What is First-Degree Heart Block?
First-degree atrioventricular (AV) block is a condition where there’s a delay in the signals that control your heart’s rhythm. This condition can be identified using a test called an electrocardiogram (ECG) which detects these slow signals. Here, if the time taken for a signal (referred to as the “PR interval”) to pass from the upper chambers of the heart (atria) to the lower chambers (ventricles) is more than 0.20 seconds, it can be diagnosed as first-degree AV block. Normal PR interval is between 0.12 and 0.20 seconds. If the PR interval is more than 0.30 seconds long, this condition is considered “marked”. In some cases, the heartbeat signals (P waves) can overlap with the previous heartbeat’s signals (T waves).
Most people with first-degree AV block do not have any symptoms or serious complications. For most patients, treatment usually isn’t necessary other than regularly checking for any changes or worsening of this delay in heart signal conduction. However, regular check-ups are important because patients with this heart condition have a higher chance of developing a more serious heart rhythm condition called atrial fibrillation or a more severe form of AV block.
What Causes First-Degree Heart Block?
First-degree AV block—a type of heart condition—has been linked to a high level of activity in the part of the nervous system that helps to control heart rate. This is often the case in younger patients, as many of the early studies on this condition utilized young, healthy volunteers. In older patients, the condition seems to connect to scarring changes in the heart’s system that sends electrical signals.
Furthermore, a variety of causes can lead to first-degree AV block. These include heart disease, heart attacks, electrolyte imbalances (particularly low levels of potassium and magnesium), inflammation, and various infections such as endocarditis, rheumatic fever, Chagas disease, Lyme disease, and diphtheria.
Certain medications—specifically types of drugs including antiarrhythmics and digoxin—are also known to cause this condition. Ditto for certain diseases that affects the body’s tissues (like sarcoidosis), autoimmune diseases (such as lupus, rheumatoid arthritis, and scleroderma), specific types of degenerative diseases (Lenegre and Lev diseases), and conditions that affect muscles and nerves.
Thus, there are many potential causes of first-degree AV block, varying from person to person.
Risk Factors and Frequency for First-Degree Heart Block
As people get older, they are more likely to develop a heart condition known as first-degree AV block. Until the age of 60, only about 1.0% to 1.5% of people have this condition. But, after turning 60, about 6.0% of people have it. First-degree AV block is more common in males than females, and it often occurs in athletes. Many young athletes have a higher chance of getting it, with more than 10% experiencing this heart condition. This might be due to their heightened physical activity levels.
- First-degree AV block becomes more common as people age.
- Up to the age of 60, about 1.0% to 1.5% of people have it.
- For those 60 and older, roughly 6.0% have the condition.
- It is more common in males, with two males having it for every female.
- Above 10% of young athletes may have it, suggesting that high physical activity can increase the risk.
Signs and Symptoms of First-Degree Heart Block
First-degree AV block, a heart condition, is usually symptomless. Many people might not know they have it until a routine heart test, called an electrocardiogram, shows it. When this prolonged PR interval – a measure of time in the heart’s electrical cycle – is noticed, doctors will ask about your medical history. They’ll be interested to know whether you’ve had any heart disease present since birth or that you’ve developed over time, whether heart disease runs in your family, and whether you’ve been diagnosed with neuromuscular disease. In severe cases of first-degree AV block where the PR interval exceeds 0.30 seconds, you might experience breathlessness, a general feeling of discomfort, a lightheaded sensation, chest pain, or fainting due to unsynchronized heart muscle contractions. This causes discomfort as your heart’s two upper chambers contract against closed heart valves.
- Breathlessness
- General feeling of discomfort
- Lightheadedness
- Chest pain
- Fainting
Typically, there are no specific signs of first-degree AV block that a doctor could detect by examination. Nevertheless, a general check for signs of heart disease is recommended. This might include listening for abnormal heart sounds, checking the neck for obvious veins, palpating for fluid buildup in the peripheral extremities, or inspecting the skin for signs like blue discoloration, unusual finger shape, or other signs of chronic heart disease.
