|Year : 2017 | Volume
| Issue : 3 | Page : 189-196
Journey from two-dimensional to four-dimensional strain and left ventricle torsion in the evaluation of coronary artery disease
V. Amuthan1, R. V. A. Ananthcal2
1 Emeritus Professor of Cardiology, The Tamil Nadu Dr. MGR Medical University, Chennai, Tamil Nadu, India
2 Jeyalakshmi Heart Centre, Madurai, Tamil Nadu, India
|Date of Web Publication||12-Dec-2017|
Dr. V. Amuthan
HIG II/12, Karpaga Nagar, Avaniapuram, Madurai - 625 012, Tamil Nadu
Source of Support: None, Conflict of Interest: None
The use of echocardiography in the diagnosis of suspected myocardial infarction has been classified as appropriate. The use of regional strain which is a dimensionless measurement of deformation, expressed as a fractional or percentage change from an object's original dimension, greatly enhances the accuracy of detecting the regional wall motion abnormality in a scale (-20 to +20) ten times that of eye balling. Speckle-tracking echocardiography (STE) is a novel technique which has emerged as one of the best methods that analyses motion and strain by tracking natural acoustic reflections and interference patterns within an ultrasonic window. In patients with acute myocardial infarctions (MIs), accuracy for the prediction of global functional improvement as well as LV remodelling by 2D STE is comparable with that of late gadolinium enhancement cardiac magnetic resonance (CMR) imaging. Global longitudinal strain (GLS) has evolved as one of the most robust parameter, and this has been shown to identify subclinical LV dysfunction.3D STE has emerged as an alternative non -invasive technique to assess LV rotation. In anterior wall myocardial infarction, systolic twist is decreased, and diastolic untwisting is depressed in accordance with LV systolic dysfunction. These results suggest the significant impact of global LV systolic function on LV twist and twist-displacement loops in patients with anterior wall MI. Although to date, no prognostic information exists on the role of rotational parameters of LV function, further ongoing studies would shed more light on this important technique.
Keywords: Coronary artery disease, echocardiography, four-dimensional strain
|How to cite this article:|
Amuthan V, Ananthcal R. Journey from two-dimensional to four-dimensional strain and left ventricle torsion in the evaluation of coronary artery disease. J Indian Acad Echocardiogr Cardiovasc Imaging 2017;1:189-96
|How to cite this URL:|
Amuthan V, Ananthcal R. Journey from two-dimensional to four-dimensional strain and left ventricle torsion in the evaluation of coronary artery disease. J Indian Acad Echocardiogr Cardiovasc Imaging [serial online] 2017 [cited 2018 Oct 19];1:189-96. Available from: http://www.jiaecho.org/text.asp?2017/1/3/189/220535
| Introduction|| |
Echocardiography remains one of the marvels of the 21st century and is one of the most important tools in the evaluation of coronary artery disease. The 2011 appropriate use criteria for echocardiography classified use of echocardiography in the diagnosis of suspected MI as appropriate. We shall review the role of echocardiography in the diagnosis and prognosis of coronary artery disease with special reference to strain and left ventricular (LV) twist and torsion.
