the beat of the heart

Dr. Knight was talking to me about a generic electrocardiogram (EKG) print out, and I wasn’t following her as much as I would have liked, so we decided that I should learn about it. I am currently trying to teach myself how to read one so I can understand what is actually going on in the heart when looking at a monitor. I wrote down some notes on it, but I figured it would be good to have it all in one place for myself, complete with some pictures that are much clearer than my drawings. The process of learning this involved regurgitating my knowledge of the heart, which has waxed and waned over the past five or so years, but it is amazing what the brain can remember.

Anyway, I first┬áresearched how EKGs function: the electrodes placed on the body detect electrical changes on the skin that happen when the heart muscle depolarizes and repolarizes. These changes are very tiny so the EKG must amplify them in order to extract anything meaningful from it. Using the following two images and some great information from Wikipedia, I’m starting to understand more of the physiological intricacies.

The P wave represents the depolarization that spreads from the sinoatrial (SA) node throughout the atria. There is a brief zero volage period, also referred to as the isoelectric period, after the P wave. This represents the time during which th eimpulse is traveling within the atrioventricular (AV) node and the bundle of His, the collection of cells specialized for electrical conduction.

The QRS complex represents ventricular depolarization, and the T wave represents ventricular repolarization, which takes longer than depolarization. The P-R interval is the period of time from th eonset of the P wave to the begining of the QRS complex, which is essentially the time between onset of atrial depolarization and ventricular depolarization. Finally, the ST segment is the isoelectric (remember, zero voltage) period following QRS where the entire ventricle is depolarized.

Sorry this entry was super drone. I need this information, and I could not think of any fun analogies to map onto the different waves. My inability to lighten up this content is definitely indicative of how little I am grasping, but you gotta start somewhere.

P.S. My heart has been beating for 21 years today. If my heart beat at an average of around 72 beats per minute for my entire life, it has given me a hefty 795,251,520 beats. You’ve done me good, heart.