Chou's Electrocardiography in Clinical Practice: Adult and Pediatric

736 Pages·2008·60.56 MB·English

by  Borys Surawicz MD MACC

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CHOU’SELECTROCARDIOGRAPHYINCLINICALPRACTICE ISBN:978-1-4160-3774-3
SIXTHEDITION
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ThePublisher
LibraryofCongressCataloging-in-PublicationData
Surawicz,Borys,1917-
Chou’selectrocardiographyinclinicalpractice/BorysSurawicz,TimothyK.Knilans.—6thed.
p.;cm.
Includesbibliographicalreferencesandindex.
ISBN978-1-4160-3774-3
1.Electrocardiography—Interpretation.2.Heart—Diseases—Diagnosis.I.Knilans,TimothyK.II.Chou,
Te—Chuan,1922-Electrocardiographyinclinicalpractice.III.Title.IV.Title:Electrocardiographyin
clinicalpractice.
[DNLM:1.Electrocardiography—methods.2.HeartDiseases—diagnosis.WG140S961c2008]
RC683.5.E5C4542008
616.10207547—dc22
2007048392
ExecutivePublisher:NatashaAndjelkovic
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PrintedintheUnitedStates
Lastdigitistheprintnumber: 9 8 7 6 5 4 3 2 1
ThiseditionisdedicatedtoDr.Te-ChuanChou,theauthorofthefirstfoureditions,asamarkofrespectfor
his scholarship and understanding of this subject.
PREFACE
After the publication of his textbook Clinical myocardial infarction (STEMI) and non-STEMI,
Electrocardiograpy in 1956, Dr. Louis Katz was stresstest,QTinterval,andpacemakers.Dr.Tim-
saidtodeclarethatelectrocardiographywasfully othy Knilans updated the section on pediatric
explored,implyingnoneedforfurtherinvestiga- electrocardiography,mostextensivelythechapter
tionsinthisfield.Similarverdictshavebeenpro- on cardiac arrhythmias. Given that the backbone
nouncedinsubsequentyears,provingthemtobe of an ECG textbook are the illustrations, many
consistently wrong in the face of the continuing figures in this edition were added and replaced.
flow of new information about the electrocardio- I am indebted to Drs. HJJ Wellens, APM
gram (ECG) in synchrony with the continuing Gorgels, and PA Doevedans, authors of the
progress in other areas of cardiology. monograph The ECG in Acute Myocardial Infarc-
As envisioned by the author of the first four tion and Unstable Angina, for their permission
editions, Dr. Chou, this text is primarily clinical, to reproduce several figures, and to Dr. Serge
with sufficient basic science foundation and S.Baroldforallowingustoincludenewinforma-
bibliographytounderstandthegenesisofdiverse tion and figures in the chapter on cardiac pace-
ECG patterns. In the 7 years since the publica- makers. I am grateful to Mrs. Terri Scott for her
tion of the fifth edition, valuable new infor- invaluable secretarial assistance.
mation emerged that necessitated complete
revisionofthesections dealingwithST-elevation BORYSSURAWICZ,M.D.,M.A.C.C.
vii
CONTRIBUTING AUTHORS
Lawrence E. Gering, M.D., F.A.C.C. Borys Surawicz, M.D., M.A.C.C.
Owensboro Mercy Health System Professor Emeritus
Owensboro, Kentucky; and Indiana University School of Medicine
Riverview Hospital Indianapolis, Indiana
Noblesville, Indiana
Morton E. Tavel, M.D., F.C.C.P.
Timothy K. Knilans, M.D. The Indiana Heart Institute
Associate Professor, Pediatrics Care Group, Inc.
University of Cincinnati School of Medicine Indianapolis, Indiana
Director, Clinical Cardiac Electrophysiology
and Pacing
The Children’s Hospital Medical Center
Cincinnati, Ohio
ix
(cid:1) ADULT
SECTION I
ELECTROCARDIOGRAPHY
1
Normal Electrocardiogram:
Origin and Description
OriginoftheElectrocardiogram NormalECG
DepolarizationandRepolarization PWave
Dipoles PRInterval
PotentialDeclinewithIncreasing VentricularActivation(QRSComplex)
Distancefromthe Heart
CommonNormalVariants
SolidAngleTheorem
VolumeConductor S1S2S3Pattern
RSR1PatterninLeadV
1
MethodsofRecording “EarlyRepolarization”Variant
ECGLeads PoorRWaveProgression inPrecordial
Vectorcardiography Leads
Magnetocardiography Athlete’sHeart
BodySurfaceMapping ObesityandEdema
Signal-AveragedECG
theory is based on an elementary model of a
Origin of the Electrocardiogram
single fiber surrounded by a homogeneous
medium. In such fibers, during resting the pos-
The waveform of the electrocardiogram (ECG) itive and negative boundaries are equal and
recorded from the body surface depends on the opposite in sign for the extent of the conductor.
