Left Posterior Fascicular Block

What Is Left Posterior Fascicular Block?

The left Posterior Fascicular block (Lpfb) is defined by irregular contraction of heart muscles, whereby it travels to the inferior and posterior portion of the left ventricle of the heart and does not conduct electrical impulse transmission from the atrioventricular node.

Instead, the wave-front moves rapidly through the left anterior fascicle and bundle branch which resulted to a right axis deviation that commonly seen on the ECG or electrocardiography.

The Lpfb is rare condition that can affect anyone of us. When your cardiologist told you that you have a bundle branch block it means that you are showing abnormal pattern based from your distinctive ECG reading.

The bundle branches play major function in terms of the cardiac electrical system, it is the structure that normalizes the hearth rhythm and coordinates the pumping mechanism of the heart. As we will recall our knowledge about heart’s mechanism, the heart beats are liable for its own electrical signal.

Left Posterior Fascicular Block

When an electrical signal is sent through the heart the muscle contracts. Therefore, an organized distribution of the electrical signals or the electrical impulses is a vital requirement in efficiently functioning of the heart.

Have you ever asked yourself where do the electrical impulses come from? The signals are created in the sinus node in the upper right atrium, then extents across both atria which cause the atria to beat, and after passing to the atria it goes through the AV node. Next, the electrical impulses enters in the ventricle via the his bundle.

From His bundle, the signals penetrate the 2 bundle branches mainly the right bundle branch and left bundle branch. These two branches allocate the electrical signals across the right and left ventricles, respectively which results them to beat. When these branches are acting normally, the right and left ventricles are contract altogether.

However, when something hinders and hampers the signal transmission across the different atria it causes blockage or causes abnormalities in the homeostasis of heart rhythm.

We determined already that bundle branches are being divided into two (right and left bundle branches). While the right bundle branch doesn’t have divided fascicles. The left bundle branches itself are divided into 2 major branches mainly the anterior and posterior fascicles. In rare cases the blockage can happen in just of the fascicles and these blockages is called as the “hemiblock” or (fascicular block).

In general, when blockage occurs in the anterior fascicle it is being diagnosed as left anterior fascicular block whereas if the blockage happened in the posterior fascicle, it is being called as the left posterior fascicular block.

What happens during the Lpfb?

According to Dr. Edward Burns, during the blockage in the Lpfb in terms of reaching the ventricle, the first electrical vector is directed upwards and leftwards causing the small R waves in the lateral lead (I and avVL) and small Q waves in the inferior leads mainly the II, III, and aVf.

Left Posterior Fascicular Block picture

Then, the major wave of depolarization are spread along the free Lv wall in downward and rightward motio, leading to the production of large positive voltages (tall R waves) in the inferior leads and deep S waves in the lateral leads.

The process performs for about 20 milliseconds longer than simultaneous conduction for both fascicles which results to a slight opening of Qrs.

Finally, the signals or the electrical impulses reaches the inferior leads results to an increased R wave peak time equals to the time from the onset of the Qrs to the peak of the R wave in aVf.

Reading an ECG to find hemiblock abnormalities shouldn’t be ignore because it gives a hint to search for an underlying heart disease.


The Left Posterior fascicular Block or significantly known as the “left posterior hemiblocks” are approach diagnostically by defining some its criteria;

According to Edward Burns who is a passionate emergency physician and a zealous interpreter of ECG working in Prehospital and Retrieval Medicine at Sydney Australia. Some of the benchmarks to diagnose accurately the Lpfb are the following,

  • The right axis deviation must > +90°
  • Frontal Plane axis between 90° and 180° for adults
  • Small R waves with deep S waves (rS) pattern in Leads I and aVL
  • Small Q waves with tall R waves (qR) waves in leads II, III and aVF
  • QRS duration less than 120 ms or slightly prolonged between 80-110ms
  • Prolonged R wave peak time in aVF
  • Amplified QRS voltage in the limb leads
  • No occurrence of right ventricular hypertrophy
  • No signs of any other cause for right axis deviation

Clinical significance

The Ecg is the primary device to visualize the heart’s electrical impulse, as it moves through the heart. When there is an abnormal movement of the impulse based from the ECG reading it gives the doctor a hint that there’s something happening in the heart’s mechanism.

The occurrence of Lpfb is quietly rare and always relates with Rbbb. For instance, in Argentina and other Latin American countries cases of Chagas disease is endemic.

Left Posterior Fascicular Block or Left Posterior Hemiblocks with or without Right Bundle Block Branches (Rbbb may be found in cases of severe chagasic myocarditis.

For the reason that, the posterior division of Lbb(Left Bundle Branch) is the least defenseless segment of the intraventricular conduction system, the rate of Lphaccompanied with RBB is an indication of complete heart blockage.

As a matter of fact, when the conduction system experienced severe lesion they alter the conduction in the posterior fascicle, it is self-evident that the Righ bundle branch (Rbb), the anterior of Lbb (left bundle brunch are also involved. Therefore, it gives a significant evidence of AV block in Rbbbwith Lph.


Some possible treatment can be used below but specific treatment is always dependent on the blockage degree and clinical symptoms present. Generally, treatment includes some clinical protocols;

  • An intensive cardiac evaluation (determining the severity of the pathological ailment).
  • Eating health food and maintaining health diet. (Reducing intake of fats and Carbohydrates).
  • Regular Physical activities such as jogging, running, walking. These activities help to maintain the cardiovascular activities and maintain the normal rhythm of heart.
  • Replacement of oral supplements such as taking polyunsaturated fat than saturated fats, these includes like olive oil and flax seed oil in order to mend overall heart conditions.
  • Reduce salt intake.
  • Omega 3 fatty acids and vitamins intake are highly recommended.
  • Maintaining healthy lifestyle. (Eliminate smoking or drinking since it causes vasoconstriction in blood circulation).


  1. https://www.verywell.com/right-bundle-branch-block-rbbb-1745785
  2. https://www.symptoma.com/en/info/left-anterior-fascicular-block
  3. https://www.reference.com/health/treatment-left-anterior-fascicular-block-49f438a4b3fefc62#
  4. E:\dr\Left posterior\Left Posterior Fascicular Block – LITFL ECG Library.html
  5. E:\dr\Left posterior\Isolated left posterior fascicular block_ a reliable marker for inferior myocardial infarction and associated severe coronary artery disease. – PubMed – NCBI.html

Leave a Reply

Your email address will not be published.