Premature ventricular complex
Today's article is about premature ventricular complex (PVC).
Premature ventricular complex occurs when a premature beat arises from an ectopic focus within the ventricles. In the majority of cases, PVCs have no known cause and may occur spontaneously.
Courtesy of Dr. Roig
Criteria
- Wide QRS (>0.12 sec) unless it originates in the upper part of the interventricular septum (narrow QRS).
- Discordant ST-T changes opposite to the major deflection of QRS.
- The PVC occurs prematurely with respect to the baseline RR interval.
PVCs may occurs in a pattern of:
- Isolated: only one PVC.
- Bigeminy: every other beat is a PVC.
- Trigeminy: every third beat is a PVC.
- Quadrigeminy: every fourth beat is a PVC.
- Quintageminy: every fifth beat is a PVC.
- Couplet: two consecutive PVCs.
- Ventricular tachycardia: three or more PVCs consecutive.
PVCs may be either:
- Unifocal: Monomorphic with a fixed coupling interval due to a single ventricular focus.
- Multifocal: Polymorphic with variable coupling intervals due to multiple ventricular foci.
- Multiformed: Polymorphic but a fixed coupling interval. The impulse originates from a single ventricular focus but the morphology differs due to differing exit sites or conduction through the ventricles.
In regards to the compensatory pause:
- Complete pause: The premature beat does not reset the sinus pacemaker due to either VA block or the sinus node being refractory at time of premature impulse arrival. The subsequent sinus beat occur on time based on the underlying sinus rate (PVCs very often occurs with compensatory pause).
- Incomplete pause: Premature impulse enters the SA node and resets its timing causing the next sinus P wave to appear earlier than expected (commonly seen in the PACs).
PVCs may result in an incomplete compensatory pause if:
- VA conduction: Retrograde atrial activation resets the sinus node and the next beat may occur slightly early.
- Interpolated PVC: The PVC occur so early that it cannot be conducted through a refractory AV node, however sinus rate is slow enough to allow the AV node and ventricle to recover prior to the next sinus beat, therefore the sinus rhythm continues on time.
- Concealed conduction: Retrograde activation of the AV node by the PVC results in PR prolongation (AV node is partially refractory). Continued anterograde and retrograde activation may eventually cause impulse block.
Possible causes: Normals, stress, anxiety, excess catecholamines, hypokalemia, hypomagnesaemia, hypercalcemia, myocardial ischemia, abuse of alcohol, tobacco, caffeine, drugs, others.
Graphic explanation from EKGDX App. Note the compensatory pause based on the PP interval.
Isolated PVC (beat #2).
PVCs in a pattern of bigeminy.
PVCs in a pattern of trigeminy.
PVC in a pattern of quadrigeminy. Courtesy of Andreas Roeschl, MD
PVCs in a pattern of quintageminy.
Two PVCs in a row (couplets).
Nonsustained ventricular tachycardia (three PVCs in a row).
Interpolated PVC.
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