Mean Electromechanical
AP /At
An Indirect Index of the Peak Rate of Rise of Left Ventricular Pressure
GEORGE DIAMOND,
MD*
JAMES S. FORRESTER, MD
KANU CHATTERJEE, MEBS
STANLEY WEGNER, BA
H.J.C. SWAN, MB, PhD, FACC
Los Angeles,
California
From the Department of Cardiology, CedarsSinai Medical Center and the Department
of
Medicine, University of California at Los Angeles, Calif. This study was supported in part
bv Contract Nl-H-PH-68-1333
under the Myoc&dial
Infarction
Research
Unit Program,
National Heart and Lung Institute, the National Institutes
of Health, Department
of
Education
and
Welfare,
United
Health,
Hostesses Charities and U.S. Public Health
Service Grant 5 SO1 RR 05468. Manuscript
received
October 27, 1971; revised manuscript received
December
27, 1971. accepted March 31, 1972.
*Present
address: Valley Forge General
Hospital, Phoenixville, Pa. 19460.
Address for reprints: James S. Forrester,
MD, Department
of Cardiology,
Cedars of
Lebanon Hospital, 4833 Fountain Ave., Los
Angeles, Calif. 90029.
338
September 1972
Eighteen patients with acute myocardial infarction were studied by
means of pulmonary arterial and left ventricular catheterization. An
indirect index of the maximal rate of rise of left ventricular pressure,
dP/dt, was derived from measurement of developed isovolumic pressure (arterial diastolic minus left ventricular diastolic) and the preejection period (PEP): mean electromechanical AP/At = developed
pressure/PEP.
The correlation of this index with left ventricular
dP/dt was excellent (r = 0.66), with a residual variance of 6 percent.
In 50 subjects with acute myocardial infarction AP/At also correlated closely with the presence of pulmonary vascular congestion
and shock and with ultimate survival. In contrast, mean arterial pressure, left ventricular filling pressure, left ventricular ejection time
(LVET), preejection period and LVET/PEP demonstrated marked
overlap between groups. Mean electromechanical
AP/At was
accurate and useful as an indirect index of left ventricular dP/dt and,
thus, of the functional state of the left ventricle.
Accurate serial evaluation
of left ventricular
function would be of considerable value in the management
of patients
with acute myocardial
infarction
and other serious cardiovascular
states. No presently
available single index of myocardial
contractile
state is entirely suitable,
since each is at least partly dependent
on loading conditions
of the
heart.132 Although the maximal rate of rise of left ventricular
pressure
(dP/dt)
is one of the most useful reflectors of contractility,ax*
its clinical use is limited not only by its dependence
upon preload and afterload, but also by the need for direct left ventricular
catheterization.
Several investigators
have attempted
to eliminate
the latter requirement by estimating
left ventricular
dP/dt
indirectly
from arterial
pressure or systolic time intervals. 5 However, use of these techniques
ignores the dependence
of left ventricular
dP/dt
on left ventricular
filling pressure.
With the recent development
of a pulmonary
arterial
balloon catheter,6
a safe, reliable
and readily applicable
method for
measurement
of filling pressure is now available,
The purpose of the
present study was to develop an easily obtainable
indirect
index of
left ventricular
dP/dt requiring
minimal
intravascular
invasion.
Results
indicate
that
this index,
termed
mean
electromechanical
AP/At,
is of practical
clinical
acute myocardial
infarction.
use in the management
of patients
with
Methods
Fifty patients
with acute myocardial
infarction,
ranging in age from 40 to
80 vears. were studied in the Mvocardial
Infarction
Research Unit from 2 to
24 hours’after
admission.
Left ventricular
ejection time (LVET) and preejection period (PEP) were obtained
from the phonocardiogram
and indirect
carotid pulse tracing according
to the method of Weissler et al.,7 using the
standard
limb lead of the electrocardiogram
with the most prominent
Q wave.
