Basics of Heart Function
The heart is a muscle about the size of your fist. The heart works like a pump and beats about 100,000 times a day.
A healthy adult heart generally beats 60 to 100 times a minute, but it can beat faster or slower at times. For example, physical activity, strong emotion, certain medicines, fever, or infection can make the heart beat faster. A person's heart rate generally slows down during sleep.
Normal Rhythm ECG
Understanding the Heart's Electrical System
The heart has an internal electrical system that controls the speed and rhythm of the heartbeat. With each heartbeat, an electrical signal spreads from the top of the heart to the bottom. As it travels, the electrical signal causes the heart to contract and pump blood. The process repeats with each new heartbeat. A problem with any part of this process can cause an arrhythmia.
What is an Arrhythmia?
An arrhythmia (ah-RITH-me-ah) is a change in the heart's rhythm that causes the heart to beat too fast, too slow, or irregularly.
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.
What Causes an Arrhythmia?
An arrhythmia happens when some part of the heart's electrical system doesn't function as it should. Most arrhythmias are harmless, but some can be serious or even life threatening.
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.
How Are Arrhythmias Diagnosed?
Arrhythmias can be hard to diagnose, especially types that only cause symptoms every once in a while. Doctors use several methods to help diagnose arrhythmias, including family and medical history, physical exam, and diagnostic tests and procedures.
- 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).
What are the symptoms of arrhythmias
- Fast or slow heart beat
- Skipping beats
- Weakness, lightheadedness, dizziness, fainting
- Chest pain
- Shortness of breath
Can Medicines affect the heart?
Medicines can change the electrical patterns of the heart. If the electrical patterns change too much, abnormal heart rhythms may occur. These abnormal heart rhythms can be dangerous. These changes can be seen on an electrocardiogram (ECG). One of these changes in the electrical activity of the heart may be a lengthening of the QT interval.
What is a QT interval?
The QT interval is a measurement on the ECG. This measurement reflects the duration of electrical activity that controls contraction of the heart muscle. In a normal, healthy heart the QT interval stays within acceptable limits.
Many medicines have the potential to prolong the QT interval, such as medicines used to treat abnormal heart rhythms, infections, allergies and mental illnesses.
Sometimes the QT interval becomes prolonged when too high a dose of the medicine is used or if the medicine is combined with another drug that changes how the body processes the first drug.
A long QT interval can lead to an abnormal heart rhythm called Torsades de Pointes (torsades). In very rare circumstances, torsades may cause death.
Torsades de pointes on an ECG
Long QT Syndrome
Long QT Syndrome (LQTS) refers to a condition in which there is an abnormally long QT interval on the ECG. Long QT Syndrome can be inherited and is called "congenital long QT". On the other hand, LQTS can be induced either by medicines or abnormal levels of the salts (potassium and magnesium) normally found in the blood and is then called "acquired long QT".