ECG 1 Lecture Notes PDF

ECG 1 February 22, 2024 J. Mohan, PhD. Lecturer, Physiology Unit, Faculty of Medical Sciences, U.W.I., St Augustine. Room 104, Physiology Unit. [email protected] February 22, 2024 Dr. J. Mohan 1 References:  Hall, J.E. (2021). Guyton and Hall Textbook of Medical Physiology. 14th Edition, El...

ECG 1 February 22, 2024 J. Mohan, PhD. Lecturer, Physiology Unit, Faculty of Medical Sciences, U.W.I., St Augustine. Room 104, Physiology Unit. [email protected] February 22, 2024 Dr. J. Mohan 1 References:  Hall, J.E. (2021). Guyton and Hall Textbook of Medical Physiology. 14th Edition, Elsevier, Saunders.  Costanzo L.S. (2014). Physiology. 5th Edition, Elsevier, Saunders.  Costanzo L.S. (2019). BRS Physiology (Board Review Series). 7th Edition, LWW.  Koeppen B.E. & Stanton B.A. (2010). Berne & Levy Physiology. 6th Edition. Mosby, Elsevier.  Marieb, E. & Hoehn, K. (2010). Human Anatomy & Physiology. 8th Edition, Pearson, Benjamin Cummings.  Le T, Hwang W, Muralidhar V, White J. (2017). First Aid for the Basic Sciences: Organ Systems, 3rd Edition (First Aid Series) 3rd Edition, McGraw-Hill.  Klabunde, Richard E. Cardiovascular Physiology Concepts. (3rd Edition). Wolters Kluwer, 2022. February 22, 2024 Dr. J. Mohan 2 Objectives 1.1. Describe properties of a sound waves. Record the an physical ECG and provide basic interpretation of an ECG including rate, rhythm, and axis. 2. Explain transduction and processing of sound. 2. Recognize ECG features of tachycardia, bradycardia, block, analysis Wolff-Parkinson-White 3. Describe the useAV of Fourier in the processing of(WPW) sound. syndrome, bundle branch block, flutter, and fibrillation. 4. Describe Brainstem Auditory Evoked Potentials (BAEPs) and their clinical applications. 3. Describe ECG changes associated with ventricular hypertrophy, myocardial ischemia and changes in 5. Explain the principles underlying audiometric tests. extracellular electrolytes. February 22, 2024 Dr. J. Mohan 3 12 – lead ECG Recording h t t p http://www.imperialendo.co.uk/Newskills/ecg/index.html February 22, 2024 Dr. J. Mohan 4 Leads of the ECG Recording Figure 1-36; Le T et al, 2017 February 22, 2024 Dr. J. Mohan 5 Components of the ECG Normal EKG Paper Speed 25 mm/sec 0.04 sec ≈ 0.83 sec J 0.12-0.20 sec 0.36-0.40 sec Time and voltage calibrations are standardized as shown. February 22, 2024 Dr. J. Mohan Figure 11-1; Guyton& Hall, 6 2021 Components Normal EKG of the ECG P wave = atrial depolarization. , voltage ~ 0.1-0.3 mv PR interval =time interval between onset of atrial depolarization and onset of ventricular depolarization. QRS complex = depolarization of ventricles, consisting of the Q, R, and S waves. voltage ~ 1.0-1.5 mv from top of R wave to bottom of S wave QT interval = time interval between onset of ventricular depolarization and end of ventricular repolarization. R-R interval = time interval between 2 QRS complexes. T wave = ventricular repolarization. voltage ~ 0.2-0.3 mv ST segment = completed ventricular myocardial depolarisation. Time and voltage calibrations are standardized as shown. J point = end of the S wave, isoelectric point February 22, 2024 Dr. J. Mohan 7 12 – lead ECG Recording -another look Standard 12-lead ECG is a 10-second strip Bottom 1 or 2 lines – full rhythm strip of a specific lead Other leads will span only about 2.5 seconds https://www.healio.com/cardiology/learn-the-heart/ecg-review/ecg-interpretation-tutorial/approach-to-ecg-interpretation February 22, 2024 Dr. J. Mohan 8 Slide showing normal duration of ECG components Biopac Manual, Lesson 5, p 78 4th Edn February 22, 2024 Dr. J. Mohan 9 Depolarisation and Repolarisation Waves REST +++++ ----- Positive charge on the inside of cell relative to the outside = depolarisation By convention, the direction of an electrical current is said to flow from areas that are negatively charged to those that are positively charged Voltmeter – records the electrical potential from cell surface A. Partial depolarisation – the potential inside the fiber becomes slightly positive inside and negative outside – depolarisation current travels from left to right (towards the +ve electrode) – voltmeter records an upward deflection single cardiac muscle fiber February 22, 2024 Figure 11-2; Guyton & Hall, 2021; modified Dr. J. Mohan 10 Depolarisation and Repolarisation Waves REST +++++ ----- Positive