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From the Division of Cardiology (S.T., H.I., K.I., Y.T., N.N., Y.H.,
K.F., T.M.), Sakurabashi Watanabe Hospital, and First Department of Medicine
(T.M., M.H.), Osaka University School of Medicine, Osaka, Japan.
Correspondence to Hiroshi Ito, MD, Division of Cardiology, Sakurabashi Watanabe Hospital, 2–4-32 Umeda, Kita-ku, Osaka 530, Japan.
Methods and Results—We recorded short-axis IBS images before
and 3, 7, and 21 days after reperfusion in 26 patients with AMI and
obtained the cyclic variation of IBS in the normal and infarct zones.
When cyclic variation showed synchrony and asynchrony, we expressed its
magnitude as positive and negative values, respectively, called the
phase-corrected magnitude. We also measured average wall motion score
(dyskinesis, 4; normal, 0) of the infarct segments. The phase-corrected
magnitude was lower in the infarct zone than in the normal zone before
reperfusion (0.3±2.5 versus 5.2±1.7 dB, P<.05). At
day 3, the phase-corrected magnitude increased by 2.1±2.6 dB despite
no improvement in wall motion. Improvement in wall motion was observed
only at day 21. The patients with the phase-corrected magnitude of
Conclusions—In patients with AMI, cyclic variation of IBS is
blunted during ischemia but recovers much faster after
reperfusion than the improvement in wall motion. The greater
phase-corrected magnitude at day 3 may be a predictor of better
functional improvement.
Ultrasonic tissue characterization with IBS offers a promising method
for the assessment of myocardial contractile performance
independent of wall motion.8 9 10 11 12 13 14 15 16 17 Normal
myocardium exhibits cardiac cycle-dependent variation of
IBS that reflects the intramural contractile performance. In
animals, the cyclic variation of IBS is blunted promptly by
ischemia and is augmented after
reperfusion.18 19 20 21 22 The recovery of wall motion
lags behind the recovery of the cyclic variation after brief periods of
myocardial ischemia. In patients with reperfused AMI, Milunski
et al23 documented that the obvious recovery of
cyclic variation of IBS is observed a mean of 7 days after
coronary reperfusion regardless of minimal improvement in wall
motion. Therefore, the analysis of cyclic variation of IBS may
have a potential to detect the viable myocardium early
after reperfusion.
In this study, we characterized the temporal changes in cyclic
variation of IBS at days 1, 3, 7, and 21 of reperfusion in patients
with AMI. We compared these changes with the temporal recovery of
regional wall motion to elucidate whether we can predict the functional
recovery in individual patient with ultrasonic tissue characterization
in the early stage of AMI.
Acoustic Densitometry
Protocol
Data Analysis
We determined the magnitude (in decibels) of cyclic variation of IBS as
the difference between the minimal and maximal values in a cardiac
cycle averaged over at least two consecutive beats. Absolute
calibration is unnecessary for measurement of the magnitude of cyclic
variation. Because the regional contraction in the infarct zone may not
be necessarily synchronized exactly with global contractile events, we
calculated a time delay for regional cyclic variation with respect to
global ventricular mechanical
systole.26 27 After measuring the interval from
the upstroke of QRS complex to the nadir of the cyclic variation at
each site, we divided the value by QT interval to determine the
normalized delay (unitless). We also corrected the magnitude of cyclic
variation with respect to the phase of regional contraction. In this
study, a mean of the normalized delay in the normal segment was
1.0±0.1. Therefore, if the normalized delay value was >1.2 (mean+2 SD
of normal), we considered it indicative of asynchronous (or delayed)
contraction or passive stretching and multiplied the magnitude by -1.0
(the phase-corrected magnitude). This is an approximation to the
phase-weighted amplitude.19 28 If the normalized
delay value is
Two independent observers who blinded to patients' clinical data
analyzed the wall motion at the site of region of interest in
each study with following scoring system: 4 indicates dyskinetic; 3,
akinetic; 2, severely hypokinetic; 1, hypokinetic; and 0, normal. In
the evaluation, we carefully examined the systolic thickening
in the central portion of each segment. In cases of disagreement, a
third observer established the consensus. We also evaluated the
recovery of wall motion in the risk segments showing asynergy at
baseline study. To do this, we divided the left ventricle into 17
segments (8 segments on each short-axis slice at the levels of the
mitral valve and midpapillary muscle, and apical segment on the apical
long-axis view).5 The same observers scored each
segment using the scoring system previously described. We defined wall
motion score index as an average of segmental scores of the risk
segments at days 1 and 21.
