A heart block occurs when the electrical current is delayed as it passes through the atrioventricular node, the bundle of His or both bundle branches. These areas of the heart are located between the upper and lower chambers.
There are three types of heart block:
- First degree, when there is only a slight (a fraction of a second) delay in the electrical current as it goes through the atrioventricular node to the lower chambers (ventricles) of the heart
- Second degree, when the current is blocked from time to time (intermittently) and only some of the electrical impulses reach the lower chambers of the heart. Some forms of second-degree heart block develop into third-degree heart block.
- Third degree, when there is no current from the upper chambers of the heart reaching the lower chambers. In this case, the beating of the lower chambers of the heart is controlled by the atrioventricular node, the bundle of His or the ventricles (lower chambers) themselves. All of these are slower than the heart¿s normal pacemaker, the sinus or sinoatrial node). This causes a heart beat that is often irregular and unreliable. Third-degree heart block is a serious arrhythmia that can cause fainting.
The signs of heart block depend on the degree to which the electrical current is interrupted or blocked.
First-degree heart block may produce no noticeable symptoms.
In second-degree heart block, the heartbeat may be slow, irregular or both.
In third degree heart block, the ventricles (lower chambers) beat very slowly, less than 50 beats per minute or even as slowly as 30 beats per minute. With this condition, you may feel tired, dizzy or faint. The lower the heart rate, the more severe the symptoms will be.
A variety of factors can cause heart block including:
- Age. Most types of heart block are more common among older people.
- Drugs, particularly ones that slow conduction of the electrical impulses through the atrioventricular node, such as beta-blockers, diltiazem, verapamil and miodarone
- Fitness level. First-degree heart block is common among well-trained athletes, teenagers and young adults.
- Having a highly active vagus nerve
- Having had certain diseases, including rheumatic fever, sarcoidosis that affects the heart or other diseases that are caused by structural defects in the heart
If you have first-degree heart block, it may be discovered with an electrocardiogram (ECG), done to diagnose another condition. Your doctor will take your medical and family history and do a physical examination. The slow or irregular heart rate of second- or third-degree heart block may be heard by the doctor during the course of the examination. An electrocardiogram will confirm the diagnosis.
No treatment is needed for first-degree heart block, even if it is caused by heart disease. Depending on how severe their symptoms are, some people with second-degree heart block may need an artificial pacemaker. Almost everyone with third-degree heart block require an artificial pacemaker. In an emergency, a temporary pacemaker may be used until a permanent one is implanted. Most people who are given a pacemaker will need it for the rest of their lives, even if the heart rhythm returns to normal if the underlying cause of the heart block (such as a heart attack) is treated.
