Cardiac Axis Determination 

My pleasure, Sharon Yang! I’m so glad you got something out of it.

@@TomBouthillet can you explain more about the split axis? You said that the difference is divided, but what u divided was the total.

@@tasieprecious1678 Maybe it's a figure of speech? In the U.S. when we say "split the difference" we mean "cut it in half." So if you calculate both axes, one is 60 and the other is 90, by "splitting the difference" you would settle on 75.

@@TomBouthillet I understand, but the difference between 90 and 60 is 30, then when divided into half, we have 15. Or do you mean addition of both degrees not subtraction?

@@tasieprecious1678 Thanks for the follow-up. I understand the confusion now. The difference between 60 and 90 is 30 but if you "split the difference" between 60 and 90 the answer would be 75. So I think this is semantics. For example, I just prompted Bard (Google's A.I.): "If I asked you to "split the difference" between 60 and 90 what would you say?" and Bard replied, "If you asked me to "split the difference" between 60 and 90, I would say 75. This is because 75 is the average of 60 and 90." I did the same exercise with ChatGPT and it replied, "If you asked me to split the difference between 60 and 90, I would calculate the midpoint between these two numbers. The difference between 90 and 60 is 30, so to find the midpoint, you would add half of that difference (which is 15) to 60. Therefore, the midpoint between 60 and 90 is 75."

Thank you, Asil H! I do have a hyperkalemia video in the pipeline.

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I’m glad to hear it was helpful!

Yes

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That is great to hear! Awesome compliment.

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@@TomBouthillet sir can you see my ecg please

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Wonderful! Thanks, olatunji oladipo!

www.ecgmedicaltraining.com/wp-content/uploads/2016/02/rapid-axis-1024x411.png

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Good point. Computer algorithms are good at certain things but not rhythm analysis!

Yes, that's true. It's not a perfect model.

Quadrant method and speed method? It’s difficult to know what’s enough for a given individual. I use all three methods all the time and for me that’s best. Do what works for you.

Thanks, lana!

Right Bundle Branch Block: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-6exhMIuofR0.html

Left Bundle Branch Block: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-bp-J6n-MPlU.html

I was illustrating what I call a split axis. Because it wasn't clear whether lead I or lead aVL was the equiphasic lead, I calculated both the perpendicular leads, lead II (-) and lead aVF (-). Those have values of -90 and -120. If you split the difference you get -105. The computer measures the axis at -110. That's not the preferred method for this ECG but it can be done.

I think i have got it...we don't have to see the values to determine the polarity...rather that little arrow ...at aVL -30 degrees the little arrow is pointing upward so it will produce positive deflection....and at aVL +150 the little arrow is pointing downward so it produces negative deflection

Yes, definitely.

That’s just a quirk in the hexaxial reference system. Because the positive electrode for aVR is up on the right shoulder, a normal axis moves away from that positive electrode and produces a negative QRS in that lead. Look at the little down arrow next to 30 degrees. That lets you know the QRS should be negative for a value of 30.

The electrical activity of the heart is generated by the movement of ions across the cell membranes of cardiac muscle cells. When these ions move, they create an electrical field that can be detected by electrodes placed on the skin. The ECG machine amplifies this signal and displays it on a graph. The ECG trace is not a direct representation of the electrical activity of the heart cells. Instead, it is a representation of the net electrical field as it is detected by the electrodes.

Well your patient’s skin, like everyone else, is composed of cells

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Thanks for the tip, SireSquish! I am not familiar with the vector addition method but I will check it out.

Hi, Butch! If you look at the hexaxial reference system, the spokes for lead II and lead aVL are perfectly perpendicular. Same for lead I and lead aVF (which is why you use those leads for the quadrant method). upload.wikimedia.org/wikipedia/commons/5/56/Hexaxial_reference_system.svg

Interesting question and reply

Thanks for the comment, Andrew. May I please have an exact time stamp?

@@TomBouthillet 29:00. Is it because the QRS is negative in lead aVF that you went to the -90 as opposed to +90? Earlier 14:20, same reasoning? Because QRS is negative in aVR?

@@Flash236926 Yes, that is exactly right. The polarity of the QRS complex determines the value. It corresponds to the little up and down arrows around the hexaxial reference system. Great question!

@@TomBouthillet Thank you sir. Making medical school easier.

@@Flash236926 Glad to help.

This is the dilemma with screening young athletes with 12-lead ECGs. Unless there is clear evidence of left ventricular hypertrophy / hypertrophic cardiomyopathy, a long/short QT interval, a Brugada pattern, arrhythmogenic right ventricular dysplasia, Wolff-Parkinson-White pattern (delta waves), or concerning arrhythmias, there is a chance the athlete will not be signed off because “normal” is the hardest diagnosis in medicine. If you’re worried you could see if you can schedule an echocardiogram but insurance may not pay for it. Good luck resolving the issue!

The positive electrode for lead aVL is the left arm electrode. When a depolarization wavefront moves toward a positive electrode, it creates an upright QRS.

No I think there’s some misunderstanding. I get it’s positive QRS but my question is in the ecg paper it’s showing positive avL so technically the vector should’ve pointed towards positive axis which is 150 in the downwards. But instead of positive you plotted the arrow on -30 in the axis. Why so ?

@@Persephone7770 Why do you say that a positive QRS in lead aVL should result in a positive axis? The positive electrode for lead aVL is in the left superior quadrant.

I’m so sorry I got confused with the positive sign and didn’t notice that actually the positive is in superior quadrant

Thank you sir

My pleasure! Glad you enjoyed it.