ECG has been for me a mystery, and then I thought, "Ok, I need to decipher ECG language for the love of God." I've been watching videos, reading books, writing notes, and drawing. So I thought that another good way to memorize and share as educational purposes is writing a post about ECG.
The ECG shows the electrical activity of the heart in the form of waves on a tiny orange square of striped paper. The orange stripes are divided into blocks of five tiny squares. The horizontal represents time the measured with each tiny square as 0.04 seconds, thus a block of five is 0.20 seconds. So far, so good, right?
The vertical strips measure the amplitude in millimeters or mm or electrical voltage in millivolts or mv. Each tiny square is 0.1 mV; thus, a block of 5 is 0.5 mV.
The letters that make up the ECG are P, Q, R,S, T,and U.
Before getting to know each letter better, important tips about placing the leads of each ECG pad are necessary for a good reading of the electrical waves. ECG devices come in 3, 4, 5, or 12 leads. Now let's talk about the 5 lead, mostly used and called telemetry. You need to make sure you place each pad on the intercostal space between the bony ribs, never on bony areas, or you won't be able to see the waves properly. If the skin is oily, you can wipe it down, or if there's too much hair, shave the hair off.
White RA, right arm
Black LA, left arm
Brown C, chest
Green RL, right leg
Red LL, left leg
Nmonic to help you remember the pads' placement is:
White (clouds or snow) over Green ( tree or grass)
Black (smoke) over Red (fire)
Brown (chocolate) is close to the heart
P wave means to FIRE from the SA (Sinus Atrial) node, the impulse that generates a P wave with amplitude 2 to 3 mm high and time duration of 0.06 to 0.12 seconds.
PR interval is the trajectory of the impulse from the atria SA node through the AV (Atrioventricular) to the bundle of His, and finally right and left bundle branches, with a duration of 0.12 to 0.20 seconds.
The QRS complex means ventricular depolarization, or in other words, the ventricles contract and create a pulse. QRS amplitude is 5 to 30 mm high and duration 0.06 to 0.10 seconds.
The ST segment represents the end of ventricular depolarization ( contraction) and the beginning of ventricular recovery, or in other words, repolarization. This very place is also known as the J point. Normal amplitude is 0.5 to 1.0 mm. If the ST segment is depressed, inverted 0.5 or more below the baseline may be myocardial ischemia or digoxin toxicity. If the ST segment is elevated more than 1.0mm above the baseline might be myocardial injury.
T wave means ventricular recovery. Amplitude is 0.5 mm to 10 mm. If the T wave is bumpy, a P wave might be hidden in it. A tall T wave might be hyperkalemia, myocardial injury. An inverted T wave might be myocardial ischemia.
QT Prolonged QT interval might be a dangerous arrhythmia called Torsades de Pointes. A short QT interval might be digoxin toxicity or hypercalcemia.
U wave, if present, represents the recovery of the Purkinje fibers.
The colors on this classic ECG are just a way to memorize: Fire as stimulation or depolarization, green as recovery or repolarization, and a plant in a vase to remember it's resting quietly. The purple looks like a tight dress to remember the ventricular contraction. The brown means just brown. I couldn't think of anything. Next post, I'll try to improve the drawings as I'm planning on drawing the Arrhythmias and their interpretation.
The wonderful sources of material for this post, using the paraphrasing technique, are a book called"ECG Interpretation Made Incredible Easy," Third edition, Lippincott Williams & Wilkins. The pictures are from Dynamic Health and/or Healthstream, and the use is for educational purposes only.
#ekg #introductiontoekg
