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It can have harmful effects in two ways. First, when the heart beats too rapidly, it performs inefficiently (since there is not enough time for the ventricles to fill completely), causing blood flow and blood pressure to diminish. Second, it increases the work of the heart, causing it to require more oxygen while also reducing the blood flow to the cardiac muscle tissue, increasing the risk of ischemia or infarction.
Tachycardia is a general symptomatic term that does not describe the cause of the rapid rate. Common causes are autonomic nervous system or endocrine system activity, hemodynamic responses, and various forms of cardiac arrhythmia.
An increase in sympathetic nervous system stimulation causes the heart rate to increase, both by the direct action of sympathetic nerve fibers on the heart, and by causing the endocrine system to release hormones such as epinephrine which have a similar effect. Increased sympathetic stimulation is usually due to physical or psychological stress (the so-called "fight or flight" response), but can also be induced by stimulants such as caffeine.
Endocrine disorders such as pheochromocytoma can cause epinephrine release and tachycardia independent of the nervous system.
The body contains several feedback mechanisms to maintain adequate blood flow and blood pressure. If blood pressure decreases, the heart beats faster in an attempt to raise it.
This can happen in response to a decrease in blood volume (through dehydrationDehydration is the removal of water ( Greek hydros from an object. There are many methods of dehydration, with the most common being the application of dry heated air. This causes evaporation of the surface water, which is replaced by water internally. or bleedingBleeding is the loss of blood from the body. Children are put more in danger by bleeding as they have less blood to lose. The average adult human will be in medical danger after 2 liters (2 quarts) and could die of hypovolemic shock if more blood is lost.), or an unexpected change in blood flow. The most common cause of the latter is orthostatic hypotensionOrthostatic hypotension (also known as postural hypotension is a sudden fall in blood pressure that occurs when a person assumes a standing position. Symptoms, which generally occur after sudden standing, include dizziness, lightheadedness, blurred vision (also called postural hypotension), a sudden drop of blood pressure that occurs with a change in body position (e.g., going from lying down to standing up). When tachycardia occurs for this reason, it is called postural orthostatic tachycardia syndrome (POTS).
An electrocardiogramECG may also refer to the East Coast Greenway''. An Electrocardiogram ECG or EKG abbreviated from the German Elektrokardiogramm is a graphic produced by an electrocardiograph, which records the electrical voltage in the heart in the form of a continuous s tracing can distinguish several different forms of rapid abnormal heartbeat:
If the heart's electrical systemThe normal electrical conduction in the heart allows the impulse that is generated by the SA node of the heart to be propagated to (and stimulate) the myocardium (muscle of the heart). When the myocardium is stimulated, it contracts. It is the ordered sti is functioning normally, except that the rate is over 100 beats per minute, it is called sinus tachycardia. This is caused by any of the factors mentioned above, rather than a malfunction of the heart itself.
Supraventricular tachycardiaA supraventricular tachycardia SVT is a rapid rhythm of the heart in which the origin of the electrical signal is either the atria or the AV node. These rhythms do not require the ventricles for either initiation or maintenance. This is in contrast to ven (SVT) occurs when an abnormal electrical impulse originates above the ventricles, but instead of causing a single beat and a pause, it travels in circles and causes many rapid beats. Ventricular tachycardia (VT or "V-tach") is a similar phenomenon occurring within the tissue of the ventricles, causing an extremely rapid rate with poor pumping action. Both of these rhythms normally last for only a few seconds (paroxysmal tachycardia), but if VT persists it is extremely dangerous, often leading to ventricular fibrillationVentricular fibrillation V-fib is a cardiac condition which consists of a lack of coordination of the contraction of the muscle tissue of the large chambers of the heart. The ventricular muscle twitches randomly, rather than contracting in unison, and so.
Arrhythmias can be treated using drugs, intervention or implantable devices. See also: Bradycardia
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