What Is a Heart Block?

For the heart to supply every cell of the body with enough blood it should contract properly with the rate between 55-60 and 80-90 beats per minute. Heart rhythm should be regular with equal intervals between contractions, because the lack of oxygen transferred with blood that can be provoked by a heart disease affects the functioning of all body cells.

Heart contractions that ensure its work occur under the influence of electrical impulses which are generated and carried out through all the parts of the heart with the help of the electrical conduction system of the heart. Normally, electrical signal is generated in the sinoatrial node (heart’s natural pacemaker) located in the upper part of the right atrium. It travels to the atria and then through atrioventricular (AV) node to the ventricles causing the heart to contract and pump blood. Heart block is a condition in which the electrical signal is disturbed or slowed when travelling through the heart.

Heart block types Depending on the place where conduction can be disturbed heart block is divided into the following types:

• Sinoatrial (SA) heart blocks. They are characterized by partial or complete interference in the spread of electrical signals from the sinoatrial node. Individuals with this type of block rarely have severe symptoms. However, in some patients it may cause fainting, chest pain, signs of shock, and altered mental status. It’s not a life-threatening condition and most often don’t require any treatment; however, it’s still the most common indication for a pacemaker implantation.
• Atrioventricular (AV) heart blocks. They are characterized by partial or complete blockage of the signal transmission from the atria to the ventricles. There are three types of AV blocks:
  1. First-degree block – the conduction is slowed, but there are no skipped beats. It may be physiologic in well-trained athletes and young people with increased vagal tone.
  2. Second-degree block – one or more of the atrial electrical signals fail to travel to the ventricles. It can cause light-headedness, fainting or dizziness.
  3. Third-degree block – it’s a complete heart block in which there is no electrical connection between the atria and the ventricles. Most patients with this type of AV block require a pacemaker.
• Infra-Hisian heart blocks – the conduction is blocked at the level of His (a collection of cells specialized for electrical conduction).
• Bundle branch blocks – disrupted electrical conduction within the right and left bundle branches.

Causes In general, heart blocks result from the progression of certain diseases:

• Thyrotoxic myocarditis;
• Diffuse disorders of the connective tissues;
• Heart defects and tumors;
• Myxedema;
• Amyloidosis and sarcoidosis;
• Syphilis that affected the heart;
• Myocardial defects associated with rheumatism;
• Myocardial infarction and cardiosclerosis.

Other common causes include:

• Drug intoxication;
• Increased stress during strenuous physical activity;
• Congenital intrauterine development pathologies;
• Certain surgical interventions.

Diagnosis This condition is usually diagnosed during routine tests for other disorders. Methods used for the heart block diagnosis include:

• Electrocardiogram (ECG) - the main method confirming the presences of a heart block. It can be performed at rest or while exercising.
• Holter monitoring – a long-term recording of the patient’s ECG using a portable device.

Treatment Heart block treatment depends on the type of the condition the patient has. Some heart blocks, like first-degree ones, don’t need any treatment. More severe forms of heart blocks may require implantation of a pacemaker.