Tachycardia is an abnormally fast heart rate. In adults, the heart normally beats 60-100 times per minute. A heart rate greater than 100 beats per minute is termed tachycardia.
Tachycardia may occur in children as well as adults. In newborns and infants, tachycardia is defined as a heart rate greater than 150 beats per minute.
There are numerous causes of tachycardia and the condition is very common. Although some forms are harmless, others are potentially lethal.
Basic heart functions
The heart comprises four chambers: two upper chambers (atria) and two lower chambers (ventricles). The heart’s natural pacemaker, the sinoatrial node (SA node), is a tiny collection of cells located in the right atrium that produces each heartbeat.
The SA node generates the electrical signals that control the speed (heart rate) and pattern (rhythm) of the heartbeats. These impulses cause the atria to contract and pump blood into the ventricles. The SA node also sends electrical impulses to another collection of cells, the atrioventricular node (AV node). The AV node conducts the impulses down an electrical pathway to the ventricles, which contract and pump blood out of the heart to the lungs and the rest of the body.
Any type of abnormal heart rate or rhythm is termed an arrhythmia. Tachycardia is a type of arrhythmia where the electrical signals controlling the heart travel across the heart faster than normal, triggering the heart to beat too rapidly.
Types and Causes of Tachycardia
Numerous conditions can cause tachycardia. The severity of these problems can range from benign to life threatening. Common causes include:
- Underlying heart disease
- Blood loss
- Overactive thyroid
- Emotional distress
- Medication side effects
- Street drugs
- Alcohol abuse.
Types of tachycardia
- Sinus tachycardia. Often sinus tachycardia is a normal response to certain situations such as exercise, anxiety, distress, or fever. Certain disorders such as thyroid disease, anemia, and low blood pressure are also associated with sinus tachycardia.
- Atrial fibrillation (AF). AF is characterized by chaotic electrical signals, triggering the atria to quiver rapidly and irregularly. Atrial fibrillation is often associated with heart disease, an overactive thyroid, or alcoholism. Frequently, AF causes blood clot formation inside the heart, which increases a person’s risk for stroke.
- Atrial flutter. This arrhythmia is similar to atrial fibrillation, except the rhythm is less chaotic.
- Supraventricular tachycardia (SVT) or paroxysmal supraventricular tachycardia (PSVT). This arrhythmia starts with electrical signals above the ventricles that travel down an abnormal electrical pathway or extra pathway. An extra pathway is the hallmark of Wolff-Parkinson-White syndrome - the leading cause of SVT in children and adolescents.
- Ventricular tachycardia (VT). VT is triggered by an electrical abnormality within the ventricles. During VT, the ventricles may fill poorly and inadequately pump blood. Sometimes a person becomes pulseless during VT - a fatal event unless immediately corrected.
- Ventricular fibrillation (VF). VF is a rapid, chaotic rhythm, in which the ventricles fail to pump blood at all. VF is a fatal arrhythmia, unless immediately converted to a normal rhythm. VF is usually related to underlying heart disease. Rarely, a blunt blow to the chest wall of a healthy person precipitates VF.
Symptoms of Tachycardia
Certain non-life-threatening types of tachycardia evoke no apparent symptoms. However, more deleterious forms interfere with the heart’s pumping ability, resulting in a number of serious events.
- Feeling the heart beating too fast (palpitations)
- Shortness of breath
- Chest pain
- Loss of consciousness (syncope).
Complications of tachycardia
- Unstable low blood pressure
- Heart failure
- Blood clots
- Sudden death (cardiac arrest).
When a patient’s symptoms and physical examination suggest an arrhythmia, a physician performs tests to diagnose the disorder and assess for the presence of underlying diseases.
- Electrocardiogram (ECG). This test records the electrical activity of the heart. An ECG is very limited because arrhythmias often come and go. Unless an individual is experiencing an episode of tachycardia at the time of the exam, the ECG result is normal.
- Holter monitor. A wearable device continuously records the ECG for a period of 24 to 48 hours.
