A premature ventricular contraction occurs when a focus in the ventricle generates an action potential before the next scheduled sinoatrial nodal action potential.
There are four main characteristics of premature ventricular contractions:
Premature, occurring earlier than expected if measured against previous R-R intervals.
- Ectopic, originating outside of the SA node, and thus the QRS morphology would be different from the normal morphology when the action potential travels through the normal conduction system.
- Wide complexes; because they come from the ventricles and do not use the normal ventricular conduction system, action potentials need to travel from myocyte to myocyte, which is much slower, creating a wide QRS complex. Unlike premature atrial contractions, or PACs, usually narrow-complexed because they use the normal ventricular conduction system (unless a baseline right or left bundle branch block is present).
- Compensatory pause following the contraction; the extra action potential causes the SA node to become refractory to generating its next scheduled beat, and thus it must “skip a beat” and will resume exactly two P-P intervals after the last normal sinus beat.
Ventricular bigeminy occurs when every other beat is a PVC.
No treatment is necessary for PVCs. If symptomatic, beta-blockers or antiarrhythmic drugs can be effective. Rarely, ablation of PVCs is needed.
1. Chou’s Electrocardiography in Clinical Practice: Adult and Pediatric, 6e
2. Surawicz B, et al. AHA/ACCF/HRS Recommendations for the Standardization and Interpretation of the Electrocardiogram. Circulation. 2009; doi:10.1161/CIRCULATIONAHA.108.191095.