Reproducibility of Data
Statistics
Cyclic Variation of IBS Before Reperfusion
Temporal Changes in Cyclic Variation and Wall Motion After
Reperfusion
As a whole, there was no significant changes in the magnitude of cyclic
variation in the infarct region from baseline to the second study, and
it was still lower than that in the remote normal region (2.6±2.0
versus 5.2±1.4 dB, P<.05). The normalized time delay value
slightly decreased to 1.10±0.38 at day 3, but it was still higher than
that in the normal zone (1.10±0.38 versus 0.93±0.15,
P<.05). Phase-corrected magnitude of cyclic variation
significantly increased from baseline to day 3 (0.3±2.5 versus
2.1±2.6 dB, P<.05) (Fig 4
Prediction of Wall Motion Improvement From Phase-Corrected
Magnitude
The patients were divided into two groups according to this value for
phase-corrected magnitude: those with the phase-corrected magnitude of
Cyclic Variation of IBS in Infarct Segment
Several mechanisms are postulated to explain the cyclic variation of
IBS: (1) changes in acoustic impedance, which is related to passive
elastance; (2) changes in fiber orientation or shape from
diastole to systole; and (3) changes in elastic modules
during sarcomere shortening. In open-chest dogs, Wickline et
al12 showed that cyclic variation of IBS in the
myocardium parallels contractile performance.
However, wall thickening is not linearly related to the magnitude of
the cyclic variation in dogs with acute coronary occlusion
followed by reperfusion.19 30 Although influenced
by wall thickening, cyclic variation of IBS appears to reflect the
intramural contractile performance rather than geometric
phenomenon.8 9 10
Mechanisms responsible for the temporal delay of cyclic variation of
IBS are also unclear. In open-chest dogs, Brown et
al31 documented postsystolic shortening
and thickening of myocardium during coronary
ligation. Early diastolic or postsystolic events
may be related to persisting contraction or delayed relaxation within
the ischemic myocardium32 33
and perhaps to effects of stretching or passive
distention,11 although it is hard to
differentiate these events. Thus, the delayed cyclic variation that we
observed may reflect postsystolic events and ultimately provide
an approach for their detection and quantification. Because these
events are considered to be unfavorable to global left
ventricular contraction, we expressed the corrected
magnitude of cyclic variation as a negative value if the cyclic
variation exhibited asynchronous contraction.
Effect of Reperfusion
Milunski et al23 observed the temporal changes in
wall motion and cyclic variation of IBS in the infarct zone until a
mean of 7 days after reperfusion. However, the temporal changes in the
phase-corrected magnitude of the cyclic variation until the
convalescent stage of AMI and their relation to the recovery of wall
motion remain unknown. Our data demonstrated that the phase-corrected
magnitude increased until day 7 but did not exhibit a significant
changes at day 21. On the other hand, we observed substantial
improvement in wall motion of the infarct segment only at day 21. At
day 21, the majority of the infarct segment (88%) exhibited a
synchronous contraction pattern. This finding clearly demonstrated that
the improvement in wall motion lags behind the recovery of cyclic
variation of IBS and is in agreement with the results of an
experimental study that used a model of modest ischemic injury
("stunned" myocardium).
Although the recovery of the cyclic variation of IBS may be
accomplished within 7 days after reperfusion, the improvement in wall
motion requires
Magnitude of Cyclic Variation and Myocardial Viability
Study Limitations
One of the disadvantages of IBS imaging in its current form is that
there is a relatively narrow dynamic range before which system
saturation occurs. However, the problem regarding narrow dynamic range
can be minimized by reducing the transmit power. Another disadvantage
of IBS imaging in its current form is a significant degradation in
spatial resolution compared with conventional two-dimensional
echocardiography.
