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An arrhythmia is an abnormal heart beat. Two groups of arrhythmia are bradycardia and tachycardia. Bradycardia is a heart rate slower than 60 beats per minute (bpm). Tachycardia is a heart rate faster than 100 bpm. Two forms of tachycardia are sinus tachycardia and supraventricular tachycardia. There is little difference between supraventricular tachycardia and sinus tachycardia. Sometimes sinus tachycardia is even considered a type of supraventricular tachycardia.
Tachycardias affect normal heart function by speeding up the contraction of the heart muscle. This has the potential to cause compromises in blood flow, an increased risk of stroke or sudden cardiac arrest. In most cases, however, sinus and supraventricular tachycardia are not dangerous.
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Sinus tachycardia is a normal increase of heart rate to over 100 bpm. It occurs as a result of exercise as well as fever, anxiety, medications, anemia or cardiomyopathy. When a clear cause of the sinus tachycardia exists, it is considered appropriate. Physicians deem sinus tachycardia as inappropriate if there is no discernible reason for the condition.
In sinus tachycardia, the heart beats normally, and blood flow is not changed. The electrical impulses controlling the heart beat fire correctly and automatically from the sino-atrial (SA) node, the heart's pacemaker. Symptoms can include dizziness, fatigue, shortness of breath (SOB) and sweating. Doctors can diagnose sinus tachycardia by having patients wear a Holter monitor or event monitor outside a hospital. Within a medical setting, doctors generally use an electrocardiogram (EKG or ECG).
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Supraventricular tachycardia (SVT) is an abnormally fast heart rate of over 100 bpm, sometimes reaching upwards of 300 bpm. This arrhythmia begins in the electrical conduction system inside the atria of the heart. The onset of SVT can be immediate, and it can last for minutes or hours with cessation as quick as its beginning. Often, patients can not readily identify a trigger for the arrhythmia. The excessive rate of beating keeps the chambers of the heart from adequately filling between contractions, and the body does not receive sufficient blood flow. Symptoms are similar to those of sinus tachycardia and include dizziness, palpitations, chest pain and SOB. Doctors usually diagnose SVT using an EKG, or by having the patient wear a Holter monitor or an event monitor outside the hospital setting.
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With SVT, impulses in the atria fire rapidly and cause interference with the SA node. But in sinus tachycardia, the heart is functioning normally; only the SA node is firing at a higher than normal rate. Also SVTs can originate from several different spots within the atria. The cause for the overlapping impulse conduction in SVTs is not entirely elucidated and differs from patient to patient. Blood flow is usually not interrupted in sinus tachycardia, except in extreme cases, but can be disrupted as a result of SVT.
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Mayo Clinic: Tachycardia
Heart Rhythm Society: Heart Rhythm Disorders
American Heart Association: Tachycardia
Texas Arrhythmia Institute: Other Atrial Tachycardias
Heart Racing: Inappropriate Sinus Tachycardia
University of California San Francisco Benioff Children's Hospital: Supraventricular Tachycardia
Mayo Clinic Proceedings: Supraventricular Tachycardia: Diagnosis and Management