Diagnostic criteria

  QRS width is < 120 ms .

  The QRS axis at the frontal plane is between
-45 degrees and -90 degrees.

  There is
qR pattern in lead aVL.

  The R-peak time in lead aVL is 45 ms or more.




Clinical significance

  QRS width is < 120 ms .

  The QRS axis at the frontal plane is between
-45 degrees and -90 degrees.

  There is
qR pattern in lead aVL.

  The R-peak time in lead aVL is 45 ms or more.




References

  Circulation 2009;119:e235-e240

  Circulation 2007;115:1154-1163





ECG 1. Left anterior fascicular block.

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ECG 2. Left anterior fascicular block.

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ECG 3. Left anterior fascicular block in another subject.

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ECG 4. The ECG above belongs to a 46 years-old hypertensive man who has echocardiographically confirmed left ventricular
hypertrophy. It shows right bundle branch block and left anterior fascicular block.
According to Gubner criteria, there is also left ventricular hypertophy pattern.

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ECG 5a. The ECG above belongs to a 25 years-old puerpera (one day after childbirth). Atrial bigeminy is seen.

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 5b. 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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EGG 6. The ECG above belongs to a 58 years-old man with hypertrophic cardiomyopathy.
All the leads other than aVR, V1 and V2 show q waves. The patient did not have previous myocardial infarction.
Abnormal q waves may be observed in patients with hypertrophic cardiomyopathy but without previous myocardial infarction.
There is also left anterior fascicular block.

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