The IBS signal is influenced by gain setting. We set the time-gain
control to the identical value in each patient, and only total gain was
controlled to clearly depict the IBS image. The difference in total
gain should not influence the magnitude of the cyclic variation of
IBS.
Clinical Implications
Myocardial contrast echocardiography or
dobutamine stress echocardiography is
another method by which to assess myocardial viability in the early
stage of AMI.5 6 7 Because of technical
limitations, these methods cannot be applied to all acute patients.
Compared with these methods, ultrasonic tissue characterization is
simple; therefore, ultrasonic tissue characterization should be a new
diagnostic modality for evaluating myocardial viability at
the bedside in patients with AMI.
Received July 10, 1997;
revision received September 29, 1997;
accepted September 30, 1997.
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© 1998 American Heart Association, Inc.
Clinical Investigation and Reports
Ultrasonic Tissue Characterization Predicts Myocardial Viability in Early Stage of Reperfused Acute Myocardial Infarction
Abstract
Top
Abstract
Introduction
Methods
Results
Discussion
References
Background—The aim of the
present study was to characterize temporal changes in cyclic
variation of ultrasonic integrated backscatter (IBS), which reflects
intrinsic contractile performance, in patients with reperfused
acute myocardial infarction (AMI) and to elucidate the clinical value
of tissue characterization in predicting myocardial viability. 
2.0 dB at day 3 showed significantly lower wall motion score at day
21 than did the other patients (1.7±0.6 versus 2.4±0.5,
P<.01).
Key Words: myocardial infarction • echocardiography • reperfusion • myocardial contraction • ultrasonics
Introduction
Top
Abstract
Introduction
Methods
Results
Discussion
References
One of major problems
facing modern cardiology involves the evaluation of
myocardial viability within a region of acute ischemic injury.
This issue is particularly important in the era of rapid interventional
treatment for AMI. Methods based on wall motion analysis fail
to differentiate viable tissue from irreversibly damaged
myocardium until and unless wall motion
improves.1 2 3 4 Assessment of regional myocardial
perfusion with myocardial contrast echocardiography
or assessment of wall motion response to dobutamine stress
is another promising approach for evaluating myocardial
viability.5 6 7 However, these approaches are
performed in only a small number of acute patients because of technical
limitations.
Methods
Top
Abstract
Introduction
Methods
Results
Discussion
References
Study Population
The study group included 26 consecutive patients with AMI who
underwent successful coronary angioplasty within 24 hours after
symptom onset. Eligible criteria were (1) no prior myocardial
infarction, (2) totally or subtotally occluded infarct-related artery
(Thrombolysis in Myocardial Infarction grade 0 or 1) at
initial coronary angiography, (3) the postprocedural
stenosis of <50%, (4) no ischemic event during
follow-up, (5) patent infarct-related artery 1 month later, and (6)
adequate echocardiographic image quality. The diagnosis
of AMI was made on the basis of ischemic pain of 30 minutes'
duration, ST-segment elevation of 1 mm in two or more contiguous
ECG leads, and an increase in creatine kinase of more than three times
the normal value. ß-Blockers and calcium channel blockers were
administered at the discretion of the attending physician. No patients
were being treated with the positive inotropic agents. One of the
investigators obtained informed consent from each patient. The study
protocol was approved by the hospital ethics committee.
We used a special software package (Acoustic Densitometry)
developed by Hewlett-Packard incorporated into a commercially available
echocardiograph (SONOS 1500). This system is capable of
providing either conventional echocardiographic images
or two-dimensional images in which gray level is displayed proportional
to IBS amplitude. Sixty frames from consecutive cardiac cycles (30
frames/s) are displayed after scan conversion and are stored on the
optical disk. The system has a unique feature by which the transmit
power, log compression, and time-gain compensation values are displayed
on the screen and are stored with the images, which allows an operator
to adjust the system to the same values at any follow-up examination.
