What is heart block?
The heartbeat is created by an electrical signal that starts in the heart’s upper right chamber (right atrium). The signal is produced in an area of specialized cells in the atrium called the sinus node.
The electrical signal moves down through the heart to the atrioventricular (AV) node, another cluster of specialized cells that is located in the center of the heart between the atria and ventricles. The AV node is sometimes referred to as an electrical relay station because its function is to slow the electrical current before it passes to the lower chambers of the heart (ventricles). From the AV node, the electrical current travels to the ventricles along special fibers embedded in the heart walls. When the current arrives in the ventricles, they contract and pump blood out to the body.
In people with heart block, also called AV block, the electrical signal that controls the heartbeat is partially or completely blocked from reaching the ventricles.
What are the different types of heart block?
Heart block is classified as first-, second- or third-degree, depending on the extent of electrical signal impairment.
In first-degree heart block, the electrical impulse moves more slowly than normal through the AV node but it still conducts each signal. This condition is common in highly trained athletes. It can also be caused by drugs, particularly those that slow electrical impulse conduction through the AV node, such as beta-blockers, diltiazem, verapamil, digoxin and amiodarone.
Second-degree heart block is broken down into two categories: Type I and Type II.
Type I heart block (also called Mobitz Type I or Wenckebach's AV block) is the less serious form of second-degree heart block. In this condition, the electrical signal goes slower and slower until the heart actually skips a beat.
In patients with Type II heart block (also called Mobitz Type II), some of the electrical signals do not reach the ventricles, and the pattern is irregular. Individuals with this type of heart block may have a heartbeat that is slower than normal. The area that is blocked is lower in the conduction system and is often associated with more severe conduction disease.
In patients with third-degree (complete) heart block, the electrical signal is not sent from the atria to the ventricles. The heart compensates by producing electrical signals from a specialized pacemaker area in the ventricles. These signals make the heart contract and pump blood, but at a rate that is much slower than normal.
Who is at risk for heart block?
Heart block can be present at birth (congenital), but most heart block develops after birth. In general, the risk of acquired heart block increases with age, along with the incidence of heart disease.
First-degree heart block is common among well-trained athletes, teenagers, young adults, and people with a highly active vagus nerve. People with a variety of heart disease, including coronary artery disease, rheumatic heart disease, sarcoidosis or other structural heart disorders, are also at risk for developing first-degree heart block.
What causes acquired heart block?
Acquired heart block has many possible causes, including heart attack (the most common cause), heart disease, an enlarged heart (cardiomyopathy), heart failure and rheumatic fever. Sometimes heart block occurs as a result of injury to the heart during open heart surgery, as a side effect of some drugs, or after exposure to a toxin.
What are the symptoms of heart block?
First-degree heart block often does not cause symptoms. It may be detected during a routine electrocardiogram (ECG/EKG), but the patient’s heart rate and rhythm are usually normal.
Symptoms of second- and third-degree heart block include fainting, dizziness, fatigue, shortness of breath and chest pain. In third-degree heart block, the symptoms reflect the severity of the slow heart rate. In some cases this may be dangerous and need immediate medical attention.
How is heart block diagnosed?
If your primary care physician suspects that you have heart block, he or she probably will refer you to a cardiologist for a complete cardiac evaluation. At the Sydell and Arnold Miller Family Heart & Vascular Institute, our cardiologists will start by obtaining your medical records from your primary care physician, including records of any heart tests you have had done.
Your cardiologist will review your complete medical history with you and ask you questions about your overall health, your diet and activity level, and your family medical history. The cardiologist also will want to know about any medications you are taking (prescription or over the counter) and whether you smoke or use drugs.
You will undergo a complete physical exam during which the doctor will listen to your heart and check your pulse to measure your heart rhythm and heart rate. He or she will check you for signs of heart failure, such as fluid retention in the legs and feet.
An ECG is a useful test to diagnose heart block. An ECG records the heart’s electrical activity. The test produces a graph that shows the heart rate and rhythm and the timing of the electrical signals as they move through the heart.
Cardiologists can look at the graph created during an ECG and determine whether a patient has heart block and how severe it is, based on the patterns of the heartbeat, rhythm and signal timing.
Your cardiologist may want to record your heart’s electrical signals over a longer period of time. If so, you will be asked to wear a portable ECG. A Holter monitor is a type of portable ECG that is worn for 24 to 48 hours. The Holter monitor continuously records the heart’s electrical activity. An event monitor is another type of portable ECG that is worn for a longer period of time and records the heart’s electrical activity at specified times, rather than continuously.
An electrophysiology study is another useful tool to help diagnose heart block. This minimally invasive test uses thin, flexible wires (catheters) that are placed onto the heart’s surface to record the heart’s electrical activity. The Miller Family Heart & Vascular Institute includes some of the world’s leading experts in electrophysiology who are highly skilled at creating “maps” of the heart’s electrical activity using electrophysiology studies for the most accurate diagnosis and treatment.
How is heart block treated?
In some people, the heart block goes away when the underlying cause is removed (eg, making changes to medication) or treated (e.g., managing the patient’s heart disease).
The right treatment for heart block depends on the severity of the condition and whether it is associated with any symptoms. First-degree heart block usually does not require treatment. Second-degree heart block may not require treatment in patients who are highly trained athletes, but many patients do require treatment if they have symptoms. Third-degree heart block almost always requires treatment.
If you have symptomatic second-degree heart block, your cardiologist may recommend treatment with a pacemaker. A pacemaker is a credit card-sized device that is implanted just under the skin in the chest or abdomen during a procedure performed in the electrophysiology lab. The pacemaker uses electrical pulses to keep your heart beating normally. In 2009, Cleveland Clinic specialists performed more than 4,000 procedures in the electrophysiology lab, including more than 1,300 pacemaker and defibrillator implants.
Third-degree heart block is often first diagnosed as an emergency situation. In these patients, it is almost always necessary to implant a pacemaker, unless the problem can be reversed by stopping medications that may cause it.
What is the outlook for people with heart block after treatment?
If you have first-degree heart block, ask your cardiologist if you need to take any precautions or change the way you take your medications. Usually, people with first-degree heart block can continue their usual activities.
If you have second-degree or third-degree heart block, your cardiologist will talk with you about how to maintain a healthy heart through diet and exercise. If you have second-degree heart block but do not need a pacemaker, your cardiologist determine what type of follow-up monitoring and care you may need.
What kinds of activity and follow-up are recommended for people with pacemakers?
If you have a pacemaker for second- or third-degree heart block, your cardiologist may recommend some restrictions about the types of exercise you can participate in (such as contact sports), but in general, a pacemaker will not seriously restrict your ability to take part in sports and leisure activities.
Your cardiologist will want to periodically check your pacemaker to make sure that it continues to meet your needs. Many Cleveland Clinic patients who have pacemakers use a special monitoring system that allows them to use a phone to send information from their pacemaker to their doctor’s office. It is important to follow your doctor’s instructions for pacemaker monitoring so he or she can ensure your pacemaker is correctly regulating your heartbeat.
If you have a pacemaker, you should avoid close contact with magnetic devices and any device that sends out an electrical field. When traveling, tell airport security screeners that you have a pacemaker, and carry a card that states the type of pacemaker you have. It is important to tell all of your doctors, your dentist and other healthcare providers that you have a pacemaker. Some medical procedures, such as magnetic resonance imaging (MRI), can interfere with pacemakers.
Where can I learn more about heart block?
For more information about heart block and treatments available at Cleveland Clinic, or to make an appointment with a Cleveland Clinic specialist, please call 800.659.7822 to talk with a Heart & Vascular Resource Nurse.