<unk>  <unk> L) is a common abnormal heart rhythm that starts in the<unk>  chambers of the heart. When it first occurs, it is usually associated with a fast heart rate and is classified as a type of supraventricular tachycardia.<unk>  is characterized by a sudden-onset (usually) regular abnormal heart rhythm on an electrocardiogram (ECG) in which the heart rate is fast. Symptoms may include a feeling of the heart beating too fast, too hard, or skipping beats, chest discomfort, difficulty breathing, a feeling as if one's stomach has dropped, a feeling of being light-headed, or loss of consciousness. Although this abnormal heart rhythm typically occurs in individuals with cardiovascular disease (e.g. high blood pressure, coronary artery disease, and cardiomyopathy) and diabetes mellitus, it may occur spontaneously in people with otherwise normal hearts. It is typically not a stable rhythm, and often degenerates into<unk>  fibrillation <unk> . However, it does rarely persist for months to years. Similar to the abnormal heart rhythm<unk>  fibrillation,<unk>  also leads to poor contraction of the<unk>  chambers of the heart. This leads to the pooling of the blood in the heart and can lead to the formation of blood clots in the heart which poses a significant risk of breaking off and traveling through the bloodstream resulting in strokes. A supraventricular tachycardia with a ventricular heart rate of 150 beats per minute is suggestive (though not necessarily diagnostic) of<unk> . Administration of adenosine in the vein (intravenously) can help medical personnel differentiate between<unk>  and other forms of supraventricular tachycardia. Immediate treatment of<unk>  centers on slowing the heart rate with medications such as beta blockers (e.g., metoprolol) or calcium channel blockers (e.g., diltiazem) if the<unk> fected person is not having chest pain, has not lost consciousness, and if their blood pressure is normal (known as stable<unk> . If the<unk> fected person is having chest pain, has lost consciousness, or has low blood pressure (unstable<unk> , then an urgent electrical shock to the heart to restore a normal heart rhythm is necessary. Long-term use of blood thinners (e.g., warfarin or apixaban) is an important component of treatment to reduce the risk of blood clot formation in the heart and resultant strokes. Medications used to restore a normal heart rhythm (antiarrhythmics) such as ibutilide effectively control<unk>  about 80% of the time when they are started but<unk>  recurs at a high rate (70–90% of the time) despite continued use.<unk>  can be treated more definitively with a technique known as catheter ablation. This involves the insertion of a catheter through a vein in the groin which is followed up to the heart and is used to identify and interrupt the electrical circuit causing the<unk>  (by creating a small burn and scar).<unk>  was first identified as an independent medical condition in 1920 by the British physician Sir Thomas Lewis (1881–1945) and colleagues.<unk> L is the second most common pathologic supraventricular tachycardia but occurs at a rate less than one-tenth of the most common supraventricular tachycardia<unk>  fibrillation). The overall incidence of<unk> L has been estimated at 88 cases per 100,000 person-years. The incidence of<unk> L is significantly lower (~5 cases/100,000 person-years) in those younger than age 50 and is far more common (587 cases/100,000 person-years) in those over 80 years of age.
Atrial flutter
Ventricular flutter
Sinus arrhythmia
Supraventricular tachycardia
Atrial fibrillation
Ventricular fibrillation
Left bundle branch block
Junctional tachycardia