What causes bigeminy?

Causes of Bigeminy

Bigeminy is most commonly caused by premature ventricular contractions (PVCs) occurring in specific patterns, but can also result from electrolyte abnormalities, QT interval prolongation, cardiac channelopathies, medication effects (especially digitalis), or underlying structural heart disease. 1

Definition and Patterns

Bigeminy refers to a cardiac rhythm pattern where every normal heartbeat is followed by a premature beat, creating a repetitive paired pattern. While ventricular bigeminy (with PVCs) is most common, bigeminy can also originate from:

• Ventricular bigeminy: PVCs alternating with normal beats (most common form) 1
• Atrial bigeminy: Premature atrial contractions (PACs) following each normal beat 2
• Junctional bigeminy: Premature junctional contractions alternating with normal beats 2
• Blocked atrial bigeminy: Can simulate sinus bradycardia when P waves are blocked 3

Primary Causes

1. Cardiac Structural Disease

• Ischemic heart disease/coronary artery disease
• Cardiomyopathies (hypertrophic, dilated, arrhythmogenic right ventricular)
• Valvular heart disease
• Congenital heart abnormalities 1

2. Electrophysiological Mechanisms

• Reentry circuits: Traditional explanation for many bigeminal rhythms 4
• Early afterdepolarizations: Particularly in patients with prolonged QT intervals 4
• Enhanced automaticity: Increased excitability of cardiac tissue 5
• Triggered activity: From calcium overload or other cellular mechanisms 2, 5

3. QT Interval Abnormalities

• Prolonged QT interval (>0.5 seconds) strongly associated with bigeminy 4
• Can indicate risk for torsades de pointes, especially when bigeminy is present 1, 4
• Long QT syndrome (LQTS) patients may develop bigeminy as a warning sign 3, 4

4. Medication Effects

• Digitalis toxicity: Can cause ventricular bigeminy or trigeminy even at therapeutic doses 6
• Other pro-arrhythmic medications (Class I antiarrhythmics, certain antibiotics, antipsychotics)
• QT-prolonging drugs in susceptible individuals 1

5. Cardiac Channelopathies

• Long QT syndrome (LQTS)
• Brugada syndrome
• Catecholaminergic polymorphic ventricular tachycardia (CPVT)
• Short QT syndrome 3, 1

6. Physiologic and Metabolic Factors

• Electrolyte abnormalities (particularly hypokalemia, hypomagnesemia)
• Hypoxia
• Acidosis
• Thyroid dysfunction
• Caffeine, alcohol, or stimulant use
• Stress or heightened sympathetic tone 1

Special Considerations

Concealed Bigeminy

• PVCs separated by an odd number of normal beats
• Results from a specific conduction pattern where some impulses are blocked 2, 7
• Has similar clinical implications as regular ventricular bigeminy 2

Rule of Bigeminy

• Self-perpetuating pattern where each normal beat triggers a PVC
• In patients with prolonged ventricular repolarization, may be caused by early afterdepolarizations 4
• Often seen in patients with long QT intervals (>0.5 seconds) 4

Hemodynamic Effects

• Can cause effective bradycardia
• May produce apical-radial pulse deficit
• Can result in relative hypertension with wide pulse pressure 1

High-Risk Features

Bigeminy requires more urgent attention when associated with:

• QTc >500 ms
• Syncope or presyncope
• Hemodynamic compromise
• Occurrence during exercise
• Family history of sudden cardiac death
• Underlying structural heart disease 3, 1

Understanding the specific cause of bigeminy is essential for appropriate management, as treatment should target the underlying mechanism rather than just the rhythm itself.