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CVS-2.pptx

This document provides an overview of electrocardiography (ECG). It discusses the basics of ECG recording and waves, types of ECG leads, vector analysis, and interpretation of normal and abnormal tracings. The objectives are to explain how ECG is recorded, discuss normal waves and intervals, describe the relationship to heart electrical axis, and differentiate normal and abnormal ECGs. Key points covered include the normal P, QRS, and T waves; types of bipolar and unipolar leads; cardiac electrical axis; and manifestations of conditions like hypertrophy, conduction blocks, and arrhythmias on ECG.

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6/10/2022 1
Outline • Objectives • Overview • Electrocardiogram (ECG) waves • Types of ECG Leads • Application of ECG – Vectorial Analysis of Potentials Recorded in Different Leads • Interpretation of abnormal ECG tracing 6/10/2022 2
Objectives At the end of this session the students will able to: • Explain the way electrocardiogram (ECG) is recorded. • Discuss the normal waves, segments & intervals of the ECG. • Describe the relationship of the ECG to the electrical axis of the heart. • Differentiate normal and abnormal ECG tracing. 3 6/10/2022
4 Electrocardiography Overview The technique was developed by the Dutch physiologist named Willem Einthoven. Electrocardiogram (ECG) is the record of electrical activity of the heart that is conducted through the body fluid. It is recorded from the surface of the body using highly sensitive electrodes. It is the algebraic sum of the action potentials of cardiac muscle fibers during each cardiac cycle. ECG provides events about arrhythmia, hypertrophy, myocardial damage (ischemia and necrosis). 6/10/2022
Electrocardiography Overview… ECG Conventions • Each mm in the horizontal direction is 0.04 second. • 1mV input→10mm deflection (vertical) • Paper speed =25mm/sec. • Recording points =wrist, ankle, skin on chest – Right leg = ground (earth) 6/10/2022 5
Electrocardiography Overview… • The direction of deflection of the ECG trace indicates the relationship between the direction of the vector of the electrical current flow and the axis of the lead. – An upward deflection on an ECG means the current flow vector is toward the positive electrode – A downward deflection means the current flow vector is toward the negative electrode. 6/10/2022 6
Electrocardiogram • There are two major components of an ECG: – Waves & – Segments • Waves appear as deflections above or below the baseline. • Segments are sections of baseline between two waves. • Intervals are combinations of waves and segments. • Different waves of the ECG reflect depolarization or repolarization of the atria and ventricles. 6/10/2022 7
Electrocardiogram... • The P-wave is produced by atrial depolarization. • The QRS-complex by ventricular depolarization. • The T-wave by ventricular repolarization. • The U wave is due to slow repolarization of the papillary muscles. • Atrial repolarization is masked by QRS complex. • PR interval: The time between the beginning of the P wave and the QRS complex. – Atrial depolarization and conduction through AV node & bundle. • QT Interval: depolarization and repolarization of the ventricle. 8 6/10/2022
6/10/2022 9 Normal Durations in seconds Intervals/waves Average Range Events in the Heart during Interval P-Wave duration 0.08-0.1 Complete Atrial Depolarization PR interval 0.18 0.12–0.20 Atrial depolarization and conduction through AV node QRS duration 0.08 0.06 - 0.1 Ventricular depolarization and atrial repolarization QT interval 0.40 0.35-0.43 Ventricular depolarization plus ventricular repolarization ST interval (QT minus QRS) 0.32 0.30 - 0.33 Ventricular repolarization ECG Waves & Intervals durations Electrocardiogram...
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Electrocardiogram... 6/10/2022 11 During atrial depolarization current spreads from the right atrium downward toward the atrioventricular (AV) junction and left leg. During ventricular depolarization • Spread of ventricular depolarization consists of two major sequential phases:  Septal depolarization (left to right)  Spread of depolarization from apex to base in to out
Electrocardiographic Leads • Electrocardiographic lead is a combination of two wires and their electrodes to make a complete circuit between the body and the electrocardiograph. • Twelve leads are used for ECG tracing: – Three bipolar leads – Nine unipolar leads A. Bipolar Leads • The standard limb leads—leads I, II, and III—each record the differences in potential between two limbs. 6/10/2022 12
Electrocardiographic Leads... Lead I • In lead I, the negative terminal of the electrocardiograph is connected to the right arm and the positive terminal to the left arm. • An upward deflection is recorded when the left arm becomes positive relative to the right. Lead II • In lead II, the electrodes are on the right arm and left leg, with the leg positive. 13
Electrocardiographic Leads... • When the right arm is negative with respect to the left leg, the electrocardiograph records positively. Lead III • In lead III, the electrodes are on the left arm and left leg, with the leg positive. • The electrocardiograph records positively when the left arm is negative with respect to the left leg. 6/10/2022 14
Electrocardiographic Leads... • Normal electrocardiograms recorded from the three standard electrocardiographic leads:- – The P-wave is up ward – The QRS-complex is mainly up ward in all the three leads. 6/10/2022 15
