.ecg-calc-box {
background-color: #ffffff;
padding: 25px;
border-radius: 8px;
box-shadow: 0 4px 6px rgba(0,0,0,0.1);
margin-bottom: 30px;
border-top: 4px solid #e74c3c;
}
.ecg-input-group {
margin-bottom: 20px;
}
.ecg-input-group label {
display: block;
margin-bottom: 8px;
font-weight: bold;
color: #333;
}
.ecg-input-group input {
width: 100%;
padding: 12px;
border: 1px solid #ccc;
border-radius: 4px;
font-size: 16px;
box-sizing: border-box;
}
.ecg-btn {
background-color: #e74c3c;
color: white;
padding: 12px 24px;
border: none;
border-radius: 4px;
cursor: pointer;
font-size: 16px;
width: 100%;
transition: background-color 0.3s;
}
.ecg-btn:hover {
background-color: #c0392b;
}
.ecg-result {
margin-top: 25px;
padding: 15px;
background-color: #f0f4f8;
border-left: 5px solid #3498db;
display: none;
}
.ecg-result h3 {
margin-top: 0;
color: #2c3e50;
}
.ecg-metric {
font-size: 2em;
font-weight: bold;
color: #e74c3c;
}
.ecg-interpretation {
margin-top: 10px;
font-weight: bold;
}
.status-normal { color: #27ae60; }
.status-warning { color: #f39c12; }
.status-alert { color: #c0392b; }
.ecg-article h2 {
color: #2c3e50;
border-bottom: 2px solid #ecf0f1;
padding-bottom: 10px;
margin-top: 30px;
}
.ecg-article p, .ecg-article li {
line-height: 1.6;
color: #444;
}
.ecg-table {
width: 100%;
border-collapse: collapse;
margin: 20px 0;
}
.ecg-table th, .ecg-table td {
border: 1px solid #ddd;
padding: 10px;
text-align: left;
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.ecg-table th {
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}
Understanding the 300 Method for ECG Interpretation
The 300 Method (also known as the Sequence Method) is one of the most popular and rapid techniques used by medical professionals to estimate heart rate from an electrocardiogram (ECG) strip. It is particularly effective when the patient's heart rhythm is regular.
ECG paper typically prints at a standard speed of 25 mm/second. On this paper:
- One small square represents 0.04 seconds (1 mm).
- One large square (made of 5 small squares) represents 0.20 seconds (5 mm).
- There are 300 large squares in one minute (60 seconds / 0.20 seconds = 300).
How to Calculate
To use this calculator or perform the calculation manually, follow these steps:
- Identify a QRS complex (specifically the R wave) that falls on or near a heavy black line (the start of a large square).
- Count the number of large squares until the next R wave (the R-R interval).
- Divide 300 by the number of large squares found.
Formula: Heart Rate (BPM) = 300 รท Number of Large Squares
Quick Reference Sequence
Many clinicians memorize the sequence of numbers associated with each large square line to estimate rate instantly:
| Large Squares (R-R) |
Heart Rate (BPM) |
Classification |
| 1 |
300 |
Extreme Tachycardia |
| 2 |
150 |
Tachycardia |
| 3 |
100 |
Normal Limit / Mild Tachycardia |
| 4 |
75 |
Normal Resting Rate |
| 5 |
60 |
Normal Limit / Mild Bradycardia |
| 6 |
50 |
Bradycardia |
When is this method accurate?
The 300 method assumes a regular rhythm. If the distance between R waves varies significantly (irregular rhythm, such as in Atrial Fibrillation), this method will not provide an accurate heart rate. In such cases, the "6-Second Method" is preferred, where you count the number of QRS complexes in a 6-second strip and multiply by 10.
function calculateECGRate() {
var squaresInput = document.getElementById('largeSquares');
var resultDiv = document.getElementById('ecgResult');
var bpmOutput = document.getElementById('bpmOutput');
var interpretationOutput = document.getElementById('interpretationOutput');
var squares = parseFloat(squaresInput.value);
if (isNaN(squares) || squares <= 0) {
alert("Please enter a valid number of large squares (greater than 0).");
resultDiv.style.display = "none";
return;
}
// Calculation Logic: 300 / large squares
var bpm = 300 / squares;
// Round to nearest integer for standard reporting
var bpmRounded = Math.round(bpm);
// Determine Interpretation
var interpretationText = "";
var statusClass = "";
if (bpmRounded = 60 && bpmRounded 100 && bpmRounded < 160) {
interpretationText = "Result indicates Sinus Tachycardia (Fast Heart Rate).";
statusClass = "status-alert";
} else {
interpretationText = "Result indicates Extreme Tachycardia or Flutter.";
statusClass = "status-alert";
}
// Update DOM
bpmOutput.innerHTML = bpmRounded + "
";
interpretationOutput.innerHTML = interpretationText;
interpretationOutput.className = "ecg-interpretation " + statusClass;
resultDiv.style.display = "block";
}