The American Journal of CARDIOLOGY
Volume 30
MEAN
ELECTROMECHANICAL
I33 LV
dP/dt
n LVET/PEP
20 g
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AP/At-DIAMOND
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zoao
loo0
LV
dP/dt
3ooo
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Figure 2.
Effect of digitalis on indexes of left ventricular function in 3 patients. Changes in left ventricular
AP/At
parallel
those of left ventricular dP/dt.
.
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Figure 1. Correlation of left ventricular
dP/dt with (A) AP/At
and (B) LVET/PEP in 18 patients with acute myocardial infarction. There is a precise linear correlation of dP/dt with AP/At,
illustrated by the regression line, but not with LVET/PEP.
Left ventricular
filling pressure was estimated as pulmonary arterial end-diastolic
or pulmonary capillary wedge
pressure using a balloon-flotation
catheter6 inserted by
cutdown procedure into an antecubital vein. Arterial pressure was measured either directly or by sphygmomanometer. In 18 patients, 1e:ft ventricular
catheterization
was
performed at the bedside by a method previously described.* The frequency response of the catheter system
used was flat * 5 percent up to 15 Hz. The first derivative
of left ventricular
pressure was obtained with use of an
active differentiating
circuit, calibrated
with a triangle
wave generator. All analog data were recorded at paper
speeds of 5,25 and 100 mm per second.
Mean electromechanical
AP/At was calculated as de]pressure/PEP,
where
developed
veloped
isovolumic
isovolumic
pressure
equals arterial
diastolic
pressure
minus left ventricular
filling pressure. Left ventricular
failure was determined clinically as the presence of posttussive pulmonary
rales .or a ventricular
gallop third
sound in association with radiologic evidence of pulmonary vascular congestion, or both.9 Cardiogenic shock was
defined according to the definition of Swan et al.le On the
basis of these definitions, 14 patients
had left ventricular
failure and 10 were in shock at the time of study.
Results
Relation of LV dP/dt,
AP/At and LVET/PEP:
Figure 1A demonstrates
the relation
between simultaneously
determined
mean
electromechanical
September
AP/At and left ventricular
dP/dt in 18 patients.
The
correlation
was excellent
(r = 0.96, P <O.OOl) over a
wide range of values.
The average variance
was 8
percent. In contrast,
there was only a fair correlation
(r = 0.76) and marked variance
(42 percent) between
the
noninvasive
index
LVET/PEP
and
either
electromechanical
AP/At
or left ventricular
dP/dt
(Fig. 1B). In 3 subjects
digitalis
was given to augment the contractile
state. In all 3 patients
left ventricular
dP/dt
and electromechanical
AP/At
increased
in parallel,
whereas
LVET/PEP
did not
(Fig. 2).
Relation
of AP/At
to preload
and afterload:
Figure 3 illustrates
the relation
of mean electromechanical
AP/At to ventricular
preload (left ventricular filling
pressure)
and afterload
(mean
arterial
pressure)
in 50 subjects
with acute myocardial
infarction.
There was a fair correlation
of AP/At with
afterload
(r = 0.81) and a rough negative
correlation
of AP/At with preload (r = -0.46).
Relation of AP/At to clinical status:
When patients were classified
on the basis of the presence of
pulmonary
vascular
congestion
and
cardiogenic
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Relation of AP/At to afterload (mean arterial presFigure 3.
sure) and preload (left ventricular filling pressure) in 50 patients
with acute myocardial infarction. As with left ventricular
dP/dt,
there is a general positive correlation with afterload, and a general negative correlation with preload.
1972
The American
Journal of CARDIOLOGY
Volume 30
339
MEAN ELECTROMECHANICAL
AP/At-DIAMOND
ET AL.
Discussion
-I
1 LVET/PEP
1
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LVF
OMP
UNCOMP
SHOCK
LVF
SHOCK
Figure 4.
Relation of AP/At and LVET/PEP to clinical status
in 50 patients with myocardial
infarction.
