Calculating Heart Rate from Ecg

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ECG Heart Rate Calculator

.ecg-heart-rate-calculator { font-family: sans-serif; border: 1px solid #ccc; padding: 20px; border-radius: 8px; max-width: 500px; margin: 20px auto; background-color: #f9f9f9; } .ecg-heart-rate-calculator h2 { text-align: center; margin-bottom: 20px; color: #333; } .calculator-inputs { display: grid; grid-template-columns: 1fr 1fr; gap: 15px; margin-bottom: 20px; } .input-group { display: flex; flex-direction: column; } .input-group label { margin-bottom: 5px; font-weight: bold; color: #555; } .input-group input { padding: 8px; border: 1px solid #ddd; border-radius: 4px; font-size: 1em; } button { display: block; width: 100%; padding: 10px 15px; background-color: #4CAF50; color: white; border: none; border-radius: 4px; font-size: 1.1em; cursor: pointer; transition: background-color 0.3s ease; } button:hover { background-color: #45a049; } .calculator-result { margin-top: 20px; padding: 15px; background-color: #e7f3fe; border: 1px solid #b3e0ff; border-radius: 4px; font-size: 1.2em; text-align: center; color: #333; } function calculateHeartRate() { var rrInterval = parseFloat(document.getElementById("rrInterval").value); var ecgPaperSpeed = parseFloat(document.getElementById("ecgPaperSpeed").value); var smallBoxWidth = parseFloat(document.getElementById("smallBoxWidth").value); var largeBoxWidth = parseFloat(document.getElementById("largeBoxWidth").value); var resultDiv = document.getElementById("result"); if (isNaN(rrInterval) || isNaN(ecgPaperSpeed) || isNaN(smallBoxWidth) || isNaN(largeBoxWidth) || rrInterval <= 0 || ecgPaperSpeed <= 0 || smallBoxWidth <= 0 || largeBoxWidth 0) { heartRate = 60 / rrInterval; } // Method 2: Using number of large boxes between R waves // Assumes standard ECG paper speed if not provided, but we have it. if (largeBoxWidth > 0 && ecgPaperSpeed > 0) { var timePerLargeBox = largeBoxWidth / ecgPaperSpeed; // seconds var calculatedHeartRateFromLargeBoxes = 60 / (timePerLargeBox * (rrInterval / timePerLargeBox)); // This is redundant if rrInterval is given. // A more direct way if only boxes are given: // If the user could input number of large boxes instead of RR interval, this would be: // var numLargeBoxes = parseFloat(document.getElementById("numLargeBoxes").value); // if (!isNaN(numLargeBoxes) && numLargeBoxes > 0) { // heartRate = 60 / (numLargeBoxes * timePerLargeBox); // } } // Method 3: Using number of small boxes between R waves if (smallBoxWidth > 0 && ecgPaperSpeed > 0) { var timePerSmallBox = smallBoxWidth / ecgPaperSpeed; // seconds // If the user could input number of small boxes instead of RR interval, this would be: // var numSmallBoxes = parseFloat(document.getElementById("numSmallBoxes").value); // if (!isNaN(numSmallBoxes) && numSmallBoxes > 0) { // heartRate = 60 / (numSmallBoxes * timePerSmallBox); // } } // The primary calculation should be based on the R-R Interval in seconds, // as it's the most direct measure of the time between heartbeats. // The paper speed and box widths are typically used to *determine* the R-R interval // if it's not directly provided or measurable in seconds. // For this calculator, we assume R-R Interval in seconds is provided. if (heartRate > 0) { resultDiv.innerHTML = "Estimated Heart Rate: " + heartRate.toFixed(0) + " bpm"; } else { resultDiv.innerHTML = "Could not calculate heart rate. Please check your inputs."; } }

Understanding ECG and Calculating Heart Rate

An Electrocardiogram (ECG or EKG) is a non-invasive medical test that records the electrical activity of the heart over a period of time. It is performed using small electrodes attached to the skin of the chest, arms, and legs. The ECG machine sums up the tiny electrical changes in the heart with each beat. This electrical activity causes the heart muscle to contract and pump blood.

