Understanding ECG Heart Rate Calculation
The electrocardiogram (ECG) is a crucial diagnostic tool that records the electrical activity of the heart. One of the most common measurements derived from an ECG is the heart rate, which indicates how many times the heart beats per minute (BPM).
Methods for Calculating Heart Rate from ECG:
- Using Large Boxes: The standard ECG paper is printed on a grid. Each large square (or box) on this grid typically represents 0.20 seconds when the paper speed is set to 25 mm/sec. You can measure the time between two consecutive R waves (the tallest peak in the QRS complex), which represents one heartbeat. If you count the number of large boxes between R waves, you can calculate the heart rate using the following formula:
Heart Rate (BPM) = 300 / (Number of large boxes between R-R intervals)
This formula is a quick estimation and works best for regular rhythms.
- Using Small Boxes (More Precise): Each large box contains five small boxes, and each small box represents 0.04 seconds at a paper speed of 25 mm/sec. For more precise calculations, especially with irregular rhythms, you can count the number of small boxes between R waves and use the formula:
Heart Rate (BPM) = 1500 / (Number of small boxes between R-R intervals)
- Using Paper Speed (General Formula): The most general formula, which accounts for different paper speeds, is derived from the fact that the paper speed determines how much time each unit of distance represents.
Time per R-R interval (seconds) = (R-R Interval in large boxes) * (0.20 seconds/large box) / (Paper Speed in mm/sec / 25 mm/sec)
Heart Rate (BPM) = 60 / Time per R-R interval (seconds)
Our calculator primarily uses the simplified "300 / large boxes" method, assuming a standard paper speed of 25 mm/sec, but allows for adjustment if your paper speed differs.
Interpreting the Results:
A normal resting heart rate for adults typically falls between 60 and 100 beats per minute. Rates below 60 BPM are considered bradycardia, and rates above 100 BPM are considered tachycardia. However, these are general guidelines, and what is considered normal can vary based on factors like age, fitness level, and medical conditions.
Disclaimer: This calculator is for informational purposes only and should not be used as a substitute for professional medical advice. Always consult with a qualified healthcare provider for any health concerns or before making any decisions related to your health or treatment.
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function calculateEcgHeartRate() {
var rRIntervalInput = document.getElementById("rRInterval");
var paperSpeedInput = document.getElementById("paperSpeed");
var resultDisplay = document.getElementById("ecgResult");
var rRInterval = parseFloat(rRIntervalInput.value);
var paperSpeed = parseFloat(paperSpeedInput.value);
if (isNaN(rRInterval) || rRInterval <= 0) {
resultDisplay.textContent = "Please enter a valid number of large boxes (greater than 0).";
return;
}
if (isNaN(paperSpeed) || paperSpeed <= 0) {
resultDisplay.textContent = "Please enter a valid paper speed (greater than 0).";
return;
}
var heartRate;
var secondsPerLargeBox;
// Assuming standard 25mm/sec paper speed if not specified or if user wants to use the 300 rule directly
if (paperSpeed === 25) {
// Standard formula: 300 / number of large boxes
heartRate = 300 / rRInterval;
} else {
// More general calculation:
// 1 large box = 0.20 seconds at 25mm/sec.
// At a different speed, the time represented by a large box changes.
// Time represented by one large box = (0.20 seconds / 25 mm/sec) * paperSpeed
secondsPerLargeBox = (0.20 / 25) * paperSpeed;
var rRIntervalInSeconds = rRInterval * secondsPerLargeBox;
if (rRIntervalInSeconds <= 0) {
resultDisplay.textContent = "Error calculating R-R interval in seconds.";
return;
}
heartRate = 60 / rRIntervalInSeconds;
}
if (isNaN(heartRate) || heartRate <= 0) {
resultDisplay.textContent = "Could not calculate heart rate. Please check your inputs.";
} else {
resultDisplay.textContent = "Estimated Heart Rate: " + heartRate.toFixed(1) + " BPM";
}
}