Thursday, August 25, 2016
000. INTRODUCTION - LỜI NÓI ĐẦU
PREFACE – LỜI NÓI ĐẦU
Learning
about ECG interpretation from books such as The ECG Made Easy or The ECG in
Practice is fine as far as it goes, but it never goes far enough. As with
most of medicine there is no substitute for experience, and to make the best
use of the ECG there is no substitute for reviewing large numbers of them.
ECGs need to be interpreted in the context of the patient from whom they were
recorded. You need to learn to appreciate the variations of normality and of
the patterns associated with different diseases, and to think about how the
ECU can help patient management.
Although
no book can be a substitute for practical experience, 150 ECG Problems goes a
stage nearer the clinical world than books that simply aim to teach ECG
interpretation. It presents 150 clinical problems in the shape of simple case
histories, together with the relevant ECG. It then invites the reader to
interpret the ECG in the light of the clinical evidence provided, and to
decide on a course of action before looking at the answer. Having seen the
answers, the reader may feel the need for more information, so each one is
cross-referenced to The ECG Made Easy and/or The ECG in Practice.
The ECGs
in 150 ECG Problems range from the simple to the complex. About one-third of
the problems are of a standard that a medical student should be able to cope
with, and should be answered correctly by anyone who has read The ECG Made
Easy. A junior doctoi specialist nurse or paramedic should get another third
right, if they have read The ECG in Practice. The remainder should challenge
the MRCP candidate. As a very rough guide to the level of difficulty of each
problem, each answer is graded using stars (see the summary box of each answer):
one star represents the easiest records, and three stars the most difficult.
The ECGs
are arranged in random ordei not in order of difficulty, to maintain the
reader’s interest. Readers are invited to attempt their own interpretation
before looking at the star rating - after all, in a real-life situation one
never knows which patient will be easy and which will be difficult to
diagnose or treat. In this fourth edition there are many new ECGs, mainly to
provide examples that reproduce more clearly. However to maintain the “real
world” approach, some technically poor records have deliberately been
included. The balance between easy, moderately difficult and very difficult
records has been maintained.
I am
extremely grateful to Alison Gale, my copy-editor and to Rich Cutler of
Helius. Their patience, understanding and attention to detail made the preperaration
of this new edition an easy and satisfying experience for me.
John Hampton
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INTRODUCTION: MAKING THE MOST OF
THE ECG
LỜI GIỚI THIỆU: KHAI THÁC TỐI ĐA
ECG
Recording
and reporting an ECG should never be an end in itself. The ECG is a basic and
valuable tool in the investigation of cardiac problems, and it can be helpful
in the case of non-cardiac problems too, but it must always be viewed in the
context of the patient from whom the record came. The ECG must never be a
substitute for taking a proper medical history and carrying out a careful
physical examination. Because it is simple, harmless and cheap, the ECG is
usually the first investigation in a patient with possible cardiac disease
and it may be followed by the plain chest X-ray, the echocardiogram,
radionuclide studies, CT and MR imaging, and cardiac catheterization and
angiography - but none of these are substitutes. The ECG, a recording of the
electrical activity of the heart, gives information that can be obtained in
no other way. However even though it is irreplaceable, it is not infallible.
ECGs are
recorded from a wide variety of patients, in an attempt to help with a wide
variety of possible diagnoses. An ECG is frequently recorded in the course of
‘health screening’, but here it must be regarded with considerable caution.
It can not be assumed that individuals who present themselves for screening
are asymptomatic - the process may be being used as a substitute for a
consultation with a doctor. The ECG itself may cause difficulties of
interpretation, for there are a dozen or more normal variants. Minor
abnormalities, such as nonspecific ST segment or T wave changes, will have
diagnostic and prognostic significance if the individual has symptoms that
may be cardiac in origin, but these changes can be of no importance in
totally healthy people. It is rare for an ECG to demonstrate anything of
importance in a totally healthy individual, although in athletes the
detection of abnormalities suggesting asymptomatic hypertrophic
cardiomyopathy is important.
In
patients with chest pain, the ECG is important but sometimes misleading. It
is essential to remember that the ECG can remain normal for some hours after
the onset of a myocardial infarction. Too often patients are sent home from
an A & E department because their ECG is normal, despite a reasonably convincing
story of ischaemic chest pain. Under such circumstances the ECG should be
repeated several times to see if changes are appearing, and patient
management should depend on the plasma troponin level rather than on the ECG.
Nevertheless the ECG is important for deciding treatment in a patient with
chest pain, for the management of a patient with myocardial infarction with
ST segment elevation is quite different from that of a patient whose ECG
shows a non-ST segment elevation infarction.
