An arrhythmia is a problem with the rate or rhythm of the heartbeat. During an arrhythmia, the heart can beat too fast, too slow, or with an irregular rhythm.
A heartbeat that is too fast is called tachycardia. A heartbeat that is too slow is called bradycardia.
Most arrhythmias are harmless, but some can be serious or even life-threatening. When the heart rate is too fast, too slow, or irregular, the heart may not be able to pump enough blood to the body. Lack of blood flow can damage the brain, heart, and other organs.
Understanding the Heart's Electrical System
To understand arrhythmias, it helps to understand the heart's internal electrical system. The heart's electrical system controls the rate and rhythm of the heartbeat.
With each heartbeat, an electrical signal spreads from the top of the heart to the bottom. As the signal travels, it causes the heart to contract and pump blood. The process repeats with each new heartbeat.
Each electrical signal begins in a group of cells called the sinus node or sinoatrial (SA) node. The SA node is located in the right atrium (AY-tree-um), which is the upper right chamber of the heart. In a healthy adult heart at rest, the SA node fires off an electrical signal to begin a new heartbeat 60 to 100 times a minute.
From the SA node, the electrical signal travels through specialized pathways in the right and left atria. This causes the atria to contract and pump blood into the heart's two lower chambers, the ventricles.
The electrical signal then moves down to a group of cells called the atrioventricular (AV) node, located between the atria and the ventricles. Here, the signal slows down just a little, allowing the ventricles time to finish filling with blood.
The electrical signal then leaves the AV node and travels along a pathway called the bundle of His. This pathway divides into a right bundle branch and a left bundle branch. The signal goes down these branches to the ventricles, causing them to contract and pump blood out to the lungs and the rest of the body.
The ventricles then relax, and the heartbeat process starts all over again in the SA node.
A problem with any part of this process can cause an arrhythmia. For example, in atrial fibrillation, a common type of arrhythmia, electrical signals travel through the atria in a fast and disorganized way. This causes the atria to quiver instead of contract.
What Causes an Arrhythmia?
An arrhythmia can occur if the electrical signals that control the heartbeat are delayed or blocked. This can happen if the specialized nerve cells that produce electrical signals don't work correctly, or if electrical signals don't regularly travel through the heart.
An arrhythmia also can occur if another part of the heart starts to produce electrical signals. This adds to the signals from the specialized nerve cells and disrupts the regular heartbeat.
Smoking, heavy alcohol use, use of certain drugs (such as cocaine or amphetamines), use of particular prescription or over-the-counter medicines, or too much caffeine or nicotine can lead to arrhythmias in some people.
Intense emotional stress or anger can make the heart work harder, raise blood pressure, and release stress hormones. In some people, these reactions can lead to arrhythmias.
A heart attack or an underlying condition that damages the heart's electrical system also can cause arrhythmias. Examples of such conditions include high blood pressure, coronary heart disease, heart failure, overactive or underactive thyroid gland (too much or too little thyroid hormone produced), and rheumatic heart disease.
In some arrhythmias, such as Wolff-Parkinson-White syndrome, the underlying heart defect that causes the arrhythmia is congenital (present at birth). Sometimes, the cause of an arrhythmia can't be found.
Who Is At Risk for an Arrhythmia?
Millions of Americans have arrhythmias. They're very common in older adults. About 2.2 million Americans have atrial fibrillation (a common type of arrhythmia that can cause problems).
Most serious arrhythmias affect people older than 60. This is because older adults are more likely to have heart disease and other health problems that can lead to arrhythmias.
Older adults also tend to be more sensitive to the side effects of medicines, some of which can cause arrhythmias. Some medications used to treat arrhythmias can even cause arrhythmias as a side effect.
Some types of arrhythmia happen more often in children and young adults. Paroxysmal supraventricular tachycardias (PSVTs), including Wolff-Parkinson-White syndrome, are more common in young people. PSVT is a fast heart rate that begins and ends suddenly.
Major Risk Factors
Arrhythmias are more common in people who have diseases or conditions that weaken the heart, such as:
- Heart attack
- Heart failure or cardiomyopathy, which weakens the heart and changes the way electrical signals move around the heart
- Heart tissue that's too thick or stiff or that hasn't formed normally
- Leaking or narrowed heart valves, which make the heart work too hard and can lead to heart failure
- Congenital heart defects (problems that are present at birth) that affect the heart's structure or function
Other conditions also can increase the risk for arrhythmias, such as:
- High blood pressure
- Infections that damage the heart muscle or the sac around the heart
- Diabetes, which increases the risk of high blood pressure and coronary heart disease
- Sleep apnea (when breathing becomes shallow or stops during sleep), which can stress the heart because the heart doesn't get enough oxygen
- An overactive or underactive thyroid gland (too much or too little thyroid hormone in the body)
Also, several other risk factors can increase the risk of arrhythmias. Examples include heart surgery, certain drugs (such as cocaine or amphetamines), or an imbalance of chemicals or other substances (such as potassium) in the bloodstream.
What Are the Signs and Symptoms of an Arrhythmia?
Many arrhythmias cause no signs or symptoms. When signs or symptoms are present, the most common ones are:
- Palpitations (feelings that your heart is skipping a beat, fluttering, or beating too hard or fast)
- A slow heartbeat
- An irregular heartbeat
- Feeling pauses between heartbeats
More severe signs and symptoms include:
- Weakness, dizziness, and lightheadedness
- Fainting or nearly fainting
- Shortness of breath
- Chest pain
How Are Arrhythmias Diagnosed?
Arrhythmias can be hard to diagnose, especially the types that only cause symptoms every once in a while. Doctors use several methods to help diagnose arrhythmias, including medical and family histories, physical exam, and diagnostic tests and procedures.
Doctors who specialize in the diagnosis and treatment of heart diseases include:
- Cardiologists. These doctors take care of adults who have heart problems.
- Pediatric Cardiologists. These doctors take care of babies, children, and youth who have heart problems.
- Electrophysiologists. These doctors are cardiologists or pediatric cardiologists who specialize in arrhythmias.
Medical and Family Histories
To diagnose an arrhythmia, your doctor may ask about your signs and symptoms. He or she may ask about what symptoms you're having, whether you feel fluttering in your chest, and whether you feel dizzy or lightheaded.
Your doctor also may ask about other health problems you have, such as a history of heart disease, high blood pressure, diabetes, or thyroid problems.
He or she may ask about your family' s medical history, including:
- Does anyone in your family have a history of arrhythmias?
- Has anyone in your family ever had heart disease or high blood pressure?
- Has anyone in your family died suddenly?
- Are there other illnesses or health problems in your family?
Your doctor will likely want to know what medicines you're taking, including over-the-counter medications and vitamin or mineral or nutritional supplements.
Your doctor may ask about your health habits, such as physical activity, smoking, or using alcohol or drugs (for example, cocaine). He or she also may want to know whether you've had episodes of intense emotional stress or anger.
Your doctor will listen to the rate and rhythm of your heart and for a heart murmur (an extra or unusual sound heard during your heartbeat). He or she also will:
- Check your pulse to find out how fast your heart is beating
- Check for swelling in your legs or feet, which could be a sign of an enlarged heart or heart failure
- Look for signs of other diseases, such as thyroid disease, that could be causing the problem