Download quantification of regional myocardial function following acute

Seminars in Cardiology, 2003, Vol. 9, No. 3
ISSN 1648-7966
QUANTIFICATION OF REGIONAL MYOCARDIAL
FUNCTION FOLLOWING ACUTE MYOCARDIAL
INFARCTION BY ULTRASONIC STRAIN RATE AND
STRAIN IMAGING
Giedrius Davidavičius, Nerijus Misonis, Virginija Grabauskienė
Clinic of Heart Diseases, Vilnius University; Center of Cardiology and Angiology, Vilnius University
Hospital Santariškiu˛ Klinikos, Lithuania
Received 10 March 2003; accepted 25 August 2003
Keywords: Doppler myocardial imaging, strain rate, strain, regional myocardial function.
Summary
Objectives: The rapid diagnosis and early risk stratification of patients presenting with acute myocardial infarction (AMI) is important. In experimental setting ultrasonic strain rate (SR) and strain (S) have
been shown to identify changes in deformation predictive of ischemia. We sought to evaluate and compare
regional myocardial function at “the risk zone” (ARZ) supplied by the culprit coronary artery (CCA) and at
the remote (R) area during AMI (25 patients) and control zone (10 healthy subjects) using SR/S.
Design and Methods: Longitudinal deformation (LD) was from the apical views to assess function in
the septum (SW) and inferior (IW) walls. Both SW mid and apical segments were considered ARZ segment
if the CCA was left anterior descending artery. IW and basal segments of the SW were ARZ, if CCA was
the right coronary artery or left circumflex branch.
Results: Segments were scored according to the standard wall motion score (WMS) and compared
to the findings of SR/S imaging. The amplitude of peak systolic SR (pSR), maximal systolic S (pS), and
overall maximal S (OS) were decreased in infarcted segments (p < 0.05 vs R, vs control (C)). The pS was
lower than OS indicating that in many infarcted segments, maximal shortening was delayed and occurred
during early diastole. Infarcted segments evaluated as having a WMS = 3 had a tendency to lower values
of pS and OS (p < 0.05).
Conclusions: The strain rate/strain magnitude and changes in time interval values reliably identify
infarcted segments and differentiating those from remote zone segments. Longitudinal deformation
parameters provided statistically significant additional information and allowed a rapid diagnosis of area
and extent of myocardial infarction in this high risk group.
Seminars in Cardiology 2003; 9(3): 46–51
During the last two decades, the efficacy of
reperfusion therapy for acute myocardial infarction
(AMI) has been established [1]. The duration of occlusion and the size of the area at risk determine
the ultimate infarct size. The non-invasive monitoring of regional myocardial function is of major clinical
relevance in the management of acute and chronic
ischemic syndromes with both therapeutic and prognostic implications. In daily practice, echocardiography is widely used to identify segmental asynergy [2]. Ultrasonic strain rate (SR) and strain (S)
measurements have been suggested recently as a
new non-invasive method of quantifying regional myocardial deformation. SR is a measure of the re-
gional myocardial velocity gradient; strain is the time
integral of SR and represents the local magnitude of
deformation. These parameters can measure local
deformation independently of overall heart motion
and thus could better characterize local contractility than DMI velocities alone. The accuracy of such
segmental deformation measurement has been validated during experimental ischemia [3]. Several reports have demonstrated the potential clinical value
of this technique in the quantitative assessment of
regional myocardial asynergy [4]. It is shown in experimental works and in clinical studies that SR and
S have different responses in quantifying ischemic
and stunned myocardium and is able to characterize regional myocardial response during coronary
artery occlusion and reperfusion [5,6]. These paCorresponding address: Giedrius Davidavičius, Center of Carrameters have been extensively investigated in the
diology and Angiology, Vilnius University Hospital Santariškiu˛
experimental setting but few data on how disease
Klinikos, Santariškiu˛ str. 2, 2021 Vilnius, Lithuania
E-mail: [email protected].
processes in the clinical environment alter these pa-
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Seminars in Cardiology, 2003, Vol. 9, No. 3
rameters are available. Thus, the aim of our study is
to evaluate regional myocardial function using SR/S
measurements in patients with AMI. To evaluate the
range of changes in regional myocardial function at
“the risk zone” of the culprit artery and remote area
during AMI using Doppler myocardial imaging (DMI)
indices strain rate and strain.