The dynamic range of the IBS processor is 40 dB.
We routinely performed multiple-plane
echocardiographic examination in the coronary
care unit before catheterization to establish the
diagnosis; this took a mean of 10 minutes. We used a sector scanner
equipped with acoustic densitometry (carrier frequency, 2.5 or 3.75
MHz). Each patient rested in a left decubitus position and breathed in
a relaxed manner. We recorded two-dimensional
echocardiographic images on 1.25-cm S-VHS videotape.
Then, we depicted two-dimensional IBS images of the short-axis plane at
the level of the papillary muscles and transferred the sequential 60
images (2 seconds) onto the 600-megabyte optical disk. This procedure
took <2 minutes. We repeated the multiplane two-dimensional
echocardiographic examination and the recording
of IBS images at 3, 7, and 21 days after the onset of AMI. The transmit
power, compression setting, and individual values of time gain
compensation were kept constant at each IBS study in individual
patients.
We analyzed the digitally acquired images with the
acoustic densitometry package to construct time-intensity waveforms of
the IBS. We divided the short-axis image of the left ventricle into
eight segments. We defined the segment at risk as the segment showing
severe hypokinesia, akinesia, or dyskinesia at baseline study. In the
analysis, we excluded the segments of the inferior
septum and the lateral wall because of the unreliability of waveform of
the cyclic variation in these segments. In these segments, the angle
between ultrasound beam and fiber orientation is shallow, so the
magnitude of IBS is significantly reduced.24 25
We placed the ovoid region of interest at the center of the segments at
risk and in the remote normal region in each patient at each
examination. We used the largest possible region of interest, which did
not include endocardial and epicardial reflectors. An experienced
echocardiographer manually adjusted the location of the
site on a frame-by-frame basis to keep the site within the myocardial
midwall throughout a cardiac cycle. Then, a curve of IBS versus time
was reconstructed. 
1.2, the phase-corrected magnitude is the same as the
measured magnitude value.
We determined intraobserver and interobserver variabilities of
measuring the magnitude and normalized delay value of cyclic variation
of IBS by measuring the two variables in 10 randomly selected
records twice by the same observer and by two independent
observers, respectively. Intraobserver and interobserver variabilities
of the magnitude of IBS were 4.2±4.0% and 5.1±4.2% (absolute
difference), respectively. Intraobserver and interobserver
variabilities of normalized delay values were 4.2±3.2% and 4.7±2.4%
(absolute difference), respectively.
All data are expressed as mean±SD. Multiple comparisons were
made with a one-way ANOVA, and individual data were compared with the
use of Scheffé's F test for factor analysis. Statistical
analysis of temporal changes in certain variables was
computed with ANOVA and Scheffé's F test for repeated measures.
Differences were considered significant at P<.05.
Results
Top
Abstract
Introduction
Methods
Results
Discussion
References
Patient Characteristics
Among the 26 patients (mean age, 59±12 years; age range, 36 to 77
years), 23 patients (81%) were male and 3 patients were female
(Table
). All patients had one-vessel disease. Anterior,
inferior, and posterior myocardial infarction was found in
16, 7, and 3 patients, respectively. The mean time from the
symptomatic onset to coronary reperfusion was
6.5±4.6 hours. The peak creatine kinase level was 3052±2050 IU/L.
Twenty-three patients (92%) subsequently developed Q-wave infarction,
and the other 3 manifested non–Q-wave infarction.
View this table:
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Table 1. Clinical Characteristics and IBS Data for 26 Study Patients
Cyclic variation of IBS was present in all 26 normal regions
and averaged 5.2±1.7 dB in magnitude. The average normalized time
delay of cyclic variation was 0.95±0.19 (Figs 1 and 2).