| Regional Wall Motion Analysis in Coronary Artery Disease|| |
Echocardiographic evidence of regional wall motion abnormalities (RWMAs) occurs before electrocardiographic (ECG) changes and can occur within seconds of coronary arterial occlusion as early as 12.5 s in studies reported., There are a number of other causes of RWMAs, including a prior infarction, focal myocarditis, prior surgery, left bundle branch block, ventricular preexcitation through an accessory pathway, and cardiomyopathy. In the emergency department, routine eyeballing usually picks up the presence of regional wall motion abnormality and the territories involved. The American Society of Echocardiography has recently recommended a 17-segment model for this [Figure 1]a,[Figure 1]b,[Figure 1]c,[Figure 1]d., In a 17-segment model, beginning at the anterior junction of the interventricular septum and the right ventricular (RV) free wall and continuing counterclockwise, basal and mid ventricular segments should be labeled as anteroseptal, inferoseptal, inferior, inferolateral, anterolateral, and anterior. The apex is divided into five segments, including septal, inferior, lateral, and anterior segments, as well as the “apical cap,” which is defined as the myocardium beyond the end of the LV cavity. A Bull's eye plot can be constructed where the outer ring represents the basal segments, the middle ring represents the segments at mid papillary muscle level, and the inner ring represents the distal level. The anterior insertion of the RV wall into the LV defines the border between the anteroseptal and anterior segments. Starting from this point, the myocardium is subdivided into six equal segments of 60°. The apical myocardium in the 17-segment models is divided instead into four equal segments of 90°. In the17-segment model, an additional segment (apical cap) is added in the center of the Bull's eye. However, this methodology depended considerably on the expertise of the interpreter and showed relatively low interobserver agreement. For this purpose, myocardial strain (i.e., the relative lengthening or shortening of the myocardial segment expressed as a percentage of its initial length) and strain rate (i.e., the rate of this lengthening or shortening) imaging was introduced.
|Figure 1: Standardized myocardial segmentation and nomenclature for tomographic imaging of the heart. (a) Showing apical 3 chamber, 2 chamber, and 4 chamber views and current American Society of Echocardiography nomenclature. (b) Short axis at basal, mid left ventricle level nomenclature. (c) Short axis at apical level nomenclature. (d) Three-dimensional derived tomographic slices: (1) Apical 4 chamber view, (2) apical 2 chamber view, and (3) apical 3 chamber view A1 to A3 apical tomographic cuts from the apex toward mid left ventricle M1 to M3 tomographic mid left ventricle cuts from apex to basal level B1 to B3 tomographic basal left ventricle cuts The top and bottom starting points of the transverse short axis slices can be adjusted|
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| Strain Imaging in Localization and Decision-Making in Coronary Artery Disease|| |
The regional strain is a dimensionless measurement of deformation, expressed as a fractional or percentage change from an object's original dimension. The LV myocardium consists of circumferential fibers in the mid-wall layer and longitudinal fibers in the endocardial and epicardial layers, and myofibril orientation changes continuously from right-handed helix in subendocardium to left-handed helix in subepicardium. LV function is determined by the sum of contraction and relaxation in these 3 layers [Figure 2]. Speckle-tracking echocardiography (STE) is a novel technique which has emerged as one of the best methods that analyses motion and strain by tracking natural acoustic reflections and interference patterns within an ultrasonic window. The image-processing algorithm tracks user-defined regions of interest which are comprised of blocks of approximately 20–40 pixels containing stable patterns that are described as “speckles,” “markers,” “patterns,” “features,” or “fingerprints.” [Figure 3] illustrates an example of STE. The two-dimensional (2D) echocardiography derived longitudinal strain is analyzed using propriety software in Quad view and Bull's eye plot or the automated functional imaging. The ease with which we derive information similar to nuclear scans is really amazing. However, this wonderful technique is hampered by inter vender nonagreement and the difference in reports done on different equipment. There are many efforts to correct this by the publication of definitions for a common standard for 2D STE. Consensus document published by the EACVI/ASE/Industry Task Force to standardize deformation Imaging is the latest one.
