Ectopic Complexes
Ectopic beats
The pacemakercells in the sinusnode 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
- Atrial ectopic pacemaker: frequency 50-60bpm
- Nodal ectopic pacemaker frequency 50bpm
- Ventricular ectopic pacemaker frequency 30-40bpm
Examples
AV-nodal complexes
Originate from the AV node. The AV node fires before the sinusnode. The ECG shows a QRS complex with a comparable morphology as during sinus rhythm as these extra beats are conducted further through the normal conduction system. When the extra follows very soon after the earlier one, aberrant conduction can occur. The extra beat does not have a p-wave in front of it. Sometimes an inverted p-wave can be seen in or at the end of the QRS complex.
Ventricular premature beat (VPB) / Ventricular extrasystole (VES)
Bigemini
Every sinus beat is followed by a ventricular extrasystole.
Trigemini
Every second sinus beat is follow by a ventricular extrasystole.