The heart rate can be calculated from the ECG strip since it is printed at a constant speed.
For regular rhythm, the heart rate can be calculated by:
(1) divide the number of 0.4 second time lines (1 mm) in a P-P or R-R interval into 1500.
(2) divide the cycle length (time between peaks of 2 successive P or R waves) expressed in seconds into 60.
If the heart rate is irregular, measure several R-R intervals:
(1) number of 0.4 second lines over the intervals
(2) count the number of R-R intervals
(3) divide #1 by #2 to get an average interval
(4) divide #3 into 1500
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