Diagnosis of Bigeminy
Bigeminy is diagnosed on electrocardiogram by identifying a repetitive pattern where every normal heartbeat is followed by a premature beat, creating characteristic paired complexes. 1
ECG Diagnostic Criteria
The diagnosis of bigeminy is based on specific electrocardiographic findings that vary by the origin of the premature beats:
Ventricular Bigeminy
- Pattern recognition: Every sinus beat is followed by a premature ventricular complex (PVC), creating an alternating rhythm 1, 2
- QRS morphology: The premature beats have a different (typically wider) QRS morphology compared to sinus beats 2
- Coupling interval: May be relatively fixed or variable depending on the underlying mechanism 3
- P wave relationship: Sinus P waves continue unrelated to the PVCs, demonstrating AV dissociation 2
Atrial Bigeminy
- Pattern recognition: A premature atrial beat follows each sinus beat 4, 2
- P wave morphology: Premature P waves have different morphology and mean vector compared to sinus P waves 4
- Conduction patterns: The premature atrial beat may be conducted normally, with aberration, or blocked 4
- Critical pitfall: Blocked atrial bigeminy can simulate sinus bradycardia—carefully examine T waves for hidden blocked P waves 4
Junctional Bigeminy
- Premature junctional beats coupled to sinus beats, or occurring with atrial fibrillation 2
Essential Diagnostic Steps
Initial 12-Lead ECG
- Obtain a standard 12-lead ECG to identify the bigeminal pattern and characterize QRS morphology 1
- Assess for underlying structural heart disease markers (prior MI, left ventricular hypertrophy, bundle branch blocks) 1
- Measure QT/QTc interval, as prolonged QTc >500 ms with bigeminy indicates extremely high risk for torsades de pointes 4, 3
Extended Monitoring
- 24-48 hour Holter monitoring is recommended to quantify the burden of premature beats, assess persistence versus intermittency, and detect more malignant arrhythmias 1
- Extended monitoring beyond 24 hours should be considered for patients with intermittent symptoms 1
Physical Examination Findings
- Effective bradycardia: The premature beats may not generate palpable pulses, creating apparent bradycardia 1
- Apical-radial pulse deficit: Discrepancy between apical heart rate and radial pulse rate 1
- Wide pulse pressure with relative hypertension may be observed 1
Mechanism-Based Diagnosis
Understanding the mechanism helps confirm the diagnosis:
Reentrant Bigeminy
- Most common in structural heart disease with fixed anatomical substrates 5
- Characterized by relatively constant coupling intervals 3, 6
- Ultrahigh resolution mapping may reveal continuous low-amplitude potentials connecting beats, confirming reentry 6
Triggered Activity (Early Afterdepolarizations)
- Associated with prolonged QT interval (QTc >0.5 seconds) 3
- Relatively fixed coupling interval 3
- Onset after short-long RR sequences 3
- Prominent U waves often present 3
Concealed Bigeminy
- Manifests as PVCs separated by an odd (or sometimes even) number of sinus beats 2, 7
- Constant relationship between coupling interval and number of intervening sinus beats 7
- Has the same clinical implications as overt ventricular bigeminy 2
Conduction Block Patterns
- 3:2 Wenckebach block at the AV junction or SA node can create bigeminal patterns 2
- Two-level Wenckebach periodicity in reentrant pathways may cause intermittent bigeminy 8
Critical Diagnostic Pitfalls to Avoid
- Do not mistake blocked atrial bigeminy for sinus bradycardia—always scrutinize T waves for hidden P waves 4
- Avoid inaccurate heart rate estimation due to effective bradycardia from non-conducted premature beats 1, 5
- Do not diagnose both premature atrial beats and PVCs on the same strip without carefully searching for premature P waves preceding wide QRS complexes, as aberrant conduction is more common 4
- Never dismiss bigeminy as benign without excluding structural heart disease through comprehensive evaluation 5