Six step
interpretation
Step 1. Is the any electrical activity?
Check the ECG to see if there is electrical activity on every one of the leads. If any areas are completely flatlined, this may suggest that one of the leads has fallen off. A completly straight flatline suggests that a lead has fallen off. In cases of asystolic cardiac arrest there is usually a small degree of baseline wandering. Always make sure to check your patient, and not treat solely on the findings of the ECG.
In this ECG every single lead shows evidence of electrical activity
This ECG shows an absence of electrical activity in leads II, III and aVF. It is likely that the green electrode has fallen off the body of this patient. As the other leads still show electrical activity, we can safely say that this is not an ECG of a patient in asystole
In this ECG every single lead shows evidence of electrical activity
Step 2. What is the rate?
Method 1: Divide 300 by the number of large square in between 2 different QRS complexes. This can only be used if the rhythm is regular.
Method 2: Mark off six seconds on the ECG trace (30 large squares). Count the number of QRS complexes that occur in six seconds then multiply this number by 10 to get the heart rate in beats per minute
Divide 300 by the number of large squares between two different QRS complexes 300/3 = 100bpm
Count the number of QRS complexes that occur in six seconds (30 large squares). Multiple this number by 10. 9 QRS's in 6 secs, therefore 90 QRS's in 60 secs
Divide 300 by the number of large squares between two different QRS complexes 300/3 = 100bpm
Step 3. Is the Rhythm irregular?
Heart Rhythm can be described in 3 ways
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Regular (metronome-like with every beat equally spaced)
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Regularly Irregular (every beat not equally spaced but there is a distinct repeating pattern)
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Irregularly Irregular (sporadic pattern of beats with no clear spacing)
Each beat is evenly spaced. This particular rhythm shows sinus bradycardia (sinus rhythm but with a heart rate less than 60bpm)
In this trace the rhythm is irregular but the pattern repeats itself. it is regularly irregular. This particular rhythm is known as ventricular bigeminy as a ventricular ectopic beat occurs after each sinus beat
In the trace there is no repeating pattern as to when a QRS complex will appear. The spacing is erratic. This particular rhythm is known as atrial fibrillation
Each beat is evenly spaced. This particular rhythm shows sinus bradycardia (sinus rhythm but with a heart rate less than 60bpm)
STEp 4. broad or narrow qrs complexes?
Normally it takes less than 0.12 seconds for ventricular depolarisation to happen. The QRS complex duration reflects this by being narrow (lasting less than 3 small squares in duration).
If the QRS is broader than this, it suggests that either:
(1) the electrical signals are not propagating via the normal His-purkinje system; or,
(2) there is an electrolyte abnormality, causing a slowing of depolarisation.
The QRS complexes here are less than 3 small squares (0.12 seconds) in duration
The QRS complexes here are broad (greater than 0.12 seconds in duration) This particular ECG shows a right bundle branch block, which is the cause of the broad QRS
A broad QRS complex shows that the electrical activity in the ventricles is moving via myocyte to myocyte connections, rather than via the His-purkinje system. It may also electrolyte abnormalities like hyperkalaemia
The QRS complexes here are less than 3 small squares (0.12 seconds) in duration
Step 5. Are there Any p-waves
Check ALL of the different leads to establish whether there is a presence or absence of distinct p-waves. Absence of p-waves before the QRS complex can occur in some of the following conditions :-
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Atrial Fibrillation (shown below)
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Supraventricula tachycardias
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Junctional rhythms
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Hyperkalaemia
This trace shows atrial fibrillation and a left bundle branch block. There are no p-waves to be seen
This trace shows the presence of p-waves in every lead
This trace shows atrial fibrillation and a left bundle branch block. There are no p-waves to be seen
Step 6. What is the P:QRS relationship
It's important to check that
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(1) there is a P-wave for every QRS complex; and
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(2) that there is a QRS complex for every P-wave.
By doing this you can see whether there are any extra beats or dropped beats. Heart blocks are common arrhythmias that cause dropping of the QRS complex, like in the example below
There is one p-wave for every QRS complex
In this example there are missing QRS complexes. Every third QRS complex has been dropped as the p-waves are not conducting through to the ventricles. This is an example of a second degree heart block
There is one p-wave for every QRS complex
