Understanding ECG Heart Rate Calculation
Calculating your heart rate from an Electrocardiogram (ECG or EKG) is a fundamental diagnostic technique.
The ECG records the electrical activity of the heart over time. Each "R wave" in the ECG complex represents
the electrical impulse that causes the ventricles to contract, which is essentially a heartbeat.
Method 1: Using the RR Interval
The most common and accurate method for calculating heart rate from a rhythm strip involves measuring the
time between two consecutive R waves (the RR interval). This interval directly represents the duration of
one cardiac cycle.
The formula is:
Heart Rate (beats per minute) = 60 / RR Interval (seconds)
For example, if the RR interval is measured to be 0.80 seconds, the heart rate would be 60 / 0.80 = 75 BPM.
Method 2: Using ECG Grid and Sampling Rate (Manual Estimation)
If you don't have a precise measurement of the RR interval but have access to the ECG paper and know its
sampling rate (how many small or large boxes represent a certain amount of time), you can estimate the heart rate.
However, the calculator above uses a more direct method assuming you can measure the RR interval in seconds.
If you were to use the grid method, you would:
- Determine the duration of one small box (e.g., 0.04 seconds) or one large box (e.g., 0.20 seconds) based on the ECG's calibration.
- Count the number of small boxes between two consecutive R waves.
- Multiply the number of boxes by the duration of one box to get the RR interval in seconds.
- Then use the formula: Heart Rate = 60 / RR Interval (seconds)
Alternatively, if you know the sampling rate (Hz, which is samples per second) and you count the number of
samples between two R waves, you can calculate the RR interval:
RR Interval (seconds) = Number of Samples / Sampling Rate (Hz)
And then calculate the heart rate as before. This calculator uses the sampling rate in conjunction with the RR interval.
How This Calculator Works:
This calculator simplifies the process. You need to measure the time between two consecutive R waves (the RR interval)
in seconds. If you also know the ECG's sampling rate, you can input it, though the primary calculation relies on the RR interval.
The calculator then applies the formula: Heart Rate (BPM) = 60 / RR Interval (seconds).
function calculateHeartRate() {
var rrIntervalInput = document.getElementById("rrInterval");
var samplingRateInput = document.getElementById("samplingRate");
var resultDisplay = document.getElementById("result");
var rrInterval = parseFloat(rrIntervalInput.value);
var samplingRate = parseFloat(samplingRateInput.value);
if (isNaN(rrInterval) || rrInterval <= 0) {
resultDisplay.innerText = "Invalid RR Interval";
return;
}
if (isNaN(samplingRate) || samplingRate <= 0) {
// If sampling rate is not provided or invalid, we still calculate based on RR interval
// as it's the primary determinant. The sampling rate is more for context or advanced calculations.
var heartRate = 60 / rrInterval;
resultDisplay.innerText = Math.round(heartRate) + " BPM";
return;
}
// While sampling rate isn't directly used in the primary 60/RR formula,
// it's crucial for understanding the accuracy of the RR interval measurement itself,
// or for alternative calculation methods if RR interval is not directly measured in seconds.
// For this calculator, we prioritize the direct RR interval measurement.
var heartRate = 60 / rrInterval;
resultDisplay.innerText = Math.round(heartRate) + " BPM";
}
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