An abnormally fast heart rate. It may arise due to a normal physiological process, such as during exercise, the ingestion of drugs such as caffeine and amphetamine, or generalized disorders such as serious infections or hyperthyroidism. It may also be due to specific disorders of the heart that disrupt the normal electrical pathways of the heart muscle, in which case the heart rate may be irregular. Extremely rapid heart rates do not allow time for adequate pumping of the blood at each beat and result in heart failure.
Name of Symptom/Sign:Tachycardia
Classifications and external resources
| ICD-10 | R00.0 |
|---|---|
| ICD-9 | 785.0 |
Tachycardia is an abnormally rapid beating of the heart, defined as a resting heart rate of 100 or more beats per minute in an average adult.
Tachycardia is a general symptomatic term that does not describe the cause of the rapid rate.
Autonomic and endocrine causes
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 (adrenaline), which have a similar effect.
Endocrine disorders such as pheochromocytoma can cause epinephrine release and tachycardia independent of the nervous system.
Hemodynamic responses
The body contains several feedback mechanisms to maintain adequate blood flow and blood pressure.
This can happen in response to a decrease in blood volume (through dehydration or bleeding), or an unexpected change in blood flow.
Fever and infection leading to sepsis are also common causes of tachycardia, primarily due to increase in metabolic demands and compensatory increase in heart rate.
Tachycardic arrhythmias
An electrocardiogram tracing can distinguish several different forms of rapid abnormal heartbeat:
If the heart's electrical system is functioning normally, except that the rate is in excess of 100 beats per minute, it is called sinus tachycardia.
Supraventricular tachycardia (SVT) occurs when an abnormal electrical impulse originates above the ventricles, but instead of causing a single beat and a pause, it causes rapid local impulse cycling and initiates many rapid beats.
Ventricular tachycardia
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.
Abnormal accelerated ventricular rhythm with a usual rate of 150-200 beats/minute.
Exercise-induced ventricular tachycardia
Exercise-induced ventricular tachycardia is a phenomenon related to sudden deaths, especially in patients with severe heart disease (ischaemia, acquired valvular heart and congenital heart disease) accompanied with left ventricular dysfunction.
Both of these rhythms normally last for only a few seconds to minutes (paroxysmal tachycardia), but if VT persists it is extremely dangerous, often leading to ventricular fibrillation.
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