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BASIC 12 LEAD ELECTROCARDIOGRAM INTERPRETATION ELECTROCARDIOGRAPHY - graphic recording of electrical potential generated by the heart Electrophysiology: 3 components that produce electric currents, initiating cardiac contraction 1. cardiac pacemaker cells...

BASIC 12 LEAD ELECTROCARDIOGRAM INTERPRETATION ELECTROCARDIOGRAPHY - graphic recording of electrical potential generated by the heart Electrophysiology: 3 components that produce electric currents, initiating cardiac contraction 1. cardiac pacemaker cells 2. specialized conduction tissue 3. heart muscle SA node / Sinus node - located within the upper posterior wall of the R atrium - a collection of pacemaker cells that exhibits automaticity where depolarization stimulus for normal heartbeat originates AV node - stimulus of depolarization slows within the AV node, allowing blood to enter the ventricles Phases of cardiac electrical activation: 1. depolarization of the SA node 2. spread of depolarization wave through the right and left atria 3. atrial contraction 4. stimulation of pacemaker and specialized conduction tissues in the AV node and HIS bundle and the right and left bundle branches 5. spread of depolarization waveforms through the ventricular wall 6. ventricular contraction Phase 0 – the rapid upstroke corresponds to the onset of the QRS complex Phase 2 – (plateau), corresponds to the isoelectric ST segment Phase 3 – active repolarization, corresponds to the inscription of the T wave Conduction System Pacemakers of the Heart  SA Node - Dominant pacemaker with an intrinsic rate of 60 - 100 beats/minute.  AV Node - Back-up pacemaker with an intrinsic rate of 40 - 60 beats/minute.  Ventricular cells - Back-up pacemaker with an intrinsic rate of 20 - 45 bpm. Sinus Rhythm  TheSA (Sinus) Node is the heart’s dominant pacemaker.  Theability of a focal area of the heart to generate pacemaking stimuli is known as Automaticity.  The depolarization wave flows from the SA Node in all directions. Atrio-Ventricular (AV) Valves  Prevent blood backflow to the atria  Electrically insulate the ventricles from the atria AV Conduction  AV node is situated on right side of interatrial septum near the ostium of the coronary sinus  When the wave of depolarization enters the AV Node, depolarization slows, producing a brief pause, thus allowing time for the blood in the atria to enter the ventricles. Normal Impulse Conduction Sinoatrial node AV node Bundle of His Bundle Branches Purkinje fibers  Electrocardiography A recording of the electrical activity of the heart over time Gold standard for diagnosis of cardiac arrhythmias Helps detect electrolyte disturbances (hyper- & hypokalemia) Allows for detection of conduction abnormalities Screening tool for ischemic heart disease during stress tests Helpful with non-cardiac diseases (e.g. pulmonary embolism or hypothermia Impulse Conduction & the ECG Sinoatrial node AV node Bundle of His Bundle Branches Purkinje fibers ELECTROCARDIOGRAM is a graphical record of electric potentials generated by the heart muscle during each cardiac cycle. The signals are detected on the surface of the body using electrodes attached to the extremities and chest wall. These signals are then amplified by the electrocardiograph machine and displayed on special graph paper. Indications for ordering an electrocardiogram 1. To determine cardiac rate 2. To accurately define cardiac rhythm 3. To diagnose old or new myocardial infarction 4. To identify intracardiac conduction disturbances 5. To aid in the diagnosis of ischemic heart disease, pericarditis, myocarditis, electrolyte abnormalities and pacemaker malfunction  EKG Leads Leads are electrodes which measure the difference in electrical potential between either: 1. Two different points on the body (bipolar leads) 2. One point on the body and a virtual reference point with zero electrical potential, located in the center of the heart (unipolar leads)  EKG Leads The standard EKG has 12 3 Standard Limb Leads leads: 3 Augmented Limb Leads 6 Precordial Leads The axis of a particular lead represents the viewpoint from which it looks at the heart.  Chest Leads V1 Red 4th ICS RPSB V2 Yellow 4th ICS LPSB V3 Green between V2 and V4 V4 Brown 5th ICS LMCL V5 Black 5th ICS LAAL CHEST LEADS Precordial Leads Summary of Leads Limb Leads Precordial Leads Bipolar I, II, III - (standard limb leads) Unipolar aVR, aVL, aVF V1-V6 (augmented limb leads) Types of ECG Recordings  Bipolar leads record voltage between electrodes placed on wrists & legs (right leg is ground)  Lead I records between right arm & left arm  Lead II: right arm & left leg  Lead III: left arm & left leg The “PQRST” P wave - Atrial depolarization QRS - Ventricular depolarization T wave - Ventricular repolarization Elements of the ECG: P wave: Depolarization of both atria; Relationship between P and QRS helps distinguish various cardiac arrhythmias Shape and duration of P may indicate atrial enlargement PR interval: from onset of P wave to onset of QRS Normal duration = 0.12-2.0 sec (120-200 ms) (3-4 horizontal boxes) Represents atria to ventricular conduction time (through His bundle) Prolonged PR interval may indicate a 1st degree heart block The PR Interval Atrial depolarization + delay in AV junction (AV node/Bundle of His) (delay allows time for the atria to contract before the ventricles contract)  QRS complex: Ventricular