Electrocardiographic Leads... Einthoven’s Triangle: • The bipolar standard limb leads form equilateral triangle of Einthoven drawn around the heart. • Einthoven’s law: If electrical potentials of any two of the three leads are given, the 3rd one can be determined by: – Lead II = Lead I+ Lead III, can estimate electric potential of each of the leads. 6/10/2022 16
Electrocardiographic Leads... B. Unipolar (V) Leads • There are additional nine unipolar leads that record the potential difference b/n an exploring electrode and an indifferent electrodes. Chest Leads (Precordial Leads) • There are six unipolar chest leads designated V1–V6. 6/10/2022 17
Electrocardiographic Leads... • Chest lead records mainly the electrical potential of the cardiac musculature immediately beneath the electrode. • In leads V1 and V2, the QRS recordings of the normal heart are mainly negative (down ward). Conversely, the QRS complexes in leads V4,V5, and V6 are mainly positive (upward) b/c the chest electrode in these leads is nearer the heart apex. 6/10/2022 18
Electrocardiographic Leads... Augmented limb leads • There are three unipolar limb leads. • In this type of recording, two of the limbs are connected to the negative terminal of the electrocardiograph and the third limb is connected to the positive terminal. • When the positive terminal is on the right arm: – The lead is known as the aVR lead; 6/10/2022 19
Electrocardiographic Leads... – When on the left arm, the aVL lead; – When on the left leg, the aVF lead • Normal recordings of the augmented unipolar limb leads are all similar to the standard limb lead recordings, except that the recording from the aVR lead is inverted. 6/10/2022 20
6/10/2022 21
Acceptable Variations in Normal ECG P wave • The P wave is normally upright in all leads except aVR. • When the QRS complex is predominantly downward in lead V1, the P wave may also be inverted. QRS complex • In most people the QRS complex is tallest in lead II, but in leads I and III the QRS complex is also predominantly upright. • It is common for the S wave to be greater than the R wave in lead III, and the cardiac axis can still be considered normal when the S wave equals the R wave in lead II. 6/10/2022 22
Acceptable Variations in Normal ECG… The size of R and S waves in the chest leads • In lead V1 there should be a small R wave and a deep S wave, and the balance between the two should change progressively from V1-V6. • In lead V6 there should be a tall R wave and no S wave. – Balance between R wave and S wave is significant for identifying a degree of cardiac axis deviation. Q waves • Is the normal depolarization of the interventricular septum from left to right. • Seen in any of leads I, II, aVL, or V4-V6. 6/10/2022 23
Acceptable Variations in Normal ECG… • Septal Q waves are usually less than 2 mm deep and less than 1 mm across. The ST segment • Should be horizontal and 'isoelectric‘ • But occasionally slopes upwards in leads V2-V5 after deep S wave. The T wave • In a normal ECG the T wave is always inverted in lead aVR & V1 but is usually upright in all the other leads. • The T wave is the most variable part of the ECG. 6/10/2022 24
Acceptable Variations in Normal ECG… • U waves are commonly seen in the anterior chest leads of normal ECGs. • It is thought to represent repolarization of the papillary muscles. • A U wave is probably only important if it follows a flat T wave. – Which is the characteristic of hypokalaemia. Variations in ECG pattern in athletes: – Tall P waves (>2.5mm) – Tall R waves and deep S waves 6/10/2022 25
Acceptable Variations in Normal ECG… • Prominent septal Q waves • Slight ST segment elevation • Tall symmetrical T waves • T wave inversion, especially in lateral leads • Prominent U waves 6/10/2022 26
Application of ECG • By analyzing electrical potential fluctuations in ECG record, one can gate some insight into: – Heart rate determination. – Anatomical orientation of the heart. – Relative size of heart chambers (Hypertrophy). – A variety of disturbances of rhythm and conduction block. – Extent, location and progress of ischaemic heart disease (e.g. myocardial infarction). 6/10/2022 27
Vectorial Analysis of Potentials Recorded in Different Leads • During ventricular depolarization, current flows mainly downward from the base of the ventricles toward the apex than in the upward direction. • This is shown by the summated vector of the potential generated. 6/10/2022 28
Vectorial Analysis of Potentials Recorded in Different Leads... • Axes of the three bipolar and three unipolar limb leads are placed with their relative axis and angles. • The direction from negative to positive electrode is called axis of the lead. • In lead I, the electrodes lie in the horizontal direction with the positive electrode to the left; the axis of lead I is, therefore, 0 degree. • From this zero reference point, the scale of vectors rotates clockwise. 6/10/2022 29
Vectorial Analysis of Potentials Recorded in Different Leads... Mean electrical axis of the heart • Mean electrical axis of the ventricles [vector showing current flows from base of ventricles (-ve) toward apex (+ve)]. • It is determined from standard limb leads • Normal mean electrical axis of the heart is about 59-60o. 6/10/2022 30
Vectorial Analysis of Potentials Recorded in Different Leads... • The normal mean QRS vector in the frontal plane is b/n -30o and +110o. • Mean QRS vectors greater than +110o are said to represent right axis deviation. – Right axis deviation suggests right ventricular hypertrophy – Right bundle branch block • Right ward angulation of the heart: – At the end of deep inspiration, – Normally in tall, lanky people whose hearts hang downward. 6/10/2022 31
32 6/10/2022
