APC may be observed in apparently healthy subjects without any organic heart disease.

  The incidence of APC increases in any disease causing atrial dilatation.

  An APC may sometimes
trigger the onset of atrial fibrillation or atrial flutter.

 
Blocked APCs as bigeminal rhythm may result in symptomatic bradycardia

      (
exercise intolerance and fatigue ).




How can you differentiate a blocked APC from 2nd degree atrioventricular block?

  In 2nd degree atrioventricular block, the shape of the P wave and the PP interval does not change.



Reference

  Indian Pacing Electrophysiol J. 2013;13:114-117.





ECG 1.
The P wave of the APS is abnormally shaped when compared with the P wave of the sinus beat .
The ventricular premature beat does not have a preceding P wave.

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ECG 2. Atrial premature systole.
The abnormally shaped
P wave of the premature beat is different from P wave of the sinus beat .

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ECG 3. Atrial premature beat.
Premature P wave has deformed the T wave of the preceeding beat. Deformed T wave has a
different shape than the shape of the preceeding
normal T wave.

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ECG 4. The fourth beat from the left is
atrial premature systole with aberration . Premature P wave has deformed the T wave
of the preceding beat.
Deformed T wave has a different shape than the shape of the preceding normal T wave .

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ECG 5. The pause in the middle is due to the
blocked APS . The P wave , which is buried in the terminal part of the T wave of
the preceeding beat has come so early that it has found the AV node at the refractory period. The refractoriness did not permit
conduction to the ventricles and QRS complex was not formed.

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ECG 6.
PR interval of the APS may be longer than PR interval of the sinus beat

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ECG 7.
Some of the atrial premature beats have not been conducted by aberration. On the other hand some other atrial
premature beats
are conducted by aberration . P waves of the A P S have different shapes than that of the P waves of the
sinus beats
.

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ECG 8.
Blocked APC . APCs coming too early, will not be conducted. Calibration is 5 mm/mV.

Prof. Dr. Bulent Oran has donated this ECG to our website.





ECG 9.
The first 2 P waves are conducted normally. The T wave of second QRS has a different shape than other T waves, since
there is a P wave deforming it . Since this too early P wave is conducted to the ventricles by aberration, it results in a
wide QRS complex
. The succeeding P wave is also conducted normally to the ventricles. Then an early P wave comes and
results in a narrow QRS complex since it is not so early to be conducted by aberration.
This is again followed by a
normally conducted P wave.

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ECG 10a. The ECG above belongs to a 25 years-old puerpera (one day after childbirth).
P waves with at least 3 different
shapes
show wandering atrial pacemaker. When P waves originate from various atrial foci, their shapes also vary.

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ECG 10b. Her ECG next day shows atrial bigeminy.
Every P wave originating from the sinus node is followed by a premature
P wave originating from an ectopic focus
in the atria.
The premature P wave is negative in the above ECG, suggesting a low atrial focus.
However, all atrial premature beats should NOT necessarily be negative.
Negativity of the P wave is related to its focus, but not to its prematurity.


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ECG 10c. A few hours later, her ECG shows that atrial premature contractions are now coming earlier and being conducted with
aberration.
Some P waves are conducted normally to the ventricles . Some premature P waves are conducted with left
anterior fascicular block (LAFB)
while some others are conducted with left bundle branch block (LBBB) morphology.

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