Some paramedics are not proficient at estimating the heart rate using the large block method for heart rate calculation.
I realize that modern ECG machines calculate the heart rate, but I my attitude toward machines is similar to Ronald Reagan’s attitude toward the Soviet Union. “Trust but verify.”
I created the following image using nothing but PowerPoint.
Or, if it helps you to remember it fast-to-slow: 300, 150, 100, 75, 60, and 50.
Why is this important?
A “normal” heart rate for an adult is 60 to 100. In other words, there should be between 3 and 5 large blocks between R waves. If there are less than 3, it’s a tachycardia. If there are more than 5, it’s a bradycardia.
Many tachyarrhythmias present with heart rates around 150Â (for example, 2:1 flutter).
If a heart rhythm is so fast that it only shows 1 large block between R waves, then you know the rate is about 300, and you need to suspect an accessory pathway. Sometimes this turns out to be atrial flutter with 1:1 conduction. If the rhythm is atrial fibrillation, and the shortest R-R interval is 1 large block or less (actually 6 small blocks or less) then leave the drugs for rate control in the drug box! You’re probably looking at atrial fibrillation with WPW, and almost all drugs for rate control are contraindicated.
Anytime you’re holding a rhythm strip in your hand, take a good look at the R-R intervals, and get a feel for how many large blocks are between the R waves. Before long, you’ll be able to estimate the heart rate at a glance!
Large Block Method to Calculate Heart Rate at ECG Medical Training