|
 
 |
| REVIEW ARTICLE |
|
| Year : 2023 | Volume
: 7
| Issue : 2 | Page : 137-146 |
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Role of Strain Imaging in Ischemic Heart Disease
Manish Bansal, Ravi R Kasliwal
Department of Cardiology, Medanta - The Medicity, Gurgaon, Haryana, India
| Date of Submission | 09-Aug-2023 |
| Date of Acceptance | 18-Aug-2023 |
| Date of Web Publication | 30-Aug-2023 |
Correspondence Address:
Manish Bansal
Department of Cardiology, Medanta Heart Institute, Medanta - The Medicity, Gurgaon - 122 001, Haryana
India
 Source of Support: None, Conflict of Interest: None
DOI: 10.4103/jiae.jiae_47_23
The potential utility of strain imaging as a tool for quantitative assessment of myocardial contractile function has already been demonstrated in many cardiac conditions. Numerous studies have explored its utility in patients with coronary artery disease (CAD) also. Almost the entire spectrum of CAD has been studied and several different strain parameters and indices derived from global or regional longitudinal, circumferential, radial and area strain as well as left ventricular rotation have been employed. These studies have mostly shown that strain imaging can have an incremental role in the diagnosis and prognosis assessment of CAD. However, a few important limitations are there. Most importantly, CAD involves the left ventricle in a segmental manner and unfortunately, segmental strain at present has significant measurement variability rendering it unsuitable for routine clinical use. Nevertheless, strain imaging has many potential uses in CAD. This review describes the current understanding about the role of strain imaging in the evaluation and management of CAD.
Keywords: Circumferential strain, global longitudinal strain, longitudinal strain, post-systolic shortening, segmental strain
How to cite this article:
Bansal M, Kasliwal RR. Role of Strain Imaging in Ischemic Heart Disease. J Indian Acad Echocardiogr Cardiovasc Imaging 2023;7:137-46 |
How to cite this URL:
Bansal M, Kasliwal RR. Role of Strain Imaging in Ischemic Heart Disease. J Indian Acad Echocardiogr Cardiovasc Imaging [serial online] 2023 [cited 2023 Sep 27];7:137-46. Available from: https://jiaecho.org/text.asp?2023/7/2/137/384775 |
| Introduction | |  |
Echocardiography plays an important role at every step in the evaluation and management of patients with coronary artery disease (CAD). Since CAD affects the heart non-uniformly, a segmental or regional wall motion abnormality (RWMA) is the most characteristic echocardiographic finding seen in CAD. The entire echocardiographic assessment of CAD revolves around the recognition of RWMAs and assessment of their distribution, severity, and the hemodynamic consequences.
Visual wall motional analysis is the method used for assessing RWMAs during echocardiography. Although extensively used, it has some limitations which are also well-recognized. First, visual assessment is subjective and hence, inherently susceptible to observer variability. Second, it requires considerable operator expertise. And lastly, visual analysis is unable to detect subtle changes in the myocardial contractile function, thus compromising its sensitivity.
Over the last two decades, strain imaging has emerged as a useful tool for the quantitative assessment of myocardial function. Left ventricular (LV) global longitudinal strain (GLS) has already become an established parameter for quantifying LV systolic function and is being increasingly used in many different indications. As discussed below, LVGLS is useful for the evaluation of CAD also. However, given the segmental nature of the disease, segmental strain is more relevant for use in CAD patients. Numerous studies have explored the utility of segmental strain for this purpose and have shown its potential benefit. However, unlike the GLS, segmental strain has significant measurement variability and is therefore not yet ready for routine clinical use. This has been a major challenge limiting the transition of strain imaging from being a research tool to its clinical application in the evaluation and management of CAD. Despite these challenges, strain imaging has several potential applications in CAD patients. In addition, strain imaging also provides valuable insights into the pathophysiology of CAD. For these reasons, an understanding of the current role of strain imaging in CAD is in order. This review describes the fundamental principles of strain imaging as applicable to CAD and summarizes the key findings from the studies exploring its utility in CAD patients.
| Fundamentals of Strain Imaging Relevant to Its Use in Coronary Artery Disease | | |
Strain is a measure of myocardial deformation and refers to the percentage change in the length of a myocardial segment during the given phase of cardiac cycle. Strain rate is the rate at which this change occurs. A negative value of strain and strain rate indicates myocardial shortening whereas a positive value denotes lengthening or stretching.
