Bigeminal rhythm

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Rim Halaby, M.D. [2]

Synonyms and keywords: Bigeminy, bigeminal beat

Overview

Bigeminy is a type of cardiac arrhythmia in which abnormal heart beats occur every other concurrent beat. The abnormal heart beat can originate from the atrium, AV node or the ventricle. A typical example is bigeminal rhythm resulting from premature ventricular contractions/complexes (PVC). Following the PVC there is a pause and then the normal beat returns, only to be followed by another PVC. The continuation of this pairing of beats is an example of bigeminy. Other forms of abnormal beats include PAC, escape beats and parasystole.^[1]

Classification

Atrial bigeminy
Junctional bigeminy
Ventricular bigeminy
Concealed bigeminy
Escape capture bigeminy^[2]

Pathophysiology

Several mechanisms can be involved in the creation of a bigeminal rhythm, such as:

Ectopic firing of electrical impulses
Abnormalities in electrical impulse generation
Abnormalities in electrical impulse conduction^[2]

Differential Diagnosis

Trigeminal and Quadrigeminal Rhythms

If every other beat is abnormal, you can describe the rhythm as bigeminal. If every third beat is abnormal, it is trigeminal; every fourth would be quadrigeminal. Typically, if every fifth or more beat is abnormal, the abnormal beat would be termed occasional.

Bigeminal premature ventricular contractions	Normal, PVC, Normal, PVC...
Trigeminal premature ventricular contractions	Normal, Normal, PVC, Normal, Normal, PVC...
Quadrageminal premature ventricular contractions	Normal, Normal, Normal, PVC; Normal, Normal, Normal, PVC...
Occasional escape complexes	Normal, Normal, Normal, Normal, Pause, Escape...

Couplets and Triplets

Bigeminy is contrasted with couplets, which are paired abnormal beats. If these concurrent beats number three, they are called triplets and are considered as a brief run of non-sustained Ventricular tachycardia or NS-VT.

Bigeminal premature ventricular contractions	Normal, PVC, Normal, PVC...
Bigeminal Couplets	Normal, Normal, PVC, PVC, Normal, Normal, PVC, PVC...
NS-VT	Normal, Normal, PVC, PVC, PVC, PVC, Normal, Normal, PVC...

Diagnosis

ECG

Shown below is an EKG depicting atrial bigeminy. The EKG shows a regularly irregular rhythm at a rate of about 75/minute. There are two different P wave morphologies best seen in lead V1.

Copyleft image obtained courtesy of ECGpedia,http://en.ecgpedia.org/wiki/Main_Page

Shown below is an EKG depicting bigeminy. The pacemaker is an atrial pacer set at 30/min. Note the marker channel documenting atrial pacing and then sensing of the QRS in the refractory period of the pacemaker. The paced atrial beats seem to stimulate a normal sinus beat and hence create the bigeminal rhythm.