Strain Rate Imaging for Assessment of Regional
Myocardial Function
Results From a Clinical Model of Septal Ablation
Theodore P. Abraham, MD; Rick A. Nishimura, MD; David R. Holmes, Jr, MD;
Marek Belohlavek, MD, PhD; James B. Seward, MD
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Background—Regional myocardial function assessment is essential in the management of coronary artery disease (CAD).
Tissue Doppler imaging (TDI) by depicting local myocardial motion can potentially quantify regional myocardial
function. Strain rate imaging (SRI) that depicts regional deformation is less susceptible to cardiac translation and
tethering and may be superior to TDI for regional function analysis. We examined regional myocardial function using
TDI and SRI in a unique clinical model of a small, discrete myocardial infarction.
Method and Results—Ten patients with severely symptomatic septal hypertrophy underwent basal septal ablation via
intracoronary alcohol injection and had TDI and SRI pre- and postablation. Invasive hemodynamics showed no
appreciable change in global function. Peak systolic strain rate was significantly lower postablation versus preablation
(⫺0.5 versus ⫺1.2 s⫺1, P⬍0.001) and when comparing infarct and noninfarct areas (⫺0.5 versus ⫺1.5 s⫺1, P⬍0.001).
In contrast, peak systolic tissue velocities were similar pre- and postablation (3.9 versus 2.9 cm/s, P⫽0.16) and between
infarct and noninfarct areas (2.9 versus 2.2 cm/s, P⫽0.13). SRI analysis demonstrated reduced systolic function in the
peri-infarct zone and preserved systolic function in the remote nonischemic zone.
Conclusion—In the clinical setting of a small, discrete infarct unaccompanied by changes in global function, SRI
accurately depicted changes in regional function. These data suggest that SRI may be the optimal method for objective,
quantitative assessment of regional myocardial dysfunction. (Circulation. 2002;105:1403-1406.)
Key Words: imaging 䡲 tissue 䡲 myocardium
⬎50 mm Hg) from January 2000 to September 2000. Ten healthy
volunteers served as controls.
T
here is currently no optimal method for quantifying regional
myocardial systolic dysfunction by echocardiography. Tissue Doppler imaging (TDI)1,2 depicts local myocardial motion
and may enable quantitation of myocardial function. Because
TDI is influenced by cardiac translational motion and myocardial tethering, it may be imprecise when discrete areas of the
myocardium are involved. Strain rate imaging (SRI), which
describes myocardial deformation, is theoretically less susceptible to translation or tethering and is potentially superior to TDI
in regional myocardial function assessment.3,4 The optimal
model to compare the ability of TDI and SRI to assess regional
myocardial function requires a localized infarction that does not
change global function. Septal ablation for treatment of patients
with hypertrophic obstructive cardiomyopathy (HCM) results in
a discrete area of infarction. We evaluated regional function
assessment by TDI and SRI in this unique clinical model of a
myocardial infarction.
Cardiac Catheterization
Alcohol ablation was performed as described elsewhere.5 Patients
who came to the catheterization laboratory were fasting and under
light sedation. A temporary pacemaker was placed in the apex of the
right ventricle in all patients. The target septal perforator artery was
selected via coronary angiography (Judkins technique) and contrast
echocardiography (Optison, Mallinckrodt Inc). A septal perforator
artery was selected if the myocardial segment enhanced by the
contrast injection into that artery was the site of contact from the
systolic anterior motion of the mitral valve leaflets. One to 3 mL of
absolute alcohol was injected into the distal end of the inflated
balloon in the septal perforator artery.
Invasive Hemodynamics
Pressures were measured in the left ventricle (LV), aorta (AO), and
left atrium using high fidelity manometer-tipped pressure transducer
catheters (Millar Instruments) inserted through a transseptal approach as previously described.6 Pressures were directly recorded in
a digital format at 5 ms intervals during held end expiration, before
and after the ablation.
Methods
Patients
The study group consisted of consecutive patients undergoing septal
ablation for severe symptomatic HCM (resting outflow tract gradient
Received December 5, 2001; revision received January 30, 2002; accepted January 30, 2002.
From the Division of Cardiovascular Diseases, Mayo Clinic, Rochester, Minn.
Correspondence to Rick A. Nishimura, MD, Cardiovascular Diseases, Mayo Clinic, 200 First Street SW, Rochester MN 55905. E-mail
[email protected]
© 2002 American Heart Association, Inc.