In the short-axis image, the center of all infarct segments showed
akinesia at baseline study. The magnitude of cyclic variation in the
infarct segments decreased significantly to 1.9±1.7 dB
(P<.05). No cyclic variation was detectable in 7 of 26
infarct segments. Even when these 7 regions were excluded from the
average, the magnitude of cyclic variation was still lower than normal
values, averaging 2.5±1.5 dB. Normalized time delay of cyclic
variation was measurable in 16 infarct segments, and the value was
significantly longer than that in the normal zone (1.25±0.49,
P<.05). Normalized delay value was >1.2 in 7 patients,
indicating asynchronous contraction or passive stretching. Thus, the
phase-corrected magnitude was significantly lower in the infarct
regions than in the normal regions (0.3±2.5 versus 5.2±1.7,
P<.05).
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Figure 1. Cyclic variation of IBS in the normal posterior
wall (left) and infarct anterior wall (right) in a patient with
anterior wall myocardial infarction. Cyclic variation in the normal
posterior wall shows synchronous contraction, but it shows an
asynchronous pattern in the infarct anterior wall. The magnitude is
significantly lower in the infarct zone than in the normal zone.
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Figure 2. Normalized time delay (left), magnitude (middle),
and phase-corrected magnitude (right) of cyclic variation of IBS at
baseline in the normal and infarct zones. Normalized time delay was
significantly greater and magnitude and phase-corrected magnitude were
significantly lower in the infarct zone than in the normal zone. Values
are expressed as mean±SD. *P<.05,
P<.01.
Cyclic variation of IBS was present in 23 of 26 infarct
segments at 3 days later (Figs 3 and 4). Cyclic variation was detectable at
this phase in 7 patients in whom no cyclic variation was detectable at
baseline. The number of patients showing asynchronous contraction
decreased from 7 to 3 at day 3 (Table
).
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Figure 3. Cyclic variation of IBS in the infarct anterior
zone at baseline (left) and 3 days after reperfusion (right). At
baseline, infarct site manifests reduced and slightly delayed cyclic
variation with reference to the R wave. At day 3, it manifests
synchronous contraction, and its magnitude increased
significantly.
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Figure 4. Temporal changes in the phase-corrected magnitude
(left) and wall motion score (right) in the center of the infarct zone.
The phase-corrected magnitude significantly increased 3 days after
reperfusion, whereas wall motion score remained unchanged at day 3.
Wall motion score significantly decreased only at day 21. Values are
expressed as mean±SD. *P<.05 vs day 1. ). However, there was no
significant improvement in wall motion in the center of the infarct
segment. The phase-corrected magnitude increased to 3.0±3.6 at day 7,
but it did not show a significant increase after that. In contrast,
wall motion score significantly decreased only at day 21 (day 1 versus
day 21, 3.0±0.0 versus 2.4±0.8, P<.05).
We assessed the potential of the phase-corrected magnitude for
predicting functional improvement in the infarct segments (Figs 5 and 6).
Using an ROC curve, we examined the sensitivity and specificity of
various cutoff points of phase-corrected magnitude at day 3 for
predicting viable myocardium.27 29
The ROC curve is a plot of sensitivity against 1-specificity as the
positive/negative cutoff point is varied. Definition of viable
myocardium was wall motion score index of 2, in the
convalescent stage. Based on this curve configuration, we considered
the optimal cutoff point to predict viable myocardium appears to lie
around the phase-corrected magnitude of 2 dB, which is a median value
of this magnitude at day 3.
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Figure 5. ROC curve for determining the optimal threshold of
the phase-corrected magnitude at day 3 for predicting wall motion
improvement in the convalescent stage. Each number indicates the cutoff
value for phase-corrected magnitude at day 3. Arrow highlights the
optimal cutoff point. For details, see the text.
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Figure 6. Temporal changes in wall motion score index (WMSI)
in group A (phase-corrected magnitude at day 3, 2.0 dB; n=14) and
group B (corrected magnitude at day 3, <2.0 dB; n=12). WMSI
significantly decreased until the convalescent stage in both groups,
but WMSI at day 21 was significantly lower in group A than in group B.