|Figure 2: Longitudinal, circumferential, radial strain, and left ventricle torsion|
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|Figure 3: Quad view and automated functional imaging (AFI). (a) Tracked apical three chamber loop with color coding of the 6 myocardial segments. (BIL: Basal infero lateral, MIL: Mid infero lateral, AL: Apical lateral, AS: Apical septal, MAS: Mid anterior septum, BAS: Basal anterior septum). (b) Average segmental strain graphically displaced. Each color line corresponds to the same color-coded myocardial segment. (c) Color display of peak systolic strain. Color scale shown on the right corner. (-20% given red color and +20 given blue color). (d) M mode representation of peak systolic strain. Myocardial segments are color coded, strain color scale same as in (c). (e) Automated functional imaging (polar map or Bull's eye plot) from the same patient, and (f) Comparison figure showing all the 17 segments recommended by the American Society of Echocardiography. Color scale shown in C is used|
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In patients with acute myocardial infarctions (MIs), accuracy for the prediction of global functional improvement as well as LV remodeling by 2D STE is comparable with that of late gadolinium enhancement cardiac magnetic resonance (CMR) imaging. The prediction of segmental functional improvement is noninferior compared with of late gadolinium enhancement CMR in patients with ST-elevation MIs (STEMIs). [Figure 4] and [Figure 5] are from a patient with anterior wall STEMI before and after percutaneous intervention with the deployment of a drug eluting stent in the left anterior descending artery. [Figure 6] is from a patient with inferior wall STEMI with triple vessel disease and totally cutoff right coronary artery (RCA). Based on the physiological information from the strain-based automated functional imaging, the intervention was done in RCA only.
|Figure 4: Bull's eye map demonstrating infarct localization in a 42-year-old male with anterior wall STEMI. Peak systolic images recorded from (a) apical 4 chamber view, (b) apical 2 chamber view, (c) apical 3 chamber view, (d) automated functional imaging map showing the area of decreased strain in anterior septum and anterior wall at basal and mid left ventricle level and the left ventricle apex with strain value marked in each segment localizing the infarct to left anterior descending artery, (e) three-dimensional tomographic 12 segmental views cuts mentioned in Figure 2, frozen in peak systole clearly reduced systolic thickness in segments supplied by left anterior descending, (f) left coronary angiogram showing total cutoff of left anterior descending immediately after origin, and (g) normal right coronary angiogram|
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|Figure 5: Same patient with anterior wall STEMI after revascularization (a) in two dimensional apical four chamber, two chamber and long axis views with longitudinal peak systolic strain derived automated functional imaging clearly showing better strain parameters. (b) Three-dimensional derived 12-segment tomographic slices during peak systole, showing improved systolic thickening in segment supplied by left anterior descending. (c) The deployment of a drug eluting stent in left anterior descending with final result showing TIMI 3 flow|
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|Figure 6: Bull's eye map demonstrating infarct localization in a 62-year-old female with inferior wall ST-elevation myocardial infarctions. (a) Peak systolic images recorded from apical 4 chamber, 2 chamber, and 3 chamber view with automated functional imaging map showing the area of decreased strain in inferior septum and inferior wall at basal and mid left ventricle level and the left ventricle apex with strain value markedly rin educed in each segment localizing the infarct in the right coronary artery territory. (b) Three-dimensional tomographic 12-segmental view with slices mentioned in Figure 2, frozen in peak systole, clearly showing reduced systolic thickness in segments supplied by right coronary artery. (c) Right coronary angiogram showing total cut off of right coronary artery immediately after origin. Left coronary angiogram showing discrete lesions in left anterior descending artery and ramus|
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| Current Status of Three-Dimensional Myocardial Strain Estimation|| |
With developments in three-dimensional (3D) transducer technology and improvements in hardware and software, 3D data sets with adequate temporal and spatial resolution are now possible, and these 3D approaches can measure 3D strain from a multi-beat acquisition with a frame rate set above 40 frames/s. The ability to estimate true 3D myocardial motion and deformation using various 3D STE approaches may provide cardiologists with a better view of regional myocardial mechanics, which may be important for diagnosis, prognosis, and therapy.
| Left Ventricle Torsional Deformation and Speckle Tracking Echocardiography|| |
Shortening and lengthening which are the basic functions of the myocardial fibers result in a systolic twist followed by a diastolic untwisting of the LV due to helical orientation of the fibers. In systole, the LV apex undergoes a counterclockwise rotation about its longitudinal axis as viewed from the apex [Figure 2]c, preceded by a brief clockwise rotation due to the earlier shortening of the subendocardial fibers during isovolumic contraction. Rotation of the LV base in systole is opposite in direction compared to apical rotation, with a brief counter clockwise rotation during isovolumic contraction followed by a clockwise rotation during LV ejection [Figure 2]d. This motion has been compared with that used to squeeze water out of a wet towel. The main determinant of the LV twist is the apical rotation.
