—Cyclic changes in the heart rate during breathing. Common in children and often found in adults, as well.
—The sinus node sends out electrical signals faster than usual, speeding up the heart rate.
Sick Sinus Syndrome
—The sinus node does not fire its signals properly, so the heart rate slows down. Sometimes the rate changes back and forth between a slow (bradycardia) and fast (tachycardia) rate.
Premature Supraventricular Contractions or Premature Atrial Contractions (PAC)
—A beat occurs early in the atria, causing the heart to beat before the next regularly expected heartbeat.
Supraventricular Tachycardia (SVT), Paroxysmal Atrial Tachycardia (PAT)
—A series of early beats in the atria speed up the heart rate. In paroxysmal tachycardia, repeated periods of very fast heartbeats begin and end suddenly.
—Rapidly fired signals cause the muscles in the atria to contract quickly, leading to a very fast, steady heartbeat.
—Electrical signals in the atria are fired in a very fast and uncontrolled manner. Electrical signals arrive in the ventricles in a completely irregular fashion, so the heartbeat is completely irregular.
—Abnormal pathways between the atria and ventricles cause the electrical signal to arrive at the ventricles too soon and to be transmitted back into the atria. Very fast heart rates may develop as the electrical signal ricochets between the atria and ventricles.
Premature Ventricular Complexes (PVC)
—An electrical signal from the ventricles causes an early heart beat that generally goes unnoticed. The heart then seems to pause until the next beat of the ventricle occurs in a regular fashion.
—The heart beats fast due to electrical signals arising from the ventricles (rather than from the atria). If sustained, this can lead to an emergency medical condition.
—Electrical signals in the ventricles are fired in a very fast and uncontrolled manner, causing the heart to quiver rather than beat and pump blood. This is a life-threatening condition and is the primary cause of sudden cardiac death.
Long QT Syndrome
—Diagnosed on the basis of
(ECG), long QT syndrome may be inherited or acquired (eg, secondary to other causes), with the most common cause being medication. Patients with long QT syndrome are prone to syncope (fainting spells) and palpitations. They are also at an increased risk for sudden cardiac death.
Conduction block can occur anywhere along the heart’s electrical pathway (eg, near the AV node or along the bundle branches that conduct impulses into each of the ventricles). This abnormality is detected on ECG. It may be completely asymptomatic or it may cause your heart rate to slow down, which in turn may cause fainting spells, dizziness, and feeling of skipped heartbeats.
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Ganz, LI, Friedman, PL. Supraventricular tachycardia.
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Harrison's Principles of Internal Medicine. 14th ed. McGraw-Hill; 1998.
Lok NS, Lau CP. Prevalence of palpitations, cardiac arrhythmias and their associated risk factors in ambulant elderly.
Int J Cardiol.
National Heart, Lung, and Blood Institute website. Available at:
Pucheu A, LaCroix H, Tonet JL, et al. Ventricular arrhythmias. In: MacFarlane PW, Lawrie TDV, (eds).
Comprehensive Electrocardiography: Theory and Practice in Health and Disease.
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Weber BE, Kapoor WN. Evaluation and outcomes of patients with palpitations.
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Last reviewed September 2012 by Michael J. Fucci, DO
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