6 step approach

Welcome to this section on cardiac rhythm recognition.

Within this next part of the module we wish to share with you a systematic approach to interpreting cardiac rhythms.

The objectives of what we are going to cover in this part are to allow you to understand the 6 stage approach to rhythm recognition and then to apply this approach to a series of rhythm strips to identify common arrhythmias. It may be useful to take a few moments just to reflect back on the normal conduction system of the heart of referring back to the ‘HEARTe 1: Healthy heart and investigations: Common cardiac investigations module‘ and remind yourself of where the normal pacemaker, the sino-atrial node is situated, it’s normal rate of depolarisation or firing, how the impulses are then transmitted to and through the AV node and then rapidly down the specialised conduction tissue to the bundle of His, the right and left bundle branches and the purkinje fibres throughout the ventriclular myocardium.

It may also be helpful to take a moment or two to think about what types of patients in your area might you monitor and why?. ( Pause )

One of the commonest reasons for cardiac monitoring is too identify the patient’s underlying cardiac rhythm. Cardiac monitoring may allow the early detection and management of potential life threatening arrhythmias, allowing prompt treatment to be initiated to prevent cardiac arrest.

Patients who are at risk of a cardiac event are also often monitored and these include patients who present with chest pain, collapse, syncope, palpitations, shock, following (cardiac) arrest or who may be undergoing some kind of treatment and require monitoring for the duration of their treatment.

It’s important to remember however that cardiac monitoring only tells us about the electrical activity of the heart and not its mechanical function therefore even when we can see a rhythm strip that we expect to be associated with a good cardiac output we could have a patient with no cardiac output i.e. in cardiac arrest. We may see a rhythm on the cardiac monitor which we think is Ventricular fibrillation or VF, a life threatening rhythm, and find on examining our patient it is only artefact due to patients movement. Therefore any time your patient’s rhythm changes on a cardiac monitor please go back and assess your patient.

It’s also important to remember that cardiac monitoring will not reliably detect the presence of cardiac ischemia. To determine this you need to record a 12 lead ECG for the analysis of ischemia or myocardial infarction.

With those thoughts in mind then, we are going to move on and consider how to read a rhythm strip using a 6 stage approach. This uses the following 6 questions each of which we will consider in turn.

The first question you should consider in looking at any rhythm strip on the screen is:

• 1. Is there is any ‘co-ordinated’ electrical activity ie that which you would expect to be associated with a cardiac output?
  For those of you familiar with UK resuscitation council intermediate or advanced life support courses, you may previously have used the question ‘is there any electrical activity present?’ We have chosen to add the word co-ordinated because even in a life threatening arrhythmia such as ventricular fibrillation there is electrical activity on the screen however this activity is chaotic, variable, and not co-ordinated.

The next thing you want to ask is:

• 2. What is the ventricular rate?
  This information may appear on your cardiac monitor, if it does not you may have to print off a strip and calculate the Heart rate . The normal ventricular rate should range between 60 and 100 beats per minute therefore anything that’s below 60 would be a bradycardia and anything above 100, a tachycardia , so immediately you can see with any rhythm how you can begin to categorise it into either a normal rate, a bradycardia or a tachycardia.

Next we want to consider the QRS complexes:

• 3. Are the QRS complexes regular or irregular?
  Sometimes it’s difficult to determine this on a screen particularly if the rhythm is very fast. Therefore it can be helpful to print off a strip where possible, and by using a piece of paper to mark the position of 2 or 3 QRS complexes then move this along to determine if these match up further along the strip. If they do match this means that the rhythm is regular. Regularity can be helpful in determining again the particular rhythm you are dealing with, for example one of the commonest arrhythmias people have is atrial fibrillation which will be irregular in its appearance. Also if the rhythm is irregular you should also consider is it regularly irregular? i.e. can you see a pattern forming?

Having determined if the rhythm is regular or not then ask yourself:

• 4. Is the QRS width normal or prolonged?
  Remember the normal QRS should be less than 0.12 seconds or 3 small squares on ECG paper. If this is longer than 3 small squares or 0.12 seconds then it’s telling us there is some delay in conduction throughout the ventricle. For the purposes of rhythm interpretation, we are going to consider that any broad complex (>0.12 secs) is likely to have been initiated in the ventricle. On the other hand, narrow complexes that fall within the normal range of less than 0.12 seconds or 3 small squares, have been initiated in the AV node or above that is in the atria and rapidly conducted down the specialised tissues.

Having determined the origin of the rhythm that we are seeing we then move on to consider:

• 5. Is there atrial activity present?
  So can you see P waves, are they upright and rounded as you’d expect? If you can’t see P waves is there any other evidence of atrial activity.. for example fibrillation or flutter waves?

And finally if there are P waves (or other atrial activity) present we, then want to consider:

• 6. Is this related to ventricular activity?
  Again this relationship may be helpful in determining whether there is any sort of conduction problem between the atria and ventricles so for example is there one P wave before each QRS? If not can you see any pattern emerging or delay occurring?

So having answered these 6 simple questions you should be able to try to interpret or at least describe any rhythm that you are presented with. Remember even if you don’t always get the name of the rhythm correct, you would be able to describe what you are seeing on the cardiac monitor, share this information with a more experienced colleague and allow them to make the interpretation of the rhythm.