For details, see the text. *P<.05 vs day 1.2.0 dB were considered group A (14 patients), and those with the
phase-corrected magnitude of <2.0 dB were considered group B (12
patients). Fig 6 compares the wall motion score index between the two
groups at days 1 and 21. Wall motion score index in the infarct
segments was comparable between the two groups at day 1 (group A versus
group B, 2.8±0.1 versus 2.9±0.1, P=NS). Wall motion score
index significantly decreased in the convalescent stage in both groups,
but it was significantly lower in group A than in group B (1.7±0.6
versus 2.4±0.5, P<.01) at day 21. This result indicates
that the greater values for the phase-corrected magnitude at day 3 are
suggestive of the better functional improvement of the
postischemic myocardium.
Discussion
Top
Abstract
Introduction
Methods
Results
Discussion
References
Before coronary reperfusion, the cyclic variation of IBS
in the infarct zone is markedly blunted and even shows asynchronous
waveform in patients with AMI. The phase-corrected magnitude of cyclic
variation significantly increased despite the minimal improvement in
wall motion 3 days after reperfusion. It progressively increased until
day 7. An improvement in wall motion, however, was found only at day
21; therefore, an increase in the phase-corrected magnitude precedes an
improvement of wall motion. In addition, our data indicated that the
greater values for the phase-corrected magnitude at day 3 are
associated with the better functional improvement of the
postischemic myocardium. Thus, the ultrasonic
tissue characterization can provide a useful measure of intramural
contractile function, relatively independently of wall motion, and may
permit the prediction of wall motion recovery in very early stage of
reperfused AMI.
Several experimental and clinical studies have documented that the
cyclic variation of IBS is promptly blunted and often shows substantial
time delay compared with left ventricular systole, which
implies asynchrony, during myocardial ischemia. In patients
with AMI, we also observed the marked reduction in the magnitude of
cyclic variation and the significant increase in the time delay in the
infarct segment before reperfusion. The pattern of cyclic variation,
however, varies among patients. Cyclic variation was not detectable in
7 of 26 patients. Apparent asynchronous contraction was observed in 7
patients (27%). In 5 patients (patients 1, 7, 23, 25, and 26), the
absolute magnitude of cyclic variation was comparable to or greater
than that in the normal segment, but their pattern appears to be a
mirror image of normal cyclic variation pattern. This asynchronous
pattern of cyclic variation may be caused by stretching or passive
distention of ischemic myocardium during systole.
Although wall motion of the infarct zone was evaluated as akinesia
before reperfusion, the intramyocardial contraction pattern varies
among patients and the analysis of IBS is useful to assess the
pathophysiology of the wall motion abnormalities.
In animals, the reduced magnitude of cyclic variation of IBS
during ischemia gradually increased after coronary
reperfusion.18 19 20 21 22 Milunski et
al23 documented that partial recovery of cyclic
variation, which included an increase in the magnitude of cyclic
variation and a decrease in the normalized time delay, was observed at
a mean of 7 days after reperfusion in patients with AMI despite minimal
recovery of wall motion. In this study, we investigated the temporal
changes in the cyclic variation 3 days after reperfusion. The results
are a little different from their results because temporal changes in
cyclic variation varied among patients with the pattern of cyclic
variation of IBS at baseline. An increase in the magnitude of cyclic
variation was observed 3 days after reperfusion in 15 of 19 patients
showing synchronous or no detectable cyclic variation at baseline
study, but the other 4 patients showed a decrease in the magnitude. In
these 4 patients, the contribution of progressive myocardial damage
after reperfusion was speculative. The patients showing the
asynchronous pattern of cyclic variation at baseline
represented a decrease in the absolute magnitude, and thus
coronary reperfusion does not always lead to a increase in the
phase-corrected magnitude of cyclic variation. In the majority of these
patients, however, the normalized delay decreased to the normal range,
and the corrected magnitude increased 3 days after reperfusion. These
data imply that reperfusion usually augments the cyclic variation in
case of synchronous contraction and diminishes the delayed relaxation
or passive stretch in cases of asynchronous segmental contraction,
resulting in an increase in the corrected magnitude as early as 3 days
after reperfusion. At this phase, however, no substantial improvement
in the segmental motion was detectable in the center of myocardial
infarction. 21 days. This early recovery of cyclic variation of
IBS that we observed is consistent with the hypothesis that
ultrasonic tissue characterization provides a useful measure of
regional intramural contractile function, relatively independent of
wall motion. The delay of wall motion recovery may be attributed to
several causes. First, the recovery of intramural contraction would be
heterogeneous early after reperfusion. Even though some
fraction of the infarct segment exhibits synchronous intramural
contraction, the wall motion might not improve if the other fractions
show delayed contraction or passive stretch. Second, the increased
afterload imposed on the injured but functional myocardium
by neighboring normal segments could constrain improvement of wall
motion despite the salvage of the tissue. Only after residual
contractile function has improved possibly with an increase in the
number of actively contracting myocardium, fiber shortening
and regional wall motion improve. Finally, myocardial ischemia
promptly breaks the intracellular structures that mediate between
sarcomere shortening and myocardial
contraction.34 The recovery of this intracellular
structure requires several days. In such instances, the augmented
sarcomere shortening, which produces cyclic variation, does not
necessarily result in improvement in wall motion.