Circulation is available at http://www.circulationaha.org
DOI: 10.1161/01.CIR.0000013423.33806.77
1403
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Circulation
March 26, 2002
Figure 1. Color M-mode images of the septum.
2D images on the left indicate the M-mode cursor
position (white line). In TDI, red indicates systolic
and blue indicates diastolic motion (a). Yellow-red
indicates shortening and blue-white indicates
lengthening in SRI (c). Pre (a) and postablation (b)
TDI reveal no difference in the infarct segment (➪).
Preablation SRI (c) depicts normal systolic strain
rate (red) in the basal segment (➪), replaced by
green (no shortening or lengthening) postablation
(d). Mid and apical septal segments (➡) demonstrate normal strain rates (red). Left ventricle and
aortic pressure tracings (LV/AO) demonstrate
reduction in postablation gradient (*). S indicates
systole; d, diastole; Š—‹, duration of systole and
diastole; ⌬, sample site for trace B; and ‘, sample
site for trace A in Figure 2.
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Echocardiography
Apical imaging, before and after ablation, was performed using a 2.5
MHz phased array probe with a System FiVe ultrasound machine
(GE Vingmed). Single walls were imaged using a narrow sector
angle with the wall parallel to the ultrasound beam.
Image Analysis
Analysis was performed by 2 independent, blinded observers using
custom software (TVI v6.3b, GE Vingmed). Myocardial motion was
coded such that in TDI, motion toward and away from the transducer
was coded red and blue, respectively, and in SRI, yellow-red
indicated shortening and blue-white indicated lengthening (Figure 1a
and 1c, respectively). Color M modes and peak systolic velocities
(TV) and strain rates (SR) were obtained by placing the cursor at the
midmyocardial level in each wall. Tissue velocities were also
normalized to end diastolic ventricular length.7 The infarct zone was
the area highlighted by intramyocardial contrast. To examine
changes in myocardial function around the infarct, SR was measured
in the peri-infarct zone (midseptum) and in a nonischemic zone
(apical septum). All measurements were taken from an acceptable
tracing, and the final value was the average of 3 measurements.
Statistics
Continuous variables are expressed as mean⫾SD. Pre- and postablation hemodynamic, TDI, and SRI variables are compared using a t
test. A P value ⬍0.05 was considered significant. Peak values within
2 SD of the mean for normals were set as the cutoff for sensitivity,
specificity, and accuracy calculations.
Results
Septal infarct was characterized by a reduction in LV outflow
tract gradient and septal artery occlusion on angiography. All
TABLE 1.
invasive indices of systolic and diastolic function remained
unchanged (Table 1). Peak systolic SR was lower post versus
preablation, whereas pre- and postablation peak systolic TV
(raw and normalized) were similar (Table 1). Also, SR was
lower in the infarct segments versus normal segments (⫺0.5
versus ⫺1.5 s⫺1, P⬍0.01). Peak systolic TV was similar in
infarct and normal segments (raw: 3.0 versus 2.4 cm/s,
P⫽0.13; normalized: 0.30 versus 0.32, P⫽0.4). Sensitivity,
specificity, and accuracy of SRI and TDI are presented in
Table 2. Systolic SR indicated reduced function in the
peri-infarct zone (⫺0.7⫾0.2s⫺1) and normal function in the
nonischemic zone (⫺1.2⫾0.14 s⫺1; Figure 2). No postinfarct
increase in systolic SR was observed in the normal zone
(preinfarct versus postinfarct: ⫺1.3 versus ⫺1.2 s⫺1,
P⫽0.09).
Discussion
This study demonstrates the ability of SRI to accurately
depict regional myocardial function in a clinical model of a
small myocardial infarction. Infarct segments demonstrated
lower SR and absence of a shortening pattern postablation.
SRI analysis also demonstrated an area of systolic dysfunction surrounding the infarct with no augmentation of contractile function in the normal zone. The myocardial infarction in
this study was of a size that measurements were not confounded by global changes in systolic or diastolic function.
