What is bigeminy?

Understanding Bigeminy

Bigeminy is a cardiac rhythm characterized by the alternation of a normal beat with an abnormal beat, creating a pattern where every other heartbeat is premature or abnormal. 1

Types of Bigeminy

Bigeminy can occur at different levels of the cardiac conduction system:

• Atrial bigeminy: A premature atrial contraction (PAC) follows each normal sinus beat 2
• Junctional bigeminy: Premature junctional contractions alternate with normal beats 2
• Ventricular bigeminy: The most common form, where premature ventricular contractions (PVCs) alternate with normal beats 2
• Concealed bigeminy: PVCs separated by an odd number of sinus beats 2

Mechanisms

Bigeminy can result from several mechanisms:

• Ectopic firing: Abnormal electrical impulses originating outside the sinoatrial node 2
• Delayed afterdepolarizations (DADs): Abnormal calcium handling in cardiac cells 1
• Triggered activity: Spontaneous depolarizations during or after normal cardiac action potentials 1
• Reentry circuits: Electrical impulses traveling in circular pathways 3
• Early afterdepolarizations: Particularly in patients with prolonged ventricular repolarization 3
• Autonomic imbalance: Often with vagal predominance 1

Risk Stratification

The American Heart Association stratifies bigeminy into risk categories 1:

High-Risk Features

• QTc interval >500 ms
• Associated with syncope or presyncope
• Evidence of hemodynamic compromise
• Occurrence during exercise
• Family history of sudden cardiac death

Moderate-Risk Features

• Frequent episodes (>10% of total beats)
• Associated mild symptoms
• Occurrence in patients with known heart disease

Low-Risk Features

• Asymptomatic patients
• Normal cardiac structure and function
• Normal QT interval
• Suppression with exercise

Clinical Implications

Bigeminy can have several important clinical implications:

• Misdiagnosis: Can be misdiagnosed as sinus bradycardia when premature beats are not conducted 1
• Warning sign: Ventricular bigeminy in patients with long QT intervals may signal risk for torsades de pointes 1, 3
• Cardiomyopathy risk: Frequent PVCs in a bigeminal pattern can lead to tachycardia-induced cardiomyopathy 1

Common Triggers and Associated Conditions

Bigeminy can be triggered or exacerbated by:

• Electrolyte abnormalities: Particularly hypokalemia and hypocalcemia 1
• Thyroid dysfunction: Both hyperthyroidism and hypothyroidism 1
• Structural heart disease: Including hypertrophic and dilated cardiomyopathy 1
• Endocrine disorders: Diabetes mellitus, pheochromocytoma, primary aldosteronism 1
• Myocardial ischemia: Can trigger bigeminy 1
• Medications: Particularly QT-prolonging drugs 1
• Lifestyle factors: Caffeine, alcohol, stress 1

Diagnostic Approach

The American College of Cardiology recommends different diagnostic approaches based on risk stratification 1:

• For all patients: 12-lead ECG to assess QT interval and evidence of structural heart disease
• High-risk patients: Echocardiography, exercise stress testing, extended monitoring, electrophysiology study if indicated
• Moderate-risk patients: Echocardiography, 24-hour Holter monitoring, exercise testing
• Low-risk patients: Follow-up ECG in 1 month if frequent

Management Considerations

Management should be tailored according to risk category 1:

• High-risk patients: Treat underlying heart disease, consider antiarrhythmic therapy if symptomatic, correct electrolyte abnormalities, avoid QT-prolonging medications, consider ICD if associated with life-threatening arrhythmias
• Moderate-risk patients: Treat underlying conditions, consider beta-blockers for symptomatic patients, manage electrolytes, regular follow-up
• Low-risk patients: Reassurance, avoidance of triggers, no specific antiarrhythmic therapy needed

Important Clinical Pitfalls

• Failing to identify high-risk features that require immediate attention
• Overlooking underlying structural heart disease or electrolyte abnormalities
• Misdiagnosing bigeminy as sinus bradycardia when premature beats are not conducted
• Not recognizing bigeminy as a potential warning sign for more serious arrhythmias in patients with long QT syndrome
• Underestimating the risk of tachycardia-induced cardiomyopathy with persistent bigeminy