.ecg-heart-rate-calculator {
font-family: sans-serif;
border: 1px solid #ddd;
padding: 20px;
border-radius: 8px;
max-width: 500px;
margin: 20px auto;
background-color: #f9f9f9;
}
.calculator-inputs .form-group {
margin-bottom: 15px;
display: flex;
flex-direction: column;
}
.calculator-inputs label {
margin-bottom: 5px;
font-weight: bold;
color: #333;
}
.calculator-inputs input[type="number"] {
padding: 10px;
border: 1px solid #ccc;
border-radius: 4px;
box-sizing: border-box; /* Important for consistent padding */
}
.calculator-inputs button {
background-color: #4CAF50;
color: white;
padding: 12px 20px;
border: none;
border-radius: 4px;
cursor: pointer;
font-size: 16px;
margin-top: 10px;
}
.calculator-inputs button:hover {
background-color: #45a049;
}
#ecgResult {
margin-top: 20px;
padding: 15px;
border: 1px solid #eee;
background-color: #fff;
border-radius: 4px;
text-align: center;
font-size: 18px;
color: #555;
}
function calculateHeartRateECG() {
var rrInterval = parseFloat(document.getElementById("rrInterval").value);
var ecgPaperSpeed = parseFloat(document.getElementById("ecgPaperSpeed").value);
var smallBoxes = parseFloat(document.getElementById("smallBoxes").value);
var bpm = "N/A"; // Default to N/A
if (!isNaN(rrInterval) && rrInterval > 0) {
// Method 1: Using RR Interval directly
bpm = 60 / rrInterval;
} else if (!isNaN(smallBoxes) && smallBoxes > 0 && !isNaN(ecgPaperSpeed) && ecgPaperSpeed > 0) {
// Method 2: Using number of small boxes and paper speed
// Assuming each small box is 1mm and paper speed is in mm/sec
// Time per small box = 1mm / (speed in mm/sec)
// RR Interval (seconds) = number of small boxes * (1mm / speed in mm/sec)
var timePerSmallBox = 1 / ecgPaperSpeed;
var calculatedRrInterval = smallBoxes * timePerSmallBox;
bpm = 60 / calculatedRrInterval;
} else {
document.getElementById("ecgResult").innerHTML = "Please enter valid RR Interval or Small Boxes and Paper Speed.";
return;
}
if (!isNaN(bpm)) {
document.getElementById("ecgResult").innerHTML = "Estimated Heart Rate: " + bpm.toFixed(0) + " bpm";
} else {
document.getElementById("ecgResult").innerHTML = "Calculation Error. Please check your inputs.";
}
}
Understanding Heart Rate Calculation from an ECG
An electrocardiogram (ECG or EKG) is a non-invasive test that records the electrical activity of the heart over a period of time. It's a crucial tool for diagnosing various heart conditions. One of the fundamental pieces of information derived from an ECG is the heart rate, often expressed in beats per minute (bpm). Calculating this from the ECG tracing involves understanding the timing of the heart's electrical impulses.
How the Heart Beats and ECG Readings
Each heartbeat is initiated by an electrical impulse generated in the sinoatrial (SA) node, the heart's natural pacemaker. This impulse travels through the heart, causing the muscle to contract and pump blood. The ECG machine records these electrical signals as waves and complexes on a graph. The 'R' wave in the QRS complex typically represents ventricular depolarization, which corresponds to the main contraction of the ventricles. The time between consecutive 'R' waves (the RR interval) directly reflects the duration of one cardiac cycle.
Methods to Calculate Heart Rate from an ECG
There are several common methods to calculate heart rate from an ECG tracing, depending on the information available from the ECG printout:
1. **Using the RR Interval (Most Accurate):**
This is the most precise method if you can accurately measure the time between two consecutive R waves.
* **Formula:** Heart Rate (bpm) = 60 / RR Interval (in seconds)
* **Explanation:** Since there are 60 seconds in a minute, dividing 60 by the time it takes for one heartbeat (the RR interval in seconds) gives you the number of heartbeats that would occur in one minute.
2. **Using the Number of Small Boxes (if Paper Speed is Known):**
ECG paper is printed on a grid. Standard ECG paper moves at a specific speed, usually 25 mm/sec. Each small box on the grid is typically 1 mm wide.
* **Step 1: Determine the time for one small box.**
* If paper speed is 25 mm/sec, then 1 mm represents 1/25 = 0.04 seconds.
* If paper speed is 50 mm/sec, then 1 mm represents 1/50 = 0.02 seconds.
* **Step 2: Count the number of small boxes between two consecutive R waves (the RR interval in small boxes).**
* **Step 3: Calculate the RR interval in seconds.**
* RR Interval (seconds) = Number of small boxes * Time per small box (seconds)
* **Step 4: Calculate Heart Rate.**
* Heart Rate (bpm) = 60 / RR Interval (in seconds)
* **Simplified Formula (for 25 mm/sec paper speed where 1 small box = 1mm):**
* Heart Rate (bpm) = 60 / (Number of small boxes * 0.04) = 1500 / Number of small boxes.
3. **Using the Number of Large Boxes (if Paper Speed is Known):**
Large boxes are typically made up of 5 small boxes.
* **Step 1: Count the number of large boxes between two consecutive R waves.**
* **Step 2: Calculate the RR interval in seconds.**
* For 25 mm/sec paper speed (where 1 large box = 5mm): RR Interval (seconds) = Number of large boxes * (5mm / 25 mm/sec) = Number of large boxes * 0.2 seconds.
* **Step 3: Calculate Heart Rate.**
* Heart Rate (bpm) = 60 / RR Interval (in seconds)
* **Simplified Formula (for 25 mm/sec paper speed):**
* Heart Rate (bpm) = 60 / (Number of large boxes * 0.2) = 300 / Number of large boxes.
### When to Use This Calculator
This calculator is designed for scenarios where you have an ECG tracing and want to quickly estimate the heart rate. You can input the measured RR interval directly, or if you know the number of small boxes between R waves and the ECG paper speed, you can use those values.
### Example Calculation
Let's say you're looking at an ECG tracing and measure the time between two consecutive R waves to be **0.75 seconds**.
Using the calculator:
* Input for "RR Interval (seconds)": `0.75`
* Click "Calculate Heart Rate".
The calculator will perform the calculation:
`60 / 0.75 = 80`
**Result:** The estimated heart rate is **80 bpm**.
Alternatively, imagine you count **20 small boxes** between two R waves on an ECG strip printed at the standard **25 mm/sec** speed.
Using the calculator:
* Input for "ECG Paper Speed (mm/sec)": `25`
* Input for "Number of Small Boxes": `20`
* Click "Calculate Heart Rate".
The calculator will use the second method:
* Time per small box = 1mm / 25 mm/sec = 0.04 seconds.
* RR Interval = 20 small boxes * 0.04 seconds/box = 0.8 seconds.
* Heart Rate = 60 / 0.8 = 75 bpm.
**Result:** The estimated heart rate is **75 bpm**.
Accurate measurement of the RR interval or the number of boxes is crucial for a reliable heart rate calculation. For critical medical decisions, always consult with a qualified healthcare professional who can interpret the ECG in its entirety.