(Atrioventricular [AV] Block)
Definition
The heart is comprised of four chambers: two upper chambers (atria) and two lower chambers (ventricles). The sinoatrial (SA) node, located near the top of the right atrium, produces electrical signals that are sent to the atrioventricular (AV) node. The AV node, also located in the right atrium, then sends the signals to the ventricles, which are the primary pumping chambers of the heart. When the heart is functioning well, the electrical signals are transmitted smoothly from the atria to the ventricles, causing rhythmic muscle contractions that pump blood to the rest of the body.
Heart block occurs when the electrical signals from the sinoatrial node are too slow (bradycardia). (Heart block does NOT mean that blood is being literally blocked from the heart.)
There are three types of heart block, ranging from mild to serious:
• First-degree heart block: This is the mildest form of heart block. In this case, the electrical signals from the SA node move more slowly than normal to the AV node, but all signals reach the ventricles. There are usually no symptoms, and heartbeat and rhythm are normal. This type of heart block is often found in well-trained athletes.
• Second-degree heart block: A second-degree heart block means that some of the electrical signals are not reaching the ventricles. This causes “dropped beats.” There are two types of second-degree heart block:
o Type I second-degree heart block: (also called Mobitz Type I or Wenckebach’s AV block) The electrical signals become increasingly delayed with each heartbeat, ultimately causing a beat to be missed.
o Type II second-degree heart block : (also called Mobitz Type II) In this type of heart block, some of the electrical signals do not reach the ventricles. This is less common, but more serious.
• Third-degree, or complete, heart block: This is the most serious type of heart block. In this condition, no electrical signals are able to reach the ventricles. The ventricles compensate by contracting on their own, but at a much slower rate than is safe for the heart to maintain full function.
Third-degree heart block is extremely serious and requires immediate care from your doctor. First- and second-degree heart block should be diagnosed by your physician, who will help you determine the best course of treatment, if any.
Anatomy of the Heart
Causes
Heart block often occurs when there is underlying heart disease. The causes of heart block include:
• History of heart disease (myocardial infarction, congestive heart failure, valvular problems, endocarditis)
• Hereditary heart defect
• Use of certain types of medications, such as:
o Beta blockers (eg, propanolol)
o Calcium channel blockers (eg, verapamil, diltiazem)
o Digitalis
Risk Factors
The following factors increase your chance of developing heart block. If you have any of these risk factors, tell your doctor:
• History of heart disease
• Use of medications such as beta blockers, calcium channel blockers, or digitalis
Symptoms
If you experience any of these symptoms, do not assume it is due to heart block. These symptoms may be caused by other, less serious health conditions. If you experience any one of them, see your physician.
• Dizziness or lightheadedness
• Fainting (syncope)
• Chest pain
• Shortness of breath
Diagnosis
Your doctor will ask about your symptoms and medical history, and perform a physical exam. He or she may also refer you to a cardiologist or arrhythmia specialist.
Tests may include the following:
• Electrocardiogram (ECG): a test that records the heart's activity by measuring electrical currents through the heart muscle
• Echocardiogram: a test that uses high-frequency sound waves (ultrasound) to examine the size, shape, and motion of the heart
Treatment
The course of treatment will depend on the type of heart block you have. Generally, treatment is not necessary for first-degree heart block.
Talk with your doctor about the best treatment plan for you. Treatment options include the following:
• Pacemaker: A pacemaker may be inserted for some cases of second-degree heart block, and all cases of third-degree heart block. A pacemaker is a device that generates electrical signals to stimulate heart muscle contractions.
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Prevention
To help reduce your chances of getting heart block, take the following steps:
• Obtain treatment for any underlying heart problems or heart disease. This will help prevent heart block.
• If possible, avoid medications that can cause heart block, such as beta blockers, calcium channel blockers, and digitalis.
• Maintain a healthy weight and lifestyle. Get regular exercise, eat a heart-healthy diet, and minimize stress.
• Avoid excessive consumption of alcohol and caffeine.
• Stop smoking.
