The lead ECG misleadingly only has 10 electrodes sometimes also called leads but to avoid confusion we will refer to them as electrodes. These comprise 4 limb electrodes and 6 chest electrodes. When electrical activity or depolarisation travels towards a lead, the deflection is net positive. When the activity travels away from the lead the deflection is net negative. This can often be seen in V4 see Figure 3.
The ECG can be broken down into the individual components. For the purpose of this we will look at lead II see Figure 4. There are many different systems to interpret the ECG.
This system ensures you will never miss anything:. Our medical articles are the result of the hard work of our editorial board and our professional authors. Strict editorial standards and an effective quality management system help us to ensure the validity and high relevance of all content. Read more about the editorial team, authors, and our work processes. Already registered? Your email address will not be published. Although this specific article does not address ECG changes which can occur with abnormal calcium levels, you are correct that both hypocalcemia and hypercalcemia would have effects on the ST segment duration, with hypocalcemia making it longer while hypercalcemia would make it shorter.
Hi Please note that the Tenting of T wave occurs in Hyperkalaemia. May be typographical error. It is given as hypercalcaemia in the article. You are correct and we have changed it. Hyperkalemia causes tenting of the T-wave, but is only seen in less than half of patients with elevated potassium. Thanks for pointing out the error. Thanks for pointing this out, and sorry for the delay in answering. Some background may be helpful here. Although the conventional definition of bradycardia is a heart rate less than 60 beats per minute with a normal P wave vector on the surface ECG, several professional societies, including the Am.
Heart Assoc, define bradycardia as a rate less than A rate less than 50 beats per minute may in fact be a more pragmatic definition, as most people with sinus rates in the 50s are asymptomatic. Many well-trained athletes will have rates in the low 50s or even the high 40s.
It is important to note that the rate at which a patient is labeled as having bradycardia is somewhat age dependent, and the rate should always be correlated with any new symptoms. Best, Stan. Lecturio is using cookies to improve your user experience. By continuing use of our service you agree upon our Data Privacy Statement.
Are you more of a visual learner? A collection of data interpretation guides to help you learn how to interpret various laboratory and radiology investigations. A comprehensive collection of medical revision notes that cover a broad range of clinical topics. A collection of anatomy notes covering the key anatomy concepts that medical students need to learn.
A collection of interactive medical and surgical clinical case scenarios to put your diagnostic and management skills to the test. Each clinical case scenario allows you to work through history taking, investigations, diagnosis and management. A collection of free medical student quizzes to put your medical and surgical knowledge to the test! Table of Contents. This guide demonstrates how to read an ECG using a systematic approach.
If a patient has a regular heart rhythm their heart rate can be calculated using the following method:. As a result, you need to apply a different method:.
Mark out several consecutive R-R intervals on a piece of paper, then move them along the rhythm strip to check if the subsequent intervals are similar. If you are suspicious that there is some atrioventricular block AV block , map out the atrial rate and the ventricular rhythm separately i. As you move along the rhythm strip, you can then see if the PR interval changes , if QRS complexes are missing or if there is complete dissociation between the two.
Cardiac axis describes the overall direction of electrical spread within the heart. Read our cardiac axis guide to learn more. If P waves are absent and there is an irregular rhythm it may suggest a diagnosis of atrial fibrillation. The PR interval should be between ms small squares.
The tough part is identifying the more subtle ECG changes. Know when ST segment elevation is due to ischemia and when it is due to other causes, including left ventricular aneurysm or left ventricular hypertrophy.
Some repetition and memorization is required. The list of things that go into this category is long. Review the list below. You can never look at too many lead ECG tracings. In real life, you see full lead ECG tracings — so that is how you need to test yourself. Whether you are a medical student in clinical rotations, an EMT or an internist in practice, or another health care professional, looking at the ECGs that you will encounter in everyday practice is important.
See how the ECG fits the clinical scenario. Sometimes the best way to remember an ECG finding is to associate it with an interesting case that you experienced personally. If you can put yourself in a position to teach students or your colleagues about ECGs, you will solidify your skills tremendously.
Keep reviewing. This will keep things fresh in your mind and will even introduce you to rare ECG tracings. Back to Healio.
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