Extrasystole | Premature contraction - atrial ,nodal ,and ventricular extrasystole

Extrasystole | Premature contraction - atrial ,nodal ,and ventricular extrasystole

Extrasystole is an extraordinary (additional) contraction of the heart

It is recorded in the case when a pathological focus appears in any part of the myocardium, this focus will also generate impulse and also exites the heart

This additional excitation will compete with the normal excitation of the myocardium and creates an impulse earlier than it would occur under normal excitation (this means that the distance RR before the extrasystole is less than the distance RR between normal contractions - this will be a common symptom of all extrasystoles)

Extrasystoles have their own signs on the ecg, depending on the location of the pathological focus (in the atria, in the AV node or in the ventricles of the heart)

Atrial Extrasystoles

Is is formed when an ectopic pacemaker appears in the atrium

Criteria for atrial extrasystole:
-distance RR before the extrasystole is less than the distance RR between normal contractions
-positive, negative or biphasic P wave, different from other P waves
-in this lead QRS complex is not changed

Depending on the location of the pathological focus in the atria , then we will have different forms of the P wave

Extrasystole from the AV node

In this case, the excitation can spread in both directions:
-upward
and along normal conductive paths starting from the AV node

Therefore, the QRS complex does not change, and the negative P wave (atrial excitation in the opposite direction) can be recorded in both ways , either before the QRS complex, or may be after the QRS complex,

and in some times it may be not recorded at all, in such case it will be hidden behind the QRS complex

Everything depends on in which part of the AV node the facus is located

If the pathological focus is located in the upper part of the AV node, then such an extrasystole will look like a lower atrial extrasystole, but differs from it in that the PQ interval is greatly shortened due to the reduced pulse delay ( slowing up ) in the AV node

When the focus is located in the middle part (the most common variant) of the AV node, the P wave is not visible at all, as the QRS complex is superimposed on it (the atria and ventricles are excited almost in tye same time), and the P wave is smaller then the QRS complex, then the P wave will hide behind the QRS complex

When the pathological focus is located in the lower part of the AV node, the P wave can be registered after the (T) wave , because atrial excitation in the opposite direction will occur lately, because when the excitation pathes oppositely through the AV node,

Criteria for AV-nodal extrasystole:

Remember that everything depends on the location of the focus !

-distance RR before the extrasystole is less than the distance RR between normal contractions
-P wave is positive,absent (the most common option), or negative
-PQ segment is shortened
-QRS complex not changed

Ventricular extrasystole

Criteria for ventricular extrasystole:
-distance RR before the extrasystole is less than the distance RR between normal contractions
-P wave is missing
-QRS complex expanded (more than 0.12 sec)
QRS complex is deformed