/n Resting Mean Amplitude (mV) Post-Exercise Mean Amplitude (mV) P Wave R Wave T Wave P Wave R Wave T Wave Lead I 0.047 0.933 0.395 0.079 0.663 0.2823 Lead II 0.065 0.351 0.372 0.88 0.881 0.2187 Lead III -0.027 -0.804 -0.238 -0.018 -1.19 -0.0857 aVR -0.068 -0.551 -0.449 -0.081 -0.594 -0.293 aVL 0.038 0.979 0.255 0.068 -0.494 0.197 aVF -0.246 -0.527 0.398 0.041 0.951 0.1057 RR-Time (seconds) RR-Time (seconds) 0.61625 0.4825 DO NOT CHANGE THIS SPREADSHEET ENTER DATA FOR YOUR TEAM UPLOAD TO BOX WHEN COMPLETE NAME THIS FILE: TeamLxxx_lab6xlsx where xxx is your team number/n BE 312 Lab #6 Lab 6: The Six-Lead Electrocardiogram I. Background The cardiac cycle involves a sequential contraction of the atria and the ventricles. These contractions are triggered by the coordinated electrical activity of the myocardial cells in the heart. The electrical currents produced by the heart are large and can be recorded through electrodes placed on the skin. The recording is known as an electrocardiogram or ECG. When diagnosing the health of the heart, electrocardiograms are recorded from specific positions around the heart and analyzed to determine existence of cardiac disease. These positions or combinations of positions are referred to as leads or views. However, the data collected from this experiment should not be used to determine the health of fitness of any subject's heart. ECG Components Cardiac action potentials contain three phases. In addition to the rapid depolarization and repolarization of the membrane potential in nerve and muscle action potentials, cardiac action potentials contain a plateau depolarization after the period of rapid depolarization. This plateau is pronounced in the potentials from ventricular fibers. A recording from a single lead, like Lead I in Figure 1, is adequate for demonstrating the basic components of the ECG. There are specific waveforms associated with the electrical activity of the atrial and ventricular fibers. These events and waveforms are: • The atrial depolarization which produces the P wave. The atrial repolarization and the ventricular depolarization which produce the QRS complex. The ventricular repolarization which produces the T wave. NormalECG-WX214-None-LabScribe v3 File Edit View Tools Settings Advanced External Devices Help @林本 Default View Off < > V2-V1 Add Function A1ECG 1.042 1- 09- 08- 0.7- 06- 05- 04- 0.3- 02- T T P 0.1- 0- -0.1- -0.2- -0.3- -04- -05- -06- -07- C1:Comp Ch 1 2.196 sec 0.865 S 2.624 sec 3.052 sec 3.480 sec N < 3.906 sec Done Calculating data for Block 1 Figure 1. ECG trace in the Main window with labels showing the P, QRS and T waves. BE 312 Lab #6 Multiple Leads There are twelve common cardiographic leads, six limb and six chest. The six limb, or coronal, leads are in the frontal plane of the body which is the plane parallel to the floor when the subject is reclining. The six chest, or precordial, leads are in the transverse plane of the body which is the plane perpendicular to the floor when the subject is reclining. Examining the electrical activity of the heart from twelve different angles can be a valuable clinical tool. The way that currents pass through different parts of the heart can indicate abnormalities or problems such as: hypertrophies, bundle branch or fascicular blocks, cushion defects, pulmonary hypertension, and more. By measuring the magnitudes of the electrical activity from different directions, the areas of the heart that are abnormal can be identified. A clinician can gain a better understanding of the health of the heart by having more views of that organ. In this experiment, students will place five electrodes on a subject and be able to record six different views of the subject's heart. Each view is often referred to as a lead. This is possible because the electrodes are used in different combinations, as either recording or reference electrodes, to create six different views of the heart. The standard limb leads, or bipolar leads, measure the potential difference between a positive recording electrode and a negative recording electrode. The standard limb leads are: • . Lead I (I): Positive electrode on the left arm and the negative electrode on the right arm. Lead II (II): Positive electrode on the left leg and the negative electrode on the right arm. Lead III (III): Positive electrode on the left leg and the negative electrode on the left arm. The augmented limb leads, or unipolar leads, measure the potential difference between a signal recording electrode and a combination of other electrodes that form a composite negative electrode. Each augmented limb lead has a view of the heart that at a right angle to one of the standard limb leads. The augmented limb lead are: • aVR: Positive electrode is on the right arm and the electrodes on the left arm and the left leg form a composite negative electrode. aVL: Positive electrode is on the left arm and the electrodes on the right arm and the left leg form a composite negative electrode. aVF: Positive electrode is on the left leg and the electrodes on the right arm and the left arm form a composite negative electrode. The diagram that describes the axes of the leads and the vectors of the ECG signals directed toward the leads is known as Eithoven's Triangle (see Figure 2). For example, the positive electrode in Lead I, which is on the left arm, has a view of the electrical activity of the heart while it is looking toward the right shoulder. As shown in the same figure, the axis of Lead I is parallel to a line that connects the shoulders. By definition, the axis of Lead I is defined as zero degrees. 