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TECHNION – Israel Institute of Technology
Department of Electrical Engineering
Physiological Signal Processing Laboratory
dLldLLaboratory
PVC definition (pvb , ves)
Ectopic (premature) ventricular complexes (PVCs)
Some patients will have regular QRS complexes interspersed with occasional unusual-looking complexes. These
unusual conformations are called PVCs This aberrant activity can cause more serious ventricular arrhythmias.
Clinical deterioration depends on the frequency of the PVCs.
A PVC is a depolarization that arises in either ventricle before the next expected sinus beat, i.e., prematurely. It
may result from the firing of an automatic focus or reentry. Since PVCs originate in the ventricle, the normal
sequence of ventricular depolarization is altered, i.e., instead of the two ventricles depolarizing simultaneously,
they depolarize sequentially. In addition, conduction occurs more slowly through the myocardium than through
specialized conduction pathways. This results in a wide (0.12 second or greater) and bizarre-appearing QRS. The
sequence of repolarization is also altered, usually resulting in an ST segment and T wave in a direction opposite
to the QRS complex.
The interval between the previous normal beat and the PVC (the coupling interval) usually remains constant when
PVCs are due to reentry from the same focus (uniform VCs). When the coupling interval and the QRS morphology
vary, the PVCs may be arising from different areas within the ventricles, or if the PVCs are arising from a single
focus, ventricular conduction may vary. Such PVCs are referred to as multifocal or more appropriately,
multiformed.
A PVC may occur nearly simultaneously with the firing of the sinus node. The antegrade impulse originating in the
sinus node (resulting in normal atrial depolarization) and the retrograde impulse traveling toward the atria from the
ventricles may meet in the AV node. Then neither can spread further because of the other's refractory period.
Since the rhythm of the sinus node is undisturbed, a fully compensatory pause usually results (i.e., the next P
wave should occur at the proper time.) However, on occasion, retrograde conduction can spread to the atria and
reset the SA node.
PVCs may occur as isolated complexes, or they may occur repetitively in pairs (two PVCs in a row). When three
or more PVCs occur in a row, VT is present. When VT lasts for more than 30 seconds, it is arbitrarily defined as
sustained ventricular tachycardia.
If every other beat is a PVC, ventricular bigeminy is present. If every third beat is a PVC, the term ventricular
trigeminy is used. If every fourth beat is a PVC, ventricular quadigeminy is present, and so forth.
A PVC that falls on the T wave (during the so-called vulnerable period of ventricular repolarization) may precipitate
VT or VF. However, PVCs occurring after the T wave may also initiate such VT.
Simple PVCs
Simple PVCs have the following characteristics:
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Occur beyond the T wave of the preceding QRS complex
Morphology is uniform
Occur in an isolated fashion and do not present in pairs or triplets
Generally exhibit constant coupling intervals with the preceding QRS complex.
This type of PVC is frequent in the general population and, as age increases, the frequency of such PVCs
increases; approximately 70 percent of persons between the ages of 40 and 60 have simple PVCs, and they are
seen in most individuals over the age of 60.
Simple PVCs that occur in persons without any type of cardiac disease do not require treatment. However, it is
important not to overlook the fact that the majority of sudden deaths occur in persons who were previously
believed to be healthy and normal. Therefore, when confronted with a patient with simple PVCs, the physician
must rule out any associated cardiac or electrolyte abnormalities that may predispose the patient to sudden death.
If the physician is confident that there is no associated heart disease, then this type of PVC should not place the
patient at increased risk for sudden death.
Complex PVCs
Complex ventricular ectopy can be defined as PVCs that:
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Occur in pairs, triplets or more prolonged runs of ventricular tachycardia
Fall in the vulnerable period of the cardiac cycle
(R on T)
Have more than one morphology
A close correlation exists between the complexity of PVCs and the risk of developing ventricular tachycardia and
fibrillation in patients with cardiac disease. Patients who have complex ventricular ectopy without apparent cardiac
disease only rarely experience life-threatening ventricular arrhythmias.
Summary of ECG criteria
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QRS: Not normal looking. Usually broadened to more than 0.12 second.
Rhythm: Irregular.
P waves: The sinus P wave is usually obscured by the QRS, ST segment or T wave of the PVC. It may,
however, sometimes be recognized as a notching during the ST segment or T wave. Retrograde P waves
may occur. The presence of a sinus P wave (when it cannot be seen) may be inferred by the presence of
a fully compensatory pause.
PVC
This ventricular ectopic - or premature ventricular contraction (PVC) - has had an
effect on all three traces in the above diagram: The ECG
QRS earlier than expected (premature) i.e. shorter RR interval than normal
QRS wider than normal (usually more than 0.12 sec)
QRS voltage higher than normal
inverted T wave
obscured P wave
next RR interval longer than normal
The arterial pressure
ejection earlier than expected
low systolic pressure generated
The CVP
large a wave
a wave at expected time(not premature)
Characteristics of (most) PVCs
wide and bizarre QRS, often with a high voltage and inverted T wave
reduced or no left ventricular ejection
large CVP a wave
fully compensatory pause
Not all PVCs are followed by a pause. If a PVC occurs early enough (especially if the heart rate is
slow), it may appear sandwiched in between two normal beats. This is called an interpolated PVC.
The sinus impulse following the PVC may be conducted with a longer PR interval because of
retrograde concealed conduction by the PVC into the AV junction slowing subsequent conduction of
the sinus impulse.
Wavelets transform
http://engineering.rowan.edu/~polikar/WAVELETS/WTtutorial.html