The level of AP/At
generally paralleled the degree of cardiac impairment from uncomplicated
(uncomp) through pulmonary vascular congestion
(LVF) to shock.
shock, electromechanical
AP/At
paralleled
the degree of cardiac
impairment
with little
overlap,
whereas
LVET/PEP
demonstrated
marked
overlap
(Fig. 4). As a prognostic
indicator,
a AP/At of 500
mm Hg/sec
separated
survivors
from nonsurvivors
with minimal
overlap over only 7 percent of the total
range: whereas mean arterial pressure,
left ventricular ejection time and LVET/PEP
were less accurate
(Fig. 5). In addition,
the individual
indexes determining
AP/At,
namely,
arterial
diastolic
and left
ventricular
filling pressures,
developed pressure (DP)
and preejection
period,
did not serve to separate
clinical groups when analyzed individually.
500
PEP
8-
LVET
Previous studies have demonstrated
the usefulness
of left ventricular
dP/dt
as an index of myocardial
contractility,
despite
its dependence
upon arterial
pressure and left ventricular
filling pressure.sv4 However,
its determination
requires
left ventricular
catheterization
and its clinical use is limited accordingly, particularly
when serial observations
are needed for the management
of acutely ill patients,
such
as those with acute myocardial
infarction.
Hence, a
reliable
index of left ventricular
function
which can
be obtained
easily and frequently
by a relatively
noninvasive
technique
would
be highly
desirable
in
clinical practice.
Systolic time intervals,
although
useful in identification of broad patient
groups, have demonstrated
enough overlap to limit their usefulness
as indexes of
function
in an individual
patient.11
The relation
between noninvasive
indexes, such as LVET/PEP,
and
directly determined
hemodynamic
indexes, as represented by the correlation
coefficient,
has not exceeded 0.9 and is usually 0.8 or less. Such coefficients
of
correlation,
while highly significant
in terms of a
general biological
relation,
are associated
with a residual variance
following regression
of 20 to 35 percent. In contrast,
the correlation
of electromechanical AP/At with left ventricular
dP/dt reported herein was such that the residual
variance
was only 8
percent.
Therefore,
although
LVET/PEP
and other
indirect measurements
may have a linear correlation
with
left
ventricular
dP/dt,
electromechanical
AP/At is considerably
more valuable
than other indirectly
determined
indexes
in predicting
the true
value of left ventricular
dP/dt
for an individual
subject.
The present
study
shows that the index
mean electromechanical
AP/At reflects the level of
left ventricular
dP/dt
to a degree of accuracy
that
2oca
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LVET/PEP
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Figure 5.
Relation of hemodynamic
variables to survival (S) and nonsurvival
(N) in 50 patients with acute myocardial
infarction.
AP/At produced a very good separation of the 2 patient groups at a level of 500 mm Hg/sec. There was marked overlap in other indexes. BP = mean arterial pressure: LVET = left ventricular ejection time; LVFP = left ventricular filling pressure: PEP = preejection
period.
340
September 1972
The American Journal of CARDIOLOGY
Volume 30
MEAN
permits
meaningful
individual
predictability
of
hemodynamic
state.
13ecause AP/At
is related
to
ventricular
loading
conditions,
changes
in mean
electromechanical
AP,‘At, like changes
in left ventricular
dP/dt,
may be used to estimate
changes in
ventricular
contractile
state
only in the absence
of major alterations
in arterial or left ventricular
filling pressure.
