Left anterior fascicular block

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Left anterior fascicular block
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Left anterior fascicular block (LAFB) is an abnormal condition of the left ventricle of the heart, [1] [2] related to, but distinguished from, left bundle branch block (LBBB).

Contents

It is caused by only the left anterior fascicle – one half of the left bundle branch being defective. It is manifested on the ECG by left axis deviation. It is much more common than left posterior fascicular block.

Mechanism

Normal activation of the left ventricle (LV) proceeds down the left bundle branch, which consist of three fascicles, the left anterior fascicle, the left posterior fascicle, and the septal fascicle. The posterior fascicle supplies the posterior and inferoposterior walls of the LV, the anterior fascicle supplies the upper and anterior parts of the LV and the septal fascicle supplies the septal wall with innervation. LAFB — which is also known as left anterior hemiblock (LAHB) — occurs when a cardiac impulse spreads first through the left posterior fascicle, causing a delay in activation of the anterior and upper parts of the LV. Although there is a delay or block in activation of the left anterior fascicle there is still preservation of initial left to right septal activation as well as preservation of the inferior activation of the LV (preservation, on the ECG, of septal Q waves in I and aVL and predominantly negative QRS complex in leads II, III, and aVF). The delayed and unopposed activation of the remainder of the LV now results in a shift in the QRS axis leftward and superiorly, causing marked left axis deviation. This delayed activation also results in a widening of the QRS complex, although not to the extent of a complete LBBB.[ citation needed ]

Diagnosis

LAFB cannot be diagnosed when a prior inferior wall myocardial infarction (IMI) is evident on the ECG. IMI can also cause extreme left-axis deviation, but will manifest with Q-waves in the inferior leads II, III, and aVF. By contrast, QRS complexes in the inferior leads should begin with r-waves in LAFB.[ citation needed ]

Effects of LAFB on diagnosing infarctions and left ventricular hypertrophy

LAHB may be a cause of poor R wave progression across the precordium causing a pseudoinfarction pattern mimicking an anteroseptal infarction. It also makes the electrocardiographic diagnosis of LVH more complicated, because both may cause a large R wave in lead aVL. Therefore, to call LVH on an EKG in the setting of an LAHB you should see the presence of a "strain pattern" when you are relying on limb lead criteria to diagnose LVH.[ citation needed ]

Clinical significance

See also

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<span class="mw-page-title-main">Bundle of His</span> Collection of heart muscle cells

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<span class="mw-page-title-main">Third-degree atrioventricular block</span> Medical condition

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<span class="mw-page-title-main">Cardiac conduction system</span> Aspect of heart function

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<span class="mw-page-title-main">First-degree atrioventricular block</span> Medical condition

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<span class="mw-page-title-main">Bundle branch block</span> Medical condition

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<span class="mw-page-title-main">QRS complex</span> Represents ventricular depolarization, which results in ventricular contraction

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<span class="mw-page-title-main">Right bundle branch block</span> Heart block in the right ventricle

A right bundle branch block (RBBB) is a heart block in the right bundle branch of the electrical conduction system.

<span class="mw-page-title-main">Left bundle branch block</span> Medical condition

Left bundle branch block (LBBB) is a conduction abnormality in the heart that can be seen on an electrocardiogram (ECG). In this condition, activation of the left ventricle of the heart is delayed, which causes the left ventricle to contract later than the right ventricle.

<span class="mw-page-title-main">Bifascicular block</span> Conduction abnormality in the heart

Bifascicular block is characterized by right bundle branch block with left anterior fascicular block, left bundle branch block, or right bundle branch block with left posterior fascicular block on electrocardiography. Complete heart block could be the cause of syncope that is otherwise unexplained if bifascicular block is seen on electrocardiography. It is estimated that less than 50% of patients with bifascicular block have high-degree atrioventricular block, although the exact incidence is unknown.

<span class="mw-page-title-main">Right axis deviation</span> Medical condition

The electrical axis of the heart is the net direction in which the wave of depolarization travels. It is measured using an electrocardiogram (ECG). Normally, this begins at the sinoatrial node ; from here the wave of depolarisation travels down to the apex of the heart. The hexaxial reference system can be used to visualise the directions in which the depolarisation wave may travel.

A left posterior fascicular block (LPFB), also known as left posterior hemiblock (LPH), is a condition where the left posterior fascicle, which travels to the inferior and posterior portion of the left ventricle, does not conduct the electrical impulses from the atrioventricular node. The wave-front instead moves more quickly through the left anterior fascicle and right bundle branch, leading to a right axis deviation seen on the ECG.

<span class="mw-page-title-main">Intraventricular block</span> Medical condition

An intraventricular block is a heart conduction disorder — heart block of the ventricles of the heart. An example is a right bundle branch block, right fascicular block, bifascicular block, trifascicular block.

<span class="mw-page-title-main">ST elevation</span> Elevation of the ST segment on an electrocardiogram

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<span class="mw-page-title-main">ST depression</span> Depression of the ST segment on an electrocardiogram

ST depression refers to a finding on an electrocardiogram, wherein the trace in the ST segment is abnormally low below the baseline.

<span class="mw-page-title-main">Left axis deviation</span> Heart condition

In electrocardiography, left axis deviation (LAD) is a condition wherein the mean electrical axis of ventricular contraction of the heart lies in a frontal plane direction between −30° and −90°. This is reflected by a QRS complex positive in lead I and negative in leads aVF and II.

<span class="mw-page-title-main">Electrocardiography in myocardial infarction</span>

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Sgarbossa's criteria are a set of electrocardiographic findings generally used to identify myocardial infarction in the presence of a left bundle branch block (LBBB) or a ventricular paced rhythm.

References

  1. Rebuzzi AG, Loperfido F, Biasucci LM (July 1985). "Transient Q waves followed by left anterior fascicular block during exercise". Br Heart J. 54 (1): 107–9. doi:10.1136/hrt.54.1.107. PMC   481860 . PMID   4015909.
  2. Chandrashekhar Y, Kalita HC, Anand IS (January 1991). "Left anterior fascicular block: an ischaemic response during treadmill testing". Br Heart J. 65 (1): 51–2. doi:10.1136/hrt.65.1.51. PMC   1024464 . PMID   1899584.
  3. Horwitz S, Lupi E, Hayes J, Frishman W, Cárdenas M, Killip T (September 1975). "Electrocardiographic criteria for the diagnosis of left anterior fascicular block. Left axis deviation and delayed intraventricular conduction". Chest. 68 (3): 317–20. doi:10.1378/chest.68.3.317. PMID   1157535.
  4. "Conduction Blocks 2006 KCUMB" . Retrieved 2009-01-20.