Ventricular Bigeminy Classification
Ventricular bigeminy is classified as a repetitive pattern where every normal sinus beat is followed by a premature ventricular complex (PVC), creating characteristic paired complexes on electrocardiogram. 1, 2
Electrocardiographic Definition
The diagnostic hallmark is the alternating pattern of one normal QRS complex followed by one premature ventricular beat throughout the rhythm strip. 1, 2 This creates a distinctive "coupled" appearance that distinguishes bigeminy from other ventricular arrhythmias. 2
Classification Within Ventricular Arrhythmias
Ventricular bigeminy falls under the broader category of ventricular ectopic complexes in the ACC/AHA classification system. 3 It represents a specific organizational pattern of PVCs rather than a distinct arrhythmia entity. 3
Key Distinguishing Features
Pattern Recognition
- Every other beat must be a PVC to qualify as true bigeminy 1, 2
- The pattern should be sustained and repetitive, not intermittent 4
- Both isolated PVCs and bigeminy patterns can coexist in the same patient 5
Coupling Interval Characteristics
Two distinct subtypes exist based on coupling intervals:
- Fixed coupling interval bigeminy: The PVC occurs at a consistent interval after each sinus beat, suggesting a reentrant mechanism 6
- Variable coupling interval bigeminy: The PVC-to-sinus interval varies, potentially indicating parasystolic mechanisms 4
Clinical Classification Context
By Hemodynamic Impact
Ventricular bigeminy can present across the hemodynamic spectrum defined by ACC/AHA guidelines 3:
- Asymptomatic: No symptoms despite the arrhythmia pattern 3, 1
- Minimal symptoms: Palpitations or awareness of irregular heartbeat 3
- Hemodynamically significant: Can cause effective bradycardia due to non-conducted peripheral pulses from PVCs, apical-radial pulse deficit, and relative hypertension with wide pulse pressure 1
By Underlying Substrate
The classification must account for structural heart disease presence 1:
- Benign bigeminy: Occurs in structurally normal hearts without high-risk features 1
- Pathologic bigeminy: Associated with ischemic heart disease, cardiomyopathy, heart failure, or electrolyte abnormalities 1, 7
High-Risk Classification Features
Certain ECG characteristics elevate bigeminy to a high-risk classification requiring urgent intervention 2, 6:
- QTc >500 ms with bigeminy indicates extremely high risk for torsades de pointes 2
- Bigeminy occurring after short-long RR sequences in long QT syndrome suggests early afterdepolarization mechanism 6
- Bigeminy in acute myocardial infarction context indicates ongoing electrical instability 2
Morphologic Subtypes
Monomorphic Bigeminy
All PVCs have identical QRS morphology, suggesting a single ectopic focus. 3
Polymorphic Bigeminy
PVCs demonstrate varying QRS morphology, indicating multiple foci or varying exit points. 3
Common Diagnostic Pitfalls
Do not confuse atrial bigeminy with ventricular bigeminy—atrial bigeminy involves premature atrial beats that may conduct normally, with AV delay, or be blocked entirely, potentially mimicking AV block. 1 Careful examination of T waves for hidden P waves is essential. 8, 2
Effective bradycardia from bigeminy can lead to inaccurate heart rate estimation, as non-conducted PVCs may not generate palpable peripheral pulses despite electrical activity. 1, 2 This can result in inappropriate management decisions if not recognized.