properties of the generator (i.e., cardiac action This means that the polarized surface is closed,
potential),thespreadofexcitation,andthechar- and no potential is recorded (Figure 1–2, top
acteristicsofthevolumeconductor.Theelectro- tracing). When the excitation wave invades
cardiographic theory attempts to integrate these the fiber and reverses the charges across the
three elements.1 membrane, currents flow outside the fiber,
Figure 1–1 shows the temporal relation inside the fiber, and across the membrane, as
between the atrial and ventricular action poten- indicated by the arrows in Figure 1–1 (second
tials and the surface ECG. The P wave is derived tracing from top). This creates potential differ-
fromatrialdepolarization,theQRScomplexfrom ences of depolarization, which disappear when
ventricular depolarization, the ST segment from the double layer again becomes homogeneous
phase 2 (plateau), and the Twave from phase 3 in the fully activated state, as shown in the
of the ventricular action potential. The activity middle tracing of Figure 1–2. Subsequently a
of the conducting system is not represented on transition from an activated to a resting state
the surface ECG. Intracardiac electrodes can be occurs, a process of repolarization shown in
used to record His bundle potential and signals Figure 1–2 (fourth and fifth tracings from top).
from other parts of the conducting system.
DEPOLARIZATION AND DIPOLES
REPOLARIZATION
The he art conta ins about 10 10 cells. Each insta nt
Potential differences generated during cardiac of depolarization or repolarization represents
activitysetupcurrentsintheconductorssurround- different stages of activity for a large number of
ing the heart. A simplified electrocardiographic cells,andanelectromotiveforcegeneratedateach
1
2 SECTIONI (cid:1) AdultElectrocardiography
Figure1–1
Timingofcardiacactionpotentialsrecorded
during inscription of an ECG complex. The action poten-
tials responsible for the atrial and ventricular activation
are designated manifest and those responsiblefor impulse
initiationandpropagationasconcealed.Seetext.
Figure1–2
Restingstate,depolarization,andrepolariza-
instant represents a sum of uncanceled potential
tioninasinglecell,thetwoendsofwhichareconnectedto
differences. A potential difference between two agalvanometer.OntherightareECGdeflectionsresulting
surfaces or between two poles carrying opposite from the polarization changes in the diagram on the left.
chargesformsadipole,themagnitude(moment), (From Surawicz B: Electrocardiogram. In: Chatterjee K,
ParmleyWW[eds]:Cardiology.Philadelphia,JBLippincott,
polarity,anddirectionofwhichcanberepresented
1991,bypermission.)
by a vector.* The ECG records the sequence of
suchinstantaneousvectorsattributedtoanimagi-
narydipolethatchangesitsmagnitudeanddirec-
tion during impulse propagation. During activity
therecordingelectrodeisinfluencedbythepoten-
tial difference across the boundary; the record of
activity, represented by an instantaneous vector,
depends on the position of the electrode within
theelectricalfieldcreatedbythedipole.
Figure 1–3 represents an electrical field with
acentrallocationofadipoleinanidealhomoge-
neousmedium.Thesolidlinesrepresentpositive
and negative isopotential lines. The maximum
potentialsaregivenvaluesofþ20and–20.They
are in close proximity to the poles of the dipole
(i.e., the source and the sink). The potentials
decrease with increasing distance from the
dipole. The vertical interrupted line that trans-
ects the dipole isa zeropotential line. The leads
totherightofthislinerecordpositivepotentials,
Figure 1–3 Electrical field generated by a dipole (-/þ).
(From Surawicz B: Electrocardiogram. In: Chatterjee K,
*A dipole is a source-sink pair separated by a short ParmleyWW[eds]:Cardiology.Philadelphia,JBLippincott,
distance. 1991,bypermission.)
1 (cid:1) NormalElectrocardiogram:OriginandDescription 3
and those to the left of the line record negative same time it can be understood that the anterior
potentials. An electrode connecting two points precordial leads, owing to their proximity to the
on the isopotential line records no potential heart,areinfluencedbythelocalpotentialsgener-
differences. ated in the structures lying directly underneath
In the prototype model of Einthoven et al.,2 the corresponding electrodes.
