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Bradycardia (slow heartbeat) means that your heart rate is slower than 60 beats per minute, either occasionally or all the time. For some people (like athletes) a slow heart rate might be normal. In others, it may be dangerous.
If you are not taking medications that slow your heart rate down, bradycardia may be caused by a blockage somewhere along the heart’s electrical pathway. Medications commonly used for high blood pressure may include including both drugs used to treat high blood pressure and/or arrhythmias. A blockage in the heart’s electrical conduction system may be caused by a congenital heart problem, or an aging process.
In either case, the slower your heart beats, the less blood it pumps throughout your body. If your heart beats too slowly, your brain and body might not get enough blood to function well, leading to any or all of the following symptoms:
- Fatigue, weakness
- Fainting (syncope) or near fainting
- Shortness of breath
Many things can cause or contribute to problems with your heart's electrical system, including:
- Heart tissue damage related to aging
- Damage to heart tissues from heart disease or heart attack
- High blood pressure (hypertension)
- Heart disorder present at birth (congenital heart defect)
- Infection of heart tissue (myocarditis)
- A complication of heart surgery
- Underactive thyroid gland (hypothyroidism)
- Imbalance of electrolytes, mineral-related substances necessary for conducting electrical impulses
- Obstructive sleep apnea, the repeated disruption of breathing during sleep
- Inflammatory disease, such as rheumatic fever or lupus
- Hemochromatosis, the buildup of iron in organs
- Medications, including some drugs for other heart rhythm disorders, high blood pressure and psychosis
Sinus node problems
Bradycardia often starts in the sinus node. A slow heart rate may occur because the sinus node:
- Discharges electrical impulses at a slower than normal rate
- Pauses, or fails to discharge at a regular rate
- Discharges an electrical impulse that's blocked before causing the atria to contract
In some people the sinus node problems may result in alternating slow and fast heart rates (bradycardia-tachycardia syndrome).
Heart block (atrioventricular block)
Bradycardia may also occur because electrical signals transmitted through the atria aren't transmitted to the ventricles (heart block, or atrioventricular block). The disruption of the electrical signal may occur in the AV node, the bundle of His, or somewhere along the left and right branches that transmit electrical signals to the ventricles. Heart blocks are classified based on the degree to which signals from the atria reach your heart's main pumping chambers (ventricles).
- First-degree heart block. In the mildest form of heart block, all electrical signals from the atria reach the ventricles, but the signal is slowed down slightly. First-degree heart block rarely causes symptoms and usually needs no treatment if there's no other abnormality in electrical signal conduction.
- Second-degree heart block. In second-degree heart block, not all electrical signals reach the ventricles. Some beats are "dropped," resulting in a slower and sometimes irregular rhythm.
- Third-degree (complete) heart block. In third-degree heart block, none of the electrical impulses from the atria reaches the ventricles. When this happens, the bundle of His or other tissues of the ventricles function as a substitute pacemaker for the ventricles. These substitutes result in slow and sometimes unreliable electrical impulses to control the beat of the ventricles.
- Bundle branch block. The interruption of an electrical signal somewhere in the right or left bundle branches — near the end of the pathway for electrical impulses — is called a bundle branch block. The seriousness of bundle branch block depends on whether both branches are affected, the presence of other types of heart block and the degree of damage to heart tissue.
To make a diagnosis and locate what and where the electrical pathway is diseased, an EKG is needed, while others tests may be necessary to check your coronary arteries and the function of your heart muscle.
If your bradycardia causes dangerous symptoms (any or all of the symptoms above), a pacemaker may be needed to correct your heart rate. If caused by medications, you should talk to your doctor about changing them.
A pacemaker is a battery-powered device that generates electronic signals. The signals, or pacing pulses, are carried along thin leads to the heart muscle. The signals cause the heart muscle to begin the contractions that cause a heartbeat.
A pacemaker is usually placed under your skin just below your collar bone. It is programmed to stimulate the heart at pre-determined rates; the settings can be adjusted at any time. Routine evaluation, sometimes even via telephone, ensures the pacemaker is working properly and monitors battery life, which generally runs from five to ten years.
Pacemakers can last anywhere from 5 to 10 years or more before the battery needs replacement. Because people may have more energy after the pacemaker is implanted, they may be able to do much more after the operation.
When do I need a Pacemaker?
The most common indication for a pacemaker is bradycardia. A pacemaker resets the heart rate to an appropriate pace, ensuring adequate blood and oxygen are delivered to the brain and other parts of the body.
Pacemakers for slow heart rates may be used in a number of conditions, including:
- Bradycardia (as we discussed).
- Atrial fibrillation – a common heart rhythm disorder in which the upper chambers of the heart beat rapidly and chaotically. Sometimes people with atrial fibrillation can also have slow rhythms. Sometimes medication used to control atrial fibrillation may result in slow rhythms that may need to be treated by a pacemaker if the medicines are still needed.
- Heart failure – a condition in which the heartbeat is not sufficient to supply a normal volume of blood and oxygen to the brain and other parts of the body. A special pacemaker is used for this type of condition.
- Syncope – a condition best known as the common faint, is usually not serious. Some patients faint when their heart rhythm becomes very slow. For a small percentage of people who experience severe and frequent fainting spells, a pacemaker may prevent the heart rate from slowing to the point of fainting.
This is a special type of pacemakers for patients who are at high risk of the deadliest forms of arrhythmias – ventricular tachycardia and ventricular fibrillation. ICDs are not just pacemakers; theyhave an internal “shocking” device that may provide the best defense against a condition called sudden cardiac arrest.
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