Posted by My project is going to look at how the heart translates an electrical signal to a contraction, and what happens when it does not fire correctly. In a normal, healthy individual, the electrical activity of the heart is straightforward. First, an excitation signal is sent from your autonomous nervous system to your sinoatrial node (SA node) which is the pacemaker of the heart. In a normal sinus rhythm, the SA node fires approximately 60-100 times per minute in a healthy adult. After the excitation signal leaves the SA node, it then travels down to the atrioventricular (AV node) which delays the excitation signal until the atria have emptied of blood. Once the signal has been delayed at the AV node, it then travels down the bundle of His, and then on to the Purkinje fibers. The Purkinje fibers are responsible for sending the electrical signal to both the left and right ventricles. Many different factors can affect this electrical process, and that is what I am going to cover next.
When medical professionals are reading an EKG, there are a few things that we look at to ensure that the heart is functioning properly and can circulate blood to all the body’s tissues. Firstly, we look for what is called a P-wave. The P-wave is a small bump before the QRS complex that shows the depolarization of the atria, meaning when the electrical signal passes through the atria. The presence of a P-wave in an EKG shows that the atria are beating properly. Next, the QRS complex is the big wave immediately following the P-wave. This complex shows the depolarization of the ventricles. The repolarization of the atria also occurs at this time, but it is hidden behind the QRS complex and unable to be seen. The ST-segment, or the line between the S and the T wave, is also an important piece of the EKG, as elevation here could suggest an ST-Elevation Myocardial Infarction (STEMI) otherwise known as a heart attack. Finally, the T wave is seen as the last wave in the formation, this is the repolarization of the ventricles.
Now that we know a little bit about what each part of the EKG means, we can investigate some rhythms that might be seen on an EKG. The first being normal sinus rhythm (NSR), this is when the heart is contracting normally at a normal rate between 60-100 BPM in adults. Next, there is sinus tachycardia. Sinus tachycardia is a rhythm that is sinus, meaning the electrical activity is coming from the SA node, but it is going faster than normal, usually at a rate of around 100-150 BPM. Lastly for the sinus rhythms, there is sinus bradycardia. This rhythm, like the two previous, is also a sinus rhythm but it is just slower than normal, contracting at a rate below 60 BPM. There are many different causes for both sinus tachycardia and bradycardia including drugs, heart defects, electrolyte imbalances, and stress. Another common rhythm that we see quite frequently is atrial fibrillation. This rhythm is when the atria are not firing correctly, and a P-wave is not seen on an EKG. A-Fib will also be an irregular rhythm and can have rates ranging from anywhere between 80-120 BPM.
Next, we will talk about some of the more dangerous rhythms that can occur in the heart. These include STEMI, elevated T-waves, and SVT. First, a STEMI is a heart attack, and it can be seen on the EKG when the ST-segment is not at its baseline. This suggests a complete blockage in a coronary artery, and it is very important to get treatment immediately. Second, elevated T-waves can be seen in patients who are experiencing hyperkalemia, or an abnormally high potassium. In extreme cases, the T-waves overcome even the QRS complexes. Finally, supraventricular tachycardia (SVT) is a tachycardia that is occurring above the ventricles, hence the name. Patients experiencing SVT will commonly have shortness of breath and chest pains. Medication and sometimes defibrillation may be needed to convert patients out of this rhythm into a normal sinus rhythm.
In this section, I will cover the rhythms that can be seen that need immediate interventions for the patient to recover. First, Torsades de Pointes is a fast rhythm that does not effectively pump the heart, and usually patients do not have a pulse with this rhythm. Ventricular fibrillation (V-Fib) and ventricular tachycardia (V-Tach) are both rhythms where the ventricles are not properly pumping, usually from an electrical abnormality within the heart. Torsades and V-Fib require defibrillation and possibly medications to restore normal heart function. V-tach is unique because patients may have a pulse with V-tach. Lastly, asystole, as the name suggests, is no electrical activity within the heart. This rhythm is the product of cardiac arrest and is a non-shockable rhythm. In asystole, there is no electrical activity in the heart and therefore defibrillation will not resolve the issue. CPR and medications need to be given to hopefully convert the patient to a shockable rhythm like V-Fib or V-Tach where defibrillation can occur and possible restore a somewhat normal rhythm that is compatible with life.
The last abnormal EKG reading that I wanted to touch on sometimes can be caused by a condition that is not related to the heart at all. Spiked helmet sign is when there is extreme ST Elevation occurring on both sides of the QRS complex. This EKG finding is indicative of imminent death, and interventions need to be taken immediately for the patient to live. Spiked helmet sign on an EKG can be caused by sepsis, anoxic brain injury, trauma, acute abdomen, and pneumothorax.
In conclusion, it is important that medical professionals have a deep understanding of the heart and its conduction system to make a correct diagnosis on a patient and give the appropriate treatments. Knowing how each step of the heart contracting corresponds to each wave on an EKG reading can be the difference between life and death in patients.
Citations:
- Littmann, L., & Monroe, M. H. (2011). The “spiked helmet” sign: a new electrocardiographic marker of critical illness and high risk of death. Mayo Clinic proceedings, 86(12), 1245–1246. https://doi.org/10.4065/mcp.2011.0647
- Neal Robert Abarbanell, Mary Ann Marcotte, Beata A. Schaible, Glenn E. Aldinger; Prehospital management of rapid atrial fibrillation: Recommendations for treatment protocols; The American Journal of Emergency Medicine;Volume 19, Issue 1,2001,Pages 6-9; ISSN 0735-6757; https://doi.org/10.1053/ajem.2001.18124.
- EMS1. (2023, June 6). Prehospital cardioversion of cardiac dysrhythmias. EMS1. https://www.ems1.com/cardiac-care/articles/prehospital-cardioversion-of-cardiac-dysrhythmias-vAANZKyl7wWQeSwQ/
- Cleveland Clinic. (2021). Heart Conduction: What Is It & How It Works. Cleveland Clinic. https://my.clevelandclinic.org/health/body/21648-heart-conduction-system
- The T Wave – Sinus Rhythm – Normal Function of the Heart – Cardiology Teaching Package – Practice Learning – Division of Nursing – The University of Nottingham. (n.d.). Www.nottingham.ac.uk. https://www.nottingham.ac.uk/nursing/practice/resources/cardiology/function/t_wave.php
In Karley’s Steam project, we are able to understand that EKG reading is very important for medical professionals so that they can diagnose a patient correctly and give the appropriate treatments they need in cases of abnormal heart rhythms. We were able to see the normal sinus rhythm, in which the heart is contracting normally; the Sinus tachycardia rhythm, where the heart rate is faster than normal; and the sinus bradycardia rhythm, where the heart rate is slower than normal. The STEMI, elevated T-waves, and SVT are the more dangerous rhythms that can occur in the heart. These require immediate treatment. Immediate interventions may be necessary for patients with life-threatening rhythms like the Torsades de Pointes in which patients don’t usually have a pulse, and the ventricular fibrillation, and asystole rhythms. Another abnormal EKG reading that Karley mentioned, was the Spiked helmet sign. This condition is not related to the heart, but rather caused by sepsis, anoxic brain injury, trauma, acute abdomen, or pneumothorax. I think that Karley’s visual was very clear and easy to understand, and she did a great job covering her objective.