depolarization Larger than P wave because of greater muscle mass of ventricles Normal duration = 0.08-0.12 seconds Its duration, amplitude, and morphology are useful in diagnosing cardiac arrhythmias, ventricular hypertrophy, MI, electrolyte derangement, etc. Q wave greater than 1/3 the height of the R wave, greater than 0.04 sec are abnormal and may represent MI ST segment: Connects the QRS complex and T wave Duration of 0.08-0.12 sec (80-120 msec T wave: Represents repolarization or recovery of ventricles Interval from beginning of QRS to apex of T is referred to as the absolute refractory period QT Interval Measured from beginning of QRS to the end of the T wave Normal QT is usually about 0.40 sec QT interval varies based on heart rate ST segment: Connects the QRS complex and T wave Duration of 0.08-0.12 sec (80-120 msec T wave: Represents repolarization or recovery of ventricles Interval from beginning of QRS to apex of T is referred to as the absolute refractory period QT Interval Measured from beginning of QRS to the end of the T wave Normal QT is usually about 0.40 sec QT interval varies based on heart rate The ECG Paper  Horizontally – One small box - 0.04 s – One large box - 0.20 s  Vertically – One large box - 0.5 mV The ECG Paper (cont) 3 sec 3 sec  Every 3 seconds (15 large boxes) is marked by a vertical line.  This helps when calculating the heart rate. NOTE: the following strips are not marked but all are 6 seconds long.  Rate  Rhythm  Axis  Hypertrophy  Ischemic or Infarction  Miscellaneous findings Guidelines in Reading the ECG Standardization QRS complex & technique morphology & Rhythm duration Rate: atrial & ST segment ventricular T-wave P wave U wave morphology & Q-T interval duration P-R interval RATE A. Rate Interpretation has three possibilities: 1. Bradycardia - (< 60 beats/min.) 2.Normal Rate – ( 60 – 100 beats per minute ) 3. Tachycardia – ( > 100 beats per minute ) B. Rate Analysis: Mnemonic: Memorize “ 300,150,100…75,60,50” = if R to R interval > 5 big squares: Bradycardia = if R to R interval between 3-5 big squares: Normal Rate = if R to R interval < 3 big squares: Tachycardia  FORMULA Heart Rate = 1500 or 300 ------------ ----------- # of small boxes # of big boxes Sinus Bradycardia Sinus Tachycardia What is the rate? 1sml =.04sec 5sml = 0.2sec 5big = 1 sec 15big = 3sec 30big = 6sec RHYTHM A. Common Rhythm Interpretations: 1. Sinus Rhythm 2. Common Supraventricular Arrythmias: a. Atrial Fibrillation b. Atrial Flutter c. Supraventricular Tachycardia 3. Heart Blocks a. First degree AV block b. Second degree AV block Mobitz type I ( Wenckebach ) c. Second degree AV block Mobitz type II d. Third degree AV block e. Left or Right Bundle Branch Block ( complete and incomplete ) 4. Ventricular Arrythmias a. Premature Ventricular Contractions b. Ventricular Tachycardia ( sustained and unsustained ) c. Ventricular Fibrillation B. Rhythm Analysis: 1. Identify the P wave Determine from the configuration if this is a sinus P 2. Check the relation of P wave to QRS a. P wave is before QRS ( normal ) b. P wave is buried or after QRS ( e.g. SVT, complete heart block ) 3. Check PR interval ( Normal PR interval: 0.12 – 0.20 sec. ) a. Short PR ( WPW syndrome ) b. Normal PR c. Prolonged PR ( 1st or 2nd degree AV block ) 4. Check QRS duration ( Normal QRS duration < 0.10 sec. ) a. Normal QRS b. Wide QRS ( Bundle branch blocks ) 5. Check the relation of R-R and P-P interval a. Equal R-R and P-P interval ( Normal ) b. P-P interval shorter than R-R interval ( Complete heart block ) c. P-P interval longer than R-R interval ( AV dissociation ) Voltage (mV) 10 mm = 1 mV Time NORMAL SINUS RHYTHM Rate 60-100 beats per minute Atrial regular Rhythm Ventricular regular Uniform in appearance, upright, normal shape, P waves one preceding each QRS complex 0.12-0.20 second PR interval 0.10 second or less. If greater than 0.10 second in QRS duration, the QRS is termed “wide” since the existence of a bundle branch block or other intraventricular conduction defect cannot be accurately detected in a single-lead. Normal ECG 1st degree AV block Ventricular fibrillation AXIS A. Axis Interpretation has Four Possibilities: 1.Normal Axis 2. Left Axis Deviation ( LAD ) 3. Right Axis Deviation ( RAD ) 4. Indeterminate Axis Getting the Axis Deviation (+ ) QRS deflection: Average QRS vector above the baseline in leads I or AVF (- ) QRS deflection: Average QRS vector below the baseline in leads I or AVF  LEAD I LEAD AVF Normal Axis + + Left Axis + - Deviation Right Axis - + Deviation Indeterminate - - Axis ISCHEMIA AND INFARCTION A. interpretation has 4 possibilities: 1. within normal limits (WNL). 50% of patients w/ CAD or chronic stable angina have normal ECGs 2. non-specific ST-T wave changes 3. myocardial ischemia changes 4. myocardial infarction changes B. Infarction and Ischemia analysis Leads involved Corresponding Areas II, III, AVF Inferior wall I, AVL High lateral wall V1,v2 Septal wall V3, v4 Anterior wall V5, v6 Lateral wall V1-v3 Anteroseptal wall V3-v6, I, AVL Anterolateral wall V5, v6, II, III, AVF Inferolateral wall Almost all leads Diffuse, global, massive Mirror image of v1, v2 Posterior LV wall V3R, v4R RV wall ECG findings in ischemia: 1. at least 1mm ST-segment depression 2. symmetrically inverted t wave 3. abnormally tall T wave 4. normalization of abnormal T wave 5. prolonged QT interval 6. arrhythmia, bundle branch blocks, AV blocks