Vectorial Analysis of Potentials Recorded in Different Leads... • Those less than -30o are designated as left axis deviation. – Left axis deviation may be due to left ventricular hypertrophy – Left bundle branch block • Left side shift of the heart itself cause left axis deviation. • Such shift occurs: – At the end of deep expiration – Common in obese people 6/10/2022 33
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ECG manifestation of Atrial Enlargement • Right atrium (RA) enlargement may cause tall, peaked P waves in the extremity or chest leads. • Left atrium (LA) enlargement may cause broad, often notched P waves in the extremity leads and a biphasic P wave in lead V1 with a prominent negative component representing delayed depolarization of the left atrium. 6/10/2022 36
ECG manifestation of hypertrophied ventricles • Left ventricular hypertrophy causes deeper right precordial S-waves and taller left precordial R- waves. • By contrast, right ventricular hypertrophy shifts the QRS vector to the right, causing increased right precordial R waves. 6/10/2022 37
Rhythm and Conduction abnormalities of the heart Conduction Block • This may occur anywhere between the S.A node and the ventricles. • A block between the SA node and the AV node occurs very rarely. • One of the more common sites of block is A-V node. • Three degrees of heart block are usually distinguished: 1. First degree heart block – PR interval prolonged, >0.21 sec – Usually due to A-V nodal delay • May be caused by increased vagal tone or systemic diseases. 6/10/2022 38
Conduction Block • Has no effect on the pumping ability of the ventricles 2. Second Degree Heart Block • Associated with organic heart disease • Not all P waves are followed by QRS complexes. a. Partial progressive AV block.  PR interval increases progressively leading to dropped beat, 2:1 block) 6/10/2022 39
Conduction Block b. Constant block: PR interval relatively fixed; the atrio-ventricular rate is a constant small number ratio, e.g. 2:1, 3:1 3. Third Degree (complete) Heart Block • Impulses completely interrupted between atria and ventricles:  QRS complexes dissociated from P waves 6/10/2022 40
Conduction Block  Results either from His bundle disease or from bilateral bundle branch block  Ventricular rate much slowed (35-40 beats/min)  Fainting often occurs due to cerebral ischaemia • Cause: organic heart disease is often the cause. • Significance: May be associated with prolonged ventricular stand still. • If cardiac arrest prolonged, can lead to cerebral ischemia, syncope, or death. • This condition is termed Stokes-Adams Syndrome. 6/10/2022 41
Arrhythmias • Abnormal impulse initiation or impulse propagation. Disturbances of impulse initiation include: – Those arise from the SA node • SA node dysfunction  bradycardia • Sympathetic stimulation of SA node  tachycardia – Those originate from various ectopic foci Possible causes of ectopic foci are: 1. Local areas of ischemia 2. Toxic irritation of the A-V node, Purkinje system, or myocardium caused by drugs, nicotine, or caffeine. 3. Mechanical initiation of premature contractions during cardiac catheterization. 6/10/2022 42
Arrhythmias… Disturbances of impulse propagation: – Conduction blocks and – Reentrant rhythms • Additional aberrant muscular or nodal tissue connection (bundle of Kent) b/n the atria and ventricles. – This conducts more rapidly than the slowly conducting AV node, and one ventricle is excited early. • Circus movements can also established in the atrial or ventricular muscle fibers. • Ectopic foci & re-entrant are the most common cause of tachyarrhythmia. • Tachy-arrhythmias can be classified as supra- ventricular or ventricular tachycardia. 6/10/2022 43
Type Conditions of Heart 1. Extra systole (premature beat) •Abnormal contraction produced during diastole •Caused by an ectopic foci •It could be atrial, nodal or ventricular extra systole •Absence of pulse (may not cause 2nd heart sounds) •Have no pathologic significance 1.1. Atrial extra systoles •Abnormal P wave but normal QRS complex •Absence of pulse •Atrial premature beats often interrupt and "reset" the normal rhythm. 1.2. Ventricular extra systole •The QRS complex of the extra systole is usually considerably prolonged. • After almost all extra systole, the T wave has an electrical potential polarity exactly opposite to that of the QRS complex. Arrhythmias… 6/10/2022 44
Arrhythmias… 6/10/2022 45
Arrhythmias… 2. Paroxysmal atrial tachycardia (PAT) •Atrial beat >160 beats/min •Caused by ectopic focus •May be associated with ventricular tachycardia that pumping capacity of the heart. 3. Paroxysmal ventricular tachycardia (PVT) •Ventricular beat =200 beats/min, • Caused by ectopic focus 6/10/2022 46
47 4. Atrial flutter • Fast and regular atrial beats (200-400 b/min). • Different parts contracting • Caused by re-entry –a wave of excitation propagating continuously within a closed circuit-a ring-like pathway around ends of vena cavae • 3:2, 3:1 AV block (AV node cannot conduct more than about 230 impulses per minute) 5. Atrial fibrillation • Fast and irregular uncoordinated atrial beats (400- 600 b/min), dissociated from ventricular beat • Small and numerous waves in ECG. • Caused by multiple re-entry. • May be caused by: mitral valve disease, coronary atherosclerosis, thyrotoxicosis, etc. 6. Ventricular fibrillation • Fast and irregular uncoordinated QRS and ventricular beats (400-600b/min) • Caused by multiple re-entry • Circulation stops • May lead to death if defibrillation was not performed 6/10/2022 47
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Voltage Abnormalities • Determined by making use of the convention for voltage calibration. Increased voltage • If the sum of QRS of 3 standard leads is greater than 4mV, then the heart is said to be hypertrophic. • Caused by pressure and volume overload hypertrophy. • Decreased voltage Caused by: • Muscle abnormalities-like myocardial infarction • Conduction problem like 1st to 3rd degree heart block 6/10/2022 50
