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 APC 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).

 
Caution: A blocked atrial premature beat may mimick sinus arrest, at first glance. In this case, we expect to see a blocked P wave deforming its preceding T wave.

  In some patients with sick sinus syndrome, an APC may be followed by symptomatic sinus pauses owing to
sinus node suppression.

  Usually, the APC resets the sinus node, resulting in the absence of compensatory pause occurs. If the APC fails to reset the sinus node, compensattory pause will be seen.
Compensatory pause is seen rarely after an APC.



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 initiate atrial fibrillation or atrial flutter.

 
Blocked APCs as bigeminal rhythm (pseudobradycardia) may result in symptomatic bradycardia. The patient will feel it as exercise intolerance and fatigue.




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

  In 2nd degree atrioventricular block, the shape of P wave and the PP interval do 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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ECG 11a. Ashman phenomenon is not specific to atrial fibrillation.
It may be observed in rhythms where long and short RR intervals follow each other.
Above is a 3-channel ECG Holter tracing from a middle-aged man.
The basic rhythm is sinus tachycardia with frequent APCs. Sweep speed is 25mm/sec.

The APC in the mid portion
is conducted normally to the ventricles producing a narrow QRS.
The next APC is blocked
resulting in a pause due to failure of conduction to the ventricles .
The following APC
is conducted aberrantly to the ventricles resulting in a wide QRS complex .
After a long RR interval, the refractory period of bundle branches will be prolonged.
If a short RR interval follows a long RR interval, then the early coming supraventricular stimulus may find
one of the bundle branchces (either right or left) in a refractory state and may be conducted aberrantly.

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ECG 11b. Above is the 50 mm/sec display of the same Holter tracing. Details are seen better.

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ECG 12. The rhythm tracing above is from the 3-channel Holter recording of a middle-aged man.
The first 6 beats from the left are normally conducted sinus beats. Then
blocked atrial premature contractions emerge as
bigeminal rhythm. The heart rate decreases below 50/minute.

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ECG 13. The ECG above is from a 52 years-old man who had undergone mitral valve replacement for severe mitral stenosis.
The above ECG was recorded 1 month after the operation. Left atrial enlargement is expected in severe mitral stenosis.
Negative component of the P wave in lead V1 suggests left atrial abnormality.
In the presence of
atrial premature beats, P waves may lack the negative component.

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ECG 14. The above ECG is from a 59 years-old woman with coronary artery disease.
It was recorded before she underwent coronary bypass surgery for LAD and Cx coronary artery stenoses.
Leads I, aVL and V2 to V6 show symmetrically negative T waves and ST segment depression (due to myocardial ischemia).
Four
atrial premature beats are also seen.

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ECG 15. The above ECG is from a 67 years-old woman with gastric cancer.
Sinus tachycardia (138/min.) and an atrial premature beat is seen. This
atrial premature beat has a compensatory pause.
Failure to reset the sinus node results in a compensatory pause.
Compensatory pause is seen very rarely after an atrial premature beat.
The
P wave of the atrial premature beat is deforming the preceding T wave.

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ECG 16a. The ECG above is from a 78 years-old hypertensive woman with a normal ECHOcardiogram.
Atrial premature beat with normal conduction to the ventricles (narrow QRS) is seen.

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ECG 16b. The ECG above belongs to the same hypertensive woman.
This time,
the atrial premature beat is aberrantly conducted to the ventricles (wide QRS).

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ECG 17. The ECG above belongs to a 57 years-old man with hypertension and morbid obesity.
Right bundle branch block is seen. The basic rhythm is sinus. There are also 3 atrial premature beats (APC).
APCs are conducted with aberration, with P waves preceeding the aberrant QRS complexes.

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ECG 18. The above ECG is from a 58 years-old woman with chronic hypertension.
It may look like sinus arrest, at first glance.
However,
the pause is due to a blocked atrial premature beat.
The
blocked atrial premature beat deforms the preceding T wave.
The simultaneously recorded lead aVR (where T waves are isoelectric in this patient) shows
atrial depolarizaton waves clearly.

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ECG 19. Above is the ECG of a 59 years-old man with coronary artery disease and heart failure.
Junctional premature beat is seen.
The P wave preceding the junctional beat is followed by a short PR interval.
This PR interval shortening is not due to accesory pathway, there is no delta wave.
This short PR interval is just due to coincidental timing of the junctional premature beat.
This is not an atrial premature beat since PP intervals and P wave configurations are the same.

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ECG 20. The above ECG belongs to a 13 years-old boy with frequent
atrial premature beats.
Atrial premature beats deform the preceding T waves.
Some atrial premature beats are conducted with
aberration resulting in wide QRS complexes.
These wide QRS complexes are not ventricular premature contractions.
There are two reasons for this: T waves preceding
the wide QRS complexes are different
(due to the deforming effect of the atrial premature beat); also there is no compensatory pause.
The seemingly
sinus arrest is in fact due to a blocked atrial premature beat.
There is no sinus arrest.

Arm electrodes were inadvertently reversed in this ECG

Prof. Dr. Nazlıhan Günal has donated the above ECG to our website.

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ECG 21.
Compensatory pause after an atrial premature beat is seen very rarely.
Failure to reset the sinus node results in a compensatory pause.

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