Difference between revisions of "Ectopic Complexes"

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(Compensatoire pauze, bij een ventrikelextrasystole)
(Compensatory or noncompensatory pause)
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==Compensatory or noncompensatory pause==
 
==Compensatory or noncompensatory pause==
De duur van de pauze die ontstaat na een extrasystole kan helpen bij het onderscheid tussen een ventrikelextrasystole en een boezemextrasystole.
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The duration of the interval following a premature beat can help in the differentiation of a atrial or ventricula premature beat.
  
===Non-Compensatoire pauze, bij een boezemextrasystole===
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===Non-Compensatory pause, following an atrial premature beat===
Wanneer sinusknoop van buiten geactiveerd wordt door een boezemextrasystole, volgt er een '''reset''' van de pacemakercellen in de sinusknoop. Bij een frequentie van bijvorbeeld 60/min, gaan de pacemakercellen 1 seconde na de reset weer vuren, zoals ze ook gewend waren te doen vóór de reset. De tijd tussen de extra slag en het volgende QRS complex is in dit voorbeeld dus 1 seconde. Het geheel van normale slag - extra slag - normale slag is korter dan wanneer je gewoon drie sinusslagen achter elkaar hebt, dit heet een '''non-compensatoire pauze''' en is dus een kenmerk van een boezemextrasystole.
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If a sinusbeat is followed by an atrial premature beat, the electrical activity of the atrial premature beat can enter the sinusnode and reset its timing. If the sinusrate was for example 60 /min, the reset pacemakercells will restart firing after 1 full second has passed. The time from the extra beat to the next QRS complex in this example is thus 1 second. The sequence "normal sinus beat" - "atrial premature beat" - "normal sinus beat" will therefore shorter than the 3 seconds it would have taken if the premature beat had not occured. This is called a non (fully) compensatory pause.
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Sometimes the electrical activity of the APB cannot enter the sinusnode due to refractoriness of the sinus node (if the interval between previosu sinusbeat and APB is short) or due to electrical block to enter the sinus node (as in sinus nodal disease).  
  
===Compensatoire pauze, bij een ventrikelextrasystole===
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===Fully compensatory pause, following a ventricular prematur beat===
Bij een ventrikelextrasystole geleid het signaal over het algemeen niet terug via de AV knoop naar de boezems. De pacemakercellen in de boezems worden dus '''niet gereset'''. Het eerstvolgende sinussignaal valt op een moment dat de kamers nog bezig zijn met de ventrikelextrasystole, pas de slag daarna wordt weer voortgeleid. De tijd tussen de ventrikelextraystole en de volgende slag is dus langer! Dit heet een '''compensatoire pauze'''. Het oorspronkelijke sinusritme is gewoon door te passeren voorbij de ventrikelextraystole. Dit is dus en kenmerk van een ventrikelextrasystole zonder retrograde geleiding.
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The electrical activity of a ventricular premature beat is usually not conducted through the AV node towards the atria. The sinus node will not be reset. If the next sinus beat finds the AV nodal tissue still refractory (and thus not conducting) there will be a pause until the next sinus beat follows. The interval between the premature ventricular beat and the next sinus beat will be longer (longer than 1 second in the above sample of a heart rate of 60 / min). This is called a fully compensatory pause. Using a calliper the preceding sinus rate can be tracked beyond the ventricular premature beat. This is a telltale sign of a ventricular premature beat without retrograde conduction.
 
 
IN ENGLISH PLEASE?
 
  
 
==Parasystole==
 
==Parasystole==

Revision as of 20:15, 4 March 2009

Author(s) J.S.S.G. de Jong
Moderator J.S.S.G. de jong
Supervisor
some notes about authorship
An atrial with a noncompensatory pause.
A ventricular extrasystole with a compensatory pause
Mycoardial cells with pacemaker activity

The pacemaker cells in the sinus node are not the only cells in the heart that can depolarize spontaneously. Actually all cardiomyoctyes have this capacity. The only reason why the sinusnode 'rules' is that it is the fastest pacemaker of the heart. From sinusnode to ventricle all healthy cardiomyocytes can function as a ectopic pacemaker. Ectopic pacemaker activity can originate from the atria (60-80 bpm), AV-node (40-60 bpm) and the ventricles (20-40 bpm). So, as the sinus rate drops (e.g. during atrial infarction), other cells can take over. The configuration of ectopic beats or extrasystoles, as seen on the ECG, reveals its origin, whether they are atrial, nodal or ventrical.

Ectopic pacemakers

Heart cells with pacemaker activity
Celltype Frequency QRS width (*)
SA node (not ectopic) 60-100 bpm narrow
Atrial 55-60 bpm narrow
AV Nodal ectopic pacemaker 45-50 bpm narrow
His bundle 40-45 bpm narrow
Bundle branch 40-45 bpm narrow or wide
Purkinje cells 35-40 bpm wide
Myocardial cells 30-35 bpm wide

(*) QRS width can only be narrow if the conduction system downstream is normal (i.e. no bundle branch block)

Compensatory or noncompensatory pause

The duration of the interval following a premature beat can help in the differentiation of a atrial or ventricula premature beat.

Non-Compensatory pause, following an atrial premature beat

If a sinusbeat is followed by an atrial premature beat, the electrical activity of the atrial premature beat can enter the sinusnode and reset its timing. If the sinusrate was for example 60 /min, the reset pacemakercells will restart firing after 1 full second has passed. The time from the extra beat to the next QRS complex in this example is thus 1 second. The sequence "normal sinus beat" - "atrial premature beat" - "normal sinus beat" will therefore shorter than the 3 seconds it would have taken if the premature beat had not occured. This is called a non (fully) compensatory pause. Sometimes the electrical activity of the APB cannot enter the sinusnode due to refractoriness of the sinus node (if the interval between previosu sinusbeat and APB is short) or due to electrical block to enter the sinus node (as in sinus nodal disease).

Fully compensatory pause, following a ventricular prematur beat

The electrical activity of a ventricular premature beat is usually not conducted through the AV node towards the atria. The sinus node will not be reset. If the next sinus beat finds the AV nodal tissue still refractory (and thus not conducting) there will be a pause until the next sinus beat follows. The interval between the premature ventricular beat and the next sinus beat will be longer (longer than 1 second in the above sample of a heart rate of 60 / min). This is called a fully compensatory pause. Using a calliper the preceding sinus rate can be tracked beyond the ventricular premature beat. This is a telltale sign of a ventricular premature beat without retrograde conduction.

Parasystole

An example of parasystole on a 12 lead ECG
This rhythm strip shows clear parasystole. Here the origin of the ectopic beats is somewhat distal to the HIS bundle.

Parasystole is the phenomenon that results from two competing pacemakers in the heart. Usually a supraventricular and nodal / ventricular pacemaker compete. For example sinusrhythm interfered by ventricular ectopic beats. The basic rhythm in this example would be sinusrhythm with e.g. a rate of 60/min. Interfering with this rate ectopic ventricular beats can be seen. Parasystole is diagnosed when the ectopic beats have a constant RR interval, e.g. 1500ms, resulting in a rate of 20 ventricular ectopic beats per minute. Fusion beats are often present as the two rhythms are dissociated.

Examples