Myocardial Ischemia and Infarction • ECG findings of ischemic heart disease vary considerably, depending on four major factors: 1. The duration of the ischemic process (acute versus chronic); 2. Its extent (large versus small); 3. Its topography (anterior versus posterior and right ventricular); and 4. The presence of other underlying abnormalities (e.g. BBB) that can mask or alter the classic patterns. 6/10/2022 51
Myocardial Infarction • A sudden, irreversible, ischemic injury due to coronary arterial narrowing or occlusion with sustained damage to a portion of the myocardium.  Elevation of the ST segment at early stage return to normal on overlaying leads.  Leads on the opposite side of the heart show ST segment depression. 6/10/2022 52 Hours few days days to weeks Very late pattern
Myocardial Infarction… • Profound ST elevation or depression in multiple leads usually indicates very severe ischemia. • Prompt resolution of ST elevation is a specific marker of successful reperfusion. • Within a period ranging from hours to days T wave inversion appear. – T wave inversion correlates with increased ventricular depolarization duration. • Other common changes in infarcted area include the appearance of a Q wave in some of the leads in which it was not previously present and an increase in the size of the normal Q wave in some of the other leads. 6/10/2022 53
6/10/2022 54
Myocardial Infarction… • The electrocardiographic leads are more helpful in localizing regions of transmural than subendocardial ischemia. • For examples, ST elevation can be seen in the following:  One or more of the precordial leads (V1 through V6) and in leads I and aVL with acute transmural anterior or anterolateral wall ischemia;  Leads V1 to V3 with anteroseptal or apical ischemia  Leads V4 to V6 with apical or lateral ischemia;  Leads II, III, and aVF with inferior wall ischemia; and  Right sided precordial lead with right ventricular ischemia. 6/10/2022 55
Myocardial Infarction 6/10/2022 56
Effects of Ionic imbalance on ECG tracing • Changes in ECF Na+ and K+ concentration would be expected to affect the potentials of the myocardial fibers. • Fall in the plasma level of Na+ may be associated with low-voltage electrocardiographic complexes. • Changes in the plasma K+ level produce severe cardiac abnormalities. • In K+ level, the first change in the ECG is the appearance of tall peaked T waves. – At higher K+ levels, paralysis of the atria and prolongation of the QRS complexes occur. – Ventricular arrhythmias may develop 6/10/2022 57
Effects of Ionic imbalance on ECG tracing... – The RMP of the muscle fibers decreases as the extracellular K+ conc. increases. – The fibers eventually become unexcitable, and the heart stops in diastole. • A decrease in the plasma K+ level causes: – Prolongation of the PR interval, – Prominent U waves, and, – Late T wave inversion in the precordial leads Hypokalemia is a serious condition, but it is not as rapidly fatal as hyperkalemia. 6/10/2022 58
Effects of Ionic imbalance on ECG tracing... • Increases in extracellular Ca2+ conc. enhance myocardial contractility. • When large amounts of Ca2+ are infused into experimental animals, the heart relaxes less during diastole and eventually stops in systole (calcium rigor). 6/10/2022 59
Thank you 6/10/2022 60

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CVS-2.pptx

  • 1.
  • 2.
    Outline • Objectives • Overview •Electrocardiogram (ECG) waves • Types of ECG Leads • Application of ECG – Vectorial Analysis of Potentials Recorded in Different Leads • Interpretation of abnormal ECG tracing 6/10/2022 2
  • 3.
    Objectives At the endof this session the students will able to: • Explain the way electrocardiogram (ECG) is recorded. • Discuss the normal waves, segments & intervals of the ECG. • Describe the relationship of the ECG to the electrical axis of the heart. • Differentiate normal and abnormal ECG tracing. 3 6/10/2022
  • 4.
    4 Electrocardiography Overview The techniquewas developed by the Dutch physiologist named Willem Einthoven. Electrocardiogram (ECG) is the record of electrical activity of the heart that is conducted through the body fluid. It is recorded from the surface of the body using highly sensitive electrodes. It is the algebraic sum of the action potentials of cardiac muscle fibers during each cardiac cycle. ECG provides events about arrhythmia, hypertrophy, myocardial damage (ischemia and necrosis). 6/10/2022
  • 5.
    Electrocardiography Overview… ECG Conventions •Each mm in the horizontal direction is 0.04 second. • 1mV input→10mm deflection (vertical) • Paper speed =25mm/sec. • Recording points =wrist, ankle, skin on chest – Right leg = ground (earth) 6/10/2022 5
  • 6.
    Electrocardiography Overview… • Thedirection of deflection of the ECG trace indicates the relationship between the direction of the vector of the electrical current flow and the axis of the lead. – An upward deflection on an ECG means the current flow vector is toward the positive electrode – A downward deflection means the current flow vector is toward the negative electrode. 6/10/2022 6
  • 7.
    Electrocardiogram • There aretwo major components of an ECG: – Waves & – Segments • Waves appear as deflections above or below the baseline. • Segments are sections of baseline between two waves. • Intervals are combinations of waves and segments. • Different waves of the ECG reflect depolarization or repolarization of the atria and ventricles. 6/10/2022 7
  • 8.