the postulated generator of cardiac activity was
a single dipole at the center of the triangle, and SOLID ANGLE THEOREM
the postulated volume conductor was both
homogeneous and unbounded. This oversimpli- The basic concept applicable to the analysis of
fied model remains useful for teaching electro- the body surface potentials states that at any
cardiography at the elementary level. It does givenpoint,therecordedpotentialisdetermined
not explain, however, the three-dimensional by the productof a solid angle subtended at this
(3D) distribution of cardiac electrical activity in point by the boundary between the opposing
theheartateachpointintimeduringthecardiac charges and the charge density per unit area
cycle. It has been suggested that the electromo- across the boundary (Figure 1–4). This means
tive forces generated by ventricular excitation that for any given charge density, the deflection
canbe expressedmore properlyby theelectrical recorded by the electrode facing the boundary
field of several dipoles rather than by that of a increases with increasing surface of the bound-
single dipole.3 aryand,conversely,thatforanygivendimension
of the boundary surface, the magnitude of the
POTENTIAL DECLINE WITH recorded deflection increases with increasing
INCREASING DISTANCE charge density across the boundary. The solid
FROM THE HEART angletheoremhasbeenfoundusefulforanalysis
of potential differences caused by injury cur-
It has been established that in the volume con- rents4 (see Chapter 7).
ductor with the properties of the human thorax,
the potential declines approximately in propor- VOLUME CONDUCTOR
tion to the square of the distance. This means
that,forpracticalpurposes,allpointsonthetorso The conductivity of tissues surrounding the
situatedatadistanceofmorethantwodiameters heartinfluencestheamplitudeoftheECGdeflec-
oftheheartareapproximately“electrically”equi- tions. Tissues with low conductivity decrease the
distant from the generator. Thus the remoteness amplitude of the ECG deflections. Low voltage
ofthe electrodesplacedonthe extremities issuf- is present when the lungs are hyperinflated or
ficienttominimizethenondipolarcomponentsof when the heart is insulated by a large amount of
the ECG caused by the proximity effect. At the fat.Lowvoltagecanalsobecausedbypericardial
Figure1–4
Potentialsgeneratedbyanexcitationwaveofsourcesandsinksarerelatedtothesolidangleoftheexcitation
waveasseenfromthefieldpoint.Thesolidangleisthefractionofaunitspheresubtendedbyathree-dimensionalobject.
Thesymbolis thepotentialgeneratedby theillustratedsource-sinkboundary.Thispotentialisdeterminedby thecharge
densityacrosstheboundary,thesolidangle,andthereciprocalofthesquareofthedistancefromtheboundarytothefield
point.(FromBarrRC:Genesisoftheelectrocardiogram.In:MacfarlanePW,LawrieTD[eds]:ComprehensiveElectrocardiol-
ogy.NewYork,Pergamon,1989.Copyright1989ElsevierScience,bypermission.)
4 SECTIONI (cid:1) AdultElectrocardiography
and pleural effusions or edema owing to the
short-circuiting action of these well-conducting
fluids.
Methods of Recording
ECG LEADS
To study the electromotive forces generated dur-
ing the propagation of cardiac impulses, it is
necessary to attach the leading electrodes to the
heart or to the body surface. When one or both
electrodes are in contact with the heart, the
ECGleadsarecalleddirect.When theelectrodes
are placed at a distance of more than two car-
diac diameters from the heart, the leads are
called indirect. Semidirect leads designate an
arrangement in which one or both electrodes
Figure 1–5
are in close proximity but not in direct contact Einthoven’s triangle showing the projection
ofavectorontheaxesofthreestandardlimbleads.(From
with the heart. The leads are considered bipolar
Surawicz B: Electrocardiogram. In: Chatterjee K, Parmley
when both electrodes face sites with similar
WW [eds]: Cardiology. Philadelphia, JB Lippincott, 1991,
potentialvariationsandunipolarwhenpotential bypermission.)
variations of one electrode are negligible in
comparison with those of the other. Of the 12
standard ECG leads, I, II, and III are indirect
and bipolar; aV , aV , and aV are indirect and
R L F
unipolar; and V through V are semidirect
1 6
and unipolar.*
The three standard limb leads were designed
byEinthoventorepresentthreesidesofanequi-
lateral triangle in which the heart is positioned
at the center (Figure 1–5). As stated previously,
this concept arose from an assumption that the
electromotive forces of the heart could be repre-
sentedbyasinglevectorcenteredinthistriangle.
According to Einthoven’s law, the magnitude of
thedeflectioninleadIIequalsthesumofdeflec-
tionsinleadsIandIII.Figure1–6illustratesthis
point.
