These are caused by the premature discharge of a ventricular ectopic focus
which produces an early and broad QRS complex.
Extrasystoles are usually
normal, being common in middle age. The patient may feel an occasional missed
Patients with no ischaemic heart disease or cardiomyopathy have an
Ventricular extrasystoles after myocardial infarction
are associated with increased mortality.
They may be the presenting feature
of viral myocarditis.
Depolarization of the ventricles occurs by an impulse originating from an ectopic ventricular focus.
There is no causally related preceding P wave since the impulse originates from the ventricles.
Since the impulse originates from an ectopic ventricular focus, depolarization wave does not propagate over fast Purkinje fibers but by cardiac myocytes which results in slow conduction and hence a wide QRS complex (>120ms).
Definition: The sum of the pre-VPC and the post-VPC intervals equals to 2 times of the interval between two sinus beats.
For a full compensatory pause to occur, there are 2 necessities:
1. There must be a stable sinus rhythm. Sinus arrhythmia
must not be seen.
2. There must be ventriculoatrial block (the VPC must not interrupt the sinus rhythmicity) or ventriculoatrial conduction occurs but fails to reset the sinus node.
Rarely a VPC may not have a compensatory pause.
During sinus rhythm, compensatory pause after a VPC is NOT seen
1. IF there is sinus arrhythmia
2. IF there is ventriculoatrial conduction resetting the sinus node.
Compensatory pause is not possible in irregularly irregular rhythms such as atrial fibrillation
or multifocal atrial tachycardia
By definition, interpolated VPC
s also do not have compensatory pauses.
After a VPC, a compensatory pause is usually observed. Usually, compensatory pause is not observed after an atrial premature beat (APB)
. Compensatory pause after an APB
is very rare. Compensatory pause after an APB
suggests that the APB
failed to reset the sinus node.
When a VPC occurs during aberration due to increased heart rate (acceleration-dependent aberration), its compensatory pause may result in temporary disappearance of the aberration.
Observation of VPS in a subject without organic heart disease is not significant.
VPS is the most common type of arrhythmia.
VPS is not specific for a certain disease.
Not all wide QRS complexes are due to VPC:
- Ventricular pacemaker stimulation
results in wide QRS (His bundle pacing is an exception).
- Aberrant conduction
of a supraventricular impulse to the ventricles (aberrancy
) causes wide QRS.
- WPW syndrome
causes wide QRS complexes.
Sometimes, artifacts may look like VPCs