Tachycardia

DEFINITION

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Tachycardia is a faster than normal heart rate at rest. A healthy adult heart normally beats 60 to 100 times a minute when a person is at rest. If you have tachycardia (tak-ih-KAHR-dee-uh), the heart rate in the upper chambers or lower chambers of the heart, or both, is increased.

Heart rate is controlled by electrical signals sent across heart tissues. Tachycardia occurs when an abnormality in the heart produces rapid electrical signals.

In some cases, tachycardia may cause no symptoms or complications. However, tachycardia can seriously disrupt normal heart function, increase the risk of stroke, or cause sudden cardiac arrest or death.

Treatments may help control a rapid heartbeat or manage diseases contributing to tachycardia.

CAUSES

Tachycardia is caused by something that disrupts the normal electrical impulses that control the rate of your heart’s pumping action. Many things can cause or contribute to problems with the heart’s electrical system. These factors include:

• Damage to heart tissues from heart disease
• Abnormal electrical pathways in the heart present at birth (congenital)
• Disease or congenital abnormality of the heart
• Anemia
• Exercise
• Sudden stress, such as fright
• High blood pressure
• Smoking
• Fever
• Drinking too much alcohol
• Drinking too many caffeinated beverages
• Medication side effects
• Abuse of recreational drugs, such as cocaine
• Imbalance of electrolytes, mineral-related substances necessary for conducting electrical impulses
• Overactive thyroid (hyperthyroidism)

In some cases, the exact cause of tachycardia can’t be determined.

Electrical circuitry of the heart

Your heart is made up of four chambers — two upper chambers (atria) and two lower chambers (ventricles). The rhythm of your heart is normally controlled by a natural pacemaker (the sinus node) located in the right atrium. The sinus node produces electrical impulses that normally start each heartbeat.

From the sinus node, electrical impulses travel across the atria, causing the atria muscles to contract and pump blood into the ventricles.

The electrical impulses then arrive at a cluster of cells called the atrioventricular node (AV node) — usually the only pathway for signals to travel from the atria to the ventricles.

The AV node slows down the electrical signal before sending it to the ventricles. This slight delay allows the ventricles to fill with blood. When electrical impulses reach the muscles of the ventricles, they contract, causing them to pump blood either to the lungs or to the rest of the body.

Types of tachycardia

Tachycardia occurs when a problem in electrical signals produces a heartbeat that is faster than normal. Common types of tachycardia include the following:

• Atrial fibrillation. Atrial fibrillation is a rapid heart rate caused by chaotic electrical impulses in the atria. These signals result in rapid, uncoordinated, weak contractions of the atria.

  The chaotic electrical signals bombard the AV node, usually resulting in an irregular, rapid rhythm of the ventricles. Atrial fibrillation may be temporary, but some episodes won’t end unless treated.

  Most people with atrial fibrillation have some structural abnormalities of the heart related to such conditions as heart disease or high blood pressure. Other factors that may contribute to atrial fibrillation include a heart valve disorder, hyperthyroidism or heavy alcohol use.

• Atrial flutter. In atrial flutter, the heart’s atria beat very fast but at a regular rate. Atrial flutter is caused by irregular circuitry within the atria.

  The fast rate results in weak contractions of the atria. The rapid signals entering the AV node cause a rapid and sometimes irregular ventricular rate. Episodes of atrial flutter may get better on their own, or the condition may persist unless treated.

  People who experience atrial flutter often experience atrial fibrillation at other times.

• Supraventricular tachycardia (SVT). Supraventricular tachycardia, which originates somewhere above the ventricles, is caused by abnormal circuitry in the heart, usually present at birth, that creates a loop of overlapping signals.

  In one form of SVT, an abnormality in the AV node may “split” an electrical signal into two, sending one signal to the ventricles and another back to the atria.

  Another common abnormality is the presence of an extra electrical pathway from the atria to the ventricles that bypasses the AV node. This may result in a signal going down one pathway and up the other. Wolff-Parkinson-White syndrome is one disorder featuring an extra pathway.

• Ventricular tachycardia. Ventricular tachycardia is a rapid heart rate that originates with abnormal electrical signals in the ventricles. The rapid heart rate doesn’t allow the ventricles to fill and contract efficiently to pump enough blood to the body. Ventricular tachycardia is often a life-threatening medical emergency.

• Ventricular fibrillation. Ventricular fibrillation occurs when rapid, chaotic electrical impulses cause the ventricles to quiver ineffectively instead of pumping necessary blood to the body. This serious problem is fatal if the heart isn’t restored to a normal rhythm within minutes.

  Most people who experience ventricular fibrillation have an underlying heart disease or have experienced serious trauma, such as being struck by lightning.

SYMPTOMS

When your heart’s rate is too rapid, it may not effectively pump blood to the rest of your body, depriving your organs and tissues of oxygen. This can cause these tachycardia-related signs and symptoms:

• Dizziness
• Shortness of breath
• Lightheadedness
• Rapid pulse rate
• Heart palpitations — a racing, uncomfortable or irregular heartbeat or a sensation of “flopping” in the chest
• Chest pain
• Fainting (syncope)

Some people with tachycardia have no symptoms, and the condition is only discovered during a physical examination or with a heart-monitoring test called an electrocardiogram.

When to see a doctor

A number of conditions can cause a rapid heart rate and tachycardia symptoms. It’s important to get a prompt, accurate diagnosis and appropriate care. See your doctor if you or your child experiences any tachycardia symptoms.

If you faint, have difficulty breathing or have chest pain lasting more than a few minutes, get emergency care, or call 911 or your local emergency number. Seek emergency care for anyone experiencing these symptoms.