قراءة تخطيط القلب
How to read ECG
Confirm details Before beginning ECG interpretation, you should check the following details:
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Confirm the name and date of birth of the patient matches the details on the ECG.
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Check the date and time that the ECG was performed.
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Step 1 – Heart rate
What’s a normal adult heart rate?
Normal: 60-100 bpm
Tachycardia: > 100 bpm
Bradycardia: < 60 bpm
Regular heart rhythm
heart rate can be calculated using the following method:
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Count the number of large squares present within one R-R interval.
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Divide 300 by this number to calculate heart rate.
Example
4 large squares in an R-R interval 300/4 = 75 beats per minute
Irregular heart rhythm
If a patient’s heart rhythm is irregular the first method of heart rate calculation doesn’t work (as the R-R interval differs significantly throughout the ECG).
As a result you need to apply a different method:
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Count the number of complexes on the rhythm strip (each rhythm strip is typically 10 seconds long).
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Multiply the number of complexes by 6 (giving you the average number of complexes in 1 minute).
Example
10 complexes on a rhythm strip
10 x 6 = 60 beats per minuet
Step 2 – Heart rhythm
A patient’s heart rhythm can be regular or irregular.
Irregular rhythms can be either:
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Regularly irregular (i.e. a recurrent pattern of irregularity)
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Irregularly irregular (i.e. completely disorganised)
Step 3 – Cardiac axis Cardiac axis describes the overall direction of electrical spread within the heart. In a healthy individual, the axis should spread from 11 o’clock to 5 o’clock.
To determine the cardiac axis you need to look at leads I, II and III.
Normal cardiac axis
Typical ECG findings for normal cardiac axis:
Lead II has the most positive deflection compared to leads I and III.
Step 4 – P waves
The next step is to look at the P waves and answer the following questions:
Are P waves present?
If so, is each P wave followed by a QRS complex?
Do the P waves look normal? – check duration, direction and shape
If P waves are absent, is there any atrial activity?
Sawtooth baseline → flutter waves
Chaotic baseline → fibrillation waves
Flat line → no atrial activity at all
Step 5 – PR interval
The PR interval should be between 120-200 ms (3-5 small squares).
Prolonged PR interval (>0.2 seconds)
A prolonged PR interval suggests the presence of atrioventricular delay
(AV block).
First-degree heart block (AV block)
First-degree heart block involves a fixed prolonged PR interval (>200 ms).
Second-degree heart block
Second-degree AV block (type 1) known as Mobitz type 1 AV block or Wenckebach phenomenon.
ECG findings in Mobitz type 1 block include prolongation of the PR interval until eventually the atrial impulse is not conducted and the QRS is dropped.
Second-degree heart block
Second-degree AV block (type 2) is also known as Mobitz type 2 AV block.
Typical ECG findings in Mobitz type 2 AV block include a consistent PR interval duration with intermittently dropped QRS complexes due to a failure of conduction.
Third-degree heart block (complete heart block)
Third-degree (complete) AV block occurs when there is no electrical communication between the atria and ventricles due to a complete failure of conduction.