Tachycardia is an increased heart rate for any reason. If a fast heart rate is caused by exercise or stress, it's called sinus tachycardia. Sinus tachycardia is a symptom, not a condition.
Most heart conditions can lead to different forms of tachycardia. Irregular heart rhythms, called arrhythmias, are one cause. An example of an irregular heart rhythm is atrial fibrillation (AFib).
Other things that may lead to tachycardia include:
- Fever.
- Excessive alcohol use, which is defined as 14 or more drinks a week for a man or seven or more drinks a week for a woman.
- Alcohol withdrawal.
- Too much caffeine.
- High or low blood pressure.
- Changes in the level of minerals in the body, called electrolytes. Examples include potassium, sodium, calcium and magnesium.
- Certain medicines.
- Overactive thyroid, called hyperthyroidism.
- A low number of red blood cells, called anemia.
- Smoking or nicotine use.
- Use of illegal stimulants such as cocaine or methamphetamine.
- Heart attack.
Sometimes the exact cause of tachycardia is not known.
How does the heart beat?
To understand the cause of tachycardia, it may be helpful to know how the heart usually works.
The heart has four chambers:
- The two upper chambers are called the atria.
- The two lower chambers are called the ventricles.
Inside the upper right heart chamber is a group of cells called the sinus node. The sinus node makes the signals that start each heartbeat.
The signals move across the upper heart chambers. Then the signals arrive at a group of cells called the AV node, where they usually slow down. The signals then go to the lower heart chambers.
In a healthy heart, this signaling process usually goes smoothly. The resting heart rate is typically 60 to 100 beats a minute. But in tachycardia, something causes the heart to beat faster than 100 beats a minute.