charge on the inside of cell relative to the outside = depolarisation By convention, the direction of an electrical current is said to flow from areas that are negatively charged to those that are positively charged Voltmeter – records the electrical potential from cell surface B. Full depolarisation ‒ voltmeter recording returns to the baseline (both electrodes are now in areas of equal negativity) ‒ completed wave is a depolarisation wave (it results from the spread of depolarisation along the muscle fiber membrane) Figure 11-2; Guyton & Hall, 2021; modified single cardiac muscle fiber February 22, 2024 Dr. J. Mohan 11 Depolarisation and Repolarisation Waves REST +++++ ----- Positive charge on the inside of cell relative to the outside = depolarisation By convention, the direction of an electrical current is said to flow from areas on cell surface that are negatively charged to those that are positively charged Voltmeter – – records the electrical potential from cell surface C. Partial repolarisation ‒ positivity returns to the outside of the fiber at the position of the left electrode while the right electrode is in an area of negativity (so, flow of electrical current opposite to A; away from +ve electrode) – see blue arrow – voltmeter records a downward deflection single cardiac muscle fiber February 22, 2024 Figure 11-2; Guyton & Hall, 2021; modified Dr. J. Mohan 12 Depolarisation and Repolarisation Waves REST +++++ ----- Positive charge on the inside of cell relative to the outside = depolarisation By convention, the direction of an electrical current is said to flow from areas that are negatively charged to those that are positively charged Voltmeter – records the electrical potential from cell surface D. Full repolarised ‒ voltmeter recording returns to the baseline (both electrodes are now in areas of equal positivity) ‒ completed wave is a repolarisation wave (it results from the spread of repolarisation along the muscle fiber membrane single cardiac muscle fiber February 22, 2024 Figure 11-2; Guyton & Hall, 2021; modified Dr. J. Mohan 13 Depolarisation and Repolarisation in the intact heart in the intact heart, the sequence by which regions repolarize is actually opposite to that of their depolarization https://microbenotes.com/electrocardiogram-ecg/ February 22, 2024 Dr. J. Mohan 14 Bipolar Limb Leads 3 Standard Leads Bipolar means that the ECG is recorded from two electrodes on different sides of the heart (i.e. on the limbs) One terminal connected to − One terminal connected to + Figure 11-6; Guyton & Hall, 2021 February 22, 2024 Dr. J. Mohan 15 Bipolar Limb Leads Lead I—The negative terminal of the ECG is connected to the right arm, and the positive terminal is connected to the left arm measures the potential difference between the two arms Lead II—The negative terminal of the ECG is connected to the right arm, and the positive terminal is connected to the left leg Lead III—The negative terminal of the ECG is connected to the left arm, and the positive terminal is connected to the left leg In these 3 limb leads, an electrode on the right leg serves as a reference electrode for recording purposes February 22, 2024 Dr. J. Mohan 16 Bipolar Limb Leads These three bipolar limb leads roughly form an equilateral triangle (with the heart at the center) that is called Einthoven's triangle Einthoven’s Law: the sum of the voltages in leads I and III = the voltage in lead II If Lead I = 0.5 mV and Lead III = 0.7 mV Lead II = 0.5 + 0.7 = 1.2 mV. Figure 11-6; Guyton & Hall, 2021 February 22, 2024 Dr. J. Mohan 17 Bipolar Limb Leads Einthoven’s Law I + III = II Figure 11-7; Guyton & Hall, 2021 February 22, 2024 Dr. J. Mohan 18 Augmented Unipolar Leads Augmented unipolar limb Leads are aVR, aVL, and aVF. Two terminals connected to −, one terminal connected to + aVR :+ right arm, − left arm, − left leg aVL: + left arm, − right arm, − left leg aVF: + left leg, − left arm, − right arm Two terminals connected to – One terminal connected to + Figure 11-10; Guyton & Hall, 2021 February 22, 2024 Dr. J. Mohan 19 Chest (precordial) Leads Chest leads (precordial leads) known as V1–V6 are very sensitive to electrical potential changes underneath the electrode. Chest electrode connected to + terminal; Negative (or indifferent) one simultaneously connected through equal electrical resistance to right