Generality
The left bundle branch block is a cardiac condition, which occurs due to the presence of a lesion or a disorder capable of blocking the electrical signal along either or only one of the two fascicles of the left bundle of the His bundle.
The left bundle branch block, therefore, is an anomaly of the so-called electrical conduction system of the heart.
Rarely, those with a left bundle branch block exhibit particular symptoms and signs.
In such situations, therapy depends on the triggering causes; triggers 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 composed of a very particular muscle tissue: the myocardium .
The peculiarity of the myocardium lies in the ability to generate and conduct nerve impulses by the contraction of the atria and the ventricles .
The source of these impulses, which are comparable to electrical signals, resides at the level of the right atrium of the heart and is called the atrial sinus node .
The atrial sinus node has the task of scanning the right frequency of contraction of the heart ( heart rate ), in such a way as to guarantee a normal heart rhythm.
The normal heart rate is also known as sinus rhythm .
To best succeed in its contractile action, the atrial sinus node uses some sorting centers for electrical impulses. These centers are the atrioventricular node, the bundle of His and the Purkinje fibers, which, together with the atrial sinus node, form the so-called electrical conduction system of the heart .
Figure: in the electrical conduction system of the heart, the atrial sinus node constitutes the main pedestal center (marker because it scans the heart rate); the atrioventricular node, the His bundle and the Purkinje fibers, on the other hand, represent the secondary marker centers, as they depend on the atrial sinus node.
What is the left bundle branch block?
The left bundle branch block is a cardiac condition, characterized by an abnormality in the electrical signal conduction system.
To be precise, the site of the abnormality lies in a precise point of the His beam (see the chapter dedicated to causes).
For obvious reasons, a problem related to the electrical signal conduction system affects the contractile capacities of the heart, hence its activity.
Causes
Immediately after the atrioventricular node - which resides in an area between atrial and cardiac ventricles - the bundle of His begins. Initially, the His bundle is a unitary structure; subsequently, however, it is divided into two branches, the right branch and the left branch .
The right branch diffuses electrical signals, originating in the atrial sinus node, to the right ventricle; the left branch, on the other hand, diffuses electrical signals to the left ventricle.
The two branches also present differences in terms of constituent nerve fibers: the right branch has a fascicle only of fibers ; on the other hand, the left branch has two, namely the left front fascicle and the left posterior fascicle.
With the term left bundle branch block, cardiologists indicate a condition that arises due to the presence of a lesion or a disorder capable of blocking the electrical signal along either or only one of the two fascicles of the left branch.
In reality, the left branch blocks that affect only one of the two files have specific wordings: in this case, we speak of anterior left emiblocco, if the left bundle branch block concerns only the front fascicle; while talking about the left posterior hemiblock, if the left bundle branch block involves only the posterior fasciculus.
WHAT CAN CAUSE A BLANCA LEFT BLOCK?
The possible causes of a left bundle branch block, an anterior left bundle or a left posterior block are:
- The presence of an aortic stenosis . Aortic stenosis indicates the presence of a narrowing or obstruction of the heart's aortic valve. The aortic valve is the element that regulates the passage of blood from the left ventricle of the heart to the aorta.
- Arterial hypertension.
- Myocardial infarction.
- Dilatative 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. A heart in such conditions contracts with greater difficulty and is less effective in its action of oxygenating the organs and tissues of the body.
- Lenegre's disease (or Lev's disease ). It is a degenerative morbid condition, characterized by fibrosis and calcification of the elements of the electrical conduction system of the heart.
- A state of hyperkalemia . Hyperkalemia indicates an excess of potassium in the body's blood.
- Digoxin intoxication. Digoxin is a digitalis glycoside, which is used in the therapeutic field as a drug to increase the strength of contraction of both atrial and ventricular myocardial fibers.
RISK FACTORS
The two most important risk factors of the left bundle branch block are:
- Advanced age. The most common causes of left bundle branch block are more frequent conditions in the elderly than in the young adult (eg hypertension).
- The presence of morbid conditions, among whose consequences there is the left bundle branch block (for example aortic stenosis, hypertension, dilated cardiomyopathy, etc.).
Symptoms and Complications
In the majority of patients, the left bundle branch block is asymptomatic, ie it does not involve the presence of any symptoms or evident sign.
In those rare subjects in which it is symptomatic, it causes episodes of syncope (also known as fainting or loss of consciousness) or pre- syncope (it is a disorder of a lower grade than syncope, but which is established in a similar way).
Syncope and pre-syncope are consequences of a slowing of the heart rate, slowing down which affects the flow of blood in the various organs and tissues of the human body, brain in the first place .
WHEN TO REFER TO THE DOCTOR?
All patients who are victims of syncope and presyncope should be referred to the doctor or the nearest hospital for tests.
Unfortunately, as long as the left bundle branch block is asymptomatic, it remains a condition identifiable only by chance, during a routine cardiological check.
COMPLICATIONS
In some unfortunate cases, people with a left bundle branch block may develop a lethal complication, known as sudden cardiac death .
Furthermore, certain left branch blocks are so complex in pathophysiology that even the most experienced cardiologist has difficulty in identifying the triggering factors.
Failure to recognize the causes of a left bundle branch block complicates the planning of adequate therapeutic treatment.
Diagnosis
The only diagnostic test that allows the identification of a left bundle branch block is the electrocardiogram ( ECG ).
Other diagnostic procedures, including physical examination, medical history, echocardiography and laboratory tests on the patient's blood, are used to identify the causes.
ECG OF A PATIENT WITH A BRANCA LEFT BLOCK
The ECG of a person with a left bundle branch block has some peculiar characteristics, including:
- Enlarged QRS complex (lasting more than 0.12 seconds)
- R anomalous wave in branch I and derivation V6
- Presence of predominantly negative QRS (pointing downwards) in V1, V2 and V3
- T-wave abnormalities, which have opposite orientation to the QRS complex
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Treatment
The treatment of a left bundle branch block varies depending on the triggers and on how serious and treatable they are.
This means that, for example, a patient with a left bundle branch block by hypertension must undergo therapies for reducing too high blood pressure; a patient with a left bundle branch block following a coronary artery disease must undergo angioplasty to clear the coronary arteries of the obstruction; etc.
If the left bundle branch block is asymptomatic and connected to conditions that do not require immediate care, doctors may find it unnecessary to resort to some kind of treatment.
WHEN NEED A PACEMAKER?
Regardless of what are the triggers of the left bundle branch block, cardiologists sometimes resort to installing a pacemaker for normalizing heart rhythm.
Specifically, they provide a pacemaker with all those individuals with a left bundle branch block that induced episodes of syncope.