Design and Methods
Study group
The study group consisted from the patients admitted to the Coronary Care Unit with the diagnosis of the first AMI in whom coronary angiography
and revascularization using either fibrinolysis or primary percutaneous coronary intervention was performed. Twenty five patients (mean age 68 ± 9.5, 12
females) were studied during the first myocardial infarction (MI). The infarct location was assessed from
the 12-lead resting electrocardiogram (ECG). All of
them had prolonged chest pain (>30 minutes) with
evolving ECG changes indicating acute myocardial
ischemia (ST-segment elevation >2 mm and/or Q
waves >3 mm in 2 adjacent leads) and a significant rise in serum-specific cardiac enzymes. Patients with a history of MI, arrhythmia, pacemaker implantation, bundle branch blocks, dilated cardiomyopathy, myocardial hypertrophy, pulmonary hypertension, significant valvular heart diseases, poor
acoustic window, coronary artery bypass grafting
were not included in the study.
Ten asymptomatic age-matched subjects (27–
48 years old, mean age 37 ± 8.0, 2 females) served
as a control group. All of them had a normal rest
ECG, echocardiogram, up-right bicycle stress test
and no history of coronary artery disease, angina,
hypertension or diabetes.
The study protocol has been approved by the
local ethics committee.
Coronary angiography and revascularization
Coronary angiograms of the right and left coronary arteries were obtained. Data were acquired
immediately after the patient had been admitted to
Cardiac Care Unit. The coronary angiography and
angioplasty procedures were performed using standard techniques. Coronary angiographic data were
available in 24 patients (Table 2). Coronary occlusion or significant coronary stenosis was defined as
an artery lumen narrowing (more than 75%) in 2 orthogonal angiograms. Two patients had a coronary
artery bypass grafting and were excluded from further examination.
ISSN 1648-7966
(CDMI). All 2D studies were performed using second harmonic imaging. Aliasing was eliminated from
the color Doppler data sets by setting appropriately
high pulse repetition frequency (PRF) values (range
16 to 21 cm/sec) for data acquisition. The imaging depth and the sector angle in each view were
adjusted to obtain the highest possible frame rates
for myocardial color Doppler acquisition, while keeping the separate wall of the left ventricle in view.
All echocardiographic images were recorded at passive end-expiration to minimize global cardiac movement. Scanning had been performed just before the
patient was transferred for the catheterization.
All patients had well-defined regional wall motion abnormalities. Color Doppler velocity mapping
of the infarcted segment was then performed in appropriate gain: velocity settings and the resulting
images were compared with two-dimensional images in attempt to assess the ability of this technique to detect and differentiate between normal and
hypocontractile myocardium.
B-mode CDMI myocardial velocity data was acquired at the frame rate of 140–190 frames/sec using the imaging sector angle of 45–60 degrees.
The 2D grey scale images were assessed visually. The color Doppler velocity data was processed
off-line to derive velocity and regional SR/S curves
for longitudinal deformation. Apical 4-chamber and
2-chamber view was used for the assessment of
either septum or inferior wall longitudinal function
respectively. Each wall was subdivided into three
segments (basal, mid ventricular and apical). Both
septal mid and apical segments, imaged in apical
4-chamber view, were considered “at-risk” segment,
if a culprit artery was the left anterior descending
coronary artery. All inferior wall segments and the
basal segment of septum were considered “at-risk”,
if a culprit artery was the right or circumflex coronary
artery.
In total, data were obtained from 150 segments
for patients with AMI; and 60 segments were analyzed as a control group. All acquired images were
stored in a digital memory of the machine and downloaded to the workstation for off-line analysis.
Echocardiographic data analysis
The CDMI data sets were analysed off-line
using dedicated software (TVI 6.0, GE Vingmed,
Horten, Norway). Regional peak systolic velocities
were measured for longitudinal motion in each of
the 3 segments of the septal and inferior left ventricular walls. Regional SR was estimated during
off-line analysis (Speqle – Software Package for
Echocardiographic data acquisition
Echocardiographic studies were performed us- Echocardiographic Quantification, University of Leuing a GE Vingmed ultrasound scanner (System VII) ven) and using the same methodology previously
with a 2.5 MHz transducer. All the patients were described [7]. To describe regional deformation in
scanned in the left lateral decubitus position us- longitudinal direction the following parameters from
ing B mode and color Doppler myocardial imaging the mean velocity and SR profiles respectively were
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Seminars in Cardiology, 2003, Vol. 9, No. 3
ISSN 1648-7966
Figure 1. Ultrasonic deformation indices (longitudinal deformation)
AVO – opening of the aortic valve; AVC – closure of the aortic valve; IVRT – isovolumic relaxation time; MVO –
opening of the mitral valve; tOM – time interval from the beginning of the Q wave on the electrocardiogram to the
maximal overall strain; tS – time interval from the beginning of the Q wave on the electrocardiogram to the maximal
systolic strain
calculated: the peak systolic SR and S, overall maximal S (OS), time interval from the beginning of the
Q wave on ECG to the OS (tOM) (Figure 1).
Statistical analysis
Statistical analysis was performed by STAT view
software (SAS Institute, Cary North Carolina). Continuous values were expressed as mean values ±
SD. All values measured were grouped segment
wise and their means compared. Qualitative values
were compared using two sample t-test. A p value
of <0.05 was considered as statistically significant.
ocardium was characterized by negative strain rate
and strain values. Maximal longitudinal shortening
expressed as maximal overall strain occurred during
the systole or just after aortic valve closure. The amplitude and time interval value of OS was similar to
maximal systolic strain in almost all segments of the
normal myocardium.
Infarcted segments
Coronary artery supplying infarcted segments
was occluded or severe stenosis was found by angiography. Prolonged ischemia resulted in myocardial wall motion abnormalities on two-dimensional
imaging. Color Doppler velocity mapping of the inResults
farcted segment was performed. We had subdivided
In total 150 myocardial segments recorded from
infarcted segments according to the wall motion in25 patients treated in Coronary Care Unit were index (Table 3). Infarcted segments data set consisted
cluded for analysis. Clinical and hemodynamic data
from analysis of 64 segments (42.7%). Characterisof patients are presented in Table 1. Coronary antic findings recorded from infarcted segment using
giography data are presented in Table 2.
SR/S are shown in (Table 3). As it was expected, the
Control segments
amplitude of peak systolic strain rate (pSR), maxThis group includes 10 healthy volunteers mean imal systolic S (pS), and OS were decreased in inage 37 ± 8.0 years. In total 60 segments were ana- farcted segments (p < 0.05 vs remote (R), vs control
lyzed as control segments. For each cardiac cycle, (C)). The pS was lower than OS indicating that in
the normal longitudinal systolic shortening of my- many infarcted segments, maximal shortening was
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Seminars in Cardiology, 2003, Vol. 9, No. 3
ISSN 1648-7966
Table 1. Baseline characteristics of patients
Number of patients
n = 25
Age (mean age ± SD)
Hypertension
Dyslipidemia
Diabetes
CK
CK-MB
Troponin I
68 ± 9.5
12
17
4
904 ± 631
94 ± 89
55.7 ± 99.4
CK – creatine kinase; CK-MB – creatine kinase MB isoenzyme; SD – standard deviation
Table 2. Patients (n = 24) coronary angiography and treatment data
1 vessel disease
2 vessel disease
3 vessel disease
Primary PCI
Fibrinolysis
Rescue PCI
Conservative treatment
CABG
n = 14 (LAD n = 7; RCA n = 6; LCx n = 1)
n=7
n=3
n = 16 (LAD n = 6; RCA n = 8; LCx n = 2)
n = 3 (LAD n = 2; RCA n = 1)
n = 3 (LAD n = 2; RCA n = 1)
n=2
n=2
CABG – coronary artery bypass grafting; LAD – left anterior descending artery; LCx – left circumflex branch; PCI
– percutaneous coronary intervention; RCA – right coronary artery
Table 3. Quantitative segmental analysis. Characteristical findings recorded from infarcted, remote and control
segment using strain rate/strain
Controls
Wall Motion Score
Number of segments
OS (%)
Ot (msec)
pS (%)
pSR (1/sec)
WMS1(Controls)
n = 60
−22 ± 4.8∧
366 ± 22∧$
−21 ± 5.4∧$
−1.46 ± 0.4∧$
Patients (n = 25)
WMS1(P)
n = 86
−18 ± 9
393 ± 66∗∧
−18.8 ± 8.4∗∧
−1.44 ± 0.87*
WMS2(P)
n = 31
−15.4 ± 4
448 ± 98
−12.6 ± 7
−1 ± 0.3
WMS3/4(P)
n = 33
−10.5 ± 7
506 ± 96
−7 ± 8
−1 ± 0.4
∗
<0.05 vs WMS2 - ∧ <0.001 vs WMS3 - $ <0.05 vs WMS2,3; values are mean ± standard deviation
OS – overall maximal strain; tOM – time to overall maximal strain; P – patients; pS – maximal systolic strain; pSR
– peak systolic strain rate; WMS – wall motion score
delayed and occurred during early diastole. Infarcted
segments evaluated as having a wall motion score
(WMS) = 3 had a tendency to lower values of pS and
OS (p < 0.05). Time interval to OS (tOM) had been
prolonged and maximal overall strain occurred during isovolumetric relaxation or early diastolic phase
(Figure 2).