arm, left arm, and left leg Figure 11-9 Figures 11-8 & 11-9; Guyton & Hall, 2021 February 22, 2024 Dr. J. Mohan 20 ECG Leads—Summary Chest (precordial) leads V1, V2 in 4th intercostal space V4−V6 in 5th intercostal space V3 between V2 and V4 Bipolar and augmented unipolar limb leads Figure 11-11; Guyton & Hall, 2021 February 22, 2024 Dr. J. Mohan 21 12 – lead ECG Recording- yet another look h t t p http://www.imperialendo.co.uk/Newskills/ecg/index.html February 22, 2024 Dr. J. Mohan 22 ECG Leads—Summary Chest leads V1, V2 in 4th intercostal space V4−V6 in 5th intercostal space V3 between V2 and V4 Bipolar and augmented unipolar limb leads From Mirvis DM, Goldberger AL: Electrocardiography. In Zipes DP, Libby P, Bonow RO, et al. (eds): Braunwald’s Heart Disease, 11th ed. Philadelphia: Elsevier, 2019. Fig 12.3. February 22, 2024 Dr. J. Mohan 23 Basic Interpretation of the ECG 1. 2. 3. 4. 5. 6. 7. Check voltage calibration Heart rhythm Heart rate Intervals (PR, QRS, QT) Mean QRS axis Abnormalities of the P wave Abnormalities of the QRS (hypertrophy, bundle-branch block, infarction) 8. Abnormalities of the ST segment and T wave 9. Compare with baseline recordings February 22, 2024 Dr. J. Mohan 24 Basic Interpretation of the ECG Voltage calibration 1.0-mV vertical signal at beginning/end of recording document the voltage calibration 1-mm vertical box =0.1 mV; 1 mV = 10-mm vertical deflection https://www.healio.com/cardiology/learn-the-heart/ecg-review/ecg-interpretation-tutorial/approach-to-ecg-interpretation February 22, 2024 Dr. J. Mohan 25 Basic Interpretation of the ECG Heart rhythm normal cardiac rhythm, = Normal Sinus Rhythm (NSR- SA node initiates AP’s which access normal atrial & ventricular conduction pathways) 1. Rate ~ 60 - 100 bpm; < 60 bpm : sinus bradycardia; > 100 bpm : sinus tachycardia 2. Normal P wave morphology and axis (upright in I, II, III) 3. Each P wave is followed by a QRS complex 4. Narrow QRS complexes (< 100 ms wide) 5. The PR interval is constant – 0.12 sec or greater i.e. 3 small boxes https://litfl.com/normal-sinus-rhythm-ecg-library/ February 22, 2024 Dr. J. Mohan 26 Basic Interpretation of the ECG Heart rhythm Regular – equal distance between R waves Irregular – varying distances between R waves  Regularly Irregular- varying distances between R waves occur in a pattern  Irregularly irregular- no pattern February 22, 2024 Dr. J. Mohan 27 Basic Interpretation of the ECG Heart Rate 2 different rates that can be determined on an ECG Atrial rate = frequency of the P waves The ventricular rate = frequency of the QRS complexes In the absence of disease, the atrial rate = ventricular rate Third degree heart block or ventricular tachycardia atrial rate ≠ ventricular rate: “AV dissociation” b February 22, 2024 Dr. J. Mohan 28 Basic Interpretation of the ECG Heart Rate Calculation 1 (Small Square Method) Normal rate is 60–100 bpm (bradycardia < 60 bpm, tachycardia > 100 bpm) ECG speed is 25 mm/sec (1 mm = 1 small box), HR can be calculated by counting the number of small boxes between two consecutive QRS complexes (also known as the R-R distance): Heart rate = 25 mm/sec × 60 sec/min Number of mm between 2 beats February 22, 2024 Dr. J. Mohan 29 Basic Interpretation of the ECG Heart Rate Calculation 2 (R wave Method) This calculation is based on the entire ECG being 10 seconds Counting the number of QRS complexes and multiply by six= the number per minute— (because 10 seconds times six equals 60 seconds or 1 minute) This is a better method when the QRS complexes are irregular, as during atrial fibrillation, in which case the RR intervals may vary from beat to beat 3 sec markers February 22, 2024 OR Count the number of QRS complexes in a 6 sec strip and multiply by 10 Dr. J. Mohan 30 Basic Interpretation of the ECG Heart Rate Calculation 3 (Large Square Method) The count-off method is a fast way to measure HR It uses the sequence “300-150-100-75-60-50” Count down the number of large boxes between two QRS complexes. = R-R distance 300/(R-R distance in #large boxes) = bpm February 22, 2024 Dr. J. Mohan 31 Examples of 10 sec ECG Strips 1 Questions What is ventricular rate ? ‒ 1500/RR distance (small boxes) ‒ Count # R waves in 10 sec; multiply x 6 (since it’s a 10 sec strip) ‒ 300/RR distance (large boxes) What is atrial rate? What is the rhythm? 2 3 February 22, 2024 Dr. J. Mohan 32