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قراءة تخطيط القلب

How to read ECG 

Confirm details Before beginning ECG interpretation, you should check the following details: 

  • Confirm the name and date of birth of the patient matches the details on the ECG. 

  • Check the date and time that the ECG was performed. 


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: 

  • Count the number of large squares present within one R-R interval. 

  • Divide 300 by this number to calculate heart rate. 


 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: 

  • Count the number of complexes on the rhythm strip (each rhythm strip is typically 10 seconds long). 

  • Multiply the number of complexes by 6 (giving you the average number of complexes in 1 minute). 


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: 

  1. Regularly irregular  (i.e. a recurrent pattern of irregularity) 

  1. 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.