ECG Rhythms......... without the Blues! - 2/5

1st October, 2006

Summary

Welcome back! In this issue we are going to look at a group of heart beats called ectopics.

You’ll often hear ectopics referred to as extrasystoles. Ectopic beats refer to impulses that occur earlier than expected in the cardiac cycle i.e. they are premature.

The two main types of ectopics that you will see are:

  • Atrial ectopics (sometimes referred to as premature atrial contractions or supraventricular ectopics)
    and
  • Ventricular ectopics (sometimes referred to as premature ventricular contractions)

ATRIAL ECTOPICS

Atrial ectopics occur when an irritable focus within the atria fires off an impulse before the sinoatrial node. This impulse travels through the atria resulting in a P wave although the P wave morphology (shape) is different to the normal P waves.

The impulse generated by the ectopic travels through the atrioventricular node and down to the ventricles like any normal impulse would. This results in a normal QRS complex.

When an atrial ectopic occurs every second beat it is known as atrial bigeminy.

What to look for on the ECG:

  • The ectopic beat comes early in the cardiac cycle
  • The P wave is present as the atria depolarise
  • The P wave shape is different to the normal ones as the impulse doesn’t originate in the SA node and therefore travels through the atria differently
  • The QRS complex the same as the normal one as once through the AV node the impulse is transmitted normally through the bundle of His and bundle branches

Look for these features in the following example of an atrial ectopic:

An atrial ectopic

Which beat do you think comes early?

Number 6 – the last beat on the strip comes in earlier than the others. This is your atrial ectopic. Note that it has a differently shaped P wave but a QRS that is the same as the others.

Atrial ectopics may occur in the following:

  • A normal benign finding
  • Anxiety
  • Drugs and stimulant e.g. alcohol, excessive smoking
  • Heart failure
  • Atrial hypertrophy
  • Electrolyte disorders

Isolated or infrequent atrial ectopics do occur in healthy individuals and are generally clinically insignificant. If they are appearing very frequently, for example more than 10 of them a minute, this may herald the onset of a more serious rhythm disturbance called atrial fibrillation – we’ll look at that in the next issue.

However in general the best form of management for atrial ectopics is often to note them then ignore them!


VENTRICULAR ECTOPICS

Ventricular ectopics occur when an irritable focus within the ventricle fires off an impulse before the sinoatrial node. The impulse travels through the ventricular myocardium resulting in a large, wide and bizarre shaped QRS complex. (usually wider than 0.12 secs)

The underlying pacing of the sinoatrial node is unaffected and so the beat after the ventricular ectopic will arrive on time. This results in a compensatory pause.

Two successive ventricular ectopics are referred to as ‘couplets’. Short burst of three or more consecutive ventricular ectopics are referred to as salvoes.
When a ventricular ectopic occurs every second beat it is known as ventricular bigeminy

What to look for on the ECG:

  • The ectopic beat comes early in the cardiac cycle
  • The P wave is not obviously visible
  • The QRS complex is a wide bizarre shape as the impulse is transmitted through the myocardium and not the conduction system. This is a slower mechanism that causes a widening of the QRS

Look for these features in the following example of a ventricular ectopic:

A venticular ectopic

Which beat do you think comes early?

If you identified number 3 well done. You may notice a pause after the ectopic. Try this exercise:

Place a piece of paper over the ectopic and make a pencil mark on the QRS of the beat immediately before the ectopic and another on the QRS immediately after the ectopic. You will have two pencil marks now. Place the first pencil mark on the beat after the ectopic – where does the second one come in? - two cycles later. You’ve just demonstrated a full compensatory pause seen after ventricular ectopics.

Uniform and Multiform Ventricular Ectopics

It is useful to observe the morphology of the ventricular ectopics you see. Ventricular ectopics of the same morphology are referred to as uniform whereas those with quite different morphology are referred to as multiform. This may be due to ectopics arising from different foci or traveling through the ventricular myocardium is different ways.

This example shows uniform ventricular ectopics:

Uniform ventricular ectopics

This example shows multiform ventricular ectopics:

Multiform ventricular ectopics

Ventricular ectopics may occur for a number of reasons but are most commonly seen in the early stages after myocardial infarction when the ventricles are irritable – they usually settle down and eventually disappear!

They may also occur in the following:

  • A normal benign finding
  • Anxiety
  • Drugs and stimulants e.g. alcohol, excessive smoking
  • Ventricular hypertrophy
  • Electrolyte disorders

Don’t get too uptight about ventricular ectopics as it is very unlikely that they will require treatment. Just keep an eye on your patient and don’t get too con¬cerned by what you see on the monitor!

Join us again in the next issue when we will examine the most commonly encountered chronic rhythm disturbance called atrial fibrillation.

In the meantime if you want to enhance your ECG skills then why not sign up for our new online ECG programme. Available for only £25! For further details see the advert in this issue or visit our web site at www.cb-training.com.


Charles Bloe BSc RGN NDN ITU cert
Lead Lecturer and CEO - Charles Bloe Training Ltd

For more information on ECG Training visit www.cb-training.com