Ecg part i
- 1. اعداد : أ . م . د . عبيد بندر خميس م . د . مصيحب صباح زكي م . م . الحسين عبد جبار علي م . م . الحسين عبد سعود حسن كربالء جامعة التمريض كلية
- 2. Objectives • Review the anatomy and physiology of the electrical conduction of the heart • Interpret the term electrocardiography • Describe the types of ECG monitoring • Interprets the basics of ECG • Determine the heart rate from ECG • Explain the cardiac rhythm determination • Understand the 12 lead ECG • Differentiate the electrode placement • Distinguish abnormal ECG from normal ECG
- 3. Electrocardiogram ECG INTRODUCTION ECG is a three letter acronym for ElectroCardioGraphy. The word is derived from electro(greek for electricity) ,cardio(greek for heart) and graph(Greek root meaning "to write“) Electrocardiography: is the recording of the electrical impulses that are generated in the heart. These impulses initiate the contraction of cardiac muscles. It is a transthoracic interpretation of the electrical activity of the heart over time captured and externally recorded by skin electrodes. The device used to produce this non invasive record is called the electrocardiograph. ECG is the gold standard for the noninvasive diagnosis of cardiac diseases and may occasionally be the only marker for the presence of heart disease.
- 4. Indications Of ECG 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 ECG is a diagnostic tool, NOT a treatment No one is ever cured by an ECG!!
- 5. Basic Electrophysiology Physiological Properties Of Myocardial Cell Automaticity: ability to initiate an impulse Excitability: ability to respond to a stimulus Conductivity: ability to transmit an impulse Contractility: ability to respond with pumping action Depolarization and repolarization of a cardiac cell generates action potential ECG is the composite representation of action potential of all cardiac cell.
- 6. Electrical Conduction System Of The Heart The electrical discharge for each cardiac cycle normally starts in a special area of the right atrium called the ‘sinoatrial (SA) node’. Depolarization then spreads through the atrial muscle fibres. There is a delay while the depolarization spreads through another special area in the atrium, the ‘atrioventricular (AV) node’. Thereafter, the electrical discharge travels very rapidly, down specialized conduction tissue: first a single pathway, the ‘bundle of His’, which then divides in the septum between the ventricles into right and left bundle branches.
- 7. Within the ventricular mass, conduction spreads somewhat moreslowly, through specialized tissue called ‘Purkinje fibres’. Sinoatrial node AV node Bundle of His Bundle Branches Purkinje fibers
- 8. SA node Atrium contraction p wave Purkinje fibers ventricles relaxation T wave AV node ventricles contraction QRS wave
- 9. P wave = atrial depolarisation. PR Interval = impulse from atria to ventricles. QRS complex = ventricular depolarisation. ST segment = isoelectric - part of repolarisation. T wave = usually same direction as QRS – ventricular repolarisation. QT Interval = This interval spans the onset of depolarisation to the completion of repolarization of the ventricles.
- 10. The adjacent figure shows the normal sinus rythem A normal sinus rythem comprises of the following waves:- • P waves- denotes atrial depolarization(electrical vector is directed from the SA node towards the AV node) • QRS complex- denotes depolarization of ventricles as well as repolization of atrium • T waves- denotes the repolarization (or recovery) of the ventricles. The interval from the beginning of the QRS complex to the apex of the T wave is referred to as the absolute refractory period. The last half of the T wave is referred to as the relative refractory period. •PR interval- beginning of the P wave to the beginning of the QRS complex * As depicted in the fig:-
- 11. •ST segment- connects the QRS complex and the T wave. •QT interval- the beginning of QRS complex to the end of the T wave U wave :- typically small, and, by definition, follows the T wave Prominent U waves are most often seen in hypokalemia, but may be present in hypercalcemia, thyrotoxicosis What differentiates a segment from an interval? A segment is a straight line connecting two waves. An interval encompasses at least one wave plus the connecting straight line. U U U
- 12. myocardial cells are the other pacemaker sites. When SA node fails, they can initiate impulse at a slow rate. Rates Of Pacemakers 1. SA node 60 – 100 bpm 2. Atrial cells 55 – 60 bpm 3. AV node 45 – 50 bpm 4. Bundle of His 40 – 45 bpm 5. Bundle branch 40 – 45 bpm 6. Purkinje cells 35 – 40 bpm 7. Myocardial cells 30 – 35 bpm ECG Lead: There are twelve leads consisting of six limb leads (I, II, III, aVR, aVL and aVF)(vertical view) and six chest leads (V1 to V6)(horzental view). The limb leads consists of standard bipolar (I, II and III) and augmented (aVR, aVL and aVF) leads. The bipolar leads were so named because they record the difference in electrical voltage between two extremities.
- 13. 12 conventional leads, physiologically divided into two groups viz: Bipolar leads- 3 Standard limb leads Unipolar leads-3 Augmented limb leads and 6 precordial chest leads Bipolar leads : These record the actual difference in potential across the two electrodes. There are three standard limb lead:- • Lead I Left arm R arm • Lead II Left foot R arm • Lead III Left foot L arm Einthoven's triangle augmented unipolar limb Leads by aVR, aVF, aVL leads
- 14. Unipolar leads 6 precordial chest leads
- 15. Placement of Chest leads. V 1 - 4th intercostal space , right of sternum. V 2 - 4th ICS left of sternum V 4 - 5th ICS midclavicular line V 3 - Midway between V2 and V4 V 5 - 5th ICS anterior axillary line. V 6 - 5th ICS mid axillary line. Placement of limb leads: Right arm (RA) Left arm (LA) Right leg (RL) Left leg (LL)
- 16. 2004 Anna Story 16 Each ECG lead provides a different view of the heart
- 17. Leads of Limb and Chest
- 18. Height = millivolts Width = Time ECG paper consists of horizontal and vertical lines. The horizontal axis of the ECG strip represents time. Each small box equals 0.04 second. The ECG strip’s vertical axis measures amplitude in millimeters
- 19. Calibration 1 Small Square = 1 mm (0.1 mV) 1 Large Square = 5 mm (0.5 mV) Vertical Axis 2 Large Squares = 10 mm (1 mV) 1 Small Square = 0.04 sec 1 Large Square = 0.2 sec Horizontal Axis 5 Large Squares = 1 sec
- 23. Rate Determination (pulse calculation ) Large Box Method Just for Regular rhythms can be quickly determined by counting the number of large graph boxes between two R waves or P waves . That number is divided INTO 300 to calculate bpm. Ex. Below : - Take tow R wave and calculate large box between it. No. of large box between R waves divided / 300 = pulse 3 large box / 300 = 100 beat/min
- 24. 6 Sec Strip ( 30 large box ) The best method for measuring regular and irregular rates with varying R-R intervals is to count the number of R waves in a 6-sec strip and multiply by (10).This gives the average number of bpm. Every 3 seconds (15 large boxes) is marked by a vertical line. Ex. Below Take 6 sec = 30 large box Calculate R wave in 30 large box = 10 R wave R wave no. X 10 = pulse .. 10 X 10 = 100 beat/min 3 sec 3 sec
- 25. Small Box Method Just for Regular rhythms. Sometimes it is necessary to count the number of small boxes between two R waves for fast heart rates. That number is divided into 1500 to calculate bpm. Ex. Below Take tow R wave and calculate small box between it. No. of small box between R waves divided / 1500 = pulse 1500 / 16 small box = 94 beat/min