Bio_165U_ECG__BP_Lab_Report__Sum_23

ECG & Blood Pressure Lab Report ECG and Electrical axis 1. In a typical ECG complex, what electrical event is represented by the: P wave SA node and atrial depolarization PR segment atria contraction QRS (R) wave ventricular depolarization T wave Ventricular repolarization 2. Is ECG an intracellular or extracellular recording of cardiac electrical activity? ECF 3. Draw a rough sketch of Einthoven’s triangle around the heart, and label the leads. Indicate the direction of the lead (negative to positive). 4. Electrode cables are sometimes referred to as leads. However, a lead is actually not a cable, but rather a measure of the change of electrical potential deep within the body between two electrodes. What happens if you 1

reverse the – and + electrodes for a lead (for example, place + on RA and – on LA rather than typical Lead I configuration?) The electrical activity will be inverted, as the polarity of the waveforms will be flipped. 5. Observe differences in recordings between Leads I, II, and III. Which lead: (you may wish to check your answers with an online source) a. accentuates the T wave? Lead I, II & III b. accentuates the R wave? Lead II 6. What is your subject’s heart rate? 58.82 bpm This means his/her R-R interval is 1.02 sec. Show calculations for R-R interval. 1beat/1.02 sec x 60 sec./1 min. = 58.82 bpm 7. Which wave has the greatest amplitude? QRS complex Give your measurement of this wave in lead II: 1.49 mV . Why is this wave the largest? Because it represents the depolarization of the right and left ventricles, which are the heart chambers with more muscle mass compared to the atria 8. Measure and record the duration of your subject’s PR interval: 0.18 s If the interval is > 200 msec, this finding is indicative of the pathology (online research) first degree heart block Extra credit (3 pts) Why are ECG waves very regular and uniform, whereas EMG waves are not? Cardiac muscle contraction is fully synchronized while skeletal muscle contraction is not 9. See pp. 47-49 in your lab manual. Use the ECGs taken from Lead I and Lead III for your subject to plot the electrical axis of your subject’s heart (see figure on 49). Record info below. Lead I QRS amplitude Lead III QRS amplitude Electrical Axis 0.87 mV 0.83 mV 59° 10. Answer the questions from Lab manual p. 49. a. When you take a deep breath, which way does your diaphragm move? downward b. This cause the apex of your heart to move: (circle) medially laterally c. Predict--with breath-holding, the angle of the electric axis will: (circle) increase decrease 11. As a practitioner, you examine a patient who is particularly stocky, even obese. This patient is likely to have (circle all correct): Left axis deviation EA > 105 o right axis deviation EA < 29 o Heart Sounds 1. Heart sounds can be detected by auscultation because valve closure produces vibrations. Can heart sounds and valve issues be detected by electrocardiography? No Briefly explain. An ECG cannot directly detect heart sounds and valve issues, as its primary purpose is to detect the electrical activity of the heart. It can detect arrhythmia (abnormal heart rhythms) and abnormal electrical events which can 2