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 Table of Contents  
ORIGINAL INVESTIGATION
Year : 2017  |  Volume : 1  |  Issue : 3  |  Page : 177-184

Speckle-Tracking echocardiography to assess global and regional left ventricular function in acute myocardial infarction


1 Department of Cardiology, Fortis Hospital, Bengaluru, India
2 Department of Non Invasive Cardiology, Hosmat Hospital, Bengaluru, India
3 Cardiology Division, Janapriya Hospital, Hassan, Karnataka, India

Date of Web Publication12-Dec-2017

Correspondence Address:
Dr. Satish C Govind
Fortis Hospitals, 154/9-B, Bannerghatta Road, Bengaluru - 560 076, Karnataka
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jiae.JIAE_24_17

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  Abstract 

Speckle tracking is a useful tool in assessing global & regional myocardial function in patients with acute myocardial infarction undergoing primary PCI. Global Longitudinal Strain (GLS) is a robust parameter to assess regional and global LV function. Global longitudinal strain helps in predicting short term outcomes in these patients and has shown to be better than ejection fraction, and as good as wall motion scoring, wall motion scoring index and myocardial performance index. A Lower global longitudinal strain parallels the rise in troponin T and CPKMB in acute myocardial infarction. Global longitudinal strain may have the potential to be an echocardiographic parameter which is useful in identifying multivessel disease. Assessment of regional myocardial function by speckle tracking echocardiography, particularly GLS, can be useful in ACS patients undergoing PCI in predicting short term recovery of the affected segments. Speckle tracking echocardiography can be used independent of the conventional markers to assess regional and global LV function.

Keywords: Acute coronary syndrome, acute myocardial infarction, global longitudinal strain, speckle-tracking echocardiography


How to cite this article:
Aniyathodiyil G, Bohra SS, Mottengar A, Govind SC. Speckle-Tracking echocardiography to assess global and regional left ventricular function in acute myocardial infarction. J Indian Acad Echocardiogr Cardiovasc Imaging 2017;1:177-84

How to cite this URL:
Aniyathodiyil G, Bohra SS, Mottengar A, Govind SC. Speckle-Tracking echocardiography to assess global and regional left ventricular function in acute myocardial infarction. J Indian Acad Echocardiogr Cardiovasc Imaging [serial online] 2017 [cited 2018 Feb 18];1:177-84. Available from: http://www.jiaecho.org/text.asp?2017/1/3/177/220530


  Introduction Top


Accurate assessment of left ventricular (LV) function is important in acute myocardial infarction (AMI), where LV ejection fraction (LVEF) is an important prognostic parameter. In a multicenter study, a progressive increase in cardiac mortality during 1-year follow-up was observed in patients who had myocardial infarction with LVEF <40%.[1] Zaret et al.[2],[3] showed that preserved LVEF at rest and during exercise is a good prognostic indicator in patients following thrombolysis. Although LVEF has the advantage of being a simple numerical parameter that reflects LV function, it is strongly influenced by loading conditions and does not correlate well with symptom status. The ability of LVEF to detect subtle changes in myocardial function is low.[4] Its value as a sequential test within individuals is constrained by limited test–retest reliability. Routinely used techniques in echocardiography have limitations of being load dependent, subjective in interpretation, and lacking in good specificity and sensitivity. Advances in cardiac imaging such as tissue Doppler imaging (TDI) and speckle-tracking echocardiography (STE) have helped us to overcome some of these limitations.

STE was introduced as a novel method to assess global and also regional systolic LV function and is able to discriminate myocardial motion and enables the angle-independent quantification of myocardial deformation in two different dimensions.[5] LV global longitudinal strain (GLS) has been found to be a better parameter to assess LV function than ejection fraction. STE is also a versatile method for assessing regional function, especially useful in the setting of myocardial ischemia due to coronary artery disease. Present methods of visually assessing wall motion abnormality are subjective and prone to errors. The use of myocardial strain by STE has the potential to overcome these limitations.

The aims of this study were as follows:

  • To assess myocardial function by combining existing conventional echocardiography methods with two-dimensional (2D) STE in patients with ST-elevation myocardial infarction (STEMI) undergoing primary percutaneous coronary intervention (PPCI)
  • To compare conventional echocardiography parameters with STE parameters as short-term predictors of adverse events after PPCI
  • To determine whether GLS is a superior parameter to predict short-term adverse cardiac events after PPCI.



  Materials and Methods Top


This was a prospective, single-center, nonrandomized study. Recruitment of patients was done over a year. The study was done at Fortis Hospitals, Bengaluru, a tertiary care cardiac hospital. Patients with STEMI, as clinically defined by the American College of Cardiology (ACC) guidelines,[5] were considered for the study. PPCI was defined as intervention in the culprit vessel within 12 h after the onset of chest pain or other symptoms without prior (full or concomitant) thrombolytic or other clot-dissolving therapy.[6] Patients after due consent and fulfilling inclusion and exclusion criteria were recruited. Inclusion criteria were patients with STEMI and above 18 years of age. Exclusion criteria were patients scheduled for coronary artery bypass grafting (CABG) during event admission, documented previous AMI or CABG, hemodynamically unstable patients, pulmonary edema, left bundle branch block, those who required a pacemaker, sustained atrial fibrillation and ectopics, significant valvular heart disease, congenital heart disease, significant pulmonary hypertension, cor pulmonale, primary myocardial disease, significant pericardial effusion, suboptimal images, and any concomitant severe systemic illness. Patient's demographic details, clinical history, clinical examination, and biochemical testing were done and findings documented.

As a hospital treatment protocol, all patients presenting with acute coronary syndrome are routinely subjected to echo by a dedicated echo machine in triage area immediately after electrocardiogram (ECG). No additional time was required or delay in treatment/intervention happened in patients undergoing this study. When patients underwent echocardiography, time taken for echo varied from 4 to 7 min with targeted image acquisition. Echocardiography was done when the process for initiating PPCI was taking place without affecting the door-to-balloon time of 90 min as recommended by ACC guideline. The post-PPCI and follow-up echocardiographic images of the patients were performed in the echocardiography room. Post-PPCI echocardiography was done at the time of discharge (minimum of 48 h after the procedure) and follow-up echocardiography was done 1 month after the event. Conventional echocardiography and STE were performed using a commercially available GE ultrasound system (Vivid 7) with a matrix phased-array adult probe. The images were transferred from the machine through storage discs to a specialized software (EchoPAC, GE) on a computer, and all images were analyzed offline at a later date. STE analysis was performed using a commercially available speckle-tracking system on the same software. Measurement was documented as average of three consecutive cardiac cycles.

Conventional echocardiography

Images were obtained in the standard tomographic views of the LV (parasternal long and short axis and apical four-chamber, two-chamber, and three-chamber views). LV diameters and wall thicknesses were measured from the 2D targeted M-mode echocardiographic tracings in the parasternal long axis according to the criteria of the American Society of Echocardiography (ASE).[7] Mitral inflow velocities were recorded using conventional pulsed-wave Doppler echocardiography, positioning a sample volume at the level of the mitral leaflet tips in the apical four-chamber view. The peak early diastolic velocity (E), peak late diastolic velocity (A), E/A ratio, and E-wave deceleration time were measured. The LV end-diastolic and end-systolic volumes at rest were computed from two- and four-chamber views, using a modified Simpson's biplane method, and the LVEF was calculated. LV filling pressure obtained by the ratio of E/e' was measured from mitral inflow E and the TDI early filling velocity (e') septal annulus from the apical four-chamber projection.[7] Wall motion scoring (WMS) and WMS index (WMSI) were calculated for all patients according to ASE 16 segment model of the LV. Myocardial performance index (MPI) was calculated for all patients using pulsed-wave Doppler in between mitral inflow and LV outflow. The sample volume was located in the LV outflow tract, just below the aortic valve (apical five-chamber view) for the measurement of the LV ejection time (ET), isovolumetric contraction time (IVCT), and isovolumetric relaxation time (IVRT). The MPI is given by IVCT + IVRT/ET.[8]

Speckle-tracking echocardiography

The 2D image gain was optimized to obtain a good image for analysis. STE images were obtained as per standard methods with attempts to have an optimal frame rate.[9] The LV long-axis regional function was assessed from the three apical views, from six basal segments (septum, lateral, inferior, anterior, posterior, and anteroseptal wall). Standard parasternal basal and apical short-axis plane images were acquired with the aim of having a frame rate of 50–80 fps. From each of the views (four-chamber, three-chamber, two-chamber), the average peak systolic strain of the segments was measured. Adequate tracking was verified and corrected, if needed.[10] A bull's eye map of average peak systolic GLS generated in each of the myocardial segments was documented. Regional strain parameters such as peak strain (during systole and postsystolic phase), peak systolic strain (peak strain during systole), end-systolic strain (ESS) (strain at the time of aortic valve closure), duration of systolic lengthening, and strain rate (during early systole) were recorded.

Follow-up of patients

All patients had their address and telephone number recorded. Any major adverse cardiovascular events (MACE) such as death (due to cardiac cause), AMI, target vessel revascularization, nontarget vessel revascularization, stent thrombosis, and in-stent restenosis defined as a stenosis occupying ≥50% of vessel diameter and occurring in the segment inside the stent or within a 5-mm segment proximal or distal to the stent and CABG were recorded at 3 months and at 6 months. In addition to MACE, other events like hospitalization for any reason such as chest pain, unstable angina, non-STEMI, acute ischemic symptoms or ischemic ECG changes or elevated cardiac biomarkers, and pulmonary edema were recorded. Patients were called for follow-up recording of echocardiogram.

Statistical analysis

SPSS (Statistical Package for the Social Sciences) V-16, (IBM, New York, USA). Appropriate descriptive statistics are provided for study variables including demographic and baseline characteristics. Descriptive statistics such as mean, median, and standard deviation are used to summarize continuous variables. Count and percentages are used to summarize categorical variables. All statistical tests were interpreted as a two-sided significance level of 0.05 and all confidence intervals at a two-sided level of 95% unless otherwise stated. Comparisons of different groups were done by paired t-test. Sensitivity and specificity are presented as receiver operator characteristic.


  Results Top


Data were recorded from fifty patients. Forty-five patients were men and five were women. The mean age of women was 58 years. All the five women had diabetes and hypertension. [Table 1] shows the baseline characteristics of the patients. The mean age of patients was 51.44 years. All patients underwent emergency coronary angiogram (CAG) and PPCI. There were 11 patients who were discharged early (<2d). Majority of our patients were discharged by 4 days. The duration of stay extended beyond 4 days in seven patients. However, the mean duration of stay in the hospital was 3.38 days.
Table 1: Baseline data

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All patients had myocardial infarction for the first time. The presence of comorbid diseases was recorded at admission as shown in [Table 2]. The history of duration of pain was recorded when the patients were in the hospital. The average duration of pain before they presented to the hospital was 5 h. Among them, 18 patients (36%) presented beyond 6 h. As they continued to have chest pain, they were taken up for primary angioplasty. Many patients presented with atypical symptoms such as epigastric discomfort, shoulder pain, and back pain which were all considered as anginal equivalents. The duration of pain was based entirely on the history given by the patient. Many patients had intermittent episodes of pain in which case the most significant pain was taken to calculate duration of pain.
Table 2: Co-morbidities

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The type of MI recorded at admission revealed the following: anterior wall MI (AWMI) in 31 patients, inferior wall MI in 12 patients, lateral wall MI in 1 patient, and posterior wall MI in 6 patients. Patients had their initial coronary angiographic data recorded. The culprit vessel was identified, and the vessels with lesions >70% were considered as diseased vessels. CAG revealed single-vessel disease in 62%, double-vessel disease in 22%, and triple-vessel disease in 16% of the patients. Baseline echocardiographic images were recorded before they were shifted for emergency CAG. Their initial thrombolysis in myocardial infarction (TIMI) flow following CAG was recorded. In our study, 60% of patients had TIMI 0 flow at presentation and only 4% had TIMI 3 flow at presentation. Since our hospital is a referral center for cardiac care, these patients would have already received antiplatelets and heparin (or low-molecular-weight heparin) before coming to the hospital. Fourteen patients had TIMI 2–3 flow at admission. On admission, all the patients had their phone numbers and address recorded. They were called for follow-up echocardiography. The minimum period before they were called for follow-up was 1 month (after the index event). A total of 31 patients had follow-up echocardiography. The average follow-up duration was 5.64 months. All of the 50 patients were interviewed by telephone calls. The events following the index event (MACE, etc.) were recorded. A total of 29 patients had events.

Echo parameters at baseline, at discharge, and at follow-up

Echocardiography was done at admission and in the hospital after a minimum of 48 h after primary angioplasty. Thirty-one patients had their follow-up echocardiogram recorded. GLS, LVEF, WMS, WMSI, and E/e' (LV filling pressures) were recorded. Their average values and standard deviation are shown in [Table 3].
Table 3: Echocardiographic parameters at admission at discharge and at follow-up

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Follow-up data

Of the total fifty patients, 31 patients came for echocardiographic follow-up. They were again classified according to the GLS values. The good group had higher LVEF, lower WMS, WMSI, and E/e' compared to moderate and mild groups. The average GLS values showed similar changes as LVEF, MPI, WMS, and WMSI. The higher GLS was associated with lower LV filling pressures. More positive GLS was associated with elevated LV filling pressures [Table 4].
Table 4: Follow-up data of left ventricular global longitudinal strain group

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Global longitudinal strain and duration of pain

Only four patients presented to our emergency department within 3 h of onset of pain. Twenty-three patients presented between 3 and 6 h and rest of them presented later than 6 h. Since the LV function deteriorates progressively with time following MI, those with duration of pain >6 h had lower GLS as compared to those who came earlier.

Global longitudinal strain and multivessel disease

Studies have shown that GLS value of >−17.9% can identify multivessel disease. In our study, 19 patients had multivessel disease. In our study, a GLS value of >−15% had a sensitivity of 73% and specificity of 32% to identify multivessel disease.

Follow-up events – major adverse cardiovascular events – and other outcomes

MACE is usually defined as a composite clinical endpoint of death, myocardial infarction, repeat intervention because of restenosis, or stent thrombosis. In our study of 50 patients, 29 patients had a total of 51 events over a follow-up duration of 6 months as shown in [Table 5].
Table 5: Events at follow-up of 6 months

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Echocardiographic parameters and events on follow-up

Of the total 29 patients with events, at discharge, GLS, MPI, WMS, WMSI, and E/e' values were compared with those patients not having any mentioned events. The values of GLS were lower in the event group compared to no event group. When the two groups were compared, GLS values were not significantly different. Studies have shown that a GLS value of lower than − 12% at discharge was associated with a higher event rates after MI similar to an EF value of <40%, MPI value of >0.47, and WMSI of 1.4. Of the 29 patients with events, GLS value of lower than − 12% could identify events in 58% of the patients. Similarly, MPI value of >0.47 could identify 72% of the patients with events. However, LVEF value of <40% could identify events in only 20% of the patients.

Global longitudinal strain groups and events at follow-up

We compared the GLS higher than −12% with GLS lower than −12% groups for occurrence of events in each group at 3 and 6 months. The GLS <−12% group had a higher number of events at 3 months and at 6 months [Figure 1].
Figure 1: Left ventricular global longitudinal strain (GLS) groups and events at follow-up

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We also analyzed the total number of events and individual events in both GLS groups. There were higher numbers of events such as pulmonary edema and revascularizations in the GLS lower than −12% group [Figure 2]. We analyzed the contribution of GLS, LVEF, MPI, WMSI, and E/e' independently for an event to occur in patients at follow-up. GLS independently contributed 68% for the event; similarly, MPI contributed 68% while the contribution of LVEF was 47%. Thus, GLS was useful in predicting outcomes at 6 months.
Figure 2: Left ventricular global longitudinal strain (GLS) group and individual events

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Regional strain and strain rate

There were 31 patients who had follow-up echocardiography. Their WMS following angioplasty was reviewed, and those segments with WMS of 2 were compared to those with WMS of 3. There were a total of 49 segments with WMS of 2 and 42 segments with WMS of 3. Regional strain parameters such as peak strain, peak systolic strain, ESS, systolic lengthening, and early systolic strain rate were recorded. Those segments with systolic lengthening were taken separately and were compared with those who did not have systolic lengthening. Strain parameters were lower in those with WMS of 3 compared to those with WMS of 2, and early systolic strain rate was more positive in segments with WMS of 3. The same segments (chosen following angioplasty) were followed up.

Regional strain parameters in those with wall motion scoring of 2 and 3 after angioplasty and follow-up

There were 49 segments with WMS of 2 and 42 segments with WMS of 3. Their strain and strain rate parameters following angioplasty and at follow-up showed that those segments with WMS of 2 had higher strain values following angioplasty and during the follow-up compared to the segments with WMS of 3. Segments with WMS of 2 also had shorter duration of early systolic lengthening, and their initial strain rate was also more negative as compared segments with WMS of 3 [Table 6].
Table 6: Regional strain and strain rate values in segments with wall motion score of 2-3 after angioplasty and follow-uo of early systolic lengthening and strain/strain rate

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Those with initial systolic lengthening were taken separately and analyzed. Of the total of 49 segments with WMS of 2, 25 segments had the initial systolic lengthening (51%). This reduced to 17 segments (8.33%) during the follow-up. There were 31 (73%) segments with WMS of 3 and early systolic lengthening which reduced to 22 (52%) on follow-up. The strain values were lower in those segments with systolic lengthening compared to those segments which did not have systolic lengthening.

Analysis of the follow-up patients

Analysis was done to identify parameters which can help to predict outcome following primary angioplasty. All the 31 patients who came for follow-up were taken up for analysis. The same segments were monitored at follow-up (segments with WMS of 2 and segments with WMS of 3). The follow-up data were segregated according to the degree of improvement based on ESS as good: 1 (ESS <-16.0%), mildly affected: 2 (ESS -16.0% to - 10.0%), moderately affected: 3 (ESS -9.0% to -6.0%), severely affected: 4 (ESS >−6%). This was done in both groups (WMS 2 and WMS 3). The postangioplasty values in each group were recorded. The comparisons of each group with their average values are shown in [Table 7].
Table 7: End-systolic strain comparison among groups of followed up segments

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In the segments with WMS of 2, there was a significant difference in the values of peak strain, peak systolic strain, and systolic strain rate in the Group 1; however, only peak strain and peak systolic strain were significantly different in Group 2 and Group 3. Group 4 showed no difference in any of the parameters. In the segments with WMS of 3, the averaged strain values was much lower compared to segments with WMS of 2, and the duration of systolic lengthening was also longer. When paired “t”-test was applied to postangioplasty and follow-up data based on the improvement, the values of peak strain and peak systolic strain were significantly different in Groups 1 and 2 but not in Groups 3 and 4. Strain rate was not significantly different in any of the groups. Duration of systolic lengthening was significantly different in Group 1 and not in other groups. It is clear from the data that the lower initial strain, positive strain rate, and longer duration of systolic lengthening are associated with poorer outcomes on follow-up. The segments which improved on follow-up irrespective of initial WMS (i.e., 2 or 3) had a higher strain, lesser systolic lengthening, and more negative strain rate.


  Discussion Top


A total of 50 first-time AMI patients were taken up for the study out of which 31 patients came for follow-up. All patients were telephonically followed up at 3 and 6 months after the index event for MACE and other cardiovascular outcomes. In our study, the mean duration of pain before presentation to emergency room with pain was 5.84 h for men and 6.64 h for women (combined mean of 5.92 h). Of the total patients, 42% of them had effort angina before presenting with MI. There were 31 patients (62%) presenting with AWMI and 31 patients (62%) had single-vessel disease. The best results for primary angioplasty are when the angioplasty is done <3 h from the onset of pain. The chances of having viable myocardium are much higher if the vessel is open. In our study, only 4% had TIMI 3 flow at presentation. An open vessel at presentation is always better than a closed vessel and has prognostic importance after thrombolysis.[11]

In our study population of a total of 50 patients, 44% had hypertension and 38% had diabetes. About 40% of the patients gave a history of smoking. Current smoking was associated with a threefold increase of MI.[12] Smoking and comorbid diseases resulted approximate 20-fold increase in death and MI.[13] Smoking was associated with early myocardial infarction. If the mean GLS was lower at presentation, their LVEF was lower and they had higher MPI, WMS, and WMSI. This was also seen following angioplasty and follow-up. Similar results were obtained by Stanton et al.[14] This association of GLS with LVEF, MPI, WMS, and WMSI was seen in all groups of GLS (poor, moderate, mild, and good) groups. Higher GLS was seen with shorter duration of chest pain.

GLS had a strong correlation with troponin-T and creatinine phosphokinase (CPK)-MB. The higher values of markers were associated with lower GLS. Liu YW, et al. examined patients on hemodialysis and found that patients with elevated troponins had lower GLS.[15] The patients were interviewed telephonically for the occurrence of MACE and recorded at 3 and 6 months. GLS value of lower than −12% at discharge was superior compared to an LVEF of <40% in identifying patients who had MACE at 6 months. GLS value of >−15% could identify multivessel disease with a sensitivity of 73% and a specificity of 32%. WMS is a useful parameter to assess regional LV function but is observer dependent which was seen in our study as some of the segments had normal strain values even though they appeared hypokinetic or akinetic. The study shows that lower peak strain, peak systolic strain, positive early systolic strain rate, and longer duration of early systolic lengthening were associated with poor recovery. Similar results were seen by others.[16],[17]

All the regional strain parameters such as peak systolic strain and peak strain were significantly lower in those segments with higher WMS and in those segments which did not improve which was statistically significant. Similar results were seen in some studies[18],[19] where the parameters like peak strain & peak systolic strain were highly specific parameters and if found good, could predict recovery. This could suggest that following primary angioplasty, regional strain and strain rate could be used independently to assess and predict recovery.

Limitations of the study

The study population consisted of only fifty patients, which may under represent the whole population presenting with similar illness. Women were under represented. Some of the findings such as the association of GLS and duration of pain and outcomes MACE were based on patients' history. Less number of patients had echocardiographic follow-up (31/50). Many patients had less than satisfactory angiographic results and multivessel disease which could have influenced echocardiographic parameters. Echocardiographic follow-up was not associated with angiographic follow-up.


  Conclusion Top


In AMI, STE-based GLS can be used to assess global and regional LV function, and it can be used in addition to the routinely used echocardiographic parameters such as LVEF, MPI, and WMSI. It can also be used to predict short-term outcomes in patients with acute MI undergoing primary PCI. GLS is a robust parameter to assess regional and global LV function and has shown to be better than LVEF and as good as WMSI and MPI. Lower GLS parallels the rise in troponin-T and CPK-MB in AMI. GLS may have the potential to be an echocardiographic parameter which is useful in identifying multivessel disease. Assessment of regional myocardial function by STE, particularly GLS, can be useful in acute coronary syndrome patients undergoing PCI in predicting short-term recovery of the affected segments. STE can be used independent of conventional markers to assess regional and global LV function.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

1.
White HD; The Multicenter Post-Infarction Research Group, et al. Risk stratification and survival after myocardial infarction. N Engl J Med 1983;309:331-6.  Back to cited text no. 1
    
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Marino P, Zanolla L, Zardini P. Effect of streptokinase on left ventricular modeling and function after myocardial infarction: The GISSI (Gruppo Italiano per lo Studio Della Streptochinasi Nell'infarto Miocardico) trial. J Am Coll Cardiol 1989;14:1149-58.  Back to cited text no. 2
    
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Zaret BL, Wackers FJ, Terrin ML, Forman SA, Williams DO, Knatterud GL, et al. Value of radionuclide rest and exercise left ventricular ejection fraction in assessing survival of patients after thrombolytic therapy for acute myocardial infarction: Results of thrombolysis in myocardial infarction (TIMI) phase II study. The TIMI study group. J Am Coll Cardiol 1995;26:73-9.  Back to cited text no. 3
    
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Marwick TH. Techniques for comprehensive two dimensional echocardiographic assessment of left ventricular systolic function. Heart 2003;89 Suppl 3:iii2-8.  Back to cited text no. 4
    
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Picard MH, Adams D, Bierig SM, Dent JM, Douglas PS, Gillam LD, et al. American Society of Echocardiography recommendations for quality echocardiography laboratory operations. J Am Soc Echocardiogr 2011;24:1-0.  Back to cited text no. 7
    
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Gilman G, Khandheria BK, Hagen ME, Abraham TP, Seward JB, Belohlavek M, et al. Strain rate and strain: A step-by-step approach to image and data acquisition. J Am Soc Echocardiogr 2004;17:1011-20.  Back to cited text no. 10
    
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Gjesdal O, Hopp E, Vartdal T, Lunde K, Helle-Valle T, Aakhus S, et al. Global longitudinal strain measured by two-dimensional speckle tracking echocardiography is closely related to myocardial infarct size in chronic ischaemic heart disease. Clin Sci (Lond) 2007;113:287-96.  Back to cited text no. 11
    
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Willett WC, Green A, Stampfer MJ, Speizer FE, Colditz GA, Rosner B, et al. Relative and absolute excess risks of coronary heart disease among women who smoke cigarettes. N Engl J Med 1987;317:1303-9.  Back to cited text no. 12
    
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Stanton T, Leano R, Marwick TH. Prediction of all-cause mortality from global longitudinal speckle strain: Comparison with ejection fraction and wall motion scoring. Circ Cardiovasc Imaging 2009;2:356-64.  Back to cited text no. 14
    
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Liu YW, Su CT, Chou CC, Wang SPH, Yang CS, Huang YY, et al. Association of subtle left ventricular systolic dysfunction with elevated cardiac troponin T in asymptomatic hemodialysis patients with preserved left ventricular ejection fraction. Acta Cardiol Sin 2012;28:95-102.  Back to cited text no. 15
    
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Ishii K, Suyama T, Imai M, Maenaka M, Yamanaka A, Makino Y, et al. Abnormal regional left ventricular systolic and diastolic function in patients with coronary artery disease undergoing percutaneous coronary intervention: Clinical significance of post-ischemic diastolic stunning. J Am Coll Cardiol 2009;54:1589-97.  Back to cited text no. 16
    
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Vartdal T, Pettersen E, Helle-Valle T, Lyseggen E, Andersen K, Smith HJ, et al. Identification of viable myocardium in acute anterior infarction using duration of systolic lengthening by tissue Doppler strain: A preliminary study Top of form. J Am Soc Echocardiogr 2012;25:718-25.  Back to cited text no. 17
    
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Voigt JU, Arnold MF, Karlsson M, Hübbert L, Kukulski T, Hatle L, et al. Assessment of regional longitudinal myocardial strain rate derived from Doppler myocardial imaging indexes in normal and infarcted myocardium. J Am Soc Echocardiogr 2000;13:588-98.  Back to cited text no. 18
    
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Edvardsen T, Urheim S, Skulstad H, Steine K, Ihlen H, Smiseth OA, et al. Quantification of left ventricular systolic function by tissue Doppler echocardiography: Added value of measuring pre- and postejection velocities in ischemic myocardium. Circulation 2002;105:2071-7.  Back to cited text no. 19
    


    Figures

  [Figure 1], [Figure 2]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7]



 

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