Remote zone segments
Remote zone segments were supplied by a
non-infarcted coronary artery. In total 86 segments
(57.3% (WMS-1)) contributed to the remote zone
data set. Normokinetic segments had a comparable
systolic SR and strain values in patients and in controls. Descriptive analysis using SR/S of the remote
segment is shown in Table 3.
Discussion
Our study shows that we are able to differentiate between the normal contracting segment and
infarcted segment using ultrasonic deformation parameter amplitude and time interval values. We suggest that segmental analysis provides additional and
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Figure 2. A typical example of strain measurements performed in the septum supplied by occluded left anterior
descendens coronary artery. The longitudinal function of the apical segment is severely altered: the maximal
systolic value is positive, time interval to maximal overall strain is prolonged (>500 ms). In contrast, a basal
segment supplied by a normal coronary artery has a normal systolic amplitude and time interval value.
IVRT – isovolumic relaxation time
valuable information to visual motion scoring in the
quantification and identification of ischemia-induced
changes in regional contractility. As we know, rapid
diagnosis and early risk stratification of patients with
acute chest pain are important in identifying patients
to whom early interventions may result the better
outcome [8].
As it was expected, longitudinal shortening had
altered in ischemic segments. The amplitude of
maximal systolic shortening was reduced in acute
ischemia. In some segments supplied by occluded
coronary artery, systolic shortening was completely
abolished and replaced by lengthening (positive systolic strain). This is in agreement with previous works
[9,10]. Moreover, we evaluated the timing interval for
peak deformation. It is interesting to note that shortening of the ischemic segment was delayed and
occurred after aortic valve closure what was early
or even late diastole for the non-ischemic myocardial surrounding segments. This phenomenon was
found by other authors [11,12] and named postsystolic shortening (PSS). Experimental animal models
suggest that PSS relates to ischemic alterations of
the systolic and diastolic function. Timely onset of
diastolic relaxation requires the uptake of cytoplasmic calcium by sarcoplasmic reticulum, which is an
energy demanding process. Alteration of this active process is the established predictor of myocar-
dial dysfunction at the level of myocyte metabolism
[13,14].
The SR and S values in normal and dyssynergic
segments in this study are comparable with those,
published by Voigt et al [10].
Our study shows that CDMI parameters SR/S
can provide information in localizing myocardial infarct territory and identifying culprit artery location. It
is important to differentiate infarcted segments from
remote ones in order to predict prognosis, left ventricular recovery and myocardial area under the risk,
to identify patients at high risk of further events such,
as reinfarction or death, and hopefully to intervene in
order to prevent these events.
Limitations
Data post-processing was time consuming taking up to 1 to 2 hours per study. The usual limitations
inherent in the angle dependency of all echocardiographic Doppler techniques apply equally to SR and
ε derived by ultrasonic auto-correlation.
Conclusions
Strain rate and strain imaging can identify, localize and quantify acutely induced segmental changes
in acute ischemia. We suggest that quantitative lon-
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Seminars in Cardiology, 2003, Vol. 9, No. 3
ISSN 1648-7966
gitudinal deformation parameters provide additional
information to visual motion scoring in the quantification and identification of ischemia-induced changes
in regional contractility in the clinical setting. It could
add a new and important parameter for the measurement of myocardial segmental function, being
relatively independent of both overall heart motion
and motion direction.
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