Tachycardia is a general term that describes a number of conditions in which the heart beats at an abnormally fast rate at rest (more than 100 beats per minute). It is a type of arrhythmia, which is an abnormal heart rhythm caused by an abnormality in the heart’s electrical system.
The word “supraventricular” means “above the ventricles.” Therefore, these tachycardias originate from above the ventricles – either from the upper chambers of the heart (atria) or from the AV node. Generally, supraventricular tachycardias come and go, so they are also known as paroxysmal supraventricular tachycardias. If they occur more regularly, they are called sustained paroxysmal supraventricular tachycardias.
The electrical system of the heart (conduction system) is a complex network of cells and fibers in the heart through which electrical impulses travel at lightning speed, triggering a heartbeat. The impulses are first sent out by the sinoatrial node (sinus node or SA node), located in the top of the upper-right chamber of the heart (the right atrium). From there, the impulses spread through the atria, causing them to contract, and then to the atrioventricular node (A-V node), where they are transmitted to the lower chambers of the heart (ventricles) via the bundle branches. Once the impulses reach the ventricles, they cause the chambers to contract and pump out blood in a routine and consistent manner.
If impulses are fired too fast – either from the heart’s normal conduction system or from other parts of the heart – the heart will beat too quickly. In many cases, a temporary rapid heartbeat is not medically significant by itself. For instance, sinus tachycardia is a normal response to increased demands on the heart during exercise. However, persistent severe tachycardia can lead to greater damage and heart malfunction.
Symptoms vary widely from lightheadedness, fatigue, chest pressure or syncope.
An arrhythmia due to an extra conducting pathway within the AV node. This allows the heart’s electrical activity to “short circuit” itself (“reentry”). Episodes of this arrhythmia may be triggered by physical or emotional stress, caffeine, cocaine or certain medications (including so-called natural or herbal remedies, which may contain stimulants).
How it is Diagnosed:
Diagnosis is made by 12-lead electrocardiogram (EKG). In cases of intermittent arrhythmias, a Holter monitor or event recorder may be required. Electrophysiology testing may be indicated in some patients to locate areas of ectopic activation, accessory pathways and to determine which patient is vulnerable for other arrhythmias.
Treatment of the underlying condition and control of any reversible factors is usually attempted in all patients. Examples include decrease in caffeine/alcohol use, control of hyperthyroidism, correction of electrolyte imbalance and control of heart failure. Depending on the cause, tachycardia may be treated with medications (e.g., antiarrhythmics, beta-blockers, calcium channel blockers) or by catheter ablation. In an emergency situation, or in the case of a sustained tachyarrhythmia, the patient may undergo cardioversion, or the use of electricity to establish a more normal heart rate.
Treatment options are largely influenced by the severity of structural heart abnormalities, symptoms, type of arrhythmias and in some case the results of EP testing.