What are the components of an ECG waveform?

A typical ECG waveform consists of different waves, segments, and intervals, each representing a specific electrical event in the cardiac cycle:

  • P wave: Represents atrial depolarization (the electrical activation of the atria).
  • QRS complex: Represents ventricular depolarization (the electrical activation of the ventricles). This is usually the most prominent part of the ECG.
  • T wave: Represents ventricular repolarization (the electrical recovery of the ventricles).
  • PR interval: The time from the beginning of atrial depolarization to the beginning of ventricular depolarization.
  • QT interval: The time from the beginning of ventricular depolarization to the end of ventricular repolarization.
  • RR interval: The time between two consecutive R waves (peaks of the QRS complex). This is the most critical measurement for calculating heart rate from an ECG.

How is Heart Rate Calculated from an ECG?

The heart rate is essentially the number of times the heart beats per minute. On an ECG, each QRS complex typically represents one heartbeat. Therefore, by measuring the time between consecutive R waves (the R-R interval), we can calculate the heart rate.

There are several ways to determine the heart rate from an ECG strip, depending on the information available:

  1. Using the R-R Interval in Seconds: This is the most direct and accurate method. If you can accurately measure the time between two consecutive R waves in seconds, the heart rate (in beats per minute, bpm) is calculated as:
    Heart Rate (bpm) = 60 / R-R Interval (seconds)
    For example, if the R-R interval is 0.75 seconds, the heart rate is 60 / 0.75 = 80 bpm.
  2. Using ECG Paper Speed and Boxes: ECGs are typically recorded on graph paper with a grid.
    • Standard Paper Speed: The most common paper speed is 25 mm/sec.
    • Small Boxes: Each small box is typically 1 mm wide, representing 0.04 seconds (25 mm/sec / 1 mm = 25 boxes/sec -> 1/25 sec/box = 0.04 sec/box).
    • Large Boxes: Each large box is typically 5 mm wide (made up of 5 small boxes), representing 0.20 seconds (5 mm * 0.04 sec/mm = 0.20 sec).
    If you know the paper speed, you can count the number of small or large boxes between two consecutive R waves to determine the R-R interval in seconds, and then use the formula above.
    • Heart Rate (bpm) = 60 / (Number of Small Boxes * 0.04)
    • Heart Rate (bpm) = 60 / (Number of Large Boxes * 0.20)
    Alternatively, for a quick estimation on standard paper speed (25 mm/sec):
    • Heart Rate (bpm) ≈ 1500 / Number of Small Boxes between R waves
    • Heart Rate (bpm) ≈ 300 / Number of Large Boxes between R waves

When to use this calculator:

This calculator is useful for healthcare professionals, students, and anyone who needs to quickly estimate heart rate from an ECG recording. By inputting the R-R interval in seconds, or by using the paper speed and box measurements to infer it, you can get an immediate result.

Example Calculation:

Let's say you have an ECG strip running at a standard speed of 25 mm/sec. You measure the interval between two consecutive R waves and find it to be approximately 0.8 seconds.

  • R-R Interval = 0.8 seconds
  • ECG Paper Speed = 25 mm/sec
  • Small Box Width = 1 mm
  • Large Box Width = 5 mm
Using the primary formula:

Heart Rate = 60 / 0.8 = 75 bpm.

If we wanted to verify using the boxes (assuming 0.8 seconds translates to a certain number of boxes):

Number of small boxes = R-R interval / time per small box = 0.8 sec / 0.04 sec/box = 20 small boxes.

Heart Rate ≈ 1500 / 20 = 75 bpm.

Number of large boxes = R-R interval / time per large box = 0.8 sec / 0.20 sec/box = 4 large boxes.

Heart Rate ≈ 300 / 4 = 75 bpm.

All methods yield the same result, confirming the heart rate is approximately 75 beats per minute.

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