    Electrocardiogram... • The P-waveis produced by atrial depolarization. • The QRS-complex by ventricular depolarization. • The T-wave by ventricular repolarization. • The U wave is due to slow repolarization of the papillary muscles. • Atrial repolarization is masked by QRS complex. • PR interval: The time between the beginning of the P wave and the QRS complex. – Atrial depolarization and conduction through AV node & bundle. • QT Interval: depolarization and repolarization of the ventricle. 8 6/10/2022
  • 9.
    6/10/2022 9 Normal Durationsin seconds Intervals/waves Average Range Events in the Heart during Interval P-Wave duration 0.08-0.1 Complete Atrial Depolarization PR interval 0.18 0.12–0.20 Atrial depolarization and conduction through AV node QRS duration 0.08 0.06 - 0.1 Ventricular depolarization and atrial repolarization QT interval 0.40 0.35-0.43 Ventricular depolarization plus ventricular repolarization ST interval (QT minus QRS) 0.32 0.30 - 0.33 Ventricular repolarization ECG Waves & Intervals durations Electrocardiogram...
  • 10.
  • 11.
    Electrocardiogram... 6/10/2022 11 During atrial depolarizationcurrent spreads from the right atrium downward toward the atrioventricular (AV) junction and left leg. During ventricular depolarization • Spread of ventricular depolarization consists of two major sequential phases:  Septal depolarization (left to right)  Spread of depolarization from apex to base in to out
  • 12.
    Electrocardiographic Leads • Electrocardiographiclead is a combination of two wires and their electrodes to make a complete circuit between the body and the electrocardiograph. • Twelve leads are used for ECG tracing: – Three bipolar leads – Nine unipolar leads A. Bipolar Leads • The standard limb leads—leads I, II, and III—each record the differences in potential between two limbs. 6/10/2022 12
  • 13.
    Electrocardiographic Leads... Lead I •In lead I, the negative terminal of the electrocardiograph is connected to the right arm and the positive terminal to the left arm. • An upward deflection is recorded when the left arm becomes positive relative to the right. Lead II • In lead II, the electrodes are on the right arm and left leg, with the leg positive. 13
  • 14.
    Electrocardiographic Leads... • Whenthe right arm is negative with respect to the left leg, the electrocardiograph records positively. Lead III • In lead III, the electrodes are on the left arm and left leg, with the leg positive. • The electrocardiograph records positively when the left arm is negative with respect to the left leg. 6/10/2022 14
  • 15.
    Electrocardiographic Leads... • Normalelectrocardiograms recorded from the three standard electrocardiographic leads:- – The P-wave is up ward – The QRS-complex is mainly up ward in all the three leads. 6/10/2022 15
  • 16.
    Electrocardiographic Leads... Einthoven’s Triangle: •The bipolar standard limb leads form equilateral triangle of Einthoven drawn around the heart. • Einthoven’s law: If electrical potentials of any two of the three leads are given, the 3rd one can be determined by: – Lead II = Lead I+ Lead III, can estimate electric potential of each of the leads. 6/10/2022 16
  • 17.
    Electrocardiographic Leads... B. Unipolar(V) Leads • There are additional nine unipolar leads that record the potential difference b/n an exploring electrode and an indifferent electrodes. Chest Leads (Precordial Leads) • There are six unipolar chest leads designated V1–V6. 6/10/2022 17
  • 18.
    Electrocardiographic Leads... • Chestlead records mainly the electrical potential of the cardiac musculature immediately beneath the electrode. • In leads V1 and V2, the QRS recordings of the normal heart are mainly negative (down ward). Conversely, the QRS complexes in leads V4,V5, and V6 are mainly positive (upward) b/c the chest electrode in these leads is nearer the heart apex. 6/10/2022 18
  • 19.
    Electrocardiographic Leads... Augmented limbleads • There are three unipolar limb leads. • In this type of recording, two of the limbs are connected to the negative terminal of the electrocardiograph and the third limb is connected to the positive terminal. • When the positive terminal is on the right arm: – The lead is known as the aVR lead; 6/10/2022 19
  • 20.
    Electrocardiographic Leads... – Whenon the left arm, the aVL lead; – When on the left leg, the aVF lead • Normal recordings of the augmented unipolar limb leads are all similar to the standard limb lead recordings, except that the recording from the aVR lead is inverted. 6/10/2022 20
  • 21.
  • 22.
    Acceptable Variations inNormal ECG P wave • The P wave is normally upright in all leads except aVR. • When the QRS complex is predominantly downward in lead V1, the P wave may also be inverted. QRS complex • In most people the QRS complex is tallest in lead II, but in leads I and III the QRS complex is also predominantly upright. • It is common for the S wave to be greater than the R wave in lead III, and the cardiac axis can still be considered normal when the S wave equals the R wave in lead II. 6/10/2022 22
  • 23.
    Acceptable Variations inNormal ECG… The size of R and S waves in the chest leads • In lead V1 there should be a small R wave and a deep S wave, and the balance between the two should change progressively from V1-V6. • In lead V6 there should be a tall R wave and no S wave. – Balance between R wave and S wave is significant for identifying a degree of cardiac axis deviation. Q waves • Is the normal depolarization of the interventricular septum from left to right. • Seen in any of leads I, II, aVL, or V4-V6. 6/10/2022 23
  • 24.
    Acceptable Variations inNormal ECG… • Septal Q waves are usually less than 2 mm deep and less than 1 mm across. The ST segment • Should be horizontal and 'isoelectric‘ • But occasionally slopes upwards in leads V2-V5 after deep S wave. The T wave • In a normal ECG the T wave is always inverted in lead aVR & V1 but is usually upright in all the other leads. • The T wave is the most variable part of the ECG. 6/10/2022 24
  • 25.
    Acceptable Variations inNormal ECG… • U waves are commonly seen in the anterior chest leads of normal ECGs. • It is thought to represent repolarization of the papillary muscles. • A U wave is probably only important if it follows a flat T wave. – Which is the characteristic of hypokalaemia. Variations in ECG pattern in athletes: – Tall P waves (>2.5mm) – Tall R waves and deep S waves 6/10/2022 25
  • 26.
    Acceptable Variations inNormal ECG… • Prominent septal Q waves • Slight ST segment elevation • Tall symmetrical T waves • T wave inversion, especially in lateral leads • Prominent U waves 6/10/2022 26
  • 27.
    Application of ECG •By analyzing electrical potential fluctuations in ECG record, one can gate some insight into: – Heart rate determination. – Anatomical orientation of the heart. – Relative size of heart chambers (Hypertrophy). – A variety of disturbances of rhythm and conduction block. – Extent, location and progress of ischaemic heart disease (e.g. myocardial infarction). 6/10/2022 27
  • 28.
    Vectorial Analysis ofPotentials Recorded in Different Leads • During ventricular depolarization, current flows mainly downward from the base of the ventricles toward the apex than in the upward direction. • This is shown by the summated vector of the potential generated. 6/10/2022 28
  • 29.
    Vectorial Analysis ofPotentials Recorded in Different Leads... • Axes of the three bipolar and three unipolar limb leads are placed with their relative axis and angles. • The direction from negative to positive electrode is called axis of the lead. • In lead I, the electrodes lie in the horizontal direction with the positive electrode to the left; the axis of lead I is, therefore, 0 degree. • From this zero reference point, the scale of vectors rotates clockwise. 6/10/2022 29
  • 30.
    Vectorial Analysis ofPotentials Recorded in Different Leads... Mean electrical axis of the heart • Mean electrical axis of the ventricles [vector showing current flows from base of ventricles (-ve) toward apex (+ve)]. • It is determined from standard limb leads • Normal mean electrical axis of the heart is about 59-60o. 6/10/2022 30
  • 31.
    Vectorial Analysis ofPotentials Recorded in Different Leads... • The normal mean QRS vector in the frontal plane is b/n -30o and +110o. • Mean QRS vectors greater than +110o are said to represent right axis deviation. – Right axis deviation suggests right ventricular hypertrophy – Right bundle branch block • Right ward angulation of the heart: – At the end of deep inspiration, – Normally in tall, lanky people whose hearts hang downward. 6/10/2022 31
  • 32.
  • 33.
    Vectorial Analysis ofPotentials Recorded in Different Leads... • Those less than -30o are designated as left axis deviation. – Left axis deviation may be due to left ventricular hypertrophy – Left bundle branch block • Left side shift of the heart itself cause left axis deviation. • Such shift occurs: – At the end of deep expiration – Common in obese people 6/10/2022 33
  • 34.
  • 35.
  • 36.
    ECG manifestation ofAtrial Enlargement • Right atrium (RA) enlargement may cause tall, peaked P waves in the extremity or chest leads. • Left atrium (LA) enlargement may cause broad, often notched P waves in the extremity leads and a biphasic P wave in lead V1 with a prominent negative component representing delayed depolarization of the left atrium. 6/10/2022 36
  • 37.
    ECG manifestation ofhypertrophied ventricles • Left ventricular hypertrophy causes deeper right precordial S-waves and taller left precordial R- waves. • By contrast, right ventricular hypertrophy shifts the QRS vector to the right, causing increased right precordial R waves. 6/10/2022 37
  • 38.
    Rhythm and Conductionabnormalities of the heart Conduction Block • This may occur anywhere between the S.A node and the ventricles. • A block between the SA node and the AV node occurs very rarely. • One of the more common sites of block is A-V node. • Three degrees of heart block are usually distinguished: 1. First degree heart block – PR interval prolonged, >0.21 sec – Usually due to A-V nodal delay • May be caused by increased vagal tone or systemic diseases. 6/10/2022 38
  • 39.
    Conduction Block • Hasno effect on the pumping ability of the ventricles 2. Second Degree Heart Block • Associated with organic heart disease • Not all P waves are followed by QRS complexes. a. Partial progressive AV block.  PR interval increases progressively leading to dropped beat, 2:1 block) 6/10/2022 39
  • 40.
    Conduction Block b. Constantblock: PR interval relatively fixed; the atrio-ventricular rate is a constant small number ratio, e.g. 2:1, 3:1 3. Third Degree (complete) Heart Block • Impulses completely interrupted between atria and ventricles:  QRS complexes dissociated from P waves 6/10/2022 40
  • 41.
    Conduction Block  Resultseither from His bundle disease or from bilateral bundle branch block  Ventricular rate much slowed (35-40 beats/min)  Fainting often occurs due to cerebral ischaemia • Cause: organic heart disease is often the cause. • Significance: May be associated with prolonged ventricular stand still. • If cardiac arrest prolonged, can lead to cerebral ischemia, syncope, or death. • This condition is termed Stokes-Adams Syndrome. 6/10/2022 41
  • 42.
    Arrhythmias • Abnormal impulseinitiation or impulse propagation. Disturbances of impulse initiation include: – Those arise from the SA node • SA node dysfunction  bradycardia • Sympathetic stimulation of SA node  tachycardia – Those originate from various ectopic foci Possible causes of ectopic foci are: 1. Local areas of ischemia 2. Toxic irritation of the A-V node, Purkinje system, or myocardium caused by drugs, nicotine, or caffeine. 3. Mechanical initiation of premature contractions during cardiac catheterization. 6/10/2022 42
  • 43.
    Arrhythmias… Disturbances of impulsepropagation: – Conduction blocks and – Reentrant rhythms • Additional aberrant muscular or nodal tissue connection (bundle of Kent) b/n the atria and ventricles. – This conducts more rapidly than the slowly conducting AV node, and one ventricle is excited early. • Circus movements can also established in the atrial or ventricular muscle fibers. • Ectopic foci & re-entrant are the most common cause of tachyarrhythmia. • Tachy-arrhythmias can be classified as supra- ventricular or ventricular tachycardia. 6/10/2022 43
  • 44.
    Type Conditions ofHeart 1. Extra systole (premature beat) •Abnormal contraction produced during diastole •Caused by an ectopic foci •It could be atrial, nodal or ventricular extra systole •Absence of pulse (may not cause 2nd heart sounds) •Have no pathologic significance 1.1. Atrial extra systoles •Abnormal P wave but normal QRS complex •Absence of pulse •Atrial premature beats often interrupt and "reset" the normal rhythm. 1.2. Ventricular extra systole •The QRS complex of the extra systole is usually considerably prolonged. • After almost all extra systole, the T wave has an electrical potential polarity exactly opposite to that of the QRS complex. Arrhythmias… 6/10/2022 44
  • 45.
  • 46.
    Arrhythmias… 2. Paroxysmal atrial tachycardia(PAT) •Atrial beat >160 beats/min •Caused by ectopic focus •May be associated with ventricular tachycardia that pumping capacity of the heart. 3. Paroxysmal ventricular tachycardia (PVT) •Ventricular beat =200 beats/min, • Caused by ectopic focus 6/10/2022 46
  • 47.
    47 4. Atrial flutter •Fast and regular atrial beats (200-400 b/min). • Different parts contracting • Caused by re-entry –a wave of excitation propagating continuously within a closed circuit-a ring-like pathway around ends of vena cavae • 3:2, 3:1 AV block (AV node cannot conduct more than about 230 impulses per minute) 5. Atrial fibrillation • Fast and irregular uncoordinated atrial beats (400- 600 b/min), dissociated from ventricular beat • Small and numerous waves in ECG. • Caused by multiple re-entry. • May be caused by: mitral valve disease, coronary atherosclerosis, thyrotoxicosis, etc. 6. Ventricular fibrillation • Fast and irregular uncoordinated QRS and ventricular beats (400-600b/min) • Caused by multiple re-entry • Circulation stops • May lead to death if defibrillation was not performed 6/10/2022 47
  • 48.
  • 49.
  • 50.
    Voltage Abnormalities • Determinedby making use of the convention for voltage calibration. Increased voltage • If the sum of QRS of 3 standard leads is greater than 4mV, then the heart is said to be hypertrophic. • Caused by pressure and volume overload hypertrophy. • Decreased voltage Caused by: • Muscle abnormalities-like myocardial infarction • Conduction problem like 1st to 3rd degree heart block 6/10/2022 50
  • 51.
    Myocardial Ischemia andInfarction • ECG findings of ischemic heart disease vary considerably, depending on four major factors: 1. The duration of the ischemic process (acute versus chronic); 2. Its extent (large versus small); 3. Its topography (anterior versus posterior and right ventricular); and 4. The presence of other underlying abnormalities (e.g. BBB) that can mask or alter the classic patterns. 6/10/2022 51
  • 52.
    Myocardial Infarction • Asudden, irreversible, ischemic injury due to coronary arterial narrowing or occlusion with sustained damage to a portion of the myocardium.  Elevation of the ST segment at early stage return to normal on overlaying leads.  Leads on the opposite side of the heart show ST segment depression. 6/10/2022 52 Hours few days days to weeks Very late pattern
  • 53.
    Myocardial Infarction… • ProfoundST elevation or depression in multiple leads usually indicates very severe ischemia. • Prompt resolution of ST elevation is a specific marker of successful reperfusion. • Within a period ranging from hours to days T wave inversion appear. – T wave inversion correlates with increased ventricular depolarization duration. • Other common changes in infarcted area include the appearance of a Q wave in some of the leads in which it was not previously present and an increase in the size of the normal Q wave in some of the other leads. 6/10/2022 53
  • 54.
  • 55.
    Myocardial Infarction… • Theelectrocardiographic leads are more helpful in localizing regions of transmural than subendocardial ischemia. • For examples, ST elevation can be seen in the following:  One or more of the precordial leads (V1 through V6) and in leads I and aVL with acute transmural anterior or anterolateral wall ischemia;  Leads V1 to V3 with anteroseptal or apical ischemia  Leads V4 to V6 with apical or lateral ischemia;  Leads II, III, and aVF with inferior wall ischemia; and  Right sided precordial lead with right ventricular ischemia. 6/10/2022 55
  • 56.