Patients
with intermittent chest pain that could be angina frequently have completely
normal ECGs at rest - and then the exercise test can be valuable. The
exercise test is to some extent being replaced by myocardial perfusion
scanning for the diagnosis of coronary disease because its predictive
accuracy depends on the likelihood of the patient having angina, because
there can be false negative or false positive results, and because exercise
tests are sometimes unreliable in women. Remember that an exercise test is
safe, but not totally safe, because arrhythmias (including ventricular
fibrillation) may be induced. Nevertheless the exercise test has the great
advantage of showing a patient’s exercise tolerance, and also showing what
limits his capability.
The ECG
also has a role in the investigation of patients with breathlessness, for it
can show changes associated with heart disease (e.g. an old myocardial
infarction) or with chronic chest disease. Evidence of left ventricular
hypertrophy may point to hypertension, mitral regurgitation or aortic
stenosis or regurgitation, and right ventricular hypertrophy may be the
result of pulmonary emboli or mitral stenosis - However all of these should
have been detected during the examination of the patient. The ECG is not a
good tool for grading the hypertrophy of the different heart chambers. It is
particularly important to remember that the ECG cannot demonstrate heart
failure: it may suggest a condition that may cause heart failure,
but is
impossible to determine from an ECG whether a patient is in heart failure or
not. However in the presence of a completely normal ECG, heart failure is
certainly unlikely.
There are
characteristic ECG appearances in several conditions that are not primarily
cardiac - for example with severe electrolyte derangement. ECG monitoring is
not an acceptable way of following electrolyte changes in conditions such as
diabetic ketoacidosis, but at least any abnormalities may prompt the
appropriate biochemical tests. The ECG has, However become important in the
development of new drugs, for any drug that causes QT prolongation - and this
is by no means uncommon - may cause sudden death due to ventricular
tachycardia.
It is in
the investigation and management of patients with possible arrhythmias that
the ECG is of paramount importance. Patients may complain of palpitations or
dizziness and syncope as a result of rhythm disturbances, and there is no way
of identifying these with certainty other than with an ECG. Dizziness and
syncope can be the result of rhythms that are either too fast or too slow for
an effective cardiac output, or of slow rhythms associated with disorders of
conduction. There may be little in the patient’s history to point
specifically to a cardiac problem when dizziness or collapse is the main
symptom, but an appropriately abnormal ECG may immediately point to the right
diagnosis. When a patient complains of palpitations there is a clearly a
heart problem of some sort, and it is usually possible to come close to a
diagnosis by taking a careful history - the patient with extrasystoles will
describe the heart ‘jumping out of the chest’ or something equally unlikely,
and the problem will be worse when lying down at night, and after smoking and
alcohol. The patient with a true paroxysmal tachycardia will describe the
sudden onset (and sometimes the sudden cessation) of the rapid heartbeat, and
if the attack is associated with chest pain, dizziness or breathlessness then
the presence of a paroxysmal tachycardia becomes highly likely.
Few
patients will have their arrhythmia at the time they are seen, but the ECG
can still give valuable clues to its nature. A patient whose ECG shows
bifascicular block, or first degree atrioventricular block together with left
bundle branch block, may have intermittent complete block and Stokes-Adams
attacks. A patient whose ECG shows pre-excitation (the Wolff-Parkinson-White
or Lown-Ganong-Levine syndromes) is at risk of paroxysmal arrhythmias -
though many people with these ECG patterns never have any problems at all. A
patient with a prolonged QT syndrome, as a result of either a congenital
defect or drug treatment, is at risk of torsade de pointes ventricular
tachycardia. Under all these circumstances, ambulatory ECG recording, by one
of a variety of techniques, may demonstrate the true nature of the arrhythmia
that causes the symptoms - but it must be remembered that many, if not most,
arrhythmias will be seen transiently in completely healthy people and only
when an abnormal ECG corresponds to symptoms can one be certain that the two
are related.
So the way
to approach the ECG, and this book - and indeed any medical situation - is to
start with the patient. If you cannot make a reasonable diagnosis from the
history, and to a lesser extent the examination, the chances of doing so as a
result of investigations are not great. The role of the ECG and of more
complex investigations is to help differentiate between the various possible
diagnoses suggested by talking to, and examining, the patient. The clinical
scenarios given with each ECG in this book are of necessity brief, but think
about them, ask yourself what the diagnosis might be, and then describe and
report on the ECG. That is the way to make the most of the ECG.
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