Rapid heart rate, defined as a rate greater than 100 beats/min.

May be a normal physiological response, such as sinus tachycardia, or may be pathologic in nature.

A marker of CV disease in the general population and among patients with known cardiovascular disease.

Can arise from any heart tissue such as the sinoatrial node the atria, AV node, or the ventricles.

The rate may be regular, irregularly irregular or regularly irregular.

Narrow QRS complexes <120ms are supraventricular, while wide complexes >120 ms can be supraventricular or ventricular in nature.

Significance depends of the type, rate, and presence of other cardiovascular factors to account for symptoms and prognosis.

Treatment depends on the underlying process and is aimed at reducing symptoms, improving physiology and preventing thromboembolism and sudden death.

Mechanisms include: automaticity, reentry, and triggered types.

Automaticity occurs in the normal state and is enhanced when catecholamine and/or sympathetic stimulation occur on cardiac tissues.

The spontaneous activation of cardiac tissue in non pacemaker cells, that are damaged with partial depolarization, may occur and lead to abnormal automaticity.

Automatic type of tachyarrhythmias are focal in nature.

Atrial fibrillation is the most common cause of irregular tachycardia.

Irregular tachycardias include atrial fibrillation, multifocal atrial tachycardia, supraventricular tachycardia with variable atrioventricular conduction such as atrial tachycardia or atrial flutter with variable AV block, sinus tachycardia with PACs or PVCs

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