Electrocardiography (ECG) DR. AMIR SAMADIAN M.D. DEPARTMENT OF PHYSIOLOGY SPRING 2020 Electrical activation of Heart In order for the Heart to pump blood : 1.Ventricles must be electrically activated 2.Contract For that : Generation of Action Potential in Pacemaker cell (SA node) à conduction and propagation of AP by specialized conductive tissue (GAP junctions!)à Excitation/depolarization of contractile cardiomyocytes à Contraction of cardiac muscle cells 2 major type of cardiac cells 1. Conductive cells (pacemaker cells) : -Automatic excitation/Generation of AP (pacemaker activity) -Conduction of excitation 2. Contractile cells : -Contraction & generation of force ( Atrial & ventricular working cardiomyocytes) Cardiac cells (Gap Junctions) https://teachmephysiology.com/wp-content/uploads/2017/03/cardiac-muscle-structure-2.jpg Cardiac conductive cells 1.Sinoatrial node (SA NODE) à main pacemaker (Automaticity!) à 60-100 bpm 2.Atrioventricular node (AV NODE) 3.Bundle of his 4.L + R bundle branches 5.Purkinje system Pacemaker cells Conductive pathway CONDUCTION VELOCITY •Reflects the time required for excitation to spread throughout cardiac tissue. •Depends on the size of the inward current during the upstroke of the action potential. The larger the inward current, the higher the conduction velocity. •Conduction fastest in the Purkinje system. •Conduction is slowest in the AV node (seen as the PR interval on the ECG), allowing time for ventricular filling before ventricular contraction. If conduction velocity through the AV node is increased, ventricular filling may be compromised. Cardiac action potential Pacemaker action potential (HIGH YIELD) elated image AUTONOMIC EFFECTS ON HR AND CV By inverse frequency effect! PSNS HAS NO DIRECT (-)IONOTROPIC EFFECT! AUTONOMIC EFFECTS ON HR AND CV AUTONOMIC EFFECTS ON HR AND CV Effect of ANS on Pacemaker cells & HR mage result for sa node sympathetic AUTONOMIC EFFECTS ON HR AND CV Contractile cardiomyocytes action potential http://www.pathophys.org/wp-content/uploads/2013/10/ActionPotential-1024x848.png COMPARISON OF DIFFERENT ACTION POTENTIALS Výsledok vyhľadávania obrázkov pre dopyt cardiac automaticity EKG - Basics 1.When Heart cells go from polarized (-resting state) to depolarized (+action potential) à a wave of electrical current is generated 2. this wave of depolarization (current) moves through Cardiac cells à causes contraction ! 3.ECG records this electrical activity by mean of 10 skin electrodes (4limb + 6chest) 4.Electrodes give us 12 real time picture of heart from different angles (12 leads) 5.Information is recorded on a ECG paper as Positive(+) or Negative(-) deflection 6.A wave of depolarization moving toward a positive electrode produces a + deflection. 7.A wave of depolarization moving away from a positive electrode records a - deflection. 8. Wave of depolarization ECG Electrodes Positive & Negative Deflections on ECG paper 12 lead ECG 1.6 limb lead ( I , II, III, aVL, aVR, aVF ) & 6 chest lead (V1-V6) 2.Bipolar leads ( I , II, III ) : using voltage difference between 2 active electrode to create an image ( 2 eye vision example :) ) 3.Unipolar leads (aVL, aVR, aVF, V1-V6) : measuring voltage in a single electrode while others are set as earth! (one eye vision ;) ) ELECTRODE PLACEMENT Bipolar limb Leads Augmented unipolar limb leads Chest leads Chest leads FRONTAL & HORIZONTAL PLANE VIEW https://cdn.shopify.com/s/files/1/0059/3992/files/Image_5.png?v=1476239877 Výsledok vyhľadávania obrázkov pre dopyt ecg leads elated image Classic ECG recording (Lead II) mage result for ecg SING IT TO ME ! ECG paper mage result for ecg paper Classic ECG on Lead II How to Read ECG ? 1.RATE 2.RHYTHM 3.AXIS 4.INTERVALS 5.WAVEFORMS 6. RATE Normal HR : 50-100 bpm HR > 100 à TACHYCARDIA HR < 50 à BRADYCARDIA 300/ Number of large boxes between 2 R Rythm https://media-us.amboss.com/media/thumbs/big_592575d76f915.jpg Is it Regular Sinus rhythm ? 1.Normal morphology of P wave 2.P before QRS and QRS after every P 3.RR and PP intervals are equal in all leads MEAN ELECTRICAL AXIS (MEA) The MEA indicates the net direction (vector) of current flow during ventricular depolarization. https://meds.queensu.ca/central/assets/modules/ECG/step_3b.jpg AXIS mage result for axis rule of thumb https://media-us.amboss.com/media/thumbs/big_59f03bf72e5d9.jpg ECG intervals Arrythmia 1.Altered automaticity 2.Altered conduction Arrythmias Ø Based on Rate à Bradyarrythmia Vs Tachyarrythmia ØBased on Location of origin à Supraventricular Vs Ventricular Ø Base on mechanism of origin à • Irregular rythms •Escape •Premature beats •Tachy-Arrythmias P Pulmonale & Mitrale https://media-us.amboss.com/media/thumbs/big_54e49bb8a54dd.jpg P Pulmonale Causes Peaked P wave Elevation of P wave > 0.25mv https://media-us.amboss.com/media/thumbs/big_54e49b2d1a4f1.jpg P Mitrale Causes M-shaped P wave Prolongation of P > 0.10s PR interval pathology (AV BLOCK) elated image Atrial fibrillation Atrial Flutter Ventricular fibrillation (VF) Ventricular tachycardia mage result for ventricular tachycardia Prolonged QRS (>120) -BBB https://upload.wikimedia.org/wikipedia/commons/3/32/Left_and_right_bundle_branch_block.png ST segment elevation and depression mage result for st elevation ecg mage result for st elevation ecg QRS amplitude Left ventricular hypertrophy (LVH): SV1 or 2 + RV5 or 6 ≥ 3.5 mV Right ventricular hypertrophy (RVH): RV1 or 2 + SV5 or 6 ≥ 1.05 mV Corrected QT interval Electrolyte disturbances and ECG mage result for electrolyte and ecg elated image Ambulatory monitoring Quiz 1 A-fib Answer A-FIB Quiz 2 Mobitz 1 Answer AV blcok (mobitz 1) Quiz 3 Sinus bradycardia Answer Sinus Bradycardia Quiz 4 A-flutter Answer A-Flutter Quiz 5 V-fib Answer V-Fib Quiz 6 Sinus-tachycardia Answer Sinus Tachycardia Quiz 7 RBBB Asnwer RBBB Quiz 8 hyperkalemia Answer HyperKalemia Quiz 9 Inferior MI Answer Inferior MI THANK YOU Resources ; •RAPID INTERPRETATION OF ECG DALE DUBIN •FIRST AID FOR USMLE 2020 •KAPLAN PHYSIOLOGY •BORON PHYSIOLOGY