Introduction

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.

Classification

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 

ECG findings

• 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 

Management

• 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 
• beta-blockers
• class I antiarrhythmic drugs – in patients with structurally normal hearts
• radiofrequency ablation 

References

1. 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
2. Strauss, David G., et al. Marriott's Practical Electrocardiography. Wolters Kluwer, 2021. 
3. https://litfl.com/premature-atrial-complex-pac/
4. CAMM, A. J., LÜSCHER, T. F., & SERRUYS, P. W. (2009). The ESC textbook of cardiovascular medicine. Oxford, Oxford University Press.