How to Recognize the Origin of PVC on ECG
The origin of PVCs can be determined by analyzing QRS morphology, axis, and transition patterns on 12-lead ECG, with right ventricular outflow tract (RVOT) PVCs showing left bundle branch block (LBBB) pattern with inferior axis and later R/S transition (≥V4), while left ventricular outflow tract (LVOT) PVCs show LBBB or RBBB pattern with inferior axis and early transition (V1-V2). 1
Key ECG Features for Localizing PVC Origin
RVOT vs LVOT Differentiation
The R/S transition point is the most critical distinguishing feature:
- RVOT PVCs demonstrate later R/S transition at V4 or beyond, reflecting the rightward origin 1
- LVOT PVCs show early transition at V1/V2, with approximately 70% displaying LBBB morphology and 30% showing RBBB morphology 1
- Both typically have an inferior axis (positive in leads II, III, aVF) 1
QRS Duration Considerations
In adults, PVC QRS duration is typically prolonged (≥0.09 seconds), but morphology is more important than duration alone 1:
- The QRS complex must be different from the patient's normal sinus QRS 1
- In infants, QRS may be normal or only slightly prolonged (<0.08 seconds) but still represents a PVC if morphology differs from sinus 1
- A critical caveat: RVOT PVCs with QRS duration >160ms may indicate early arrhythmogenic right ventricular cardiomyopathy (ARVC) rather than benign ectopy 2
Absence of Preceding P Wave
A premature abnormal QRS that is NOT preceded by a premature P wave confirms ventricular origin 1:
- This distinguishes PVCs from premature atrial contractions (PACs) with aberrant conduction 1
- In infants particularly, careful examination is needed as both PACs and PVCs can occur on the same strip 1
Specific Anatomical Localization
Aortic Cusp Origin
PVCs from aortic sinuses of Valsalva (20% of outflow tract VTs) show broad QRS with very early transition at V1-V2 1:
- Most originate from left coronary cusp, followed by right coronary cusp 1
- These require specialized mapping as the relationship between morphology and exact site is not precise enough for prediction 1
Left Fascicular Origin
Left posterior fascicular VT shows characteristic RBBB morphology with left-axis deviation 1:
- Left anterior fascicular VT demonstrates RBBB with right-axis deviation 1
- Left upper septal fascicular VT shows narrow QRS with normal or right-axis deviation 1
Advanced Morphological Features
Multiple PVC Morphologies
The presence of ≥2 different PVC morphologies significantly predicts underlying fibrotic substrate 3:
- RBBB morphology PVCs also predict fibrotic substrate presence (P<0.001) 3
- These findings warrant cardiac MRI evaluation before ablation 3
Exercise Response
PVCs that increase during exercise rather than suppress warrant further evaluation for underlying cardiac conditions 2:
- Suppression with exercise suggests benign etiology 2
- Persistence or increase suggests potential structural disease 2
Clinical Pitfalls to Avoid
Do not rely solely on QRS morphology to distinguish PVCs from supraventricular tachycardia with aberration 1:
- The specific QRS morphology is generally not helpful for this distinction 1
- However, in infants, persistent aberration beyond the first 10-20 beats is exceedingly rare, making VT the likely diagnosis 1
The relationship between surface ECG morphology and precise ventricular site of origin is not exact enough to predict which ventricle is causing the arrhythmia without electrophysiologic mapping 1: