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Wall Motion Tracking and Activation Imaging - Latest Developments and Applications for Patients with Heart Failure

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Abstract

Wall motion tracking is a relatively new tool to define regional and global wall motion, ventricular volumes and ejection fraction. Speckle-tracking echocardiography (STE) allows the calculation of a variety of myocardial function indices – including longitudinal, radial, transverse and circumferential strain, strain rate, displacement, velocity and rotation (twist and torsion) – not only as a 2D application, but also in 3D. In patients with heart failure and cardiac dyssynchrony, there remains a lack of optimal management regarding decisions to implant a cardiac resynchronisation therapy device. Many decisions are made based on data from electrocardiography. Whereas conventional echocardiographic techniques are of limited value in defining mechanical dyssynchrony, newer developments, such as 2D and 3D speckle tracking, have been shown to have significant potential to define the latest site of mechanical activation. Recent 3D STE innovations, including activation imaging, 3D strain and area tracking, open new doors to the definition of segmental delay of mechanical deformation related to time. There is considerable optimism that 3D techniques will improve the present understanding and treatment of patients with cardiac dyssynchrony.

Keywords

Speckle tracking echocardiography, regional wall motion, dyssynchrony, activation imaging, cardiac resynchronisation therapy, heart failure,

Disclosure:The author has no conflicts of interest to declare.

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DOI:https://doi.org/10.15420/ecr.2012.8.1.51

Correspondence Details:Hans Joachim Nesser, Elisabethinen Teaching Hospital, A-4020 Linz, Fadingerstrasse 1, Austria. E: hans-joachim.nesser@elisabethinen.or.at

Copyright Statement:

The copyright in this work belongs to Radcliffe Medical Media. Only articles clearly marked with the CC BY-NC logo are published with the Creative Commons by Attribution Licence. The CC BY-NC option was not available for Radcliffe journals before 1 January 2019. Articles marked ‘Open Access’ but not marked ‘CC BY-NC’ are made freely accessible at the time of publication but are subject to standard copyright law regarding reproduction and distribution. Permission is required for reuse of this content.

Wall motion tracking is an application of pattern-matching ultrasound commonly known as speckle-tracking echocardiography (STE). STE involves creating a template image using a local myocardial region in the starting frame of the image data. In the ensuing frame, an algorithm searches for the local speckle pattern that most closely matches the template. A movement vector is then created using the location of the template and the matching pattern in the subsequent frame. Multiple templates are used to observe movement of the entire myocardium. The process is then repeated by creating new templates and observing their movements in subsequent frames until the entire cardiac cycle has been assessed.

Cardiac performance is a 3D phenomenon; therefore, 2D tracking is intrinsically limited. 2D tracking follows motion occurring within the imaging plane, while the out-of-plane motion component results in noise and interferes with tracking. The inability of 2D STE to measure one of the three components of the local displacement vector is an important limitation that affects the accuracy of the derived indices of local dynamics.

Following the introduction of 3D STE by Abe et al.1 in 2008, Maffessanti et al. compared the segmental 2D and 3D STE values of six indices (radial and longitudinal displacement, rotation and radial strain [RS], longitudinal strain [LS] and circumferential strain [CS]);2 these values did not appear to correlate well, with wide variations of inter-technique agreement. The authors took a variety of 3D STE measurements of left ventricular (LV) regional wall motion and demonstrated their advantages over 2D STE measurements. Segments were classified as normal or abnormal using cardiac magnetic resonance imaging. In normal segments, 3D STE showed higher displacements, due to the out-of-plane motion component of 2D STE, and smaller standard deviations, indicating that tighter normal ranges were found with 3D. Furthermore, gradual decreases in displacement as well as reversals in rotation from base to apex were demonstrated with 3D STE. In abnormal segments, all 3D STE indices were reduced. Thus the relatively smaller normal variability of 3D STE compared with 2D STE measurements provided additional support for the superiority of 3D STE in handling the complexity of regional wall motion abnormality. While 3D STE generates over 3,000 vectors per volume and its temporal resolution is the same as the frame rate of realtime 3D data sets (20–30 volumes/second), it actually reduces the examination time to one-third that of 2D STE.3,4

The potential benefits of the 3D STE technique are evident from a recent comparison between 3D STE and sonomicrometry in anaesthetised sheep. Segmental LS, RS and CS were measured at baseline, during pharmacological stress (induced by a dobutamine and propranolol infusion) and acute myocardial ischaemia (induced by coronary artery occlusion).5 Good correlations were observed between measurements obtained by 3D STE and those obtained by sonomicrometry (LS: Pearson correlation coefficient [r]=0.89, p-value [p]<0.001; RS: r=0.84, p<0.001; CS: r=0.90, p<0.001). In each segmental study, significant correlations of the three strain components were observed (LS: r=0.65–0.68, p<0.001; RS: r=0.59–0.70, p<0.001; CS: r=0.71–0.78, p<0.001).

3D STE was also tested in vitro using a twist phantom, with the heart base rotating at 0°, 15°, 20° and 25° along a fixed apex to avoid translational motion.6 Segmental and global rotation at basal, middle and apical segments correlated well with the actual rotation (base: r=0.93, middle: r=0.92, apex: r=0.95, all p<0.001). To define the percentage change in a segmental area during systole, the area change ratio (ACR) obtained by area tracking was calculated using 3D STE versus sonomicrometry at baseline, during pharmacological stress and acute myocardial ischaemia induced by occlusion of the mid-left ascending artery.7 A strong correlation was found between ACR measurements obtained by 3D STE and those obtained by sonomicrometry (r=0.87, p<0.001).

Despite experimental data, we continue to have no true non-invasive ‘gold standard’ technique that can be used in humans to validate regional ventricular function in three dimensions. Nevertheless, 3D STE has been evaluated in a variety of clinical scenarios to determine LV volume8–11 or acute and chronic ischaemic heart disease.12–16 Compared with normal individuals, patients with hypertrophic cardiomyopathy (HC) have been shown to have increased peak LV twist (16.5 ± 4.7° versus 12.0 ± 3.9°, p<0.001), predominantly because of increased apical rotation in those with LV outflow tract obstruction (patients with obstruction 12.7 ± 4.4° versus patients with no obstruction 9.7 ± 2.8°, p=0.02).17 In this regard, 3D STE provides a novel insight into LV mechanical alterations in select patient groups, such as those with HC.

The future of 3D STE appears bright. While the assessment of right ventricular (RV) function with 2D approaches has been limited to imaging planes, initial experiences18,19 with 3D STE have been promising, showing improved evaluation of right myocardial mechanics and understanding of RV function in patients with pulmonary hypertension. More data regarding normal values of myocardial mechanics obtained by 3D STE are needed.20–23 The results of an ongoing multicentre study focusing on normal values of 3D wall motion tracking in a variety of age groups (Normal values of 3D-wall motion tracking study) will be available in the near future.

Evaluation of Dyssynchrony
According to the American Society of Echocardiography Consensus Statement, ventricular dyssynchrony is a 3D phenomenon. Therefore, the assessment of LV dyssynchrony (LVD) is another important challenge and a promising application of newer techniques. This is particularly important considering that approximately 30 % of heart failure (HF) patients with left bundle branch block (LBBB) are classified as non-responders to cardiac resynchronisation therapy (CRT) – although progress has been made with the inclusion of magnetic resonance imaging in the evaluation process. Therefore, the recognition of myocardial activation delay by echocardiographic techniques is of clinical importance and has been a challenging area of research in past years. First experiences were based on the evaluation of timing intervals between segments derived by M-mode and pulsed Doppler techniques. Although this simple approach is helpful in individual patients, its limitations must be taken into account.

Tissue Doppler Imaging
Tissue Doppler imaging (TDI) was considered a promising technique, particularly for defining the segmental mechanical delay of systolic peak and time to onset or to peak velocity, and strain or strain rate values. Unfortunately, only small, single-centre studies with advanced expertise have been able to provide adequate results, thus limiting the reproducibility, broad acceptance and routine use of the technique. Time to peak velocity is often difficult to define and the velocity curves can be difficult to interpret. Advanced automated TDI techniques using different colour codes of segments with delayed mechanical activation were added to simplify the display of dyssynchrony. In this regard, angle-corrected TDI data for colour-coded temporal activation – a technique known as dyssynchrony imaging (Toshiba, Tokyo, Japan) – have the potential to provide radial dyssynchrony data that may be an additive to dyssynchrony analysis of longitudinal velocities. In 38 patients undergoing CRT, Dohi et al.24 demonstrated a sensitivity of 95 % and a specificity of 88 % of radial dyssynchrony for predicting an acute response to treatment. The data suggest that this technique is more robust than conventional velocity imaging.

Tissue Synchronisation Imaging
Tissue synchronisation imaging (TSI) (GE Vingmed, Horten, Norway) uses automated colour coding of time to peak velocities to define segments with delayed contraction, with red colour representing severe delay. This colour coding of temporal velocity data is superimposed on the routine 2D echocardiographic images to provide visual information about the anatomical regions of interest. Two studies comparing manual TDI versus automated TSI including a total of nearly 120 patients revealed adequate results (r=0.97 and 0.95, respectively, p<0.001).25,26 Furthermore, TSI studies in patients following CRT demonstrated that baseline dyssynchrony was significantly greater in responders than in non-responders, and correlated with volumetric change during follow-up.27,28 There are imitations of TSI, which include moving the region of interest within segments – possibly resulting in alteration of the measured delay – and incorrect timing – which may be a cause of error through inclusion of peaks outside the ejection phase. TSI as well as displacement and/or dyssynchrony imaging are TDI-techniques with known limitations based on the Doppler technology and the two-dimensional approach.

2D Speckle Tracking
2D speckle tracking has the advantage of differentiating between active and passive motion independently of Doppler angle of incidence and may be used to assess dyssynchrony.29–33 Whereas Becker et al.34 used CS to determine optimal lead position, others reported the value of longitudinal dyssynchrony as predicting response to CRT.35,36 A collaborative study (Speckle tracking and resynchronization [STAR]) between three centres found RS and transverse strain with a cut-off delay of 130 milliseconds between opposing walls to be predictive of LV ejection fraction (LVEF) response and outcome (death, heart transplant, LV assist device).37 However, since myocardial function occurs in three dimensions, a 3D approach should improve results and overcome some of the limitations of 2D speckle tracking.

3D Speckle Tracking
The initial clinical experiences and promising results in the evaluation of LVD using 3D STE were based on a pyramidal 3D data set and were demonstrated in 2008 by our institution.38 The advantage of the 3D STE technique is that it simultaneously calculates LVEF and end-diastolic and end-systolic volumes, and furthermore that it recognises segmental deformation related to time based on a 3D data set. We described that an alteration of the pacing mode after CRT (switching from the ‘off’ to the ‘on’ position) resulted in an immediate reduction of opposing segmental wall delay and end-systolic volume (see Figure 1). LVD based on 3D STE was estimated in all its components: LS, RS and CS, and the newly developed area strain (AS – see below) and global 3D strain. Tanaka et al. produced an early study on this technique, which focused on RS in 64 subjects.39 Strain measurement was feasible in the majority of patients studied. The authors found a close correlation between the 2D- and 3D-derived speckle tracking radial dyssynchrony parameters. In addition, the 3D site of the latest LV mechanical activation was successfully quantified in a manner previously considered impossible using 2D methods or conventional realtime 3D methods that focus on passive endocardial motion alone.40 Although both 2D and 3D STE demonstrated differences in sites of earliest activation in LBBB and RV-paced patients, the sites of latest activation were similarly distributed in predominantly posterior and lateral sites. A further study, also based on RS and dealing with RV pacing versus intrinsic LBBB using 2D and 3D STE, showed a more comprehensive LVD evaluation with 3D STE.41

Area Tracking/Area Strain
Area tracking/AS is a new modality based on 3D STE and reflects 3D strain and changes of the endocardium during LV contraction and relaxation. It is related to LS and CS and represents reciprocal values of RS. AS seems to be more robust and reproducible in comparison with other deformation parameters and may be a promising non-invasive tool to identify ischaemia. It may be possible to perform it in combination with stress echocardiography in order to improve detection and quantification of ischaemic response. It has further potential to localise delayed myocardial activation, which can be used in patients with LVD. Area tracking/AS was used for the first time by Thebault et al. in dyssynchronous patients.42 The AS-related standard deviation index reflects the dispersion of the 16-segment AS peak curves and allows a rapid and more global assessment of LVD in comparison with the use of a single parameter – for example, RS.Recently, quantification of mechanical LVD with narrow QRS duration has been reported by Tatsumi et al.43 The authors used the Area Strain Index (ASI), which was calculated as the average difference between peak and end-systolic AS of LV endocardium obtained by 3D STE based on the 16-segment model. The ASI score in HF patients with narrow QRS durations was lower than in those with wide QRS durations (2.5 ± 1.3 % versus 4.2 ± 1.2 %, p<0.001). Furthermore, the prevalence of high ASI scores in HF patients with narrow QRS was significantly higher than in normal controls, putting in question the results of the Resynchronization therapy in normal QRS (RETHIN Q) study based on conventional echocardiographic parameters.44 With the benefits gained by the addition of the third motion component,which remains invisible to both TDI and 2D STE techniques, this new technique may become the method of choice for the assessment of regional LV function.

