Posted by The heart is one of the most important organs in the human body. It keeps blood flowing through the body in order to provide adequate oxygenation, nutrient absorption, and immune response. The heart’s electrical system is what allows this to happen. The objective that I am covering is: explain how the heart translates an electrical signal to a contraction.
The heart’s electrical system starts off with the sino-atrial node. The SA node is located in the right atrium and is the pacemaker of the heart (Boyett 2009). The SA node is where the action potential starts in the heart. After the action potential begins here in the SA node it propagates the rest of the heart which results in a heartbeat (Boyett 2009).
After the SA node is the atrioventricular node. This node is located at the base of the right atrium. Conduction of the action potential through the AV node is slow so that there is enough time for the atria to pump blood into the ventricles before they contract (Boyett 2009). The AV node is what contracts the atria. The AV node can also act as a backup pacemaker in case the SA node fails (Boyett 2009).
Beneath the AV node is the Bundle of His. This is where the right and left bundle branches begin. The bundle branches wrap around the ventricles and have Purkinje fibers that branch off of them (Boyett 2009). The function of the Purkinje fibers is to conduct the action potential at the same time in order to ensure the ventricles contract simultaneously (Boyett 2009).
12 lead EKGs (or ECGs) are used to take a “picture” of the heart’s electrical activity. 12 leads use 10 electrodes placed around the body. 4 limb (or core) leads are placed on the legs and arms or on the core. 6 leads are placed on the chest. 12 leads contain different waves and segments. They contain the P wave, QRS complex wave, T wave, PR interval, and the QT interval (Liu 2021).
12 lead EKGs can be used to detect rhythms such as normal sinus rhythm, ST elevation myocardial infarction, ventricular tachycardia, atrial fibrillation, ventricular fibrillation, heart blocks, and bundle branch blocks.
Normal sinus rhythm is when all the electrical pathways in the heart are working normally. A STEMI is caused when there is a blockage of blood flow to the myocardium which causes that part of the muscle to die (Cleveland Clinic 2021). Ventricular tachycardia is an abnormal heart rhythm that causes the ventricles to beat so fast that it can’t pump enough blood to the body (Cleveland Clinic 2022). The electrical signal originates in the ventricles rather than the SA node, which blocks normal electrical impulses from getting through (Cleveland Clinic 2022).
Atrial fibrillation is caused when the heart’s electrical system sends out many different electrical impulses at the same time (Cleveland Clinic 2024). This causes an irregular and fast heartbeat. Ventricular fibrillation is the most common deadly arrhythmia that is caused when the ventricles quiver instead of expanding and contracting (Cleveland Clinic 2024).
Heart blocks are caused by a blockage in the heart’s electrical system. Third degree heart blocks are the most serious type of heart block and are caused when there is a complete separation between the electrical activity in the heart’s upper and lower chambers (Roland 2025). Bundle branch blocks are caused by a blockage of the heart’s electrical system in the bundle branches. This causes the affected ventricle to beat later than the other one (Cleveland Clinic 2022).
12 lead EKGs are a great way to monitor your heart’s electrical activity. The heart’s electrical system is vital to keep us alive. It is important to take good care of your heart in order to keep it beating smoothly.
Sources:
Boyett. (n.d.). ‘and The beat goes on’ the cardiac conduction system: The wiring system of the heart – boyett – 2009 – experimental physiology – wiley online library. The Physiological Society. https://physoc.onlinelibrary.wiley.com/doi/10.1113/expphysiol.2009.046920
Author links open overlay panelXinwen Liu a, a, b, AbstractCardiovascular disease (CVD) is a general term for a series of heart or blood vessels abnormality that serves as a global leading reason for death. The earlier the abnormal heart rhythm is discovered, CostaC., MuratF., HongS., ElfwingS., RahhalM.M.A., OhS.L., MathewsS.M., LiY., HuangJ., LiuW., AcharyaU.R., YıldırımÖ., BalogluU.B., RomdhaneT.F., TanJ.H., … VincentP. (2021, June 2). Deep learning in ECG diagnosis: A Review. Knowledge-Based Systems. https://www.sciencedirect.com/science/article/abs/pii/S0950705121004494?casa_token=j9kES04IY_QAAAAA%3A9r46qcnJL2PT-xYHWO1DMtUH7EwD1js_gADGdC_sMXmoOxbfrfpHp2eLJ3uGfO5jeZHglwp-UqZq#fig1
What is a Stemi heart attack?. Cleveland Clinic. (2025, March 19). https://my.clevelandclinic.org/health/diseases/22068-stemi-heart-attack
Ventricular tachycardia: Causes, symptoms and treatment. Cleveland Clinic. (2025a, March 19). https://my.clevelandclinic.org/health/diseases/17616-ventricular-tachycardia
What are the symptoms of AFIB?. Cleveland Clinic. (n.d.). https://my.clevelandclinic.org/health/diseases/16765-atrial-fibrillation-afib
What is ventricular fibrillation?. Cleveland Clinic. (2025c, March 19). https://my.clevelandclinic.org/health/diseases/21878-ventricular-fibrillation
Roland, J. (2025, April 16). 3rd degree heart block: Causes, symptoms, outlook. Healthline. https://www.healthline.com/health/heart-disease/3rd-degree-heart-block Bundle branch block: Causes, symptoms & treatment. Cleveland Clinic. (2025a, March 19). https://my.clevelandclinic.org/health/diseases/22938-bundle-branch-block
Moore elaborated on the Unit 11 objective: “Explain how the heart translates an electrical signal to a contraction,” through a detailed description of how an EKG works. In the first four paragraphs, Moore provides an in-depth description and explanation of how the heart’s electrical system looks and operates. After these paragraphs, he explains the use of 12-lead EKGs. This is done in a humble, easy-to-understand way. He explains the function and placement of the 12 leads: “Use 10 electrodes placed around the body. 4 limb (or core) leads are placed on the legs and arms or on the core. 6 leads are placed on the chest. 12 leads contain different waves and segments.” These leads are used to detect rhythms, such as: “…ventricular tachycardia, atrial fibrillation, ventricular fibrillation…” The next three paragraphs elaborate on the symptoms and signs of a normal sinus rhythm, atrial fibrillation, and heart blocks. Normal sinus rhythms are when all of the heart’s electrical pathways are working normally. Ventricular Tachycardia is also described, “…an abnormal heart rhythm that causes the ventricles to beat so fast that it can’t pump enough blood to the body.” Atrial fibrillation occurs when many different electrical impulses occur at the same time. Heart blocks are caused by a blockage in the heart’s electrical system and vary in seriousness. This was overall very interesting to read.