Arrhythmia

An arrhythmia is a problem with the speed 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. The normal range of heartbeat is between 60 and 100 times a minute for an adult at rest. Children typically have higher heart rate than adults. The heart rate for a normal baby is about 140 times a minute.

Most arrhythmias are harmless, but some can be serious or even life threatening. When the heart rate is too slow, too fast, 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.

Symptoms and Diagnosis

Many arrhythmias cause no signs or symptoms. When signs or symptoms are present, the most common ones are:

Palpitations (a feeling that your heart has skipped a beat or is beating too hard)
A slow heartbeat
An irregular heartbeat
Feeling of pauses between heartbeats

More serious signs and symptoms include:

Anxiety
Weakness
Dizziness and light-headedness
Fainting or nearly fainting
Sweating
Shortness of breath
Chest pain

To diagnose an arrhythmia, the following tests and procedures may be used:

An EKG (electrocardiogram) is the most common test used to diagnose arrhythmias. An EKG is a simple test that detects and records the electrical activity of your heart. It shows how fast the heart is beating and its rhythm (steady or irregular). It also records the strength and timing of the electrical signals as they pass through each part of the heart.

A standard EKG test only records the heartbeat for a few seconds. It won’t detect arrhythmias that don’t happen during the test. To diagnose arrhythmias that come and go, your doctor may have you wear a portable EKG monitor that can record the heartbeat for longer periods of time. The two most common types of portable EKGs are:

Holter monitor. This device records the heart’s electrical activity continuously over a 24-hour period.
Event monitor. Event monitors are useful to diagnose arrhythmias that only occur once in a while. The device is worn continuously, but only records the heart’s electrical activity when you push a button on the device. You push the button on the device when you feel symptoms. Event monitors can be worn for 1 to 2 months, or as long as it takes to get a recording of the heart during symptoms.

Other tests used in the diagnosis of arrhythmias include:

Blood tests. These tests check the level of substances in the blood, such as potassium or thyroid hormone, that can increase your chances of having an arrhythmia.
Chest x ray. A chest x ray takes a picture of your heart and lungs. It can show whether the heart is enlarged.
Echocardiogram. This test uses sound waves to create a moving picture of your heart. Echocardiogram provides information about the size and shape of your heart and how well your heart chambers and valves are functioning. The test also can identify areas of poor blood flow to the heart, areas of heart muscle that are not contracting normally, and previous injury to the heart muscle caused by poor blood flow.
There are several different types of echocardiograms, including a stress echocardiogram. During this test, an echocardiogram is done both before and after your heart is stressed either by having you exercise or by injecting a medicine into your bloodstream that makes your heart beat faster and work harder. A stress echocardiogram is usually done to find out if you have decreased blood flow to your heart (coronary artery disease).
Transesophageal echocardiography, or TEE. This is a special type of echocardiogram that takes pictures of the back of the heart through the esophagus (the tube leading from your mouth to your stomach).
Stress test. Some heart problems are easier to diagnose when your heart is working harder and beating faster than when it’s at rest. During stress testing, you exercise (or are given medicine if you are unable to exercise) to make your heart work harder and beat faster while heart tests are performed.
During exercise stress testing, your blood pressure and EKG readings are monitored while you walk or run on a treadmill or pedal a bicycle. Other heart tests, such as nuclear heart scanning or echocardiography, also can be done at the same time. These would be ordered if your doctor needs more information than the exercise stress test can provide about how well your heart is working.
If you are unable to exercise, a medicine can be injected through an intravenous line (IV) into your bloodstream to make your heart work harder and beat faster, as if you are exercising on a treadmill or bicycle. Nuclear heart scanning or echocardiography is then usually done.
During nuclear heart scanning, radioactive tracer is injected into your bloodstream, and a special camera shows the flow of blood through your heart and arteries. Echocardiography uses sound waves to show blood flow through the chambers and valves of your heart and to show the strength of your heart muscle.
Electrophysiologic study (EPS). This test is used to assess serious arrhythmias. During an EPS, a thin, flexible wire is passed through a vein in your groin (upper thigh) or arm up to the heart. The wire records the heart’s electrical signals. Your doctor uses the wire to electrically stimulate your heart and trigger an arrhythmia. This allows the doctor to see whether an antiarrhythmia medicine can stop the problem. Radiofrequency ablation, a procedure used to fix some types of arrhythmia, may be done during an EPS.
Tilt table testing. This test is sometimes used to help determine the cause of fainting spells. You lie on a table that moves from a lying down to an upright position. The change in position can bring on loss of consciousness. The doctor monitors your symptoms, heart rate, EKG, and blood pressure throughout the test. The doctor also may give you a medicine and then monitor your response to the medicine.
Coronary angiography. This test is an x-ray exam of the heart and blood vessels. The doctor passes a catheter (thin, flexible tube) through an artery in your leg or arm up to the heart. The catheter measures the pressure inside the heart and blood vessels. A dye that can be seen on x ray is injected into the blood through the tip of the catheter. The dye lets the doctor study the flow of blood through the heart and blood vessels, which helps to diagnose blockages that can cause a heart attack.

Causes

An arrhythmia can occur when the electrical signals that control the heartbeat are delayed or blocked. This can happen when the special nerve cells that produce the electrical signal don’t work properly or when the electrical signal doesn’t travel normally through the heart. An arrhythmia also can occur when another part of the heart starts to produce electrical signals, adding to the signals from the special nerve cells and disrupting the normal heartbeat.

Stress, smoking, heavy alcohol use, heavy exercise, use of certain drugs (such as cocaine or amphetamines), use of certain prescription or over-the-counter medicines, and too much caffeine or nicotine can lead to arrhythmia in some people.

A heart attack or an underlying condition that damages the heart’s electrical system also can cause an arrhythmia. These conditions include high blood pressure (hypertension), coronary artery disease, heart failure, overactive or underactive thyroid gland (too much or too little thyroid hormone produced), and rheumatic heart disease.

For some arrhythmias, such as Wolff-Parkinson-White syndrome, the underlying heart defect that causes the arrhythmia is present at birth (congenital). Sometimes, the cause of an arrhythmia can’t be found.

Reference:

National Heart, Lung, and Blood Institute, USA.