Identifying a Premature Ventricular Contraction
A random tall QRS complex that differs in morphology from the normal sinus QRS and is not preceded by a premature P wave is indeed a premature ventricular contraction (PVC). 1
Diagnostic Criteria for PVCs
The key electrocardiographic features that define a PVC include:
- Premature abnormal QRS complex that has a different morphology compared to the patient's normal sinus QRS 1
- Absence of a preceding premature P wave before the abnormal QRS 1
- QRS duration may be normal or prolonged - importantly, in infants and some patients, the QRS duration can be normal (less than 0.08 seconds) or only slightly prolonged, but if the morphology differs from sinus rhythm, it remains a PVC 1
Important Clinical Distinction
The term "tall" QRS is less relevant than the morphology difference. What matters diagnostically is whether the QRS complex has a different shape/configuration from your normal sinus beats, not necessarily its amplitude. 1
When to Pursue Further Evaluation
The presence of PVCs warrants different levels of concern based on frequency:
- Single or infrequent PVCs in structurally normal hearts are generally benign 1, 2
- Multiple PVCs (≥2 on a single 12-lead ECG) should prompt more extensive evaluation including ambulatory Holter monitoring, echocardiogram, and exercise stress testing 1
- Frequent PVCs (>30 per hour or >1% of beats on 12-lead ECG) are associated with increased cardiovascular risk and mortality in the general population 1
- Very high burden (≥2,000 PVCs per 24 hours) carries up to 30% risk of underlying structural heart disease and warrants comprehensive evaluation including cardiac MRI 1, 3
Critical Pitfall to Avoid
Do not confuse PVCs with premature atrial beats conducted with aberrancy. While it's theoretically possible to distinguish these based on QRS morphology, the most reliable differentiator is identifying whether a premature P wave precedes the abnormal QRS complex. 1 If you see a premature P wave before the wide/different QRS, it's likely a premature atrial beat with aberrant conduction rather than a PVC. 1
Assessment of Underlying Risk
Measure the QT interval carefully during periods of normal sinus rhythm to exclude long QT syndrome, which can be associated with malignant ventricular arrhythmias. 1 Obtain an echocardiogram to assess for structural abnormalities or ventricular dysfunction, particularly if PVCs are frequent or symptomatic. 1