Heart block, or atrioventricular (AV) block, means that the electrical signal in a person’s heart does not travel through it correctly. Second degree heart block type I means that the signal sometimes does not reach the ventricles, causing skipped beats.
There are three subtypes of second-degree heart block. Type I is often benign and may not require treatment, whereas the others are more serious.
Learn more about second degree heart block type I, including symptoms, causes, treatment, and how it differs from other types of second degree heart block.
The heart has a complex electrical system. In heart block, the electrical signal does not travel from the top part of the heart — the atria — to the bottom part of the heart — the ventricles. This affects heart rhythm.
Doctors can determine the type of heart block by checking the rhythm and electrical activity of a person’s heart using an electrocardiogram (EKG). The “P wave” on the test shows when the atria contracts. The QRS complex — a combination of the Q, R, and S waves — shows when the ventricles contract.
Second degree heart block is a missed heartbeat with either a sudden or progressive delay in how long it takes for the signal to move across the atria.
Experts break this form of heart block into
- Second degree Mobitz type I: The heart’s electrical signal gets weaker, and eventually, it cannot send an electrical impulse between the atria and ventricles, causing the heart to skip a beat. This form usually does not require treatment.
- Second degree Mobitz type II: Structural damage, such as that from a heart attack, causes heart cells to fail to conduct an electrical impulse. This can lead to unstable blood flow and worsening heart block.
- Second degree high grade: This is two or more blocked P waves in a row. However, some electrical impulses travel between the ventricles and atria, differentiating it from third degree heart block.
Second degree heart block type I
In second degree heart block type II, issues with the heart’s electrical signal come on suddenly rather than intermittently. Rather than slowing the heart rate or causing skipped beats, it causes sudden changes in the rhythm below the atria.
This increases the risk of dangerous heart rhythms, fainting, and sudden cardiac death. People with type II are also
Second degree heart block type II may also progress to third degree heart block, which is a complete heart block.
Second degree heart block type I
If it does, a person may experience:
However, second degree heart block type II
- cardiomyopathy from Lyme disease
- structural diseases of the heart
- heart tumors
- infections, such as acute rheumatic fever
- hypertension, or high blood pressure
- heart attack
- deposition diseases, such as amyloidosis
Some medications used to treat heart disease may also increase the risk of heart block. These include:
- a prior heart attack
- older age
- male sex
- high blood pressure
- high fasting glucose or diabetes
- congestive heart failure
However, these risk factors may be absent in people with second degree heart block type I. This type can occur in athletes and people with otherwise healthy hearts.
No specific research has consistently found it to be more common in certain populations.
People with second degree heart block type I are
If they have no symptoms, they may not need treatment. However, if the condition causes a slow heartbeat or dangerously low blood pressure, a person may need medication, such as the drug atropine. In some cases, they may need a pacemaker.
Heart-healthy lifestyle changes designed to reduce blood pressure and cardiovascular risk factors can also be helpful. If a person develops a heart block due to another disease, a doctor may prescribe additional treatments.
People often have no symptoms, and this type of heart block does not typically progress to more severe forms of heart block. They may need no treatment at all.
Second degree heart block type I is often a benign condition that does not usually progress to more serious types of heart block. However, in some people, it may cause symptoms or indicate that a person has an underlying medical condition.
People who have signs of heart disease or an irregular heart rhythm should seek medical care.