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ECG tutorial: Ventricular arrhythmias

Jordan M Prutkin, MD, MHS, FHRS
Section Editor
Ary L Goldberger, MD
Deputy Editor
Gordon M Saperia, MD, FACC


Ventricular arrhythmias are wide complex rhythms that may be regular or irregular. These may be normal rate, bradycardic, or tachycardic, and may occur as single beats or sustained. Some ventricular arrhythmias may be present as sudden cardiac arrest.


Premature ventricular contractions (PVCs), ventricular premature beats (VPBs), ventricular premature complexes (VPCs), premature ventricular beats (PVBs), or ventricular extrasystoles (VES) are early occurring, widened QRS complexes that have a distinct morphology (resembling neither a typical left nor right bundle branch block) that is markedly different from the sinus QRS complex. Unifocal PVCs all have a single morphology. Multiple different QRS morphologies are termed multiform PVCs.

In general, there is no P wave identified before a premature QRS complex. However, there may be a normal sinus P wave present if the PVC is very late; in this situation, there is a long coupling interval (from the prior QRS complex), the P wave is not conducted, and the PR interval is shorter than the native sinus beat.

The QRS complex of a PVC is widened, often notched, and with a QRS duration usually >0.16 seconds (waveform 1). It will have a morphology that resembles a right or left bundle branch block depending upon the location of origin, but its morphology is generally not the same as a typical bundle branch block. It is assumed that the PVC originates in the left ventricle when it has a positive deflection or tall R wave in V1 (right bundle branch block configuration), while a negative complex with a deep S wave in V1 (resembling a left bundle branch block morphology) originates in the right ventricle. Other findings on the electrocardiogram (ECG) include marked repolarization abnormalities, manifested as ST segment and T wave abnormalities. Retrograde activation of the atrium is variably present; it depends upon the location of the premature beat, the time necessary for impulse conduction to the atrioventricular (AV) node, the coupling interval to the prior sinus beat, and the ability of the node to conduct retrograde to the atrium. When present, there is a retrograde P wave, usually seen within or slightly before the T wave. The interval from the previous P wave to the retrograde P wave is, however, shorter than the underlying sinus PP interval, reflecting the premature activation of the atrium. This retrograde P wave is usually negative in leads II, III, and aVF.

There can be many sinus node responses to a PVC. Most commonly, a full compensatory pause follows the PVC; thus, the PP interval between the QRS complexes before and after the premature beat is twice the PP interval between two successive sinus beats. The pause is due to retrograde AV nodal penetration of the PVC, which causes the AV node to be refractory to the next on-time sinus impulse, which is blocked. The subsequent sinus impulse does conduct through the AV node to stimulate the ventricle. In this situation, a normal appearing P wave may be seen, often buried in the ST segment or T wave of the PVC, with no QRS following it. Other cases may have retrograde activation of the atrium with an inverted P wave in the inferior leads and resultant delay of sinus node impulse generation. In this situation, the PP interval between the QRS complex before and after the PVC is less than two sinus beats.


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Literature review current through: Sep 2016. | This topic last updated: Dec 3, 2015.
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