Premature atrial contraction

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

  • 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 

  • Atrial extrasystoles can appear in various forms
    - Bigeminy – every sinus beat is followed by APB
    - Trigeminy – every second sinus beat is followed by APB
    - Couplet – two consecutive APBs
    - Triplet - three consecutive APBs
    - Non-sustained tachycardia – at least 3 beats that spontaneously resolves in less than 30 seconds.
    - Sustained tachycardia - > 30s of continuous APBs

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 Supraventricular extrasystole originating in the coronary sinus. Isolated premature atrial beat - 1st beat, with inverted P wave and narrow QRS complex.

ECG 2 Supraventricular extrasystoles (patient underwent RFA of frequent ectopy from RSPV)

ECG 3 Trigeminy - every second beat is followed by a supraventricular premature beat (purple S) - this beat is then followed by a noncompensatory pause (shorter than 2xPP)



ECG 4 Triplet of premature atrial beats. Normal sinus rhythm interrupted by three consecutive premature atrial beats - non-sustained atrial tachycardia 


ECG no. 5 Supraventricular extrasystoles with RBBB morphology. In leads V1-V6 bigeminy – every sinus beat is followed by an extrasystole with RBBB  morphology - 3rd beat – SVES


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