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Monday, 28 January 2013

Atrial Bigeminy

Please refer back to previous post for all about #ECGclass and case scenarios.

Discussion.  Case 22

A 60yr old gentleman comes to see you with a persistently raised clinic blood pressure of 158/98 mmHg. You arrange Ambulatory BP monitoring (ABPM) which reveals a mean BP of 148/94 mmHg.

In accordance with the current NICE guidelines, you arrange bloods, urinalysis and ECG in order to assess any target organ damage. Cardiovascular examination is normal other than you notice a slight irregularity in his pulse. 

His bloods for FBC, TFT, U&E's, eGFR, glucose and lipid screen are all normal. 
He has no proteinuria. 
You calculate his 10yr cardiovascular risk to be 18%. 
His ECG trace is seen below. 

He denies any chest pains, dizziness or palpitations. In fact, he feels completely well. 

Q1 What does this ECG show?

Think about the following questions before we go on:

  1. Can you see P waves? 
  2. Are they all morphologically the same? - study the rhythm strip, and look carefully in front of every QRS (You may need to zoom). First identify and exclude the T waves, then study how many other P-like wave forms you can see. 
  3. Is the PR interval normal and consistent? 
  4. Is the rhythm regular or irregular? 

Yes P waves can be seen, but they vary in morphology/size.
In this ECG, every other beat features a P-wave that is slightly different from the preceding one.
The normal sinus focus appears, as a classical rounded P wave, followed by a QRS of normal morphology. The next QRS (again normal morphology)  is preceded by a smaller 'blip' of a P wave. This smaller P wave occurs prematurely, and because of its different appearance, we know it originates from some other focus or foci.
It is known as an Atrial Ectopic or a  Premature Atrial complex (PAC)

The PR interval is normal and consistent. 
Measure it! Regardless of whether you measure from the normal P-wave, or from the PAC, the PR interval is consistent. It measures about 3.5 small squares. (normal = 3-5 small squares).

The Rhythm is Regularly irregular.
When a PAC follows every sinus beat, the rhythm is known as Atrial bigeminy.
If a PAC follows every third beat, then it is known as Atrial trigeminy.

All of these rhythms are regularly irregular.

This ECG shows Atrial Bigeminy. 

Features of Premature Atrial Complexes:

  • Since the focus originates in a different part of the atria, Atrial ectopics will have a different P wave morphology. 
  • They will still have a PQRST waveform, but it will occur prematurely.
  • The premature beat will be followed by a compensatory pause (ie. the ectopic beat doesn't reset the sino-atrial node, and the underlying sinus rhythm continues undisturbed).
Unlike ventricular ectopics, as seen in the last case (#ECGclass Case 21),  Atrial ectopic beats are followed by a normal rapid conduction through the ventricles. The QRS complex is therefore narrow and of normal morphology.
Ventricular ectopics, and so ventricular bigeminy, originate from an abnormal focus within the ventricle wall. Conduction through the ventricle is not rapid via the Bundle of His, and is therefore slowed down giving a wide QRS complex.

Atrial Bigeminy

Atrial Bigeminy is a harmless, benign rhythm.
It is frequently an incidental finding and is usually asymptomatic.  No further cardiac investigations are indicated as most people with this rhythm do not have organic heart disease (although in those with heart disease, it  seen).

It's worth asking about fatigue, smoking, alcohol use, emotional stress and caffeine intake, as these lifestyle factors have been linked to the occurrence of Atrial ectopic activity.

Q2. Are you going to offer antihypertensive medication?

In the clinical scenario given, this ECG diagnosis is an incidental finding and can safely be ignored.
But remember, why did you do the ECG?

Does the ECG show any LVH?

Of course LVH can only be truly diagnosed/excluded by an ECHO, but we can say that this ECG does not fulfil the voltage criteria for LVH.  (Refer back to the September post on LVH if necessary: Voltage Criteria for LVH )

In accordance with the Care Management Pathway of NICE CG127 Guidelines (see page 6), with an ABPM of 148/94 and no evidence of target organ damage (normal bloods, no proteinuria, no LVH) and a 10yr CVD risk of <20%, he has Stage 1 Hypertension, and doesn't need antihypertensive medication.  He should be given lifestyle advice and offered an annual BP review.

The atrial bigeminy is an innocent, incidental, ECG finding. Ignore.

Tah dah!
Thank you. :)


  1. How many beats would be sufficient to qualify for bigeminy? If there is a run of PVC-Sinus beat-PVC-Sinus beat-Sinus beat, would this pattern qualify to be called short run (3 beats)of bigeminy?

    1. I'm believe you need a repeating cycle of at least 3, to called it a bigeminy or trigeminy.

      sinus-sinus-sinus-sinus-PAC-sinus-PAC-sinus-PAC-sinus-sinus-sinus-sinus-sinus = Atrial Bigeminy
      sinus-sinus-sinus-PAC-sinus-sinus-PAC-sinus-sinus-PAC- sinus-sinus-sinus-siuns = Atrial Trigeminy

      Does that make sense?

      Same applies for PVC's to make a diagnosis of Ventricular Bigeminy or Ventricular Trigeminy.

  2. Yes, I think you'd call that a 'short run of Ventricular bigeminy'. (Don't forget you can have atrial or ventricular bigeminy etc). I assume the same definitions apply the for PAC's and PVC's, if so, the definitions on this post might help you: