ECG at a Glance (eBook)

Patrick Davey (Autor)

eBook Download: PDF | EPUB

2013
John Wiley & Sons (Verlag)
978-1-118-69973-7 (ISBN)

Infos

Highly Commended in the Cardiology category at the British Medical Association Book Awards 2009

This brand new title in the popular at a Glance seriescombines the science behind ECGs with how to use them to guide diagnosis and treatment. These key skills are fundamental for examination of the cardiovascular system and all medical students and specialist nurses are expected to be proficient at ECG interpretation.

The at a Glance approach provides a large number of clear diagrams and example ECGs alongside concise text, putting the ECGs into a clinical context, all in easy-to-absorb double-page sections.

Patrick Davey is Consultant Cardiologist at Northampton General Hospital & Honorary Senior Lecturer at the John Radcliffe Infirmary, Oxford. He was previously a Clinical Tutor at Oxford University.

Inhalt

Preface 6

Acknowledgements 7

1 Introduction to the ECG 8

2 Strengths and weaknesses of the ECG 10

Part 1 The normal ECG

3 Basis of the ECG 12

4 The normal P wave 16

5 The normal QRS complex 18

6 The T and U waves 20

Part 2 ECG abnormalities

7 Abnormalities in the shape of the P wave - left and right atrial enlargement 22

8 Increased QRS amplitude 24

9 Q waves and loss of R wave height 26

10 QRS axis deviation 28

11 Long PR interval and QRS broadening 30

12 Delta waves 32

13 ST elevation 34

14 ST depression 36

15 Mild T wave flattening 38

16 Deep T wave inversion 40

17 QT interval and U wave abnormalities 42

Part 3 Clinical syndromes

18 Acute chest pain 44

19 Chronic chest pain 46

20 Acute breathlessness 48

21 Chronic breathlessness 51

22 Palpitations 54

23 Syncope 57

24 Hypertension 60

25 Shock 62

26 Stroke 64

27 Emotion and the ECG 66

28 Sudden cardiac death 68

Part 4 Diseases

29 Acute coronary syndromes 70

30 Non-ST segment elevation myocardial infarction 72

31 ST segment elevation myocardial infarction 74

32 Aortic valve disease and hypertrophic cardiomyopathy 76

33 Mitral valve disease 78

34 Cardiomyopathy and myocarditis 80

35 Pulmonary hypertension 82

36 Congenital heart disease 84

37 Endocrine disease and electrolyte disruption 86

38 Psychological disease and its treatment 88

39 Genetic pro-arrhythmic conditions 90

Part 5 Tachyarrhythmias

40 Distinguishing supraventricular from ventricular tachycardia 92

41 Narrow complex tachycardia 95

42 Atrial ectopic beats 98

43 Atrial fibrillation 100

44 Atrial flutter and atrial tachycardia 102

45 Atrioventricular nodal re-entrant tachycardia 104

46 Atrioventricular re-entrant tachycardia 106

47 Ventricular ectopics 108

48 Non-sustained ventricular tachycardia 110

49 Monomorphic ventricular tachycardia 112

50 Polymorphic ventricular tachycardia 114

51 Ventricular fibrillation 116

Part 6 Bradyarrhythmias and related diseases

52 Sinus node disease 118

53 Left bundle branch block 120

54 Right bundle branch block 122

55 First degree atrioventricular block - long PR interval 124

56 Second degree atrioventricular block 126

57 Atrioventricular block - third degree (complete) heart block 128

Part 7 Pacemakers

58 Pacemakers - basic principles 130

59 Anti-bradycardic pacemakers 132

60 Anti-tachycardic and heart failure devices 134

Part 8 ECG-based investigations

61 External and internal loop recorders 136

62 Tilt-table test and carotid sinus massage 138

63 Twenty-four hour ECGs 140

64 The exercise stress test 144

65 Invasive electrophysiological studies 148

Part 9 Self-assessment case studies

Case studies and answers 150

Appendix 162

Index 163

Rezensionen

"This is a refreshing new book in the already crowded field
of ECG interpretation books." (Doody's Reviews, May
2009)

Pre-publication reviews:

'Very thorough list of contents, broken down logically into
sections....this is a very accessible book that is easy to read
from cover to cover.' - Postgraduate Medical Student, Warwick
University

'Once again I have been impressed by the level of input and
comprehension into each chapter. I have no doubt that my medical
students will be carrying around ECG at a Glance as much as they
already carry around Medicine at a Glance! Could I be cheeky and
ask for a copy or 2 when the book is finally printed! ' -
Consultant Cardiologist & Electrophysiologist, James Cook
University Hospital, Middlesbrough

Textauszug

3
Basis of the ECG

Fig. 3.1 The top part of the figure shows an action potential, with voltage measured by an intracellular electrode; the middle part of the figure shows the net extracellular charge at different times during the action potential; the bottom part of the figure shows ion movement into, out of and within a myocyte during the action potential. The action potential: intracellular [K+] is 130–140 mmol/L; extracellular K+ is 4–5 mmol/L. Intracellular [Na+] is 5 mmol/L, extracellular [Na+] 140 mmol/L. The resting myocyte membrane is permeable only to K+; during rest some K+ moves down its concentration gradient from the inside to the outside of the cell, with its positive charge, leaving negative charge inside the cell. This results in a potential difference between the outside and inside of the cell of –90 mV. The excess extracellular positive charge prevents more positively charged K+ moving out of the cell. During the upstroke of the action potential (phase 1), the cell membrane becomes impermeable to K+ and rapidly more permeable to Na+, which along with its positive charge moves down its concentration gradient into the cell, leaving net negative charge outside the cell, so the interior of the cell becomes positively charged to +30 mV. This positive intracellular voltage triggers the release of Ca2+ from its sarcoplasmic reticulum (SR) and other storage sites, initiating myosin contraction. During the plateau phase (phase 2), the cell membrane remains much more permeable to Na+ than K+, so the intracellular environment is positively charged. Furthermore, there is also a net flow of Ca2+ into the cell, which helps maintains net positive charge in the cell, and myosin contraction. With repolarization the membrane becomes much less permeable to Na+ than K+, so K+ again flows out of the cell (as repolarizing potassium currents), allowing the interior to become negatively charged (phase 3), so restoring the resting status. Ca2+ is removed (by SR pumps) from the cytoplasm around this time, terminating myosin contraction. The membrane permeability alters due to the opening and shutting of ion-specific membrane channels (these switch on or off according to the intracellular voltage, spontaneously over time, or in response to hormones and intracellular messengers). Intracellular ionic concentration is maintained by pumps that consume adenosine triphosphate (ATP) (e.g. the Na+K+ATP’ase membrane pump).

Fig. 3.2 Current flows between different areas of the heart either when some areas have depolarized and others are still to depolarize or, conversely, when some areas have repolarized and others are still to repolarize. (a) Here depolarized cells are shown with excess negative charge, which flows in the direction of the depolarization wavefront. (b) This shows the current flow loops round the dipole, producing current flow to the side and behind the depolarization wave.

Fig. 3.3 This shows a more complex and so more realistic pattern of current flow than Fig. 3.2b. In the centre is a dipole (labelled as – or + for the polarity at either end), which generates a complex series of looping currents around itself.

Fig. 3.4 The surface correlates of internal current flow, projected onto a torso. The pattern of current flow is complex. There is no current flow towards an observing electrode at right angles to the dipole, and maximal flow directly in front or behind the dipole.

The basis of the ECG

The ECG is a clever device designed to detect current flow. The heart generates electricity, which is transmitted to the chest wall, where it can be detected. The ECG records the pattern of spread of electricity in the various phases of the cardiac cycle. Its utility relies on the pattern of spread changing in a characteristic fashion in many diseases. In understanding the ECG, be aware that:

• Electrons carry current, which flows from areas with negative charge to areas with more positive charge; when current moves towards an observing electrode a positive deflection results and vice versa. The ECG only shows a deflection when current is moving in the heart. No current flow means no ECG deflection.
• The basis of current flow around the heart starts off as current flow within individual heart cells, which induce current flow between cells. With depolarization positively charged Na+ ions move into the cell; with repolarization, positively charged K+ move out of cells – this leaves excess negative charge outside the cell at the start of the cardiac cycle, excess positive charge outside the cell at the end of the cycle.
• Current flows from areas just depolarized (excess extracellular negative charge) into areas yet to depolarize, then onto an observing electrode. This current flow depolarizes neighbouring cells, firing action potentials, and in sequence fully depolarizing the whole heart. When fully depolarized, the extracellular charge throughout the heart is the same; there is no current flow, and no ECG deflection.
• At the end of the cardiac cycle, individual myocytes repolarize, moving positively charged K+ ions out of the cells, leaving the outside extracellular space more positive than the extracellular space of those parts of the heart yet to repolarize. Current, as electrons, moves into the repolarized area from the areas of the heart yet to repolarize.
• In summary, the heart does not depolarize or repolarize simultaneously – some areas de/repolarize before other areas, so that in depolarization, current flows into areas about to depolarize, with repolarization, current flows away from areas about to repolarize. This spread of currents give rise to a characteristic sequence of currents flowing over the heart with each heartbeat.
• The utility of the ECG in medicine is that many, but far from all, diseases change this electricity pattern in a characteristic way.
• It is crucial to remember that abnormal ECG reflect deviations in the flow of the current from normal – they may indicate something seriously wrong with the heart, they may not – abnormal ECGs do not always mean the heart is abnormal!

Fig. 3.5 The basic elements of the cardiac cycle.

Fig. 3.6 Sequence of depolarization of the heart. The impulse starts at the sino-atrial (SA) node, then activates the atria, both right (downwards and rightwards) and left (via the bundle of Bachmann). The impulse then reaches the atrioventricular (AV) node, is delayed briefly before passing into the bundle branches and more distal Purkinje fibres.

Fig. 3.7 Naming of the different ECG waves. P wave reflects atrial activation, T wave ventricular repolarization. Whether the T wave is positive (i.e. above the line) or negative (below the line) it is always called the T wave. The waves of the depolarization complex (QRS complex) are defined in the text.

Fig. 3.8 The basic ECG nomenclature, demonstrating the basic ECG, recorded at a standard paper speed of 50 mm/s, and sensitivity of 10 mm/mV, and showing the timing of the normal ECG.

The basic ECG

The ECG is the surface recording of the electricity associated with the cardiac cycle. To understand the ECG you should know: (i) the key components of the cardiac cycle; (ii) when the different parts of the heart depolarize and repolarize; (iii) where the different ECG leads are sited.

The cardiac cycle

1. 1 The heart fills during diastole and contracts during systole.
2. 2 The cardiac cycle begins with electrical activation of the atria, starting at the cardiac pacemaker in the sino-atrial (SA) node, high up in the right atrium.
3. 3 A key property of the heart is that electrical activation (i.e. depolarization of a cell sufficient to fire an action potential) of some heart cells activates adjacent cells (i.e. they become depolarized sufficient for an action potential to fire). So, activation of the SA node initiates a wave of depolarization that spreads over the right atrium and, via the bundle of Bachmann into the left atrium. Electrical atrial activation leads to co-ordinated atrial pumping.
4. 4 The electrical impulse travels downwards into the atrioventricular (AV) node, the only electrical connection between the atria and the ventricles. The AV node delays the electrical impulse, allowing atrial systole to finish before ventricular systole starts.
5. 5 After a short delay (150–200 ms), the electrical impulse crosses the AV node and enters the specialized conducting tissue of the ventricles – the bundle of His, bundle branches and their divisions.
6. 6 The specialized conducting tissue quickly (50–60 ms in health) distributes the electrical impulse throughout the ventricle and into the myocytes, initiating contraction. Though the electrical impulse spreads quickly via the specialized conducting tissue, myocyte-to-myocyte spread of electrical activity is much slower.
7. 7 The specialized conducting tissue is sub-endocardial, so the wave of excitation spreads endocardially to epicardially, and then onto an observing electrode. This accounts for most leads observing the left ventricle having a positive deflection.
8. 8 After depolarization, the action potential of the myocytes has a prolonged plateau phase, during which the ventricular myocytes are contracted, and little current flows.
9. 9...

Produkt-Details

• Erscheint lt. Verlag: 12.7.2013
• Reihe/Serie: At a Glance
• Reihe/Serie: At a Glance
• Reihe/Serie: At a Glance
• Sprache: englisch
• Themenwelt: Medizin / Pharmazie ► Allgemeines / Lexika
• Themenwelt: Medizinische Fachgebiete ► Innere Medizin ► Kardiologie / Angiologie
• Themenwelt: Medizin / Pharmazie ► Medizinische Fachgebiete ► Radiologie / Bildgebende Verfahren
• Schlagworte: Abnormalities • Cardiovascular Disease • Chronic • Conditions • Death • Delta • ecg • elevation • Enlargement • infarction • Introduction • Inversion • Kardiovaskuläre Erkrankung • Kardiovaskuläre Erkrankungen • Kardiovaskuläre Erkrankung • Kardiovaskuläre Erkrankungen • Medical Science • Medizin • Misc (other) certifications • myocardial • normal ecg • normal p • normal qrs • P • Prüfungsvorbereitung • Prüfungsvorbereitung • q waves • Radiologie u. Bildgebende Verfahren • Radiology & Imaging • Shape • Sonstige Zertifizierungen • Test Prep • wave height • Waves
• ISBN-10: 1-118-69973-4 / 1118699734
• ISBN-13: 978-1-118-69973-7 / 9781118699737