There has been considerable interest in the ability to
noninvasively diagnose and quantify regional myocardial
Hemodynamic, TDI, and SRI Data
SR, s⫺1
TV, cm/s
Mean BP,
mm Hg
LVEDP,
mm Hg
dp/dtmax,
mm Hg/s
Preablation
89⫾9
22⫾9
Postablation
100⫾11
19⫾10
0.05
0.6
n⫽10
P
␶, ms
Normalized
TV, s⫺1
Obs 1
Obs 2
Obs 1
Obs 2
1677⫾263
0.064⫾0.014
0.43⫾0.11
3.9⫾1.0
4.3⫾0.8
⫺1.2⫾0.14
⫺1.5⫾0.2
1333⫾46
0.066⫾0.016
0.34⫾0.09
2.9⫾0.8
3.5⫾0.9
⫺0.5⫾0.2
⫺0.6⫾0.25
0.2
0.8
0.06
0.13
0.08
0.001
0.001
BP indicates blood pressure; LVEDP, left ventricular end diastolic pressure; dp/dtmax, peak positive dp/dt; ␶, time constant of relaxation; TV, peak
systolic tissue velocity from infarct area; normalized TV, TV normalized to end diastolic ventricular length; SR, peak systolic strain rate from infarct
area; and Obs 1 and 2, blinded observers.
Abraham et al
TABLE 2.
Regional Cardiac Function by Strain Rate Imaging
Sensitivity, Specificity, and Accuracy of SRI and TDI
Sensitivity, %
Specificity, %
Accuracy, %
Observer
TDI
SRI
TDI
SRI
TDI
SRI
1-peak
60
90
100
100
65
95
2-peak
40
80
100
100
70
90
1-color
30
80
97
100
78
93
2-color
30
100
86
97
83
98
Peak indicates peak systolic velocity and strain rate; color, color M mode
(visual).
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contractility. In TDI, the high frequency, low amplitude blood
pool echoes are filtered out, resulting in selective measurement of myocardial velocities.1,2,8 Peak systolic TV has been
used as a quantitative measure of systolic function.9,10 TDI,
however, is often unable to reliably distinguish active contracting from an akinetic segment that is “pulled” by the
adjacent normal myocardium, thus erroneously demonstrating motion with respect to the transducer.3 Measurement of
local tissue deformation (strain) may overcome these limitations of TDI. Strain is the change in length corrected for the
initial length (ie, % deformation), and strain rate is the rate of
normalized change. Strain was initially proposed as a measure of myocardial stiffness.11 In SRI, the difference in TV
obtained from 2 points along the ultrasound beam is divided
by the intervening distance to yield the spatial gradient of
velocity, which is the strain rate.12 Absolute strain is calculated by integrating the strain rate signal. Peak systolic SR
and strain may accurately reflect local systolic function
because they measure myocardial deformation, not displacement.3 Doppler-derived strain rates have been validated in
vitro and in vivo.13,14
Prior clinical studies of TDI and SRI did not correct for
changes in global systolic and diastolic function, and only
indirectly assessed the area of infarction. In this study, the
infarction did not cause changes in global hemodynamics,
and the infarct was delineated by contrast echocardiography. We demonstrated the relative superiority of SRI over
raw and normalized TDI7 in depicting changes in regional
myocardial function after a small infarct. Furthermore, SRI
analysis reveals reduced function peri-infarct and normal
function in the remote non-ischemic myocardium. These
1405
data indicate that the region of myocardial dysfunction
extends beyond the area of the infarct, there is a graded
decrease in myocardial function from a remote nonischemic area toward the infarct, and there is no augmentation
of systolic function in the non-ischemic myocardium.
These findings are concordant with other studies of regional deformation in ischemia.15,16
Limitations
Strain rate signal can be noisy and is influenced by the angle
of insonation. The intra-operative study design precluded
independent confirmation of strain rates using MRI.
In conclusion, TDI and SRI are novel techniques that
enable quantitation of regional myocardial function. Using
a unique clinical model of a small myocardial infarction,
we demonstrated that assessment of myocardial deformation (SRI), not displacement (TDI), is an accurate indicator
of regional function. In addition, SRI allows analysis of
myocardial function in the peri-infarct and non-ischemic
zones. Our data suggest that SRI may provide optimal
objective assessment of regional myocardial function in
coronary artery disease, although evaluation in more standard clinical settings will help determine its role in clinical
practice
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Strain Rate Imaging for Assessment of Regional Myocardial Function. Results From a
Clinical Model of Septal Ablation
Theodore P. Abraham, Rick A. Nishimura, David R. Holmes, Jr, Marek Belohlavek and James
B. Seward
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Circulation. published online March 4, 2002;
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