Although a more accurate system of elec-
trode placement at points equidistant from the
heart has been proposed by other investigators,
theuseofEinthoven’sleadshasbecomeuniver-
sally entrenched. The unipolarchest leads were
Figure 1–6
introducedbyWilsonforthepurposeofdimin- Einthoven’s law. Note an isoelectric QRS
ishing the influence of the distant reference complexinleadIIasaresultofequalamplitudesofoppo-
sitepolarityinleadsIandIII.
electrode. He constructed a zero potential elec-
trode (V) by connecting the three limb electro-
desthroughequalresistancesof5000ohmstoa
terminal to the individual limb electrodes
central terminal. Wilson and coworkers5 devel- (V ,V ,V ).Subsequently,Goldberger6discon-
oped the system of unipolar chest leads and R L F
nected the resistors placed between the limb
unipolar limb leads taken from the central
and the central terminal and thus augmented
(a) the voltage of these leads about 1.5 times
(aV , aV , aV ). The relation between the stan-
*TheuseofthetermunipolarinreferencetoECGleadsis R L F
dard and unipolar augmented leads is as fol-
controversial because the potential at the central terminal
poleisnotnegligible. lows:
1 (cid:1) NormalElectrocardiogram:OriginandDescription 5
aV þaV þaV ¼0
R L F
ThedirectionofleadIis0degrees;leadII,60
degrees; lead III, 120 degrees; lead aV , 90
F
degrees; lead aV , –30 degrees; and lead aV ,
L R
–150 degrees.
Lead Display
The traditional sequence of lead display in
a standard 12-lead ECG is: I, II, III, aV , aV ,
R L
aV ,andV –V .Thissequencedisplayslogically
F 1 6
theprecordialleads,butnotnecessarilythelimb
leads, where the displayed panoramic clockwise
sequence would be: aVL, I, –aVR, II, aVF, and III. Figure 1–7 Directions of the lead axes of leads V1
The latter display was endorsed by a large num- throughV .
6
ber of leading electrocardiographers7 but has not
yet prevailed to alter the established tradition.
Intrinsic and Intrinsicoid Deflections
Vectors and Electrical Axis
When the electrical activity on the cardiac sur-
Theelectromotiveforcegeneratedbytheheartat face is recorded by means of a unipolar lead,
any instant can be represented by the vector the activation front approaching the electrode
forceofasingleequivalentdipolesituatedatthis registers an upright deflection, but as soon as
point. This vector points from the negative to the activation front reaches the electrode, the
thepositivepotential(coincidentwiththedirec- direction changes and the electrogram records
tion of the impulse propagation), and its magni- a rapid negative deflection, which is referred to
tude is proportional to the magnitude of the as intrinsic. The validity of this concept, pro-
electromotive force. The voltage registered in a posed by Lewis et al. in 1914, was supported
given lead corresponds to the projection of the by the experiments of Dower.8
cardiac vector on the axis of the lead (see Dower showed that an electrode placed on
Figure 1–5). The maximum deflection is the surface of the guinea pig heart inscribes
registered when the vector is parallel, and the a negative deflection that coincides with the
minimum deflection is seen when the vector is upstroke of the ventricular action potential in
perpendicular to the lead axis. theimmediatelysubjacentcell.InDower’sstudy,
The maximum QRS vector is used to define theintrinsicdeflectionwasmarkedmoresharply
the main axis. This vector usually corresponds ontheleftthanontherightsurfaceoftheheart.8
to the R axis. The mean QRS axis is the average Thetransitionfrompositivetonegativeisless
ofallinstantaneousvectorsduringtheQRScom- abrupt in semidirect unipolar precordial leads
plex.The general phrase “electrical heart axis in than in direct leads, which makes the intrinsic
thefrontalplane”issometimesusedinreference deflection less rapid and less distinct. For this
to the main axis and sometimes to the mean reason, this deflection was designated by
axis. This designation is meaningful only when McLeod et al. in 1930 as intrinsicoid. The onset
one dominant deflection is present in at least of an intrinsicoid deflection in the precordial
one of the limb leads. When the QRS complex leads corresponds to the peak of the tall R wave
is biphasic in all leads, the meaning of the aver- or the nadirof the deep S wave. The onset of an
age QRS axis changes because the vectorcardio- intrinsicoiddeflectionmaybedelayedifthedura-
graphic QRS loop (see later discussion) is tionof the excitationwave spreadingtowardthe
nearly circular. Such a biphasic pattern with an recording electrode is prolonged owing to
indeterminate axis is described preferably as a increased ventricular wall thickness. In the right
sequence of two main axes corresponding to precordial leads the upper limit of normal is
the initial and terminal deflections. 0.035 second, and in the left precordial leads it
Thesemidirectprecordialleadsintroducedby is 0.045 second. This interval is used mostly to
Wilson record the potential differences between diagnose ventricular hypertrophy and bundle
the chest electrodes and the central terminal branch block when the onset of the intrinsicoid
(V) electrode at locations shown in Figure 1–7. deflectionisdelayed.