  • 57.
    Effects of Ionicimbalance on ECG tracing • Changes in ECF Na+ and K+ concentration would be expected to affect the potentials of the myocardial fibers. • Fall in the plasma level of Na+ may be associated with low-voltage electrocardiographic complexes. • Changes in the plasma K+ level produce severe cardiac abnormalities. • In K+ level, the first change in the ECG is the appearance of tall peaked T waves. – At higher K+ levels, paralysis of the atria and prolongation of the QRS complexes occur. – Ventricular arrhythmias may develop 6/10/2022 57
  • 58.
    Effects of Ionicimbalance on ECG tracing... – The RMP of the muscle fibers decreases as the extracellular K+ conc. increases. – The fibers eventually become unexcitable, and the heart stops in diastole. • A decrease in the plasma K+ level causes: – Prolongation of the PR interval, – Prominent U waves, and, – Late T wave inversion in the precordial leads Hypokalemia is a serious condition, but it is not as rapidly fatal as hyperkalemia. 6/10/2022 58
  • 59.
    Effects of Ionicimbalance on ECG tracing... • Increases in extracellular Ca2+ conc. enhance myocardial contractility. • When large amounts of Ca2+ are infused into experimental animals, the heart relaxes less during diastole and eventually stops in systole (calcium rigor). 6/10/2022 59
  • 60.

Editor's Notes

  • #18 This electrode is connected to the positive Terminal of the electrocardiograph, and the negative electrode, indifferent electrode, is connected through equal electrical resistances to the right arm, left arm, and left leg all at the same time
  • #30 hexagonal reference system, coordinate system
  • #31 It can be calculated by summing the depolarization during the QRS complex in any two leads.
  • #32 Ventricles averages about 59 degrees, this axis can swing even in the normal heart from about 20 degrees to about 100 degrees. The causes of the normal variations are mainly anatomical differences in the Purkinje distribution system or in the musculature itself of different hearts.
  • #39 systemic diseases –diphtheria or rheumatic fever carotid sinus syndrome. In these patients, the pressure receptors (baroreceptors) in the carotid sinus region of the carotid artery walls are excessively sensitive. Therefore, even mild external pressure on the neck elicits a strong baroreceptor reflex, causing intense vagal-acetylcholine effects on the heart, including extreme bradycardia
  • #41 QRS complex can narrow or wide QRS complex
  • #42 Endocarditis , Syphilis, Coronary artery disease (MI)
  • #43 the brain cannot remain active for more than 4 to 7 seconds without blood supply, most patients faint a few seconds after complete block occurs because the heart does not pump any blood for 5 to 30 seconds, until the ventricles “escape.”
  • #45 Bizarre- unusual Atrial and ventricular premature beats are not strong enough to produce a pulse at the wrist if they occur early in diastole, when the ventricles have not had time to fill with blood and the ventricular musculature is still in its relatively refractory period. They may not even open the aortic and pulmonary valves, in which case there is, in addition, no second heart sound.
  • #48 This produces a characteristic saw tooth pattern of flutter waves due to atrial contractions. It is almost always associated with 2:1 or greater AV block, because in adults the AV node cannot conduct more than about 230 impulses per minute. Highvoltage alternating electrical current passed through the ventricles for a fraction of a second can stop fibrillation by throwing all the ventricular muscle into refractoriness simultaneously. This is accomplished by passing intense current through large electrodes placed on two sides of the heart.
  • #49 Depolarization reverberates round the pathway, causing a tachycardia. The anatomical requirement for this is the branching and rejoining of a conduction pathway. Normally, conduction is anterograde (forward) in both limbs of such a pathway, but an anterograde impulse may pass normally down one branch and be blocked in the other. From the point at which the pathways rejoin, the depolarization wave can spread retrogradely (backwards) up the abnormal branch.
  • #53 When the acute ischemia is transmural, the ST vector is usually shifted in the direction of the outer (epicardial) layers, producing ST elevations and sometimes, in the earliest stages of ischemia, Diagrammatic illustration of serial electrocardiographic patterns in anterior infarction
  • #55 Rapid repolarization –Elevation of the ST segment, The manifestations of this positivity , appearance of a Q wave in some of the leads in which it was not previously present and an increase in the size of the normal Q wave in some of the other leads, direction of repolarization cause inverted T
  • #58 The intracellular to extracellular potassium ratio is the primary determinate of the cardiac resting membrane potential because the potassium channels are mostly open at rest.1,7 The concentration gradient of potassium across the cardiac cell membrane is reduced when serum potassium levels increase resulting in a less negative resting membrane potential.14 This change in resting membrane potential should increase the cell membrane excitability because it decreases the difference between the resting and threshold potentials. However, this is not the only change that occurs when extracellular potassium levels are increased. Elevated serum potassium concentrations inactivate the sodium–potassium channels that are integral to allowing potassium efflux during the resting phase, so cells are much slower in reaching threshold potential. The decreased permeability of potassium will also slow the efflux of potassium out of the cell during phase 3 of repolarization, prolonging the muscle’s recovery. These changes depress upstroke velocity and progressively prolong duration of the cardiac action potential as extracellular potassium concentration increases, and they explain the ECG alterations in experimentally derived hyperkalemia.