Diagnostic criteria

  QRS width is less than 120 ms.

  The QRS axis at the frontal plane is between
90 degrees and 180 degrees: right axis deviation.

      For isolated LPFB, other causes of right axis deviation:

            - vertical heart in a slender person,

            - right ventricular hypertrophy,

            - large lateral infarction                         should be absent.

  There is
rS pattern in leads D1 and aVL.

  There is
qR pattern in leads D3 and aVF.



Clinical significance

  Isolated LPFB is very rare.

  LPFB usually accompanies right bundle branch block (RBBB).

  The development of RBBB + LPFB during acute myocardial infarction is a sign of poor prognosis.

  RBBB + LPFB has a high probability to turn into complete AV block.




References

  Circulation 2009;119:e235-e240

  Circulation 2007;115:1154-1163





ECG 1. Left posterior fascicular block.

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ECG 2. Left posterior fascicular block in a 39 years-old man.

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ECG 3. Left posterior fascicular block in another patient.

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ECG 4. The above ECG belongs to a 62 year old woman with coronary artery disease, chronic obstructive lung disease and
systemic hypertension. In addition to the left posterior fascicular block, there are also right bundle branch block, right atrial
abnormality and left atrial abnormality.

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ECG 5. The ECG above belongs to a 78 years-old woman who had undergone coronary artery bypass surgery.
LPFB and RBBB are seen.

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ECG 6. The ECG above belongs to a 75 years-old hypertensive woman who had undergone coronary artery bypass surgery
because of 3-vessel disease. LPFB and RBBB are seen.

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ECG 7. The ECG above belongs to a 55 years-old man. LPFB and RBBB are seen.

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ECG 8. The ECG above belongs to a 78 years-old man. LPFB, RBBB and frequent VPCs are seen.

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ECG 9. The ECG above belongs to a 76 years-old woman with obstruction of the right coronary and circumflex arteries.
She has hypertension and left ventricular hypertrophy. Echocardiography showed interventricular septal thickness as 1.7 cm
and posterior wall thickness as 1.2 cm. The ECG shows both LPFB and RBBB.

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ECG 10. The ECG above belongs to a 10 years-old girl with a normal ECHOcardiogram.
Incomplete right bundle branch block (RBBB pattern) is accompanied by left posterior fascicular block.
QRS axis is about + 120 degrees (right axis deviation).

Pediatric cardiologist Dr. Mahmut Gokdemir has donated this ECG to our website.

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