Activation Imaging
Activation imaging technology (Toshiba, Tokyo, Japan) was introduced recently. It uses 3D STE, particularly 3D strain or AS, to define the onset of deformation in individual segments. As a colour-coded system, significant time delay is displayed in blue and pink colours according to the grading scale (see Figure 2). The algorithm uses a threshold for differentiating between varying physiological onset of deformation (see Figure 3) and distinct delay of mechanical activation (see Figures 4 and 5). This information can be displayed as a dynamic polar plot and bag image as well, and may be superimposed onto short-axis and long-axis planes (see Figure 3). Furthermore, distribution of delayed activation can be analysed frame by frame, providing a better overview of the extension of dyssynchrony. In a first series of consecutive patients treated with CRT in our institution, immediate change of delayed activation could be defined quickly and easily when the pacing mode was changed from CRT pacing mode ‘on’ to ‘off’ (see Figure 5).

Another potential of this technique could be demonstrated in individual patients with ischaemic heart disease. Patients with transmural myocardial infarction and regional wall motion abnormality may show mechanical delay related to the scar region. This phenomenon might be explained by a systolic sequence of primary stretch followed by recoil; however, these scar areas demonstrate distinct reduction in strain values. Interestingly, these data have only been reproduced in patients with subendocardial myocardial infarction and normal regional wall motion. Further studies are needed to evaluate the reproducibility and accuracy of this new technique.

Conclusion
The results of the Predictors of response to CRT (PROSPECT) study to define dyssynchrony raised questions about the potential and accuracy of conventional echocardiographic techniques, including M-mode, pulsed and tissue Doppler echocardiography.45 Newer techniques, such as 2D and 3D speckle tracking, have shown promising results in regard to outcomes and for defining the site and timing of delayed mechanical activation – with 3D STE having some advantages over 2D STE. Nevertheless, when using these newer techniques, we must face their specific limitations and the need for careful image tracing to manually fine-tune the regions of interest and capture the appropriate regional strain for dyssynchrony analysis. Inter-vendor variability of LV deformation measurements by 3D STE is another problem that will have to be solved.46 Newer developments, such as activation imaging based on 3D strain or 3D area tracking may further improve the potential of echocardiography to better select HF patients for CRT and follow their outcomes.

