Bigeminy is a

cardiac arrhythmia Arrhythmias, also known as cardiac arrhythmias, are irregularities in the heartbeat, including when it is too fast or too slow. Essentially, this is anything but normal sinus rhythm. A resting heart rate that is too fast – above 100 beat ...

in which there is a single

ectopic beat Ectopic beat is a disturbance of the cardiac rhythm frequently related to the electrical conduction system of the heart, in which beats arise from fibers or group of fibers outside the region in the heart muscle ordinarily responsible for impuls ...

, or irregular heartbeat, following each regular heartbeat. Most often this is due to

s occurring so frequently that there is one after each sinus beat, or normal heartbeat. The two beats are figuratively similar to two

twin Twins are two offspring produced by the same pregnancy.MedicineNet > Definition of Twin Last Editorial Review: 19 June 2000 Twins can be either ''monozygotic'' ('identical'), meaning that they develop from one zygote, which splits and forms two ...

s (hence ''

bi- Numeral or number prefixes are prefixes derived from numerals or occasionally other numbers. In English and many other languages, they are used to coin numerous series of words. For example: *triangle, quadrilateral, pentagon, hexagon, octagon ...

'' + ''

gemini Gemini most often refers to: * Gemini (constellation), one of the constellations of the zodiac * Gemini (astrology), an astrological sign Gemini may also refer to: Science and technology Space * Gemini in Chinese astronomy, the Gemini constellat ...

''). For example, in ventricular bigeminy, a sinus beat is shortly followed by a

premature ventricular contraction A premature ventricular contraction (PVC) is a common event where the heartbeat is initiated by Purkinje fibers in the ventricles rather than by the sinoatrial node. PVCs may cause no symptoms or may be perceived as a "skipped beat" or felt as ...

(PVC), a pause, another normal beat, and then another PVC. In atrial bigeminy, the other "twin" is a

premature atrial contraction Premature atrial contraction (PAC), also known as atrial premature complexes (APC) or atrial premature beats (APB), are a common arrhythmia characterized by premature heartbeats originating in the atria. While the sinoatrial node typically re ...

(PAC).

Cause

After any premature ventricular contraction there is a pause that can lead to the development of bigeminy. A PVC wavefront often encounters a refractory AV node that does not conduct the wavefront retrograde. Thus the atrium is not depolarized and the sinus node is not reset. Since the sinus P wave to PVC interval is less than the normal P–P interval, the interval between the PVC and the next P wave is prolonged to equal the normal time elapsed during two P–P intervals. This is called a "compensatory" pause. The pause after the PVC leads to a longer recovery time, which is associated with a higher likelihood of myocardium being in different stages of repolarization. This then allows for re-entrant circuits and sets up the ventricle for another PVC after the next sinus beat. The constant interval between the sinus beat and PVC suggests a reentrant etiology rather than spontaneous automaticity of the ventricle. Premature atrial contractions by contrast do not have a compensatory pause, since they reset the sinus node, but atrial or supraventricular bigeminy can occur. If the PACs are very premature, the wavefront can encounter a refractory AV node and not be conducted. This can be mistaken for sinus bradycardia if the PAC is buried in the T wave since the PAC will reset the SA node and lead to a long P–P interval.

Diagnosis

Rule of bigeminy

When the atrial rhythm is irregular (as in atrial fibrillation or sinus arrhythmia) the presence of bigeminy depends on the length of the P–P interval and happens more frequently with a longer interval. As with post PVC pauses, a longer P–P interval leads to a higher chance of re-entrant circuits and thus PVCs. The term "rule of bigeminy" is used to refer to the dependence of bigeminy on the ventricular cycle length in irregular rhythms.

Classification

There can be similar patterns depending on the frequency of abnormal beats. If every other beat is abnormal, it is described as bigeminal. If every third beat is aberrant, it is trigeminal; every fourth would be quadrigeminal. Typically, if every fifth or more beat is abnormal, the aberrant beat would be termed occasional. Bigeminy is contrasted with couplets, which are paired abnormal beats. Groups of three abnormal beats are called triplets and are considered a brief run of

non-sustained ventricular tachycardia Ventricular tachycardia (V-tach or VT) is a cardiovascular disorder in which fast heart rate occurs in the ventricles of the heart. Although a few seconds of VT may not result in permanent problems, longer periods are dangerous; and multiple e ...

(NSVT), and if the grouping lasts for more than 30 seconds, it is

ventricular tachycardia Ventricular tachycardia (V-tach or VT) is a cardiovascular disorder in which fast heart rate occurs in the ventricles of the heart. Although a few seconds of VT may not result in permanent problems, longer periods are dangerous; and multiple ...

(VT).

Treatment

In people without underlying heart disease and who do not have any symptoms, bigeminy in itself does not require any treatment. If it does become symptomatic,

beta-blockers Beta blockers, also spelled β-blockers, are a class of medications that are predominantly used to manage abnormal heart rhythms (arrhythmia), and to protect the heart from a second heart attack after a first heart attack (secondary prevention). ...

can be used to try to suppress ventricular ectopy. Class I and III agents are generally avoided as they can provoke more serious arrhythmias.

References

{{Heart diseases Cardiac arrhythmia