The
negative
correlation
of electromechanical
AP/At with left ventri’cular
filling pressure is unusual in that left ventricular
dP/dt normally
rises with
filling
pressure,
presumably
as a function
of the
Starling
effect.2 This finding
may relate to diminished ventricular
functional
reserve in patients
with
acute myocardial
infarction.2
Although
left ventricular
dP/dt is a useful indicator of changes in contractility
in a given patient,2
it
is less effective
in characterizing
patient
groups,
since values for persons with mild to moderate
cardiac depression
may fall within the normal
range. In
the present
study, therefore,
a moderate
overlap of
AP/At
was seen among clinical
groups. The excellent separation
between
survivors
and nonsurvivors
by AP/At in this stud,y may reflect the tendency
for
this index to reflect best severe depression
of cardiac
contractility,
although
preload
and afterload
were
most altered in the nonsurvivor
group.
AP/At
is not necessarily
superior
to other more
traditional
measures
of cardiac
function.
Since
stroke volume
and stroke work, for example,
were
not determined
in this study, it was not possible to
compare
these
indexes
as prognostic
indicators.
Other studiesI
have s’uggested that standard
hemodynamic
determinations
are of limited value in this
regard, although
the level of stroke work, which is
largely determined
by the same factors that determine AP/At, may be of definite prognostic value.14
The correlation
between left ventricular
dP/dt and
electromechanical
AP/‘At has its theoretical
basis in
the fact that the mean rate of rise of left ventricular
pressure
during
isovolumic
systole
(developed
isovolumic
pressure
divided
by isovolumic
contraction time) parallels
peak left ventricular
dP/dt4
in
the absence of significant
aortic stenosis.
Developed
isovolumic
pressure
may be estimated
with relative
accuracy
from the arithmetic
difference
between
arterial diastolic
and left ventricular
filling pressure.
However,
isovolumic
contraction
time is difficult
to
measure
indirectly
with accuracy,
especially
in pa-
ELECTROMECHANICAL
AP/At-DIAMOND
ET AL.
tients
with acute
myocardial
infarction.12
Mean
AP/At,
therefore,
was derived from the preejection
period since directly
measured
isovolumic
contraction time has been shown to correlate
precisely with
simultaneously
and indirectly
determined
preejection period.13 The close correlation
between left ventricular
dP/dt
and mean electromechanical
AP/At
is thus not surprising.
However,
certain
limitations
are imposed by the method itself. Pulmonary
arterial
diastolic
and pulmonary
capillary
wedge pressures
may not provide a precise measurement
of left ventricular
end-diastolic
pressure,
most notably
in mitral stenosis.
Brachial
arterial
diastolic
pressure,
especially
when determined
by sphygmomanometer,
may not reflect true aortic diastolic pressure. In addition, use of the preejection
period as an index of isovolumic
contraction
time assumes
normal
left ventricular
activation
time. This assumption
would be
invalid in the presence of bundle branch block.
Clinical application:
The vascular
invasion
necessary for the determination
of AP/At is limited
to
insertion
of a pulmonary
arterial balloon catheters
at
the bedside without
fluoroscopy.
This technique
for
accurate
measurement
of left ventricular
filling pressure is now widely used in the management
of seriously ill patients. 14 By simultaneous
measurement
of preejection
period, systemic and pulmonary
arterial pressures,
the performance
of the left ventricle
can
be characterized
with a precision
not possible with
totally noninvasive
indexes.zJl
ArteriaI
puncture
is
necessary
only in the presence
of shock where pressure determinations
obtained
by sphygmomanometer
generally
correlate
poorly with direct intravascular
determinations.15
In summary, the development
of an indirect index
of left ventricular
dP/dt
extends
the clinical
use of
pulmonary
arterial pressure monitoring
to the evaluation
of left ventricular
function
when
marked
changes
in ventricular
preload
or afterload
do not
occur. Use of the index electromechanical
AP/At allows rapid, objective
serial determination
of clinical
response to therapy
and may be of value as a prognostic guide in the selection
of patients
with acute
myocardial
infarction
for the more aggressive
modes
of therapy currently
emerging.
Acknowledgment
We gratefully acknowledge the technical and nursing
assistance of Grace Meyer, RN and Docela Edwards, RN.
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The American Journal of CARDIOLOGY
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ELECTROMECHANICAL
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