Abildskov, J.A.

Green, Larry S.

Lux, Robert L.

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394
The Present Status of Body Surface Potential Mapping*
J. A. ABILDSKOV, MD, FACC, LARRY S. GREEN, MD, ROBERT L. LUX, PhD
Salt Lake City, Utah
JACC Vol 2. No 2
August 1983 394-6
More extensive sampling of electrocardiographic potentials
than is provided by the usual 12 lead examination has prom-
ise of significant medical utility. The broad objective is to
improve the electrocardiographic examination in general and
the more specific objective is to achieve a regionally selec-
tive evaluation of the electrophysiologic state of the heart.
Examples of particular clinical aims of such selective ex-
aminations are the estimation of myocardial infarct size,
detection, localization and quantification of localized car-
diac hypertrophy, localization of sites of preexcitation and
arrhythmia origin and detection of arrhythmia-prone states.
Historically, the probable utility of extensive sampling
has been recognized since early studies of the electrocar-
diogram. In 1889, Waller (1) illustrated the body surface
distribution of "inequalities of potential" as a diagrammatic
isopotential map. The six precordial leads that are a part of
the routine 12 lead electrocardiogram were introduced as a
limited form of body surface mapping compatible with avail-
able instrumentation and practical for clinical application
(2). The relation of these leads to the objectives of body
surface potential mapping was clearly expressed by Wilson
et al. (3), who described them as the best available substitute
for direct leads from the surface of the heart and reported
evidence for the conclusion that they were "in effect semi-
direct leads from that part of the ventricular surface which
is nearest the precordial electrode." These investigators (2)
also expressed a certainty that the future would see a "great
*Editorials published m the Journal of the American College of Car-
diology reflect the views of the authors and do not necessarily represent
the views of JACC or the American College of Cardiology.
From the Nora Eccles Harrison Cardiovascular Research and Training
Institute and the Cardiology Division of the Department of Internal Med-
icine, University of Utah School of Medicine, Salt Lake City, Utah. This
work was supported by Program Project Grant HL 13480 from the National
Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda,
Maryland; awards from the Nora Eccles Treadwell Foundation. Salt Lake
City, Utah, and the Richard A. and Nora Eccles Harrison Fund for Electro-
cardiographic Research, University of Utah, Salt Lake City, Utah Manu-
scnpt received January 4, 1983; revised manuscript received February 28,
1983, accepted March 7, 1983.
Address for reprints: J. A. Abildskov, MD, Cardiovascular Research
and Training Institute, Nora Eccles Harrison Building. University of Utah,
Salt Lake City, Utah 84112.
© 1983 by the American College of Cardiology
increase in the use of precordial and other special leads and
that it will bring us far greater knowledge of the electro-
cardiogram. "
Problems in Methodology
Precordial mapping. Precordial lead arrays of more than
the usual six leads have been used to detect ischemic heart
disease with stress testing and to estimate the size of an
ischemic lesion. Evidence of improved detection of isch-
emic disease and useful estimates of anterior lesion size
have been reported and suggest the possibility of improved
electrocardiographic examination by more extensive sam-
pling (4-7). Precordial mapping should, however, be dif-
ferentiated from efforts to obtain potential distributions over
the entire thorax and achieve regionally selective exami-
nation of the entire heart (8).
Potential distributions over the entire thorax. Sub-
stantial systematic studies of the extensively sampled body
surface electrocardiogram over the entire thorax have re-
quired modem electronics and computer science for the
acquisition and processing of the large amount of data col-
lected in each examination. Such studies are now in progress
and have provided convincing evidence that an improved,
clinically practical electrocardiographic examination is fea-
sible. It has been unequivocally demonstrated that sufficient
sampling of body surface potentials provides selective sen-
sitivity to individual cardiac regions and greater information
content than that of vectorcardiographic or 12 lead exami-
nations. This evidence ranges from the simple presence of
multiple poles in isopotential maps to the detection of ep-
icardial breakthrough of ventricular excitation and localiza-
tion of sites of preexcitation and ectopic ventricular exci-
tation (9-12). Identification of preexcitation sites and sites
of arrhythmia origin are examples of medically useful in-
formation in addition to providing evidence of regional sen-
sitivity of mapping. There has been remarkable progress in
the development of instrumentation for the simultaneous
acquisition of large numbers of electrocardiographic leads
and in the use of computers to utilize cardiac-generated
potential distributions for medical purposes. In other work,
0735-1097/83/$3 ()()
lACC Vol 2, No 2
August 1983 394-6
EDITORIALS 395
redundancy in the extensively sampled body surface poten-
tial distribution has been systematically investigated and it
has been shown that a relatively small number of appro-
priately chosen electrode sites can be used to estimate the
total body surface potential distribution with a high degree
of accuracy, Specific lead sets consisting of 24 and 32 elec-
trodes have been designed and are in use in clinical studies
(13,14).
Computer processing of map data. There has also been
substantial progress in the computer processing of map data
for medical purposes. In one approach, body surface map
data are used together with models of varying complexity
to predict the cardiac surface potential distribution or ar-
rangement of cardiac sources necessary to account for the
body surface data. This approach can be considered a form
of cardiac imaging in which various aspects of the electro-
physiologic state of the heart are the items responsible for
the image. Another approach to processing map data for
medical purposes consists of reducing spatial and temporal
redundancy in maps by calculating sets of independent basis
functions applicable to all maps and specifying the char-
acteristics of individual maps by coefficients (15,16), This
approach permits efficient storage of complete map data
using slightly more than 200 numbers, in contrast to the
100,000 or 200,000 numbers required to specify the original
data. More importantly, the relatively small number of coef-
ficients are amenable to standard statistical methods for sep-
aration of data into diagnostically significant categories and
may permit automated classification,
Clinical Applications
Problems in clinicalapplications. Despite the promise
of substantial utility and several years of extensive theo-
retical, experimental and clinical study, body surface po-
tential mapping still requires further research to establish its
