EKG Worksheet #1

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Brigham Young University, Idaho *

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Feb 20, 2024

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W03 Worksheet: EKG, Pulses, & Blood Pressure Follow the instructions below very carefully. Many of the items in this assignment require reading, or videos, or something else to do. Each question has either a text box that can be filled out or a box that can be checked to show completion. Be sure to type out your answers completely and expand the text boxes if you need the additional space. Question 1 --- 4 points EKG The electrocardiogram (ECG or EKG) is the standard clinical tool used to measure the electrical activity of the heart. Data obtained from an EKG provides a graphical representation of the rate, rhythm, and pattern of electrical signals produced by action potentials traveling through cardiac myocytes. Recall that in a cell at rest, the inside of the cell has a negative charge with respect to the outside. That charge reverses when an excitable tissue such as a cardiac muscle cell depolarizes during an action potential. If one group of cardiac myocytes is depolarized (positive inside and negative outside) while another group is at rest (negative inside and positive outside), we have perfect conditions to generate an electrical current. If these oppositely charged areas are then connected by some sort of a conductor, an electrical current will flow. In our bodies, the extracellular fluid acts as a conductor allowing current to flow around the heart. Electrodes placed at strategic locations can then detect that current. By attaching electrodes to a galvanometer, tracings can be recorded that give us information about the magnitude and direction of the currents. Furthermore, by placing the positive and negative electrodes at different locations on the body, the EKG will give different “views” of the electrical activity. Each unique positioning of the electrodes is referred to as a lead. For example, in lead I the positive electrode is placed on near the left arm, and the negative electrode is placed near the right arm. For lead II, the positive electrode is placed on near the left leg, and the negative electrode near the right arm. By placing the electrodes in different positions, a total of 12 standard leads can be obtained, six limb leads, and six chest leads, giving 12 unique views of the electrical activity of the heart. Watch the video, “ Electrical system of the heart ” (links to an external site) ( 9:42 mins; Electrical Systems of the Heart Transcript ) to learn about the electrical activity of the heart (about 10 minutes). This EKG Explained (links to an external site) video will explain the ECG waves ( 17:26 mins; EKG Explained Transcript (links to an external site). You can view the animation of the EKG Explained (links to an external site) here.

Describe in your own words what each wave form means on a standard EKG tracing. Your answer: P-Wave means the electrical activity that occurs as the atria contract, or atrial depolarization. This wave is defined by a tiny, vertical wave precedes every QRS complex. A positive wave deflection brought on by depolarization is also known as a P-wave. QRS System means the depolarization of the ventricles and the electrical activity that occurs during their contraction. This wave is defined by a bigger, usually angular wave. The intracellular electrical signal that travels up from the AV Node to the left ventricle is known as the Q wave. All of the electrical signals that depolarize and go through the Bundle Branches to the ventricles make up the R Wave. The electrical impulses compressing back together, and repolarizing is known as the S wave. T-wave means the recuperation of the ventricles, or ventricular repolarization. This wave is defined by following the QRS complex and is somewhat rounded.

Question 2 --- 2 points Einthoven’s Triangle Image above is downloaded from Wikicommons November 2013. Title: Einthoven Triangle; Author: Kychot; License: Creative Commons Attribution-Share Alike 3.0 Unported Einthoven's triangle is a standard bipolar 3 lead setup for an ECG tracing. By convention, lead I has the positive electrode on the left arm, and the negative electrode on the right arm, and therefore measures the potential difference between the two arms. In the lead II configuration, the positive electrode is on the left leg and the negative electrode is on the right arm. Lead III has the positive electrode on the left leg and the negative electrode on the left arm. These three leads form a triangle (with the heart at the center). This is often referred to as Einthoven's triangle, in honor of Willem Einthoven who developed the electrocardiogram in 1901. It does not matter if the leads are attached to the trunk or the end of the limb (wrists and ankles) because the limb can simply be viewed as a conductor “like a wire” originating from a point on the trunk of the body. Watch Einthoven’s Triangle (links to an external site), which will explain Einthoven’s Triangle and a standard 3-Lead ECG setup further ( 8:26 mins; Einthoven's Triangle Transcript ). If you are attending the campus lab, you will be given instructions on how to use our equipment to set up a 3-lead ECG test and perform it. Research answers for the following questions:

Explain what a PR interval is, and also explain what might cause it to change. (Be detailed. Explain the mechanisms that cause the change, and don’t just list situations that can cause change.) Your answer: The PR interval represents the time between atrial depolarization and ventricular depolarization. Abnormalities in the timing of the PR segment can indicate pathology. Atrial depolarization (the start of the P wave) and ventricular depolarization (the start of the QRS complex) mark the beginning and conclusion of the PR interval. The PR interval typically lasts between 120 and 200 milliseconds. Numerous events that impact either the AV nodal conduction, the atrial conduction, or both might result in changes in the PR interval. Changes in the conduction channel or the pace of electrical impulse production are often the mechanism causing these changes. Some changes could be a delay in conduction, an alternative pathway for conductions, or a change in the autonomic balance affecting the heart. https://www.ncbi.nlm.nih.gov/books/NBK551635/#:~:text=The%20PR%20interval %20represents%20the,atria%20and%20ventricles%20too%20quickly . Question 3 --- 2 points Blood pressure #2 what Explain what a QRS interval is. Also explain what might cause it to change. (Be detailed. Explain the mechanisms that cause the change, and don’t just list situations that can cause change.) Your answer: The heart's ventricles repolarize during the QRS interval. Raising the ion Potassium level will have the effect of changing it. The time elapsed between the first and last Q-wave deflections and the S-wave deflections is represented by the QRS interval. Hyperkalemia is one illness that might alter the QRS interval. The QRS interval may lengthen as a result of this disease. Bundle branch blockages can also happen when they are impacted by an illness or injury that limits their capabilities. Question 4 --- 2 points Explain what a QT interval is, and also explain what might cause it to change. (Be detailed. Explain the mechanisms that cause the change, and don’t just list situations that can cause change.)

Your answer: The time it takes for the ventricle and heart to depolarize and repolarize is known as the QT interval. The Long QT Syndrome is one condition that might create issues with the QT interval. You have this condition from birth. This genetic condition manifests both during and when ventricular repolarization is postponed. The heart then deviates from its regular rhythm, but it soon resumes its regular beat. Question 5 --- 2 points Explain what an ST segment is, and also explain what might cause it to change. (Be detailed. Explain the mechanisms that cause the change, and don’t just list situations that can cause change.) Your answer: The depolarization of the ventricles and the ST interval are correlated. Myocardial ischemia would be the primary reason for a ST segment intervention. Between the conclusion of the S wave and the start of the T wave, there is an isoelectric interval known as the ST interval. A heart attack, often referred to as a myocardial interference, is one mechanism or circumstance that might alter the ST interval. Question 6 --- 2 points Electrical Axis The electrical axis of the heart is the mean or average direction of the action potentials traveling through millions of cells in the heart during depolarization. The QRS complex, which represents ventricular depolarization, is used for the determination of the electrical heart axis. The term electrical heart axis usually refers to the electrical axis in the frontal plane. It is measured by the standard bipolar limb leads I, II and III (I and III are most often used).

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