Generality
The left anterior hemiblock is a cardiac condition, which arises from the presence of a lesion or a disorder capable of blocking the electrical signal along the anterior fascicle of the left branch of the bundle of His.
The left anterior hemiblock is therefore an anomaly of the heart's so-called electrical conduction system.
Rarely, those with a left anterior hemiblock suffer from particular disorders.
When this happens, the therapy depends on the triggering causes; triggering causes that can be: hypertension, aortic stenosis, myocardial infarction, etc.
Brief anatomical and functional recall of the heart
The heart is an unequal organ, which can be divided into four cavities (the right atrium, the left atrium, the right ventricle and the left ventricle) and is made up of a very particular muscle tissue: the myocardium.
The peculiarity of the myocardium lies in the ability to generate and conduct the nerve impulses by itself for the contraction of the atria and ventricles.
The source of these impulses, which are comparable to electrical signals, resides in the right atrium of the heart and is called the sinoatrial node.
The sinoatrial node has the task of marking the right heart rate of contraction (heart rate), in order to guarantee a normal heart rhythm.
Normal heart rhythm is also known as sinus rhythm.
To best succeed in its contractile action, the sinoatrial node makes use of some sorting centers for electrical impulses. These centers are the atrioventricular node, the bundle of His and the Purkinje fibers, which, together with the sinoatrial node, form the so-called electrical conduction system of the heart.
Figure: in the electrical conduction system of the heart, the sinoatrial node constitutes the main path marker (marker because it marks the heart rate); the atrioventricular node, the bundle of His and the Purkinje fibers, on the other hand, represent the secondary pathway centers, as they depend on the sinoatrial node.
What is the left anterior hemiblock?
Left anterior hemiblock is a heart condition characterized by an abnormality in the electrical signal conduction system.
To be precise, the seat of the abnormality resides in a precise point of the bundle of His (see the chapter dedicated to the causes).
For obvious reasons, a problem affecting the electrical signal conduction system alters the contractile capacity of the heart, therefore its activity.
Causes
Immediately after the atrioventricular node - which resides in an area between the atria and the cardiac ventricles - the bundle of His begins. Initially, the bundle of His is a unitary structure; subsequently, however, it is divided into two branches, the right branch and the left branch.
The right branch spreads the electrical signals, originating in the sinoatrial node, to the right ventricle; the left branch, on the other hand, spreads electrical signals to the left ventricle.
The two branches also show differences in terms of the constituent nerve fibers: the right branch has only one fascicle of fibers; on the other hand, the left branch has two, namely the left anterior fascicle and the left posterior fascicle.
With the term left anterior hemiblock, cardiologists indicate a condition that arises due to the presence of a lesion or disorder capable of blocking the electrical signal along the anterior fascicle of the left branch.
Note: The left anterior hemiblock is a type of left bundle branch block.
Left bundle bundle block is the term used by cardiologists to define a condition characterized by an injury or disorder, which blocks the electrical signal along one or both fascicles of the left bundle.
When the lesion / disorder affects only the posterior fascicle of the left branch, the resulting condition takes the name left posterior hemiblock.
WHAT CAN CAUSE A LEFT ANTERIOR HEMIBLOCK?
Possible causes of a left anterior hemiblock are:
- The presence of an aortic stenosis. Aortic stenosis is a narrowing or "obstruction in the aortic valve of the heart. The aortic valve is the heart element that regulates the flow of blood from the left ventricle of the heart to the aorta."
- Arterial hypertension. It is a constant (therefore not occasional) state of high blood pressure, compared to physiological standards indicating normality.
- Myocardial infarction (or heart attack). It is the pathological process following which the blood supply to the myocardium is less than required.
Often caused by atherosclerosis, heart attack coincides with necrosis (ie death) of the myocardial tissue and causes a reduction in the contractile capacity of the heart. - Dilated cardiomyopathy (or dilated cardiomyopathy). It is a pathology of the myocardium, characterized by a dilation of the left ventricle of the heart, with consequent stretching of its muscular wall. In such conditions, the heart struggles to contract and oxygenates the various organs and tissues of the body less effectively.
- Lenegre's disease (or Lev's disease). It is a degenerative morbid condition, which coincides with fibrosis and calcification of the elements of the electrical conduction system of the heart.
- A state of hyperkalemia. With hyperkalemia, doctors indicate an excess of potassium in the blood.
- A "digoxin intoxication. Digoxin is used therapeutically as a drug to increase the force of contraction of myocardial fibers, both atrial and ventricular.
RISK FACTORS
The two most important risk factors for left anterior hemiblock are:
- Older age. The most common causes of left anterior hemiblock are circumstances more frequent in the elderly than in young adults (eg hypertension).
- The presence of morbid conditions, among which the possible effects c "is the" left anterior hemiblock (for example aortic stenosis, hypertension, dilated cardiomyopathy, etc.).
Symptoms and Complications
In the majority of patients, the left anterior hemiblock is devoid of obvious symptoms and signs, ie it is asymptomatic.
In those rare subjects in which it is symptomatic, it causes episodes of syncope (also known as fainting or loss of consciousness) or presyncope (it is a disorder of a lower degree than syncope, but which occurs in a similar way).
Syncope and presyncope derive from a slowing of the heart rhythm, a slowdown that compromises the blood supply in the various organs and tissues of the human body, brain primarily.
WHEN TO SEE THE DOCTOR?
All patients who experience episodes of syncope and presyncope should contact their doctor or go to the nearest hospital for investigation.
Unfortunately, as long as the left anterior hemiblock lacks obvious symptoms, its identification is completely random.
COMPLICATIONS
In some unfortunate cases, people with a left anterior hemiblock can develop a life-threatening complication known as sudden cardiac death.
Furthermore, certain left anterior hemiblocks are so complex in their pathophysiology that even the most experienced cardiologist struggles to identify their triggers.
Failure to recognize the triggers of a left anterior hemiblock makes it difficult to plan an adequate therapeutic treatment.
Diagnosis
The only diagnostic test that allows the detection of a left anterior hemiblock is the electrocardiogram (ECG).
Other diagnostic procedures, including physical examination, medical history, echocardiogram, and laboratory tests on the patient's blood, are used to identify the triggering causes.
ECG OF A PATIENT WITH LEFT ANTERIOR BLOCK
The ECG of a person with a left anterior hemiblock has some peculiar characteristics, including:
- Small Q wave and high R wave, in leads I and AVL
- Small R wave and deep S wave, in leads II, III and AVF
- Deviation of the electrical axis to the left
Figure: ECG of an individual with left anterior hemiblock. From the site:
lifeinthefastlane.com
Treatment
Treatment of a left anterior hemiblock varies according to the triggering causes and how severe and treatable they are.
This means that, for example, a patient with a left anterior hemiblock from hypertension must undergo therapy for the reduction of too high blood pressure; a patient with a left anterior hemiblock from infarction following coronary artery disease must undergo angioplasty, to free the coronary arteries from obstruction; etc.
If the left anterior hemiblock is asymptomatic and related to conditions that do not require immediate treatment, doctors may find it unnecessary to resort to some kind of treatment.
WHEN DO YOU NEED A PACEMAKER?
Regardless of the causes of the left anterior hemiblock, cardiologists sometimes resort to installing a pacemaker to normalize the heart rhythm.
Specifically, all patients with a left anterior hemiblock that caused syncope are equipped with a pacemaker.
