How to Read an ECG Strip

ECG paper is a grid where time is measured along the horizontal axis.

• Each small square is 1 mm in length and represents 0.04 seconds.
• Each larger square is 5 mm in length and represents 0.2 seconds.

Voltage is measured along the vertical axis.

• 10 mm is equal to 1mV in voltage.
• The diagram below illustrates the configuration of ECG graph paper and where to measure the components of the ECG wave form Heart rate can be easily calculated from the ECG strip:

• When the rhythm is regular, the heart rate is 300 divided by the number of large squares between the QRS complexes.
• For example, if there are 4 large squares between regular QRS complexes, the heart rate is 75 (300/4=75).
• The second method can be used with an irregular rhythm to estimate the rate. Count the number of R waves in a 6 second strip and multiply by 10.
• For example, if there are 7 R waves in a 6 second strip, the heart rate is 70 (7x10=70).

Instant Feedback:

On a typical ECG grid, 5 small squares, or 1 large square, represent 0.20 seconds of time
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