heart health

Branca block

Generality

The branch block is a cardiac condition resulting from an injury or disturbance of the electrical conduction system of the heart.

There are several types of bundle branch block: the right bundle branch block, the left bundle branch block, the left front bundle, the left posterior bundle, the bifascicular block and the trifascicular block.

Often asymptomatic, the branch block can arise due to: hypertension, myocardial infarction, myocarditis, dilated cardiomyopathy, etc.

The electrocardiogram is essential for a correct diagnosis.

Treatment depends on the triggering causes.

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 branch block?

The bundle branch block is a cardiac condition, characterized by a defect in the electrical signal conduction system.

To be precise, the location of the defect lies in one point of the His beam (see the chapter dedicated to causes).

For obvious reasons, a problem affecting the electrical signal conduction system alters the activity of the heart, compromising its contractile capacities.

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 differ in terms of constituent nerve fibers: the right branch has a single bundle of fibers ; on the other hand, the left branch has two, namely the left front fascicle and the left posterior fascicle .

With the generic term branch block, cardiologists refer to a condition that arises due to an injury or a disorder capable of blocking the electrical signal along one of the two branches.

In the case of the left branch, the element that hinders the electrical signal can affect either the whole branch or only one of the two fascicles.

Thus, distinguishing the possible branch blocks according to the site of the lesion / disorder, it appears that there are:

  • The right bundle branch block : the lesion / disorder concerns exclusively the fascicle of the right bundle branch.
  • The left bundle branch block : the lesion / disorder affects the entire left bundle .
  • The left anterior hemiblock : the lesion / disorder concerns the anterior fasciculus of the left bundle branch
  • The left posterior hemiblock : the lesion / disorder affects the posterior fasciculus of the left bundle branch.
  • The bifascicular block : the lesion / disorder concerns the fascicle of the right branch and one of the two fascicles of the left branch.
  • Trifascicular block : the lesion / disorder affects the fascicle of the right bundle branch and the two fascicles of the left bundle branch.

ORIGINS OF A BLOCK OF RIGHT BRANCA

The possible causes of a right bundle branch block include:

  • Myocardial infarction (or heart attack ). It is the pathological process due to which the flow of blood destined for the myocardium is inadequate to the requests.

    Often caused by atherosclerosis, the heart attack coincides with the necrosis (ie death) of the myocardial tissue and causes a reduction in the contractile capacity of the heart.

  • Arterial hypertension . It is a constant state (therefore not occasional) of high arterial pressure, compared to the physiological standards indicating normality.
  • Some congenital anomalies of the heart . One of the best known congenital anomalies of the heart to cause a right bundle branch block is the so-called interatrial septal defect (or, more simply, interatrial defect). The defect of the interatrial septum is a real hole located in the portion of tissue that separates the right atrium from the left atrium of the heart.

    To learn more about the interatrial defect, we recommend the article here.

  • A viral myocarditis or bacterial myocarditis . The term "myocarditis" means inflammation of the myocardium. A myocarditis is viral, if the factor that triggers it is a virus; while it is bacterial, if the agent that causes it is a bacterium.
  • A condition of pulmonary embolism . In the medical field, the term pulmonary embolism indicates the obstruction of a blood vessel that leads blood from the heart to the lungs, to oxygenate it.
  • The presence of a right ventricular hypertrophy . It is a cardiac condition characterized by a thickening of the myocardium that constitutes the right ventricle. If the right ventricle is hypertrophic, the heart struggles to pump blood to the lungs, where it must flow to oxygenate itself. If left untreated, right ventricular hypertrophy can result in an even more serious condition known as the pulmonary heart (another cause of right bundle branch block).
  • The presence of a degenerative disease of the conduction system of the heart .

ORIGINS OF A BLOCK OF LEFT BRANCA

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 factors that favor the appearance of a branch block are:

  • Advanced age. Many causes of the bundle branch block are more frequent conditions in the elderly than in the young adult.
  • The presence of morbid conditions, among which the consequences is the branch block (for example hypertension, heart diseases, etc.).

Symptoms and Complications

In most cases, the bundle branch block is asymptomatic, that is, devoid of symptoms and obvious signs.

In those rare situations in which it is symptomatic, it is the cause of syncope (equivalent to fainting or loss of consciousness) or presyncope (it is a disorder of a lower grade than syncope, but which is established in a similar way).

Syncope and pre-syncope are due to a slowing of the heart rate, slowing down which affects the blood supply of the various organs and tissues of the human body, brain in the first place .

WHEN TO REFER TO THE DOCTOR?

The circumstances that make a medical consultation necessary are, for obvious reasons, possible episodes of syncope and presyncope.

Unfortunately, as long as the branch block remains asymptomatic, it remains a condition that can only be identified by chance during a routine cardiological examination.

COMPLICATIONS

The presence of a branch block can be a cause of sudden cardiac death, a complication which - as can be guessed from the name - has lethal outcomes.

Furthermore, some branch blocks have such a complex pathophysiology that it is difficult to interpret their triggering causes.

Failure to recognize the causes of a branch block makes it difficult to plan for proper treatment.

Diagnosis

Doctors recognize the presence of a branch block only through an electrocardiogram ( ECG ).

To trace the causes, on the other hand, they must use an accurate physical examination, a precise medical history, an echocardiogram and some laboratory tests on the patient's blood.

ECG OF A PATIENT WITH BRANCA BLOCK

The electrocardiogram of an individual with a bundle branch block has some peculiar characteristics, including:

  • Enlarged QRS complex (lasting more than 0.12 seconds)
  • T-wave anomalies, which have opposite orientation to the QRS complex

To know what the QRS complex is, the T wave and the other elements of an electrocardiographic trace, readers are advised to consult the article dedicated to the ECG.

Figure: ECG of a patient with right bundle branch block. From the site:

lifeinthefastlane.com

Figure: ECG of a patient with left bundle branch block. From the site:

lifeinthefastlane.com

Treatment

The treatment of a branch block depends mainly on the causes, their severity and the possibility of their treatment.

This means that, for example, a patient with a branch block of hypertension must undergo therapies to reduce a too high blood pressure; a patient with a branch block from an infarct following coronary artery disease should undergo angioplasty, to free the coronary arteries from obstruction; etc.

Doctors may find it unnecessary to treat a bundle branch block if it is asymptomatic and associated with conditions that do not require immediate treatment.

WHEN NEED A PACEMAKER?

Regardless of the causes of the branch block, cardiologists sometimes resort to installing a pacemaker for normalizing heart rhythm.

Specifically, they provide a pacemaker with all those patients with a branch block that gave rise to episodes of syncope.