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Ectopic Complexes

137 bytes added, 18:20, 17 January 2010
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[[Image:Rhythm_ventricular_premature.png|thumb|A [[Premature ventricular beats(PVB) / Venticular extrasystoles (VES)|ventricular extrasystole]] with a compensatory pause]]
[[Image:pacemaker_rates.png|thumb|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 sinus node 'rules' is that it is the fastest pacemaker of the heart. From sinusnode sinus node to ventricle all healthy cardiomyocytes can function as a ectopic pacemakerpacemakers. 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_Premature_Complexes|atrial]], nodal or [[ves|ventrical]].
==Ectopic pacemakers==
==Compensatory or noncompensatory pause==
The duration of the interval following a premature beat can help in the differentiation of a atrial or ventricula ventricular premature beat.
===Non-Compensatory compensatory pause, following an atrial premature beat===If a sinusbeat sinus complex is followed by an atrial premature beatcomplex, the electrical activity of the atrial premature beat complex can enter the sinusnode sinus node and reset its timing. If the sinusrate was sinus rate were for example 60 /min, the reset pacemakercells pacemaker cells 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 beatcomplex" - "atrial premature beatcomplex" - "normal sinus beatcomplex" will therefore be shorter than the 3 seconds it would have taken if the premature beat complex had not occuredoccurred. This is called a non (fully) compensatory pause. Sometimes the electrical activity of the APB atrial premature complex cannot enter the sinusnode sinus node due to refractoriness of the sinus node (if the interval between previosu sinusbeat previous sinus complex and APB atrial premature complex is short) or due to electrical block to enter the sinus node (as in sinus nodal disease).
===Fully compensatory pause, following a ventricular prematur beatpremature complex===The electrical activity of a ventricular premature beat complex is usually not conducted through the AV node towards the atria. The sinus node will not be reset. If the next sinus beat complex finds the AV nodal tissue still refractory (and thus not conducting) there will be a pause until the next sinus beat complex follows. The interval between the premature ventricular beat complex and the next sinus beat complex 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 With the use of a calliper caliper, the preceding sinus rate can be tracked beyond the ventricular premature beatcomplex. This is a telltale sign of a ventricular premature beat complex without retrograde conduction.
[[Image:parasystole_12lead.jpg|thumb|An example of parasystole on a 12 lead ECG]]
[[Image:Paraystole_rhythmstrip.jpg|thumb|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 , sinus rhythm might be interfered with by ventricular ectopic beats. The basic rhythm in this example would be sinusrhythm sinus rhythm with e.g. a rate of 60/min. Interfering with this rate ectopic Ectopic ventricular beats complexes can be seeninterfering with this rate and rhythm. 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.


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