place in medical practice. The scientific and technical prob-
lems are formidable, and while notable progress has been
made, the technique is not yet suitable for widespread med-
ical application, The overriding problem is common to all
clinical research involving a new or modified technique,
namely, that of obtaining adequate independent confirma-
tion that the technique provides valid and useful informa-
tion. This problem is particularly difficult in the case of
body surface potential mapping because the objective of
improving electrocardiographic examination in general is
extremely broad,
Closely related problems are those of establishing criteria
for diagnostic classification of body surface potential fea-
tures and defining optimal methods of display and analysis
to detect these features. These are also particularly difficult
problems for body surface potential mapping because of the
large amount of data collected in each examination. In view
of these problems, the most likely route by which body
surface potential mapping may become a part of actual med-
ical practice is by sufficient validation that it is a source of
substantial useful information in one or a few disease states.
In particular, significant information that is not furnished
by other procedures would justify inclusion of the technique
in medical examinations.
Ischemic heart disease. Because the unique feature of
body surface potential mapping is its ability to provide evi-
dence of the regional electrophysiologic state of the heart,
the most likely areas of clinical utility are ones involving
that state, A possible example is the evaluation of ischemic
heart disease. Coronary arteriography is the definitive means
of recognizing coronary obstruction but does not reflect
myocardial ischemia as such. Detection of regional electro-
cardiographic abnormalities due to ischemia may therefore
have different diagnostic and prognostic significance and
therapeutic implications than arteriographic findings. Mean-
ingful use of body surface potential mapping for this pur-
pose, however, will require independent validation of the
presence of ischemia. It will also be necessary to identify
sensitive and specific map features that are caused by isch-
emia and to obtain evidence that these features are impor-
tantly related to the clinical course of patients with ischemic
heart disease.
Electrophysiologic abnormalities of theheart. In prin-
ciple, the same steps-namely, independent demonstration
of disease, identification of characteristic map features and
evidence of the medical significance of these features-are
required to establish the utility of body surface mapping for
each disease entity to which maps are applied. Considering
the numerous states in which mapping has possible value,
this would represent a substantial effort, and it is appropriate
to inquire whether such effort is justified. Although a final
answer cannot be given in advance of the actual studies, a
variety of considerations strongly suggest the effort is jus-
tified, One item is the very substantial utility of the currently
used 12 lead examination, It is highly unlikely that this
constitutes the optimal electrocardiographic examination and
its considerable value despite its defects strongly suggests
that a more nearly ideal examination would have major
medical significance.
Justification for continued study of body surface potential
mapping is also provided by the great medical importance
of electrophysiologic abnormalities of the heart. Although
these abnormalities are usually secondary to some form of
organic heart disease, they are an extremely important mech-
anism of death and disability due to disordered cardiac rhythm,
It is virtually a truism that electrophysiologic abnormalities
are most likely to be detected by examination of the elec-
trophysiologic state of the heart. Some aspects of that state
can be inferred from abnormalities of wall motion and some
are appropriately evaluated by invasive procedures such as
intracardiac stimulation and electrographic recording; how-
ever, the body surface electrocardiogram is the most widely
396 EDITORIALS JACC Vol 2. No. 2
August 1983:394-6
applicable method of examination. The regional sensitivity
of body surface potential mapping has special relevance to
arrhythmias because localized abnormalities of conduction
and repolarization are important factors in these disorders.
Recognizing states predisposing to ventricular ar-
rhythmias. One of the most promising areas in which body
surface potential mapping may provide medically significant
information not available from other techniques is that of
recognizing states predisposing to ventricular arrhythmias.
The QRST deflection area has been documented to reflect
disparity of repolarization duration , which is an established
factor in reentrant arrhythmias (17-19). By combining the
regional selective sensitivity of body surface mapping and
the physiologic significance of the QRST deflection area , it
may be possible to identify the local inequalities of repo-
larization that predispose the ventricles to arrhythmias . Both
experimental and clinical observations support this possi-
bility. In dogs , a quantity based on analysis of the body
surface distribution of QRST deflection areas was shown to
increase in states of enhanced arrhythmia vulnerability (20).
In clinical studies (21,22) , multipolar distributions of QRST
deflection area have been noted in patients resuscitated from
ventricular fibrillation and in the postexercise maps of pa-
tients who also exhibited ectopic ventricular complexes. The
optimal analysis of QRST deflection area distributions for
the possible recognition of states at risk of arrhythmias is
not yet certain , but the maximal gradient of areas in local
body surface regions and the nondipolar content of distri-
bution are promising possibilities. In a recent study (23),
the multipolar content of QRST deflection area distribution
in 25 patients with recurrent ventricular tachycardia was
34% while in an age-matched group of normal subjects, it
was 12%.
In summary, clinically practical body surface potential
mapping is feasible and has promise of significantly im-
proving electrocardiographic examination by providing se-
lective sensitivity to regional electrophysiologic conditions.
The procedure is still at a research stage of development
although a variety of findings strongly suggest its medical
utility. Justification for its inclusion in clinical practice re-
quires additional studies with independent documentation
of disease . More evidence that it provides useful information
in addition to that furnished by other examinations is also
needed . The recognition of arrhythmia-vulnerable states of
disparate ventricular repolarization is a particularly prom-
ising area of clinical utility.
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The present status of body surface potential mapping 

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The present status of body surface potential mapping

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