An atrioventricular block, also known as AV block, is a condition that affects the electrical conduction system of the heart. It occurs when the electrical signals that regulate the heartbeat are delayed or blocked as they travel from the atria (upper chambers) to the ventricles (lower chambers). This disruption in the normal electrical conduction can lead to a variety of symptoms and complications.
AV blocks are classified into three different degrees:
first-degree AV block, second-degree AV block, and third-degree AV block.
First-degree AV block is the mildest form of AV block and is characterized a delay in the conduction of electrical signals from the atria to the ventricles. In this type of block, every electrical impulse is transmitted from the atria to the ventricles, but with a delay. First-degree AV block often does not cause any symptoms, and most people are unaware they have it.
Second-degree AV block is divided into two types:
Mobitz type we (Wenckebach) and Mobitz type II.
Mobitz type we AV block occurs when there is progressive lengthening of the delay between the atria and ventricles until a signal is completely blocked. Eventually, an electrical impulse fails to reach the ventricles, resulting in a skipped heartbeat. This pattern repeats itself, causing a periodic irregularity in the heart rhythm. Mobitz type we block usually does not cause significant symptoms but can occasionally lead to dizziness or fainting.
Mobitz type II AV block is a more severe form of AV block. In this type, the electrical impulses can be intermittently blocked without any progressive lengthening of the delay. As a result, there may be long pauses between heartbeats, leading to more pronounced symptoms such as dizziness, fainting, and shortness of breath. Mobitz type II block is associated with a higher risk of progressing to a complete heart block.
Third-degree AV block, also known as complete heart block, is the most severe form of AV block. It occurs when there is a complete blockage of the electrical signals between the atria and ventricles. In this type of block, the atria and ventricles beat independently, causing a significant disruption in the heart’s ability to pump blood effectively. Third-degree AV block often requires immediate medical attention and management, such as the placement of a pacemaker.
AV blocks can be caused various factors, including congenital heart defects, heart diseases (such as coronary artery disease or myocardial infarction), medication side effects (such as beta-blockers or calcium channel blockers), certain infections (such as Lyme disease), and electrolyte imbalances (such as high potassium levels).
The symptoms of AV blocks can vary depending on the type and severity of the block. In many cases, first-degree AV block does not cause any noticeable symptoms. However, second-degree and third-degree AV blocks can present with symptoms such as palpitations, dizziness, lightheadedness, fainting (syncope), chest pain or discomfort, shortness of breath, fatigue, and weakness.
Diagnosing an AV block typically involves an electrocardiogram (ECG) test, which records the electrical activity of the heart. The ECG can determine the type of AV block, its severity, and the location of the blockage within the conduction system. Additional tests, such as a Holter monitor (a portable ECG device worn for 24-48 hours) or an exercise stress test, may be conducted to capture any intermittent or exercise-induced blockages.
The management of AV blocks depends on various factors, including the type and severity of the block, the presence of symptoms, and the underlying cause. In certain cases, no specific treatment may be required, especially for first-degree AV blocks without symptoms. However, regular monitoring and follow-up with a healthcare professional are necessary.
For symptomatic AV blocks or those at higher risk of progression, treatment options may include medications, procedures, or devices to improve or control the heart’s electrical conduction.
Medications such as beta-blockers or calcium channel blockers may be prescribed to regulate the heart rate and prevent symptoms. In some cases, temporary or permanent pacemakers may be implanted to provide the necessary electrical impulses and maintain an appropriate heart rhythm. A pacemaker is a small device that is surgically placed under the skin and connected to the heart through wires (leads). It monitors the heart’s electrical activity and delivers electrical impulses when needed.
In cases of third-degree AV block, where there is a complete heart block, the placement of a pacemaker is often the preferred treatment option. Without intervention, a complete heart block can lead to life-threatening complications, including severe bradycardia (slow heart rate), heart failure, or sudden cardiac arrest.
In addition to medical management, lifestyle modifications are essential for individuals with AV blocks. This may include maintaining a healthy diet, exercising regularly (as tolerated), avoiding excessive alcohol and caffeine intake, quitting smoking, and managing stress levels. These lifestyle changes can support overall heart health and potentially reduce the risk of complications related to AV blocks.
An atrioventricular block is a condition that affects the electrical conduction system of the heart and disrupts the normal transmission of electrical signals between the atria and ventricles. AV blocks can range from mild to severe, with varying symptoms and potential complications. Prompt diagnosis and appropriate management, including medication, pacemakers, or other interventions, are crucial in mitigating symptoms and preventing adverse outcomes. Regular monitoring and follow-up with a healthcare professional are essential for individuals with AV blocks to ensure the ongoing assessment of their condition and optimized management strategies.