function calculateECGRate() {
var rWavesInput = document.getElementById('rWaveCount');
var durationInput = document.getElementById('stripDuration');
var resultArea = document.getElementById('result-area');
var bpmDisplay = document.getElementById('bpmResult');
var statusDisplay = document.getElementById('statusResult');
var methodDisplay = document.getElementById('methodExplanation');
var rWaves = parseFloat(rWavesInput.value);
var duration = parseFloat(durationInput.value);
if (isNaN(rWaves) || rWaves <= 0) {
alert("Please enter a valid number of R-waves greater than 0.");
return;
}
// Calculation: (R-Waves / Duration in Seconds) * 60 seconds
var bpm = Math.round((rWaves / duration) * 60);
// Determine Classification
var statusText = "";
var statusClass = "";
if (bpm = 60 && bpm 100 && bpm < 160) {
statusText = "Tachycardia (Fast Heart Rate)";
statusClass = "status-warning";
} else {
statusText = "Severe Tachycardia / Flutter / Fibrillation";
statusClass = "status-danger";
}
// Explanation Text
var multiplier = 60 / duration;
var explanation = "Method: Counted " + rWaves + " beats in a " + duration + "-second strip. Multiplied by " + multiplier + " to estimate the minute rate.";
// Update DOM
bpmDisplay.innerHTML = bpm + " BPM";
statusDisplay.innerHTML = statusText;
statusDisplay.className = "result-classification " + statusClass;
methodDisplay.innerHTML = explanation;
resultArea.style.display = "block";
}
How to Calculate Heart Rate in Irregular ECG Rhythms
Calculating the heart rate from an Electrocardiogram (ECG) is a fundamental skill for healthcare professionals. However, standard methods like the "300 rule" or the "1500 rule" rely on the rhythm being regular (consistent distance between R-waves). When the heart rhythm is irregular, such as in Atrial Fibrillation (Afib) or frequent premature contractions, these methods become inaccurate.
Quick Rule: For irregular rhythms, the gold standard is the 6-Second Method. Do not use the box-counting method for irregular heartbeats.
Why Standard Methods Fail on Irregular Rhythms
The standard "300 Method" involves counting the number of large boxes between two consecutive R-waves and dividing 300 by that number. This works mathematically because there are 300 large boxes in one minute (at a standard paper speed of 25mm/sec).
However, in an irregular rhythm, the distance (R-R interval) changes from beat to beat. Calculating the rate based on a short R-R interval might falsely indicate tachycardia, while a long pause might falsely indicate bradycardia. To get an accurate clinical picture, you must calculate the average ventricular rate over a longer period.
The 6-Second Method Explained
The 6-Second Method is the simplest and most reliable way to estimate heart rate for irregular rhythms. It averages the heart rate over a longer duration, smoothing out the irregularities.
Step-by-Step Guide:
Identify a 6-Second Strip: Most ECG paper has time markers at the top or bottom every 3 seconds. Select a strip that spans 6 seconds (typically 30 large boxes).
Count the QRS Complexes: Count the number of R-waves (the tall spikes representing ventricular contraction) that fall within this 6-second window. Do not count p-waves or t-waves.
Multiply by 10: Since 6 seconds is one-tenth of a minute (60 seconds), multiplying your count by 10 gives you the Beats Per Minute (BPM).
Example: If you count 8 QRS complexes in a 6-second strip, the heart rate is 8 x 10 = 80 BPM.
The 10-Second Method
Similar to the 6-second method, the 10-second method is often used because standard 12-lead ECG printouts usually record 10 seconds of data per lead line.
Formula: (Number of R-waves in 10 seconds) x 6 = BPM.
This provides slightly more accuracy than the 6-second method because it averages data over a longer period, but the multiplication is slightly less intuitive for mental math.
Interpreting the Results
Once you have calculated the rate, you can categorize the ventricular rate:
Bradycardia: Rate less than 60 BPM. This may compromise cardiac output if too slow.
Normal Rate: Rate between 60 and 100 BPM. This is the goal for rate control in atrial fibrillation.
Tachycardia: Rate greater than 100 BPM. In irregular rhythms like Afib with Rapid Ventricular Response (RVR), rates often exceed 110-120 BPM requiring medical intervention.
Common Irregular Rhythms
This calculator is specifically designed for rhythms such as:
Atrial Fibrillation: Characterized by "irregularly irregular" R-R intervals and no distinct P-waves.
Atrial Flutter with Variable Block: Sawtooth patterns with inconsistent conduction ratios (e.g., changing from 2:1 to 3:1 conduction).
Multifocal Atrial Tachycardia (MAT): Irregular rhythm with changing P-wave morphology.
Sinus Arrhythmia: A normal variation where heart rate changes with breathing, though often regular enough for standard methods, the 6-second method remains accurate.