Testing for First-Degree Heart Block
If your doctor sees that the time it takes for the electrical signals to reach from the upper to the lower part of your heart is over 0.20 seconds on an EKG (heart rhythm test), this might mean you have a mild type of heart block known as first-degree AV block. If your doctor finds this, they may ask about any heart diseases you already have or might be born with, as well as if any of your relatives have heart disease. Patients with heart disease or with relatives that have heart disease should be checked further to find out the possible causes of the longer time it takes for these signals to reach certain parts of the heart.
On the other hand, if you don’t have any symptoms or heart diseases, you might not need any additional checks. But, if you do show symptoms, have a slower electrical signal to the lower chambers of your heart, or already have heart disease, you might need more detailed tests. These additional tests can pinpoint where exactly in your heart the electrical signal is slowing down.
Treatment Options for First-Degree Heart Block
First-degree atrioventricular block (AV block) is a condition that affects the heart’s electrical system. For most people with this condition, treatment usually isn’t necessary. According to the American Heart Association (AHA) and American College of Cardiology (ACC) guidelines, a permanent pacemaker–a device that helps control the heart’s rhythm–isn’t usually recommended for people with first-degree AV block, unless their case is extreme (with a PR interval greater than 0.30 seconds) and they’re experiencing symptoms. Symptoms can include dizziness, fatigue, or shortness of breath and they are often due to the heart’s chambers (the atria and ventricles) not working together as they should.
There are, however, exceptions. For instance, patients with first-degree AV block and other conditions like a neuromuscular disease or a prolonged QRS interval, which is an unusual heart rhythm, may also be considered for a pacemaker. If the AV block is connected to a heart attack, a pacemaker might be needed as well, but doctors usually wait to see if the AV block improves as the patient recovers from the heart attack. Medication to control heart rhythm aren’t generally recommended for first-degree AV block.
Even when treatment isn’t necessary, people with first-degree AV block should have regular check-ups to make sure the condition isn’t getting worse. These check-ups might involve routine electrocardiograms (ECGs), a type of test that records the electrical activity of the heart. Further investigation is typically not necessary unless the PR interval prolongation, or delay in the heart conduction, gets worse.
Although first-degree AV block is usually considered benign, meaning it’s not harmful or severe, some research has shown that patients with this condition may have a higher chance of developing other heart conditions, such as atrial fibrillation (irregular heartbeat), needing a pacemaker, or experiencing all-cause mortality than patients with normal PR intervals. However, it’s not clear yet whether this is because first-degree AV block is more common in people with heart diseases or if first-degree AV-block itself can lead to worse conditions even if a person doesn’t have other heart diseases.
What else can First-Degree Heart Block be?
When trying to understand different heart conditions, here are some you might hear about:
- Atrioventricular block
- Atrioventricular dissociation
- Second-degree AV block
- Third-degree AV block
What to expect with First-Degree Heart Block
First-degree heart block is a condition that was initially believed to have a benign or harmless prognosis, as it does not have any direct health impacts. People with this condition usually do not show any immediate symptoms. However, the Framingham Study, which is a long-term health study, found that patients with prolonged PR intervals (indicating first-degree heart block) had twice the risk of developing an irregular heart rhythm known as atrial fibrillation. Additionally, these patients were three times more likely to need a pacemaker, which is a device that helps regulate your heart’s rhythm.
Possible Complications When Diagnosed with First-Degree Heart Block
First-degree heart block usually doesn’t show any symptoms and is often found by chance during an EKG test. It’s important, however, for patients to have regular check-ups to make sure that this condition doesn’t worsen over time and lead to more serious heart problems. Generally, patients can live a normal life without any symptoms as long as the condition doesn’t progress.
Preventing First-Degree Heart Block
People who have a first-degree heart block often don’t need any treatment. However, it’s important for them to understand the signs of this condition getting worse. These symptoms might include:
- Feeling light-headed or faint
- Sensing that your heart is skipping a beat
- Experiencing chest pain
- Having trouble catching your breath or feeling short of breath
- Feeling nauseous for no discernible reason
- Becoming tired very easily
If you have a first-degree heart block and start to notice any of these symptoms, it’s crucial to seek medical attention promptly.