.cl-hr-calculator-wrapper {
max-width: 800px;
margin: 0 auto;
font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
color: #333;
line-height: 1.6;
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.calculator-container {
background-color: #f8f9fa;
border: 1px solid #e9ecef;
border-radius: 8px;
padding: 30px;
margin-bottom: 40px;
box-shadow: 0 4px 6px rgba(0,0,0,0.05);
}
.calc-title {
text-align: center;
color: #2c3e50;
margin-bottom: 25px;
font-size: 24px;
font-weight: 700;
}
.form-group {
margin-bottom: 20px;
}
.form-group label {
display: block;
margin-bottom: 8px;
font-weight: 600;
color: #495057;
}
.form-control {
width: 100%;
padding: 12px;
font-size: 16px;
border: 1px solid #ced4da;
border-radius: 4px;
box-sizing: border-box;
transition: border-color 0.15s ease-in-out;
}
.form-control:focus {
border-color: #e74c3c;
outline: 0;
box-shadow: 0 0 0 0.2rem rgba(231, 76, 60, 0.25);
}
.btn-calculate {
display: block;
width: 100%;
padding: 14px;
background-color: #e74c3c;
color: white;
border: none;
border-radius: 4px;
font-size: 18px;
font-weight: 600;
cursor: pointer;
transition: background-color 0.2s;
}
.btn-calculate:hover {
background-color: #c0392b;
}
.result-box {
margin-top: 25px;
padding: 20px;
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border-radius: 6px;
border-left: 5px solid #e74c3c;
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.result-row {
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align-items: center;
margin-bottom: 10px;
padding-bottom: 10px;
border-bottom: 1px solid #eee;
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.result-row:last-child {
border-bottom: none;
margin-bottom: 0;
padding-bottom: 0;
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.result-label {
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color: #555;
}
.result-value {
font-weight: 700;
font-size: 20px;
color: #2c3e50;
}
.status-indicator {
font-size: 14px;
padding: 4px 8px;
border-radius: 4px;
font-weight: bold;
}
.status-normal { background-color: #d4edda; color: #155724; }
.status-brady { background-color: #cce5ff; color: #004085; }
.status-tachy { background-color: #f8d7da; color: #721c24; }
/* Content Styling */
.content-section h2 {
color: #2c3e50;
margin-top: 30px;
border-bottom: 2px solid #e74c3c;
padding-bottom: 10px;
display: inline-block;
}
.content-section h3 {
color: #34495e;
margin-top: 25px;
}
.conversion-table {
width: 100%;
border-collapse: collapse;
margin: 20px 0;
}
.conversion-table th, .conversion-table td {
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padding: 12px;
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.conversion-table th {
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.conversion-table tr:nth-child(even) {
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function calculateBPM() {
// Get input value
var cycleLengthInput = document.getElementById('inputCycleLength').value;
var resultContainer = document.getElementById('resultContainer');
var outputBPM = document.getElementById('outputBPM');
var outputClass = document.getElementById('outputClass');
// Validate input
if (cycleLengthInput === "" || parseFloat(cycleLengthInput) <= 0) {
alert("Please enter a valid Cycle Length greater than 0 ms.");
resultContainer.style.display = "none";
return;
}
// Perform Calculation: BPM = 60,000 / CL (ms)
var cl = parseFloat(cycleLengthInput);
var bpm = 60000 / cl;
// Round to 1 decimal place for precision
var bpmRounded = Math.round(bpm * 10) / 10;
// Determine Clinical Classification
var classification = "";
var statusClass = "";
if (bpmRounded = 60 && bpmRounded <= 100) {
classification = "Normal Sinus Rhythm";
statusClass = "status-normal";
} else {
classification = "Tachycardia (Fast)";
statusClass = "status-tachy";
}
// Display Results
outputBPM.innerHTML = bpmRounded + " BPM";
outputClass.innerHTML = classification;
// Reset classes
outputClass.className = "status-indicator " + statusClass;
resultContainer.style.display = "block";
}
Understanding Cycle Length and Heart Rate Conversion
In cardiac electrophysiology and ECG interpretation, the relationship between Cycle Length (CL) and Heart Rate (HR) is fundamental. While heart rate is typically expressed in beats per minute (BPM), electronic measurements of the heart (such as those from an ECG machine, pacemaker, or during an EP study) often measure the time interval between beats in milliseconds (ms).
This calculator allows medical professionals, students, and technicians to instantly convert the R-R interval (Cycle Length) measured in milliseconds into the standard clinical heart rate in BPM.
The Conversion Formula
The math behind converting milliseconds to beats per minute relies on the number of milliseconds in one minute. Since there are 60 seconds in a minute and 1,000 milliseconds in a second, there are 60,000 milliseconds in one minute.
The formula is:
Heart Rate (BPM) = 60,000 ÷ Cycle Length (ms)
Conversely, if you know the heart rate and need the cycle length:
Cycle Length (ms) = 60,000 ÷ Heart Rate (BPM)
Common Conversion Reference Table
Below is a quick reference chart for common Cycle Lengths encountered in clinical settings and their corresponding Heart Rates.
| Cycle Length (ms) |
Heart Rate (BPM) |
Classification |
| 1500 ms |
40 BPM |
Marked Bradycardia |
| 1200 ms |
50 BPM |
Bradycardia |
| 1000 ms |
60 BPM |
Lower Limit of Normal |
| 857 ms |
70 BPM |
Normal |
| 750 ms |
80 BPM |
Normal |
| 600 ms |
100 BPM |
Upper Limit of Normal |
| 500 ms |
120 BPM |
Tachycardia |
| 400 ms |
150 BPM |
Significant Tachycardia |
| 300 ms |
200 BPM |
Flutter / VT Range |
Clinical Significance
Why measure in Milliseconds?
Electrophysiologists prefer milliseconds because it offers greater precision than BPM. When mapping arrhythmias or programming pacemakers and ICDs, a difference of 10-20ms can determine whether an electrical pathway conducts a signal or blocks it. This level of granularity is lost when simply using BPM.
R-R Interval
On a standard ECG strip, the Cycle Length is equivalent to the R-R interval—the distance between the peak of one QRS complex to the peak of the next.
- Bradycardia: Cycle Length > 1000 ms (< 60 BPM)
- Normal Sinus Rhythm: Cycle Length between 600 ms and 1000 ms (60-100 BPM)
- Tachycardia: Cycle Length 100 BPM)
Example Calculation
If you measure an R-R interval of 800 ms on a patient's ECG monitor:
- Take the constant: 60,000
- Divide by the Cycle Length: 800
- Calculation: 60,000 / 800 = 75 BPM
This falls well within the normal range for a resting adult.