Tachycardia

Tachycardia

Definition:

Tachycardia is a faster than normal heart rate. 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-de-uh), the rate in the upper chambers or lower chambers of the heart, or both, are increased significantly.

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, tachycardias may cause no symptoms or complications. However, tachycardias 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.

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 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.

Causes:

Tachycardia is caused by something that disrupts the normal electrical impulses that control the rhythm 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
• High blood pressure
• Smoking
• Fever
• Drinking too much alcohol
• Drinking too many caffeinated beverages
• A side effect of medications
• 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 tachycardias
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 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 is a very fast, but regular rate of the atria 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 tachycardias (SVTs), which originate somewhere above the ventricles, are 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 is a rapid rate that originates with abnormal electrical signals in the ventricles. The rapid beat 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 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.
   

Complications:

Complications of tachycardias vary in severity depending on such factors as the type of tachycardia, the rate and duration of a rapid heart rate, and the existence of other heart conditions. Possible complications include:

• Blood clots that can cause a stroke or heart attack
• Inability of the heart to pump enough blood (heart failure)
• Frequent fainting spells
• Sudden death, usually only associated with ventricular tachycardia or ventricular fibrillation

Treatments and drugs:

The treatment goals for tachycardias are to slow a fast heart rate when it occurs, prevent future episodes and minimize complications.

Stopping a fast heart rate
A fast heartbeat may correct itself, and you may be able to slow your heart rate using simple physical movements. However, you may need medication or other medical treatment to slow down your heartbeat. Ways to slow your heartbeat include:

• Vagal maneuvers. Your doctor may ask you to perform an action, called a vagal maneuver, during an episode of a fast heartbeat. Vagal maneuvers affect the vagus nerve, which helps regulate your heartbeat. The maneuvers include coughing, bearing down as if you're having a bowel movement, and putting an icepack on your face.
  
• Medications. If vagal maneuvers don't stop the fast heartbeat, you may need an injection of an anti-arrhythmic medication to restore a normal heart rate. An injection of this drug is administered at a hospital. Your doctor may also prescribe a pill version of an anti-arrhythmic drug, such as flecainide (Tambocor) or propafenone (Rythmol), to take if you have an episode of a fast heartbeat that doesn't respond to vagal maneuvers.
  
• Cardioversion. In this procedure, a shock is delivered to your heart through paddles or patches on your chest. The current affects the electrical impulses in your heart and restores a normal rhythm. It's typically used when emergency care is needed or when maneuvers and medications aren't effective.

Preventing episodes of a fast heart rate
With the following treatments, it may be possible to prevent or manage episodes of tachycardia.

• Catheter ablation. This procedure is used most often when an extra electrical pathway is responsible for an increased heart rate. In this procedure, catheters are threaded through the blood vessels to your heart. Electrodes at the catheter tips can use heat, extreme cold, or radiofrequency energy to damage (ablate) the extra electrical pathway and prevent it from sending electrical signals. This procedure is highly effective, especially for supraventricular tachycardia. Catheter ablation can also be used to treat atrial fibrillation and atrial flutter.
  
• Medications. Anti-arrhythmic medications may prevent a fast heart rate when taken regularly. Other medications that may be prescribed — either as an alternative or in combination with anti-arrhythmic medications — are calcium channel blockers, such as diltiazem (Cardizem) and verapamil (Calan) or beta blockers, such as metoprolol (Lopressor, Toprol) and esmolol (Brevibloc).
  
• Pacemaker. A pacemaker is a small device that's surgically implanted under your skin. When the device senses an abnormal heartbeat, it emits an electrical pulse that helps the heart resume a normal beat.
  
• Implantable cardioverter-defibrillator. If you're at risk of having a life-threatening tachycardia episode, your doctor may recommend an implantable cardioverter-defibrillator (ICD). The device, about the size of a cell phone, is surgically implanted in your chest. The ICD continuously monitors your heartbeat, detects an increase in heart rate and delivers precisely calibrated electrical shocks to restore a normal heart rhythm.
  
• Surgery. Open-heart surgery may be needed in some cases to destroy an extra electrical pathway. In another type of surgery, called the maze procedure, a surgeon makes small incisions in heart tissue to create a pattern or maze of scar tissue. Because scar tissue doesn't conduct electricity, it interferes with stray electrical impulses that cause some types of tachycardia. Surgery is usually used only when other treatment options don't work or when surgery is needed to treat another heart disorder.

Preventing blood clots
Some people with tachycardias have an increased risk of developing a blood clot that could cause a stroke or heart attack. Your doctor may prescribe a drug-thinning medication, such as dabigatran (Pradaxa) and warfarin (Coumadin) to help lower your risk.

Treating an underlying disease
If another medical condition is contributing to tachycardia — for example, some form of heart disease or hyperthyroidism — treating the underlying problem may prevent or minimize tachycardia episodes.