2 BE 312 Lab #6 In a subject with a normal heart in a normal orientation, the ECG recording from Lead II will yield an R wave with the highest amplitude of all the limb leads. In Lead II, the positive electrode on the left leg has a head-on view of the electrical activity of the heart because this electrode is facing the right shoulder. The axis of Lead II is right through the septum that divides the ventricles. the septum is the site of the tissue bundles responsible for carrying the depolarization of the heart to the muscle fibers in the apex of the heart. By definition, the axis of Lead II is +60 degrees. Lead I (0° axis) Right Arm + Left Arm aVR (-1500) aVL. (300) Lead II (+600) Lead III (+1200) aVF (+900) Left Leg Figure 2. Einthoven's Triangle identifying the axes of the six limb leads. In this lab, students will attach one ground and four recording electrodes to the subject and record electrocardiograms from the positions known as Lead I and Lead II. The other four limb leads will be synthesized from the recordings from Leads I and II and a series of equations. These equations are incorporated into the LabScribe software as computed functions in the add function pull-down menu. They only need to be activated to work. If Leads I and II are recorded on Channels 1 and 2, respectively, the limb lead computed functions take the raw data recorded on these channels and derive the electrocardiograms for the other four limb leads. These leads can be displayed on any of the six available channels. The derivations used to synthesize ECG's for different leads are appended to the end of this experiment. LabScribe recording software is programmed to perform the measurements described by these equations in the Appendix. II. Setup Equipment Required • PC or Mac Computer • IXTA, USB cable, IXTA power supply • ROAM ECG 3 BE 312 Lab #6 • Alcohol swabs • Disposable ECG electrodes Settings Human Heart ->SixLeadECG-ROAM ROAM/ECG Cable Setup 1. Locate the ROAM, disconnect it from the dock (Figure 3) and place the electrodes as shown in Figure 4. iWorx TA-ROAM A1 A2 ROAM Wireless Wire LV Stim A3 A4 A5 A6 A7 PT 2 S1 S2 RAM Figure 3. The TA and ROAM removed from the dock. Figure 4. Placement of ECG electrodes. BE 312 Lab #6 2. Instruct the subject to sit quietly with their hands in their lap. Experiment Exercise 1: Six Lead ECG from Resting Subject and Analysis Aim: To record a Six Lead ECG from a resting subject and determine the QRS axis of the subject's heart. Approximate Time: 20 minutes Procedure 1. Click on the Record button. 2. Click on the AutoScale All button. Your recording should look like Figure 5 below. • If the signal on the Lead I and the Lead II channels is upside down when compared to trace click on the downward arrow to the left of the channel title and select the Invert function. The trace should now look like the one in Figure 5. Normal6LeadECG-IWX214-None-LabScribe v3 File Edit View Tools Settings Advanced External Devices Help X < V2-V1 Add Function AlLead 0.001 0.00- 0.75m- 0.25m- -0.25m- A2:Lead 0.001 0.00- 0.75m- 50.25m- -0.25m- -C1:Lead -0.000 -0.2m- -0.4m- Rm- C2Lead aVR 0.001 -0.5m- -0.00 C3:Lead aVL 0.001 0.00- -0.75m- 50.25m- -0.25m- C4VF 0.000 0.5m- 0.3m- 0.1m- 1m- 10.986 sec N < Done Calculating data for Block 1 11.736 sec M Default View Off REC 12.486 sec 13.236 sec 13.981 sec > Figure 5. Six lead ECG generated by recording Leads I and II on Channels 1 and 2, respectively. The remaining limb leads are derived by computed functions. 3. When you have a suitable trace, type Resting ECG/Pulse in the Mark box to the right of the Mark button. Click the mark button to attach the comment to the data. Record for at least 5 minutes. 4. Click Stop to halt recording. 5. Select Save As in the File menu, type a name for the file. Click on the Save button to save the data file. 5/nIII. Report Questions 1. Include completed Table 1 for your one subject in the report. For these questions (2-8) answer based on your own team data for Exercise 1 2. From which leads were upright R waves recorded? From which electrode (left arm, right arm, left leg, or right leg) and along which axis (-150, -30, 0, 60, 90, 120 degrees) were these leads "looking" at the depolarization of the ventricle? You may need to refer to the Background information to answer these questions. 3. From which leads were inverted R waves recorded? From which electrode (left arm, right arm, left leg, or right leg) and along which axis (-150, -30, 0, 60, 90, 120 degrees) were these leads looking at the depolarization of the ventricle? 4. State which lead is the isoelectric lead. 5. What is the QRS axis of the subject's heart? Is the QRS axis of your subject within the normal range of the QRS axis? Look for a reference to find the normal range. 6. Which ECG lead provided the largest R wave for the subject? 7. Which lead is closest to the QRS axis of the heart? 8. Using the Appendix equations and the Lead I, Lead II, Lead III data, calculate the augmented values and compare to the values you obtained using LabScribe.

Fig: 1