Ectopic Atrial Rhythms

This section will provide an overview of ectopic atrial rhythms, or non-reentrant rhythms that originate from the atria. The most common example of this is atrial tachycardia, but also includes accelerated atrial rhythm.

Items covered include:

• Basic concepts for understanding ectopic rhythms, such as:

  • Important definitions.

  • Localization of the ectopic atrial focus using the ECG.

  • Mechanisms of focal atrial tachycardia, which is usually an automatic focus, but can also be a micro-reentrant circuit simulating a focal origin.

  • Initiation and termination of atrial tachycardia. This includes discussing how this rhythm can have a more gradual onset and offset (via the warm-up and cool-down phenomena) as well as the response to Valsalva or vagal manoeuvres. 

• Ectopic atrial tachycardia (AT), and its many manifestations on the ECG, such as:

  • Classic AT as well as its differential diagnosis, including other supraventricular tachycardias, atrial flutter, sinus tachycardia with dextrocardia or lead misplacement, and so on.

  • AT with a long PR interval and hidden p waves.

  • AT with pseudoelectrical alternans, a phenomenon involved rate-related alternating conduction blocks causing beat-to-beat variations in QRS axis.

  • AT with aberrant conduction via bundle branch block, mimicking ventricular tachycardia.

  • AT with different degrees of atrioventricular block, including variable block and complete heart block. We will stress the importance of looking for digoxin toxicity in cases of combined atrial arrhythmia and atrioventricular block.

  • Parasystolic AT, due to the presence of a rapidly firing atrial parasystolic focus.

  • Multifocal atrial tachycardia, a unique manifestation with several concurrent and competing atrial pacemakers, causing a chaotic rhythm with multiple p wave morphologies. We will also cover conditions that may mimic multifocal atrial tachycardia, such as sinus rhythm with multiple premature atrial complexes, wandering atrial pacemaker, atrial parasystole, and atrial dissociation.