ECG Masterclass

Session 2

🫀 HOW TO FIND THE CARDIAC AXIS ON ECG – QUICK METHOD

Understanding the cardiac axis is essential for proper ECG interpretation. Fortunately, you can determine it quickly by looking at Lead I and Lead aVF.

📌 Step 1: Look at Lead I
Check if the QRS complex is positive or negative.

📌 Step 2: Look at Lead aVF
Again, see whether the QRS complex is positive or negative.

Now interpret the axis:

✅ Lead I positive + aVF positive → Normal Axis
Axis between –30° to +90°

⬅️ Lead I positive + aVF negative → Left Axis Deviation (LAD)
Axis between –30° to –90°

➡️ Lead I negative + aVF positive → Right Axis Deviation (RAD)
Axis between +90° to +180°

❌ Lead I negative + aVF negative → Extreme Axis Deviation
Axis between –90° to –180°

💡 Pro Tip:

If Lead I is positive and aVF is negative, check Lead II:
• Lead II positive → Normal axis
• Lead II negative → Left axis deviation

📚 ECG interpretation becomes easy when you follow simple steps.
Follow ECG Masterclass to Learn ECG Like a Pro and improve your clinical skills.
Daily ECG learning coming soon!

Hello everyone
After session 1
You all are requested to make clear pictures of 3 ecgs of your choice (scanned copy is prefered) and calculate the heart rate
And comment on this post about what you calculated

Don't hesitate to answer wrong. Wrong answers are the first step in learning.

Regards

🫀 ECG Masterclass (Session 1)

📌 Heart Rate Calculation from ECG – 3 Methods

Every Doctor Should Know

Before interpreting any ECG, the first step is always the heart rate.

Here are 3 quick methods you can use in clinical practice.

🔢 1️⃣ The 300 Rule (Fastest Method – Regular Rhythm)

Count the large boxes between two R waves.
Heart Rate = 300 ÷ Large Boxes
Memorize this sequence:
➡️ 1 box = 300 bpm
➡️ 2 boxes = 150 bpm
➡️ 3 boxes = 100 bpm
➡️ 4 boxes = 75 bpm
➡️ 5 boxes = 60 bpm
➡️ 6 boxes = 50 bpm
💡 Best for: Quick estimation in regular rhythms.

📏 2️⃣ The 1500 Rule (Most Accurate)

Count the small boxes between two R waves.
Heart Rate = 1500 ÷ Small Boxes

Example:
If 25 small boxes are present:
1500 ÷ 25 = 60 bpm
💡 Best for: When you want a precise heart rate.

⏱ 3️⃣ The 10-Second Rule (For Irregular Rhythms)

Count QRS complexes in 10 seconds
(= 50 large boxes on ECG paper)

Heart Rate = Number of QRS × 6

Example:
If 11 QRS complexes appear in 10 seconds:
11 × 6 = 66 bpm
💡 Best for: Atrial fibrillation and irregular rhythms

🧠 ECG Tip:
Always check rhythm regularity first, then choose the appropriate method.
📚 Follow ECG Masterclass to Learn ECG Like a Pro.

*Understanding paper speeds*

Paper output speed is the rate at which the ECG machine produces a trace

Standard output is 25mm per second

If a different paper speed is used, standard rate calculations will have to be modified appropriately

The standard paper speed is 25mm/sec:
1 SMALL square (1mm) = 0.04 sec (40ms)
5 SMALL squares (5mm) = 1 LARGE square = 0.2 sec (200ms)
5 LARGE squares = 1 second