How To Decipher The Results Of An ECG  

Posted by williamjack on December 18th, 2019

Buying PC based resting ECG for the first time? Gone are days where traditional ECG machines needed space for storage. With PC based ECG system you can read the results on your laptop or desktop screen. Here is a short guide that demonstrates how to read an ECG systematically and effectively. 

Step 1 – Heart rate

To calculate the heart rates follow this method:

1. For a regular rhythm, count the number of large squares present within one R-R interval.

2. Divide 300 by this number to calculate the heart rate

If the rhythm is irregular:

1. Count the number of complexes on the rhythm strip with each rhythm strip is 10 seconds long.

2. Multiply the number of complexes by 6 by giving you the average number of complexes in 1 minute.

A normal adult heart rate is as follows:

•  Normal = 60 – 100 bpm
•  Tachycardia > 100 bpm
•  Bradycardia < 60 bpm

Step 2 – Heart rhythm

The heart rhythm can be regular or irregular. Irregular rhythms can be either:

•  Regularly irregular (i.e. a recurrent pattern of irregularity)
•  Irregularly irregular (i.e. completely disorganized)

If you notice anything then mark out several consecutive R-R intervals on a piece of paper, then move them along the rhythm strip to check if the subsequent intervals are the same.

If you are suspicious that there is some atrioventricular block, map out the atrial rate and the ventricular rhythm separately.

Step 3 – Cardiac axis

The 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

In a normal cardiac axis:

•  Lead II has the most positive deflection compared to Leads I and III

Right axis deviation

In the right axis deviation:

•  Lead III has the most positive deflection and Lead I should be negative
•  This is commonly seen in individuals with right ventricular hypertrophy

Step 4 – P-waves

Next, we look at the P-waves look for their presence. Also, check whether each P-wave followed by a QRS complex. Check the variations in duration, direction and shape of P-waves. Check whether there is any atrial activity e.g. sawtooth baseline → flutter waves / chaotic baseline → fibrillation waves / flat line → no atrial activity at all or not.

Step 5 – QRS complex

There are several aspects of the QRS complex you need to assess:

•  Width
•  Height
•  Morphology

This a short guide to read ECG however, there a lot of things that a technician should study while learning to read the results of an ECG.