The precursor to the EKG (electrocardiogram) machine was a device referred to as a “capillary electrometer.” It turned out to be too unpredictable and expensive, but it led the way for the recording the heart’s electrical activity with skin electrodes, according to Dr. Dale Dublin, author of the book, "Rapid Interpretation of EKGs." Reading EKGs takes experience and knowledge, but calculating the heart rate with a 6-second rhythm EKG strip is not hard.
Calculating Heart Rate from a 6-Second EKG Strip
Identify an "R" wave. When looking at an EKG strip, the "R" wave is the upward-headed stroke or line. It comes after a downward "Q" wave and before another downward line, the "S" wave. It is part of a larger pattern called the QRS complex. You know it is an "R" wave because is goes up on the strip like an inverted V and is preceded and followed by a downward wave.
Find an "R" wave on a thick line. An EKG 6-second rhythm strip has many small boxes and vertical black lines. You want to find an "R" wave that is on top of one of the thick vertical lines (usually black, but could be red) as your starting point.
Count each subsequent thick vertical line on the EKG strip. After you identify a particular "R" wave on a thick vertical line, count each vertical thick line after it. The counting pattern is as follows: “300, 150, 100, 75, 60 and 50.”
Put your finger on the selected "R" wave as your starting point. As you come to the next vertical thick line (these are the heavy lines), call out “300.” For the following vertical thick line, say “150” and continue counting each thick vertical line until you come to the next "R" wave. If this "R" wave happens to fall on the line that represents "75," this is also the heart rate. There are no further calculations. Essentially, the number of thick vertical lines between two "R" waves is all you need to determine heart rate.
Each space between thick vertical lines on an EKG strip means 1/300th of a minute. For calculating a heart rate slower than 60 beats per minute, use this method: the number of cycles ("R" wave to "R" wave) multiplied by 10. If there are three cycles, the heart rate is 30 beats per minute.