- The LV rotation is defined as the myocardial rotation around the long axis of the LV. It is rotational displacement and is expressed in degrees
- The LV twist is the absolute apex-to-base difference in LV rotation referred to as the net angle (LV twist = LV apical twist – LV basal twist) also expressed in degrees
- LV torsion is defined as the base-to-apex gradient in the rotation angle along the long axis (LV torsion = LV twist/LV length), expressed in degrees per centimeter
- The LV twist rate is the systolic time derivative of LV twist. LV untwisting is usually defined as the peak diastolic time derivative of twist.
The complex motion of LV torsion and twist was initially studied by invasive tagging of the LV by radiopaque markers or Sonomicrometry and noninvasively by CMR imaging techniques. 2D and now 3D STE has emerged as an alternative noninvasive technique to assess LV rotation. Although the 2D STE correlated very well with CMR techniques, lower values for apical rotation and LV twist were reported for 2D-STE due to difficulties in selection of optimal imaging planes for such computation. This is because of limited acoustic windows and oblique orientation of the heart in the patient's chest cavity and because the 2D method computes twist directly from peak rotation values from apical and basal short axis views, it does not reflect true torsional deformation because the images are acquired separately from entirely different cardiac cycles and rotation at each level peaks at a different time in the cardiac cycle. A recent study by Ashraf et al., to compute LV twist from 3D echocardiography concluded despite lower spatiotemporal resolution of 3D echocardiography, LV twist, and torsion can be computed accurately. [Table 1] shows reference values for LV Torsion and its timing between base and Apex, base and mid, and Apex levels in 12 Healthy subjects, calculated as the circumferential-Longitudinal shear angle using CMR tagging adapted from: Left ventricular torsion: An expanding role in the analysis of myocardial dysfunction.
|Table 1: Reference values for LV Torsion and its timing between base and Apex, base and mid, and Apex levels in 12 Healthy subjects, calculated as the circumferential-Longitudinal shear angle using CMR tagging|
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| Steps in Three-Dimensional Speckle Tracking Echocardiography and Estimation of Myocardial Deformation|| |
- Step 1: It is essential to acquire multi gated images from the left ventricular apex with ECG gating and at a frame rate of more than 40 per se cond in end diastole and end systole and endocardial borders are marked [Figure 7]
- Step 2: Identification of the left ventricular myocardium – Left ventricular mass and marking of region of interest
- Step 3: [Figure 8] 3D speckle tracking is done and the results are displayed as
|Figure 7: Three-dimensional strain protocol. Step 1: Acquisition of three-dimensional data sets in (a) end diastole, (b) end systole. (c) Step 2: Identification of the left ventricular myocardium – left ventricular mass and marking of region of interest|
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|Figure 8: Step 3 and 4: After myocardial speckle tracking, the results are plotted in different ways: (a) Strain curves from different segments and (b) As automated functional imaging or Bulls' eye plot for longitudinal strain, circumferential strain, area strain, radial strain, left ventricular twist and torsion|
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- Strain curves from different segments and
- Bull's eye plot or automated functional images for longitudinal strain, circumferential strain, area strain, and radial strain.
- Step 4: In addition, left ventricular deformation imaging as viewed from the LV apex can be plotted as left ventricular twist and torsion.
| Prognostication in Myocardial Infarction|| |
LV Ejection fraction: The cornerstone of the prognostication and treatment schedule for STEMI echocardiographic evaluation starts with the evaluation of the left ventricular ejection fraction. Despite its limitations, ejection fraction has become part of the lingua franca of cardiology. The evidence base for modern cardiology is so heavily based on this simple measurement that it is unlikely to disappear. The problems in calculating EF as the ratio between stroke volume and end-diastolic volume and their solutions are enumerated in [Table 2] Adapted from Marwick.
3D imaging is available with echocardiography, magnetic resonance imaging, and computed tomography. The main attraction and advantage of 3D imaging are to avoid geometric assumptions when calculations of LV volumes are being obtained and to avoid errors created by cutting a 3D structure in two dimensions. The current software for 3D evaluation of LV ejection fraction (LVEF) is much easier and can be performed within minutes in the setting of the emergency room. The sphericity index derived from 3D echocardiography (LV end-diastolic volume divided by the volume of a sphere whose diameter is the LV end-diastolic long axis) is an added by product and is the best predictor for LV dilatation.,
| Global Longitudinal Strain|| |
Global longitudinal strain (GLS) has evolved as one of the most robust parameter, and this has been shown to identify subclinical LV dysfunction. GLS is calculated using a variety of proprietary software (EchoPAC, GE Medical Systems, Milwaukee, Wisconsin, USA; Syngo velocity vector imaging, Siemens, Mountain View, California, USA; LV analysis, TomTec GmbH, Unterschlessheim, Germany). GLS is well validated as a marker for the measurement of LV longitudinal deformation, which has emerged as a sensitive and specific marker to detect early and subtle myocardial dysfunction. In one of the recent meta-analyses, Kalam and Otahal, have shown the independent prognostic significance of GLS in patients with mild LV global impairment. The prognostic value of this information seems likely to be superior to that provided by LVEF. Left ventricular GLS before discharge after STEMI is independently associated with LV dilatation at follow-up. In another study of 576 patients who underwent echocardiography ≤24 h after primary percutaneous coronary intervention for STEMI, GLS, and wall motion score index (WMSI) were comparable and both superior for early risk assessment compared with volume-based left ventricular function indicators such as LVEF and end-systolic volume index. Compared with WMSI, the advantage of GLS is the provision of a semi-automated quantitative measure.
| Heart Failure With Preserved Ejection Fraction|| |
In anterior wall myocardial infarction, systolic twist is decreased, and diastolic untwisting is depressed in accordance with LV systolic dysfunction. These results suggest the significant impact of global LV systolic function on LV twist and twist-displacement loops in patients with anterior wall MI. [Figure 9] shows this in a patient with Anterior wall myocardial infarction, who has In Stent Restenosis (ISR) and preserved ejection fraction with reduced longitudinal and circumferential strain, preserved radial strain and reduced left ventricular twist and torsion.
|Figure 9: Comparison of three-dimensional multiplane echocardiographic recordings in this patient with left anterior descending in stent restenosis (a), with coronary angiogram in left anterior oblique projection (b), with longitudinal strain polar (automated functional imaging) map (c), and radionuclide perfusion imaging (d)|
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| Heart Failure With Reduced Ejection Fraction|| |
[Figure 10] shows abnormally reduced twist and torsion in a patient with ischemic cardiomyopathy. A decreased and delayed systolic LV torsion as well as depressed, delayed, and disorganized LV untwisting have been previously reported in patients with dilated cardiomyopathy (DCM). Moreover, paradoxical reversal of LV rotation, with the base rotating counter clockwise and the apex clockwise, with subsequent reduction or even loss of LV twist were observed in some patients with DCM. Preliminary data suggest that cardiac resynchronization therapy (CRT) may restore LV twist in patients who showed LV reverse remodeling, possibly by providing a more physiological electrical depolarization and mechanical contraction of the myofibers. CRT was done in this patient, leading to restoration of LV torsion and ejection fraction.
|Figure 10: Abnormally reduced twist and torsion in a patient with ischemic cardiomyopathy|
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| Conclusion|| |
3D speckle tracking has improved the accuracy of left ventricular deformation imaging and torsion dynamics. Although to date, no prognostic information exists on the role of rotational parameters of LV function the areas most likely to benefit from further improvements in assessing LV architecture and torsional dynamics are heart failure with preserved ejection fraction and cardiac dyssynchrony resynchronization therapy.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10]
[Table 1], [Table 2]