What is the backup method for calculating heart rate when dealing with regular rhythms?

The method for calculating heart rate in situations involving regular rhythms can be efficiently performed by counting the number of large squares between two QRS complexes and dividing by 300. This method leverages the fact that on a standard ECG strip where the paper speed is set at 25 mm per second, each large square represents 0.2 seconds, and therefore, there are 300 large squares in one minute (60 seconds). By counting how many large squares fit between the peaks of two consecutive R waves, you can easily calculate the heart rate.

For example, if there are 3 large squares between two QRS complexes, you would divide 300 by 3, yielding a heart rate of 100 beats per minute. This approach is particularly useful and quick when rhythms are consistent because it provides a straightforward calculation without the need for more complex methods. The precision of this method is beneficial when quick assessments are necessary, such as in emergency situations or when monitoring patients continuously.