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 EKG, 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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Electrocardiography is the process of producing an electrocardiogram, a recording of the heart's electrical activity. It is an electrogram of the heart which is a graph of voltage versus time of the electrical activity of the heart using electrodes placed on the skin. These electrodes detect the small electrical changes that are a consequence of cardiac muscle depolarization followed by repolarization during each cardiac cycle (heartbeat). Changes in the normal ECG pattern occur in numerous cardiac abnormalities, including cardiac rhythm disturbances, inadequate coronary artery blood flow, and electrolyte disturbances.

Bundle of His Collection of heart muscle cells

The bundle of His (BH) or His bundle (HB) ( "hiss") is a collection of heart muscle cells specialized for electrical conduction. As part of the electrical conduction system of the heart, it transmits the electrical impulses from the atrioventricular node to the point of the apex of the fascicular branches via the bundle branches. The fascicular branches then lead to the Purkinje fibers, which provide electrical conduction to the ventricles, causing the cardiac muscle of the ventricles to contract at a paced interval.

Third-degree atrioventricular block Medical condition

Third-degree atrioventricular block is a medical condition in which the nerve impulse generated in the sinoatrial node in the atrium of the heart can not propagate to the ventricles.

Electrical conduction system of the heart Aspect of heart function

The electrical conduction system of the heart transmits the signals generated by the sinoatrial node – the heart's pacemaker, to cause the heart muscle to contract, and pump blood through the body's circulatory system. The pacemaking signal travels through the right atrium to the atrioventricular node, along the Bundle of His, and through the bundle branches to Purkinje fibers in the ventricles. The Purkinje fibers transmit the signals more rapidly to stimulate contraction firstly of the right and left atrium, and then the right and left ventricles.

First-degree atrioventricular block Medical condition

First-degree atrioventricular block is a disease of the electrical conduction system of the heart in which electrical impulses conduct from the cardiac atria to the ventricles through the atrioventricular node more slowly than normal. First degree AV block does not generally cause any symptoms, but may progress to more severe forms of heart block such as second- and third-degree atrioventricular block. It is diagnosed using an electrocardiogram, and is defined as a PR interval greater than 200 milliseconds. First degree AV block affects 0.65-1.1% of the population with 0.13 new cases per 1000 persons each year.

Heart block Medical condition

Heart block (HB) is a disorder in the heart's rhythm due to a fault in the natural pacemaker. This is caused by an obstruction – a block – in the electrical conduction system of the heart. Sometimes a disorder can be inherited. Despite the severe-sounding name, heart block may cause no symptoms at all in some cases, or occasional missed heartbeats in other cases, or may require the implantation of an artificial pacemaker, depending upon exactly where in the heart conduction is being impaired and how significantly it is affected.

Left ventricular hypertrophy Medical condition

Left ventricular hypertrophy (LVH) is thickening of the heart muscle of the left ventricle of the heart, that is, left-sided ventricular hypertrophy.

T wave Repolarization of the ventricles in a human heart

In electrocardiography, the T wave represents the repolarization of the ventricles. The interval from the beginning of the QRS complex to the apex of the T wave is referred to as the absolute refractory period. The last half of the T wave is referred to as the relative refractory period or vulnerable period. The T wave contains more information than the QT interval. The T wave can be described by its symmetry, skewness, slope of ascending and descending limbs, amplitude and subintervals like the Tpeak–Tend interval.

Bundle branch block Medical condition

A bundle branch block is a defect in one the bundle branches in the electrical conduction system of the heart.

QRS complex Represents ventricular depolarization, which results in ventricular contraction

The QRS complex is the combination of three of the graphical deflections seen on a typical electrocardiogram. It is usually the central and most visually obvious part of the tracing. It corresponds to the depolarization of the right and left ventricles of the heart and contraction of the large ventricular muscles.

Right bundle branch block Medical condition

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

Left bundle branch block 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.

Bifascicular block Conduction abnormality in the heart

Bifascicular block is a conduction abnormality in the heart where two of the three main fascicles of the His/Purkinje system are blocked.

Right axis deviation 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.

Intraventricular block 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.

ST depression 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.

Left axis deviation

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.

Electrocardiography in myocardial infarction

Electrocardiography in suspected myocardial infarction has the main purpose of detecting ischemia or acute coronary injury in emergency department populations coming for symptoms of myocardial infarction (MI). Also, it can distinguish clinically different types of myocardial infarction.

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.
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