- Cardiac event recorder. A recording device, used for a month or more, is manually activated when a person experiences symptoms. A recording of each episode is transmitted by telephone to a physician for interpretation.
- Echocardiogram. A transducer emits ultrasound waves through the chest to create a visual image of the heart structures in motion.
- Stress test. The heart is monitored while a person walks or runs on a treadmill in an attempt to provoke an episode of the arrhythmia.
- Tilt table test. Medication is administered to induce tachycardia and the heart function is monitored for changes as the patient is tilted to an upright position.
- Electrophysiologic study. Electrodes are passed through blood vessels to the heart to record electrical signals. This analysis creates a detailed map of the electrical circuitry and pinpoints abnormalities. Additionally, this procedure may be used to induce arrhythmias, allowing the physician to test the effectiveness of medications for treatment.
Treatment depends on the severity of the arrhythmia and the presence of underlying diseases.
- Vagal maneuvers. Certain physical activities stimulate the vagus nerve, a nerve that naturally slows the heart rate. For example, the Valsalva maneuver - bearing down as if having a bowel movement - can slow some types of tachycardia.
- Medications. Anti-arrhythmic medications are administered to control abnormal heart rates and rhythms. Blood-thinning medication is necessary for patients with atrial fibrillation, a risk for blood clot formation and stroke.
- Catheter ablation. Catheters are inserted through blood vessels into the heart to heat or freeze tissue and destroy (ablate) abnormal electrical conduction pathways. Ablation is commonly used to treat Wolff-Parkinson-White syndrome, atrial fibrillation, and atrial flutter.
- Cardioversion. A properly timed electrical shock (in synchrony with the heart) is delivered to the chest to restore a normal heart rhythm. The most common indications for this procedure are atrial fibrillation, atrial flutter, and SVT.
- Emergency asynchronous defibrillation. Defibrillation is similar to cardioversion except the procedure more rapidly delivers higher energy shocks in an attempt to convert life-threatening arrhythmias - pulseless VT and VF.
- Implantable cardioverter-defibrillator (ICD). An ICD device is permanently implanted inside the chest to continuously monitor the heart. If VT or VF is detected, the device immediately delivers an electrical shock to restore a normal heart rhythm. ICD is indicated in persons with severe underlying heart disease at high risk for life-threatening VT or VF.
- Maze procedure. This surgery disrupts abnormal electrical pathways in the heart. Such surgery is performed when other treatment options have failed.
Some forms of tachycardia are avoidable by controlling lifestyle factors that lead to heart disease. Recommendations include quitting smoking, increasing rest, and avoiding alcohol and drug abuse.
- Marchlinski F. Chapter 233. The Tachyarrhythmias. In: Longo DL, Fauci AS, Kasper DL, Hauser SL, Jameson J, Loscalzo J. eds. Harrison’s Principles of Internal Medicine, 18e. New York, NY: McGraw-Hill; 2012.http://accessmedicine.mhmedical.com.proxy.uchicago.edu/content.aspx?bookid=331&Sectionid=40727006. Accessed March 06, 2015.
- Tachycardia/Fast Heart Rate. American Heart Association website. http://www.heart.org/HEARTORG/Conditions/Arrhythmia/AboutArrhythmia/Tachycardia_UCM_302018_Article.jsp. Accessed March 5, 2015.
- Common Tests for Arrhythmia. American Heart Association website. http://www.heart.org/HEARTORG/Conditions/Arrhythmia/SymptomsDiagnosisMonitoringofArrhythmia/Common-Tests-for-Arrhythmia_UCM_301988_Article.jsp. Accessed March 5, 2015.
- Tachycardia. Mayo Clinic website. http://www.mayoclinic.org/diseases-conditions/tachycardia/basics/tests-diagnosis/con-20043012. Accessed March 5, 2015.
- Wolff-Parkinson-White syndrome. MedlinePlus website. http://www.nlm.nih.gov/medlineplus/ency/article/000151.htm. Accessed March 5, 2015.
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