Definition

  Aberration (aberrant conduction) is conduction of the supraventricular impulse to the ventricles

      in a markedly different manner from the usual conduction
.

  Aberration is seen as bundle branch block pattern (wide QRS complex).

  Since refractory period of the right bundle branch is longer than that of the left bundle branch,

      aberration occurs as right bundle branch block in 80% of the cases.

  In patients with abnormal hearts, aberration may be also seen as left bundle branch block.

 
Any type of supraventricular rhythm may show aberrancy: sinus rhythm, nodal rhythm,

      atrial premature beat, supraventricular tachycardias, atrial fibrillation, atrial flutter with variable block.

  If aberration occurs after long-short cycle, it is called as Ashman phenomenon.




Pathophysiology

  A sudden change in the length of the previous cardiac cycle results in a refractory right or left bundle

      branch.

 
Refractoriness in any bundle branch does not allow the supraventricular impulse to propagate in

      that branch. This results in bundle branch block and hence "
wide QRS complex".



Clinical significance

  Identification of the wide QRS complex as aberration helps to exclude the diagnosis of VPS.





ECG 1a. The last beat in the above ECG
is conducted aberrantly and is due to an atrial premature contraction (APC) . One of
the reasons that this APC was conducted aberrantly is that
cardiac cyle before the beat preceeding the APC is a long cycle .
A short cycle coming after a long cycle eases aberrancy.

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ECG 1b. Above is the magnified view of last part of the ECG 1a. The
T wave , the Atrial Premature
Contraction
( APC ) deforming it and the aberrantly conducted QRS complex is seen.





ECG 2. Rate dependent aberration. In the upper tracing, it is clearly seen that aberration occurs when heart rate increases.
In the lower tracing aberration, when heart rate slows down the aberration with wide QRS complexes disappear and narrow
QRS complexes reappear.

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ECG 3. Rate dependent aberration in another patient.
The first 3 beats from the left are conducted with aberration as left
bundle branch block. As the heart rate decreases, aberration disappears and P waves are conducted normally (as narrow
QRS complexes).

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ECG 4. Rate dependent aberration in another patient. When the heart rate (HR) decreases, aberration disappears and narrow
QRS complexes (normal conduction) appear. The numbers on the upper row show instantenous heart rate while the numbers
below them show the corresponding RR intervals in miliseconds.

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ECG 5a. 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 5b. 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 5c. 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 6a. The ECG above is from a 64 years-old man. The basic rhythm is sinus with a heart rate of 60/minute.
QRS complexes are narrow. A VPC is seen in precordial leads.

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ECG 6b. A few minutes later, his second ECG was recorded.
Now, the heart rate is 75/minute and the QRS complexes are widened.
This QRS widening in the form of RBBB is called acceleration dependent aberration.

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