Speckle-tracking echocardiography (STE) is the most common echocardiographic technique used for the quantification of myocardial strain. It is a grayscale-based technique which estimates strain from the conventionally acquired two-dimensional (2D) or three-dimensional (3D) echocardiography images. Being a non-Doppler technique, it is not affected by the insonation angle and can quantify myocardial strain in multiple different directions.
The LV myocardium is composed of multiple layers of muscle fibers which are arranged in different directions. The fibers in the subendocardial layer are aligned more to the long axis of the left ventricle and are therefore responsible for its longitudinal shortening. In contrast, the fibers in the middle and subepicardial layers are arranged more obliquely and determine mainly the short-axis deformation (i.e., radial thickening, circumferential shortening, rotation and twist) of the left ventricle. Because of such arrangement, the diseases that affect the subendocardium mainly cause impairment of the longitudinal strain (LS), while the circumferential and radial strain and twist remain normal or may become exaggerated. As the disease becomes more and more transmural, there is progressive impairment of the short-axis deformation also. Thus, the impairment of only the LS tends to indicate a subendocardial pathology whereas impairment of both LS and circumferential strain (CS) indicates transmural disease.[1]
| Applications of Strain Imaging in Coronary Artery Disease | | |
Strain imaging has been used as a means to provide quantitative assessment of LV myocardial function in almost the entire spectrum of CAD. Of these, the major applications are discussed below.
Detection of coronary artery disease
Patients presenting with stable angina
Assessment at rest
In a patient with suspected CAD, the presence of an RWMA in the resting echocardiogram itself virtually confirms the diagnosis. However, diagnosing CAD in the absence of an RWMA is challenging. A quantitative parameter that could detect subtle impairment of LV systolic function could be useful in this setting.
Moustafa et al. studied 200 patients with suspected stable angina pectoris and normal resting conventional echocardiography. Of these, 150 had angiographically proven CAD, whereas the remaining 50 had normal coronary arteries. GLS was lower in CAD patients and showed a progressive reduction with increasing number of the involved coronary arteries.[2] In another study of 235 patients (133 with angiographically proven CAD), GLS was found to be significantly lower in patients with CAD. It also showed good correlation with the severity of the disease, defined according to the number of coronary vessel involvement and the SYNTAX score.[3]
Biswas et al. studied 117 subjects with angina and normal resting echocardiogram. GLS could accurately detect obstructive CAD and had a significant correlation with the SYNATX score. Optimum cutoff value of GLS to detect significant CAD was −16.5% (87.6% sensitivity, 85.7% specificity, P < 0.0001), to predict triple vessel disease was −14.5% (95.7% sensitivity, 73.4% specificity, P < 0.0001) and to predict high SYNTAX score was −13.5% (sensitivity 78.3%, specificity 87.9%, P < 0.0001).[4] Many other studies have similarly shown reduced LV GLS in CAD patients, with the degree of impairment correlating with the number of coronary vessels involvement, SYNTAX score, Gensini score or other measures of CAD severity.[5],[6],[7],[8],[9],[10] In these studies, LVGLS has been shown to improve the diagnostic performance of the multivariable models including the clinical and laboratory parameters.[7] In addition, the predictive accuracy of GLS at rest has also been shown to be comparable to that of post-exercise wall-motion score index (WMSI), thereby potentially obviating the need for a stress test.[11]
Several studies have also used segmental LS in different combinations to detect CAD. Choi et al. included 108 patients with suspected CAD who underwent echocardiography and coronary angiography. No patient had LV RWMA at rest. The patients with left main or three-vessel CAD were categorized as high-risk group, those with one-or two-vessel CAD as low-risk group and those without CAD as controls. Peak-systolic LS of the mid-and basal segments could accurately detect patients with severe CAD and a cut-off value of-17.9% provided 79% sensitivity and specificity.[12] Chaichuum et al. calculated vessel myocardial strain and strain rate for each coronary vessel and found it to correlate with the severity of coronary stenosis.[13]
A few investigators have also used 3D STE for quantifying LV strain in patients with stable angina and normal LVEF. It was found that all the 3D strain parameters including GLS, and global area strain (GAS) were significantly impaired in patients with CAD and also corelated with the Gensini score.[9],[10]
The newer STE software allow measurement of the layer-specific strain, in addition to the whole wall myocardial strain. This may have some utility as the different LV myocardial layers may not be uniformly affected. Hagemann et al. evaluated layer-specific strain in 285 prospectively enrolled patients referred with clinically suspected angina pectoris and normal LVEF (108 of them had significant CAD). Endocardial, epicardial, and mid-myocardial GLS were all significantly impaired in CAD patients. However, only epicardial and mid-myocardial GLS could independently predict CAD in a multivariable model that also included baseline clinical parameters, conventional echocardiographic measurements, and Duke score. In another study, only transmural GLS was found to be an independent predictor of CAD.[14],[15]
Post-systolic shortening, implying a delay in the myocardial contraction, is a common manifestation of myocardial ischemia [Figure 1]. It can be quantified as post-systolic index (PSI) which is calculated as the difference between the peak LS and peak systolic LS divided by peak systolic LS (in some studies, peak LS has been used as the denominator). The appearance of post-systolic shortening in response to stress is highly suggestive of ischemia and is a more sensitive marker than the reduced myocardial thickening.[16] A stress induced PSI >25% has been considered to be diagnostic of inducible ischemia. In contrast, the post-systolic shortening in the resting images is less specific and may represent myocardial ischemia, scarring or dyssynchrony. Nevertheless, in some studies, PSI at rest has also been shown to be helpful in detecting underlying CAD. Nabati et al. studied 102 patients with left bundle branch block with preserved LVEF. They found that PSI and strain delay index could identify underlying CAD in these patients.[17] | Figure 1: Post-systolic thickening in a patient with coronary artery disease. Left ventricular longitudinal strain curves in the apical long-axis view are displayed. The green dotted line represents the aortic valve closure (AVC). The basal posterior segment (yellow curve) shows significant thickening occurring after AVC (arrow). Also seen is the paradoxical stretching of the mid-posterior segment (sky blue curve). AVC: Aortic valve closure
Click here to view |
As an adjunct to stress echocardiography
Stress echocardiography is one of the most important investigations for the evaluation of CAD. The diagnosis of CAD during stress echocardiography relies on the identification of stress induced RWMAs.[18] It has high diagnostic accuracy with the sensitivity and specificity of exercise echocardiography reported as 83% and 84% respectively and that of dobutamine echocardiography as 80% and 85%, respectively. However, as mentioned above, the subjective nature of visual wall motion analysis remains a major limitation.[19],[20] Strain imaging has been employed to overcome this limitation by making the interpretation objective and quantitative.
In one of the earliest studies, Voigt et al. used Doppler-based strain imaging in 44 patients undergoing dobutamine echocardiography. All the ischemic segments exhibited post-systolic shortening and the ratio of post-systolic shortening to peak segmental LS was found to be the best quantitative parameter to identify stress-induced ischemia.[16] Post-systolic strain index has been evaluated in a very recent study also. Anderson et al. performed a study involving 146 patients with end-stage liver disease undergoing dobutamine echocardiography. A PSI value ≥0.25 in at least 2 segments in the same coronary distribution was considered an evidence of ischemia. Visual wall motion analysis had a sensitivity of 28% and specificity of 92% for detecting CAD. In comparison, peak GLS and peak stress PSI had a higher sensitivity (69% and 78%, respectively) but lower specificity (63% and 78%, respectively). Among all the echocardiographic parameters that were studied, the peak PSI provided the best balance of sensitivity and specificity and thus, had the highest diagnostic accuracy.[21]
Most of the other studies have used peak segmental LS or GLS as the strain measurements for diagnosing ischemia. These studies in general have shown that the addition of strain imaging to wall motion analysis either during exercise echocardiography or dobutamine stress echocardiography significantly improves the overall diagnostic accuracy of the test.[22],[23],[24],[25],[26],[27],[28] However, Celutkiene et al. had contrasting observations and showed that the wall motion analysis was more accurate than any of the quantitative strain parameters.[29] The accuracy of the strain imaging for the different coronary artery territories has also been studied. STE-based strain has been show to perform well in the left anterior descending artery territory but its accuracy for detecting ischemia in the posterior circulation has been sub-optimal.[27],[30] The layer-specific strain has also been assessed for its ability to detect inducible ischemia. In one of the studies, the endocardial-to-epicardial LS ratio after exercise stress was found to be useful for diagnosing inducible myocardial ischemia.[31]
Gupta et al. performed a meta-analysis of thirteen studies with 978 patients evaluating accuracy of strain imaging during stress echocardiography. Pooled area-under-the-curve for diagnosing significant CAD was 0.92 (95% confidence interval [CI] 0.89–0.94) for LS imaging as compared to 0.83 (95% CI 0.80–0.86, P < 0.001) for visual wall motion analysis. LS imaging had higher sensitivity (88% vs. 74%, P < 0.001) but comparable specificity (80% vs. 83%, P = 0.59), yielding an overall higher diagnostic accuracy than that of visual wall motion analysis.[32]
An alternative approach to incorporate strain imaging during stress echocardiography is to use it for ruling out significant CAD instead of ruling it in. In a study of 78 patients, increased GLS immediately after exercise stress excluded significant CAD, whereas the lack of an increase in GLS in response to exercise identified significant CAD.[33] In a similar study, peak GLS >20% after exercise ruled out obstructive CAD on computed tomographic coronary angiography.[34]
Segmental strain analysis is a time-consuming process, which may hinder its wider use during stress echocardiography. To overcome this, automated strain analysis approaches have been tried. In an older study, Bjork Ingul et al. evaluated an automated method for LV myocardial deformation analysis in 197 patients undergoing dobutamine echocardiography. Strain imaging was found to have significantly greater sensitivity for detection of myocardial ischemia than wall motion scoring.[35] More recently, O'Driscoll et al. performed a multicentric study that included 512 participants who underwent a clinically indicated stress echocardiography. The rest and stress images were subjected to artificial intelligence based endocardial border contouring for automated estimation of LVEF and GLS. It was found that the addition of automated LVEF and GLS at peak stress to wall motion score significantly improved the model discrimination of CAD.[36]
A unique limitation of treadmill exercise stress echocardiography is the need to quickly acquire the post-stress images to avoid missing myocardial ischemia. This represents a major challenge and one of the factors compromising the sensitivity of treadmill stress echocardiography. An innovative application of strain imaging may offer a solution to this problem. The early diastolic LV myocardial relaxation is a highly energy dependent process and the most susceptible to ischemic insult. Moreover, the ischemia-induced abnormalities of the early diastolic function persist for several minutes after the cessation of stress. Strain imaging can detect this “ischemic memory.” Under normal conditions, more than 70% of recovery of the myocardial strain occurs during the first one-third of the diastole, but in the presence of exercise-induced ischemia, this recovery is significantly prolonged (“diastolic stunning”) [Figure 2]. Ishi et al., in a study of 162 patients with stable angina, showed that the diastolic stunning could be detected even after 5–10 min of stopping exercise and was a sensitive and reliable tool for the detection of CAD.[37] | Figure 2: The concept of diastolic stunning. The solid green line represents the aortic valve closure and the orange broken line represents the initial one third of the diastole. The longitudinal strain curves at the baseline show good recovery of strain during the early diastole. However, the diastolic strain recovery is significantly prolonged (arrows) following exercise and this abnormality is apparent even in the images acquired at 5 min after the cessation of exercise
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Diagnosing coronary artery disease in the emergency room
Prompt recognition of the underlying etiology in patients presenting with suspected acute coronary syndrome (ACS) is crucial to allow their rapid triaging. Strain imaging may help in this setting.
In a study of 183 patients diagnosed with non-ST elevation ACS (NSTE-ACS), the combination of WMSI and territorial LS (TLS) was found be more accurate than WMSI alone in detecting the culprit vessel.[38] Atici et al. evaluated 150 patients with NSTE-ACS. They found that both GLS and TLS were significantly lower in patients with CAD as compared with the control group. GLS showed correlation with high-sensitivity troponin, whereas TLS correlated with the severity of CAD. On multivariate analysis, GLS and the Global Registry of Acute Coronary Events (GRACE) risk score were found to be independent predictors of CAD.[39] In another study, GLS was associated with CAD complexity and severity, whereas TLS determined the culprit artery. GLS >−14.1% detected severe CAD with 83% sensitivity and 80% specificity. TLS >−9.2% predicted acute coronary occlusion with 85% sensitivity and specificity.[40] Marques-Alves et al., in a group of 200 patients with troponin-negative NSTE-ACS, found that LVGLS had better discriminative power than LVEF or the GRACE score for diagnosing CAD.[41] The value of GLS and/or TLS in diagnosing CAD in suspected ACS patients has been shown in many other studies.[42],[43]
Zhang et al. studied 195 patients with suspected NSTE-ACS with normal wall motion and LVEF. Early systolic index (representing early systolic stretching) was found to be superior to LVEF and PSI for identifying patients with significant coronary stenosis.[44]
Establishing etiology of left ventricular systolic dysfunction
Strain imaging can also be used for differentiating non-ischemic causes of LV systolic dysfunction from ischemic LV systolic dysfunction. Impairment of LS in myocardial segments extending beyond a single coronary vascular territory can help in differentiating takotsubo cardiomyopathy from acute myocardial infarction (MI).[45],[46] In a recent study, Berti et al. compared 22 patients of takotsubo cardiomyopathy with 22 patients of extensive anterior wall MI. It was found that the extension of contractile dysfunction from LV apex to mid inferior and inferior-lateral walls (measured as the inferior-apex ratio and the inferior-lateral-apex ratio) could reliably identity takotsubo cardiomyopathy and distinguish it from extensive anterior wall MI.[46]
LV strain has also been used for the differential diagnosis of HFrEF. Vachalcova et al.[47] showed that the LV apical rotation was significantly higher in patients with ischemic HF (compared with non-ischemic cardiomyopathy), but the other parameters (including GLS) were not helpful in making this distinction. Kowalczyk et al.[48] found that the dispersion of regional peak early diastolic strain rate was a better parameter for identifying underlying CAD in patients with reduced LVEF.
Segmental LS can also help in differentiating inferior wall MI from pseudo-dyskinesis of the inferior wall.[49]
Assessment of the myocardial infarct size
The size of the infarct is a strong prognostic marker in patients presenting with acute MI. Several studies have reported that LS correlates with the infarct size.[50],[51],[52],[53] In a study on 36 patients with acute MI who received thrombolytic therapy, GLS showed good correlation with the final infarct size.[50] In another study, a combination of strain imaging and wall motion analysis was able to accurately identify patients with infarcts larger than 12% on magnetic resonance imaging (MRI).[53]
Bertini et al., in patients with acute MI, demonstrated an excellent correlation between average LS in the infarct segments and the peak cardiac troponin T levels. Moreover, the symptoms-to-balloon time had strong inverse relationship with GLS and infarct LS.[54] Similarly, in a large study involving 611 patients with acute MI, GLS showed a stronger association than LVEF with N-terminal pro-brain natriuretic peptide (NT-proBNP) levels.[55]
Myocardial viability, prediction of functional recovery and left ventricular remodeling
In patients with ischemic LV systolic dysfunction, recovery of the contractile function following reperfusion/revascularization is one of the most important determinants of long-term clinical outcomes. Strain imaging has been used in many different ways to predict this functional recovery.
Patency of the culprit artery
Total occlusion of the infarct-related artery prior to coronary angiography is associated with lower likelihood of functional recovery subsequently. Both LS and CS have been used to identify acute total occlusion.
Cho et al. studied 69 patients with acute MI. A cut-off value of −9.45% for the average infarct segments LS had 85.4% sensitivity and 67.9% specificity for predicting total occlusion of the infarct related artery and had much better accuracy than WMSI for this purpose.[56] Similarly, in the study cited above, Mghaieth evaluated 70 patients with NSTE-ASC and found that TLS was a good predictor of acute total occlusion.[40] Many other studies have shown similar results.[57],[58],[59]
Total coronary occlusion can also be identified using CS since the impairment of CS reflects transmural damage. Grenne et al. studied 111 patients with suspected NSTE-ACS who underwent echocardiography within 1 h of hospital admission. CS was found to correlate with LVEF, peak cardiac troponin I levels, and the infarct size. In addition, a territorial CS value >−10.0% could identify acute total occlusion with 90% sensitivity and 88% specificity.[60]
Transmural extent of the myocardial infarction
A myocardial segment which is transmurally infarcted has a much lower likelihood of functional recovery following revascularization. Since the impairment of CS mainly occurs when there is transmural injury, it can be used as a tool to distinguish transmural infarcts from subendocardial infarcts.
Chan et al. studied 80 patients with chronic ischemic LV systolic dysfunction. The reduction in CS identified transmurally infarcted segments on contrast-enhanced MRI.[61] LS was equally impaired in both subendocardial and transmural infarcts. Similar findings were reported by Kansal et al. in 59 patients with evidence of myocardial fibrosis on MRI.[62] Becker et al. used layer-specific CS in 56 patients with chronic ischemic LV dysfunction. Endocardial layer CS could distinguish between non-transmural infarction and no infarction, whereas epicardial CS allowed distinction between transmural and non-transmural infarction.[63]
As an adjunct to pharmacological stress echocardiography for prediction of myocardial viability
Dobutamine echocardiography is a commonly employed modality for detecting myocardial viability. An increase in the segmental contractility in response to low-dose dobutamine infusion is considered an evidence of viability. The myocardial response to dobutamine is traditionally assessed using visual wall motion analysis. Strain imaging can enhance its accuracy for this purpose.
Hanekom et al. studied 55 patients with ischemic LV dysfunction undergoing myocardial revascularization. Doppler-based strain imaging was performed in addition to conventional wall motion analysis. A repeat echocardiography was performed 9 months after revascularization to look for functional recovery. It was found that combining wall motion analysis with LS rate at low-dose dobutamine and its increment from the baseline significantly improved the accuracy of the former for prediction of functional recovery.[64] Bansal et al. used STE strain in the same cohort of the patients. It was found that STE strain had good accuracy for predicting viability in the anterior circulation but not in the posterior circulation.[65] Ran et al. used STE strain in patients undergoing adenosine echocardiography. Improvement in LS in response to adenosine infusion was able to identify myocardial viability on nuclear imaging.[66]
Strain imaging at rest and prediction of left ventricular remodeling
Several studies have shown that both segmental LS and GLS at rest can reliably predict segmental and global functional recovery, respectively.[67],[68],[69],[70],[71],[72],[73],[74]
Abate et al. studied 153 patients with acute MI, treated with primary percutaneous coronary intervention (PCI). 3D STE was performed. A cut-off value of −11.1% for segmental 3D LS had 92% sensitivity and 91% specificity for predicting functional improvement at 6 months.[67]
Khaled and Shalaby consecutively enrolled 420 patients with ACS treated with PCI during the period from January 2021 to December 2021. A GLS value >−9% was a predictor of LVEF improvement during the follow-up.[68] In another study, Shehata et al. included 400 patients who had presented with first acute ST-elevation MI and had undergone successful reperfusion. Baseline GLS was one of the most important predictors of LV functional recovery at 3 months follow-up.[69] Many other studies have shown that GLS is a powerful and independent predictor of LV functional recovery during follow-up.[67],[70],[71],[72],[73]
Apart from the peak systolic LS, other LS measurements such as systolic lengthening, post-systolic shortening, early diastolic LS rate and layer-specific LS have also been shown to predict functional recovery.[75],[76],[77],[78] In a similar manner, CS has also been shown to predict negative remodeling following MI.[79]
Assessment of the risk for sudden cardiac death
Myocardial fibrosis and scarring occurring as a consequence of MI result in electrical heterogeneity within the myocardium that serves as a substrate for premature electrical discharges, reentry and tachyarrhythmia which may eventually lead to sudden cardiac death (SCD). Strain imaging can detect mechanical dispersion (MD) as a surrogate for such electrical heterogeneity and can identify patients at risk for developing ventricular arrhythmia (VA) and SCD [Figure 3]. | Figure 3: Mechanical dispersion in a patient with coronary artery disease. All the segmental strain curves are peaking at different times. AVC: Aortic valve closure
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Haugaa et al. have performed a series of studies to demonstrate the prognostic value of MD for predicting VA risk in patients with previous MI.[80],[81] MD was calculated as the standard deviation of time-to-peak LS of all the LV myocardial segments in a 16-segment model. It was found to be an independent predictor of VA/SCD risk during the follow-up and was superior to LVEF for this purpose. GLS was also a predictor of VA risk, but LVEF was not. Many other investigators have also demonstrated the prognostic value of GLS and MD in prediction of SCD/VA risk in post-MI patients.[82],[83],[84],[85],[86] A recent meta-analysis summarized 12 such studies.[87] Some of these studies had included patients with non-ischemic LV systolic dysfunction also. Overall, LV MD was found to be a stronger predictor of VA risk as compared with GLS or LVEF.
Role of myocardial work assessment
Myocardial work assessment has emerged as a new non-invasive tool for assessing myocardial contractile function. It combines STE-based strain with peripheral blood pressure as a surrogate for LV systolic pressure to construct segmental and global pressure-strain loops. From these pressure-strain loops, several indices of myocardial contractile function can be derived such as global work index (GWI), global work efficiency (GWE), global constructive work (GCW) and the global wasted work (GWW). The main advantage of myocardial work assessment over GLS is that it is relatively load-independent.
Lin et al. enrolled 89 patients undergoing exercise echocardiography. The peak GWE was significantly lower in patients with CAD and was found to be superior to mid-myocardial, epicardial, and endocardial GLS in identifying significant CAD.[88] Edwards et al. studied 150 patients with no resting RWMA and normal LVEF who were referred for coronary angiography. Global myocardial work was the most powerful predictor of significant CAD and was superior to even GLS for this purpose. A cut-off value of 1810 mmHg% for global myocardial work had 92% sensitivity and 51% specificity for detecting significant CAD.[89] Zhang et al. showed that both global and regional myocardial work were useful in predicting high-risk CAD.[90] Other studies have also shown the potential value of exercise myocardial work assessment in the evaluation of CAD patients.[91],[92]
Overall prognosis
One of the greatest advantages of GLS is that it has strong prognostic value regardless of the underlying disease or the clinical setting. Several studies have demonstrated the same in CAD patients also. These studies have used a variety of endpoints such as all-cause mortality,[93],[94] heart failure hospitalization,[93] hard cardiac events,[94] VA,[80],[95] and a composite of the major adverse cardiac events.[96],[97] The patient subsets have also varied, including those with chronic ischemic cardiomyopathy,[93] stable CAD with relatively preserved LVEF,[97],[98],[99] those undergoing primary PCI,[96] and the patients undergoing stress echocardiography for ischemia evaluation.[94] In many of these studies, the prognostic value of GLS was incremental to that of clinical factors and LVEF.[93],[94],[97],[99]
Apart from GLS, several other strain parameters such as PSI,[98] 3D global area strain,[100] and MD[87],[101] have also been shown to predict overall outcomes in CAD patients.
Limitations
Conceptually, strain imaging appears to be a promising tool for application in CAD as it allows quantitative assessment of the LV myocardial function. The addition of strain imaging to visual wall motion analysis makes the assessment objective as well as sensitive to detect subtle changes in the myocardial contractile function. The numerous studies described above have validated this assumption and shown the potential utility of strain imaging. However, two main problems exist. First, the segmental myocardial strain has high measurement variability making its routine clinical use challenging. Second, even for GLS which has high reproducibility, it is unclear how to use it in any individual patient. The studies have shown its incremental value in the patient groups but at the individual level, the impairment of GLS is non-specific and can occur due to a variety of reasons (ageing, underlying cardiovascular risk factors, etc.) other than CAD. Moreover, the degree of GLS impairment depends on the underlying extent of myocardial ischemia and/or injury. As a result, there is no single cut-off value of GLS that can be used either for diagnosing CAD or for any other purpose in these patients. For both these reasons, the use of strain imaging in CAD remains quite limited at present.
| Conclusions | | |
The potential utility of strain imaging as a tool for quantitative assessment of myocardial contractile function has already been demonstrated in many cardiac conditions. Numerous studies have explored its utility in patients with CAD also. Almost the entire spectrum of CAD has been studied and several different strain parameters and indices derived from global or regional longitudinal, circumferential, radial and area strain as well as left ventricular rotation have been employed. These studies have mostly shown that strain imaging can have an incremental role in the diagnosis and prognosis assessment of CAD. However, the measurement variability of segmental strain, non-specific nature of GLS impairment and the lack of a single cut-off value for GLS are proving the major hurdles in the clinical application of strain imaging for the evaluation and management of CAD.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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