Recovery of cyclic variation of IBS is achieved much sooner than
the recovery of wall motion, but it the predictive value of the
ultrasonic tissue characterization for assessing the recovery of wall
motion in individual patients has been unknown. In this study, we
divided the study patients into two groups on the basis of the values
for phase-corrected magnitude 3 days after reperfusion. We used the
median value for phase-corrected magnitude at day 3 (ie, 2.0 dB). The
ROC curve analysis documented that this value seems to be an
optimal cutoff value for predicting functional improvement of infarct
zone. In fact, the functional improvement was significantly better in
patients with the phase-corrected magnitude of 2.0 dB than in those
with the lower values. In view of our results, the phase-corrected
magnitude may reflect the intramural contractile performance,
which should be related to the amount of stunned
myocardium. If the phase-corrected magnitude shows the
higher values after ischemic injury despite the minimal
improvement in wall motion, we can predict the better final functional
improvement. This estimation is quite important for the decision of the
clinical strategy because the functional improvement significantly
varies among patients despite achievement of coronary
recanalization in the early stage of AMI and
because the amount of viable myocardium determines the
final functional outcomes and patients' prognosis.
Cyclic variation of IBS is dependent on the angle between fiber
orientation and ultrasonic beam, called
anisotoropy.24 25 Time delay also varies
systematically with fiber orientation. Data in this study were obtained
exclusively from the anteroseptum and inferior and
posterior regions in the parasternal short-axis views, in which
myocardial fiber of these segments is oriented nearly perpendicular to
the ultrasound beam, thereby avoiding problems with anisotropy as much
as possible. In addition, the analysis is largely dependent on
the image quality.
Detection of regional wall motion abnormalities through
conventional two-dimensional echocardiography
facilitates the localization of the injured or infarct segments. Its
use, however, may not delineate the overall extent of myocardial
salvage early after reperfusion until and unless the recovery of wall
motion has occurred. Our results documented that an increase in the
phase-corrected magnitude precedes the improvement in wall motion in
patients with reperfused AMI. Such information cannot be obtained
through qualitative or quantitative analysis of wall motion
alone. Clinically, the analysis of the cyclic variation of IBS
may allow the rapid assessment of regional myocardial viability despite
no or minimal improvement in wall motion.
Selected Abbreviations and Acronyms
AMI
=
acute myocardial infarction
IBS
=
integrated backscatter
ROC
=
receiver operating characteristic
Acknowledgments
The authors greatly acknowledge the excellent technical
assistance of Yuzo Sakagami, Masakazu Ueda, Naoki Jonishi, and
Hideshi Shimokawa.
References
Top
Abstract
Introduction
Methods
Results
Discussion
References
1.
Charuzi Y, Beeder C, Marshall LA, Sasaki H, Pack
NB, Geft I, Ganz W. Improvement in regional and global left
ventricular function after intracoronary
thrombolysis: assessment with two-dimensional
echocardiography. Am J
Cardiol. 1984;53:662–665.[Medline]
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