Atrioventricular blocks (AV blocks) are a category of arrhythmias that occur when the electrical conduction of the heart is disrupted in the atrioventricular node (AV node). The AV node is the region of the heart that connects the atria to the ventricles and allows the transfer of the electrical impulse from the atria to the ventricles. If this conduction is disrupted, the ventricles do not receive the impulse to contract normally, thus causing a delay or even interruption of the heart contraction from the atria.
How dangerous atrioventricular blocks are depends on the severity of the block and the patient’s cardiac condition. Mild forms have a good prognosis, while severe forms pose a risk of cardiac complications. In all cases, a check-up by a Cardiologist is required who will clearly demonstrate the type and size of the specific arrhythmia.
Atrioventricular block is classified into three main degrees, depending on the severity and extent of the conduction disorder:
- First degree (first-degree AV): Conduction is slower than normal, but all electrical impulses from the atria reach the ventricles. They have no symptoms and are detected on the electrocardiogram. It does not require treatment, unless accompanied by other cardiac problems.
- Second degree (second-degree AV): It is divided into two types:
- Type 1 Mobitz block, where conduction in the atria and ventricles is still possible, but sometimes the impulses from the atria do not reach the ventricles, causing the loss of a heartbeat. They may cause dizziness or palpitations. They are detected on the electrocardiogram by a progressive prolongation of the PR interval until a contraction is lost. Usually does not require specific treatment.
- Mobitz block type 2: Some impulses do not reach the ventricles and do not cause contraction. It may cause dizziness, fainting, or palpitations. This type can be more dangerous and requires intervention. On the electrocardiogram, the impulses from the atria reach the ventricles only a few times and then are lost, with no increasing delay.
- Third degree (complete AV block): Electrical impulses from the atria do not reach the ventricles at all. The atrioventricular node does not allow the impulse to be transmitted, and the ventricles create their own rhythm, which is much slower than the normal heart rate. This condition can cause severe dizziness, fainting, fatigue, and shortness of breath due to the slow heart rate. On the electrocardiogram, there is complete cessation of conduction from the atria to the ventricles, with the two parts of the heart functioning independently. Often, the problem is treated by implanting a pacemaker to ensure the correct heart rhythm and avoid dangerous complications.
What causes atrioventricular blocks
- Heart diseases such as coronary artery disease, myocardial infarction, cardiomyopathy, inflammatory myocardial disease.
- Disorders in potassium, calcium or sodium levels.
- Certain medications can cause or worsen atrioventricular block.
- Age, as conduction can worsen over the years.
- High blood pressure, other cardiovascular abnormalities and inflammatory heart diseases.
