Premature atrial contraction = Supraventricular extrasystole (SVES) is an extra heartbeat caused by electrical activation of the atria from an abnormal site before a normal heartbeat would occur.
Also known as premature atrial complex, atrial extrasystole, atrial premature beat (APB), supraventricular premature beat.
SVES may be caused by one of several mechanisms- re-entry, automaticity or triggered activity. They originate in any part of the heart above the ventricles apart from sinoatrial node – including AV node or His bundle.
Triplet - three consecutive APBs
Atrial extrasystole are very frequent in the general population and are a common finding in Holter recordings – especially in patients over fifty or with structural heart disease.
They can be sometimes induced by - excessive drinking of coffee, tea or alcohol - physical or emotional stress - hypokalaemia - hypomagnesaemia - medication
abnormal P wave followed by a QRS complex
premature P wave usually has a different configuration based on its origin - inverted P waves arise in the lower parts of atria close to AV node
P wave may be hidden in the preceding T wave – peaked appearance of T wave
QRS complex can be identical to completely aberrant, but it is typically narrow
most SVES reset the sinus node – the pause following SVES is non-compensatory = the interval from the previous sinus P wave to the sinus P wave following APB is shorter than 2x sinus cycle length (< 2x P-P) – this can differentiate them from ventricular premature beats.
SVES can be stopped in an AV node resulting in an abnormal P wave not followed by a QRS complex with a non-compensatory pause. This is also the commonest reason for sudden stops in ECG.
SVES that comes too early may encounter refractoriness in one of the bundle branches or fascicles resulting in aberrant ventricular conduction and a different morphology of the QRS complex. Usually with a RBBB morphology – the right bundle branch has a longer refractory period.
APB may initiate a re-entrant atrial tachyarrhythmia such as atrial flutter (activation around tricuspid annulus, AV nodal reentrant tachycardia (AVNRT) or the disorganized rhythm of atrial fibrillation.
ECG 1 Triplet of premature atrial beats. Normal sinus rhythm interrupted by three consecutive premature atrial beats - non-sustained atrial tachycardia
mostly asymptomatic – does not require treatment
palpitations – felt during the next on-time beat because of increased ventricular contraction strength caused by the higher volume of blood in the ventricles
avoid tobacco, alcohol, caffeine
class I antiarrhythmic drugs – in patients with structurally normal hearts
HARRIGAN, Richard A., William J. BRADY a Theodore C. CHAN. The ECG in Emergency Medicine. Emergency Medicine Clinics of North America [online]. 2006, 24(1) [cit. 2021-01-29]. ISSN 07338627. doi:10.1016/j.emc.2005.08.001
Strauss, David G., et al. Marriott's Practical Electrocardiography. Wolters Kluwer, 2021.