References

  1. Abe Y, Kawagishi T, Ohuchi H, Accurate detection of regional contraction using novel three-dimensional speckle tracking technique, J Am Coll Cardiol, 2008;51(Suppl. A):A116.
  2. Maffessanti F, Nesser HJ, Weinert L, et al., Quantitative evaluation of regional left ventricular function using three-dimensional speckle tracking echocardiography, Comput Cardiol, 2009;36:25–8.
  3. Mor-Avi V, Lang R, Badano LP, et al., Current and evolving echocardiographic techniques for the quantitative evaluation of cardiac mechanics: ASE/EAE consensus statement on methodology and indications. Endorsed by the Japanese Society of Echocardiography, J Am Soc Echocardiogr, 2011;24:277–313.
    Crossref | PubMed
  4. Perez de Isla L, Balcones DV, Fernandez-Golfin C, et al., Three-dimensional-wall motion tracking: a new and faster tool for myocardial strain assessment: comparison with two-dimensional motion tracking, J Am Soc Echocardiogr, 2009;22:325–30.
    Crossref | PubMed
  5. Seo Y, Ishizu T, Enomoto Y, et al., Validation of 3-dimensional speckle tracking imaging to quantify regional myocardial deformation, Circ Cardiovasc Imaging, 2009;2:451–9.
    Crossref | PubMed
  6. Zhou Z, Ashraf M, Hu D, et al., Three-dimensional speckle tracking imaging for left ventricular rotation measurement, J Ultrasound Med, 2010;29:903–9.
    PubMed
  7. Seo Y, Ishizu T, Enomoto Y, et al., Endocardial surface area tracking for assessment of regional LV wall deformation with 3D speckle tracking imaging, JACC Cardiovasc Imaging, 2011;4:358–65.
    Crossref | PubMed
  8. Nesser HJ, Mor-Avi V, Gorissen W, et al., Quantification of left ventricular volumes using three-dimensional echocardiographic speckle tracking: comparison with MRI, Eur Heart J, 2009;30:1565–73.
    Crossref | PubMed
  9. Kleijn SA, Aly MF, Terwee CB, et al., Reliability of left ventricular volumes and function measurements using threedimensional speckle tracking echocardiography, Eur J Echocardiogr, 2011; 16 September [Epub ahead of print].
    Crossref | PubMed
  10. Flu WJ, van Kuijk JP, Bax JJ, et al., Three-dimensional speckle tracking echocardiography: a novel approach in the assessment of left ventricular volume and function?, Eur Heart J, 2009;30:2304–7.
    Crossref | PubMed
  11. Reant P, Barbot L, Montaudon M, et al., Robustness of a new three-dimensional echocardiographic algorithm for left ventricular volume and ejection fraction quantification: experts vs novices, Eur J Echocardiogr, 2011;12:895–903.
    Crossref | PubMed
  12. Baccouche H, Maunz M, Beck T, et al., Echocardiographic assessment and monitoring of the clinical course in a patient with Tako-Tsubo cardiomyopathy by a novel 3D-speckletracking- strain analysis, Eur J Echocardiogr, 2009;10:729–31.
    Crossref | PubMed
  13. Manovel Sanchez A, Sulemane S, Dielhoff B, et al., Myocardial area strain by three-dimensional speckle echocardiography: A novel quantitative parameter for assessment of myocardial function in ischemic heart disease, Eur Heart J, 2009;30(Suppl. 1):625.
  14. Muraru D, Beraldo M, Solda E., et al., Global 3D circumferential strain is related to infarct size and transmural extent of myocardial necrosis in patients with successfully reperfused STEMI, Eur J Echocardiogr, 2011;12(Suppl. 2):P283.
  15. Kleijn SA, Aly MF, Terwee CW, et al., Three-dimensional speckle tracking echocardiography for automatic assessment of global and regional left ventricular function based on area strain, J Am Soc Echocardiogr, 2011;24:314–21.
    Crossref | PubMed
  16. Bertini M, Delgado V, Nucifora G, et al., Left ventricular rotational mechanics in patients with coronary artery disease: differences in subendocardial and subepicardial layers, Heart, 2010;96:1737–43.
    Crossref | PubMed
  17. Moral JA, Godinez JA, Maron MS, et al., Left ventricular twist mechanics in hypertrophic cardiomyopathy assessed by three-dimensional speckle tracking echocardiography, Am J Cardiol, 2011;108:1788–95.
    Crossref | PubMed
  18. Krishnakumar S, Rajendran A, Ashraf S, et al., Simultaneously derived total cavity circumferential and longitudinal right ventricular strains using a new method for 4D cardiac mechanics: validation by sonomicrometry, J Am Soc Echocardiogr, 2009;22:P2–12, 571.
  19. Gorcsan J, Tanaka H, [Are new myocardial tracking systems of three-dimensional strain a reality in clinical practice?], Rev Esp Cardiol, 2011;64:1082–9.
    Crossref | PubMed
  20. Saito K, Okuro H, Watanabe N, et al., Comprehensive evaluation of left ventricular strain using speckle-tracking echocardiography in normal adults: comparison of three-dimensional and two-dimensional approaches, J Am Soc Echocardiogr, 2009;22:1025–30.
    Crossref | PubMed
  21. Andrade J, Cortez LD, Campos O, et al., Left ventricular twist: comparison between two- and three-dimensional speckle-tracking echocardiography in healthy volunteers, Eur J Echocardiogr, 2011;12:76–9.
    Crossref | PubMed
  22. Evangelista A, Nesser J, De Castro S, et al., Systolic wringing of the left ventricular myocardium: characterization of myocardial rotation and twist in endocardial and midmyocardial layers in normal humans employing three-dimensional speckle tracking study, J Am Coll Cardiol, 2009;53:A239.
  23. Evangelista A, Nesser J, De Castro S, et al, Three-dimensional speckle tracking study of myocardial mechanics in normal humans: demonstration of regional and segmental heterogeneity in radial, circumferential and longitudinal strain, J Am Coll Cardiol, 2009;53:A246.
  24. Dohi K, Suffoletto MS, Schwartzmann DE, et al., Utility of echocardiographic radial strain imaging to quantify left ventricular dyssynchrony and predict acute response to cardiac resynchronization therapy, Am J Cardiol, 2005;96:112–6.
    Crossref | PubMed
  25. Van de Veire NH, Bleeker GB, de Sutter J, et al., Tissue synchronisation imaging accurately measures left ventricular dyssynchrony and predicts response to cardiac resynchronisation therapy, Heart, 2007;93:1034–9.
    Crossref | PubMed
  26. Yu CM, Zhang Q, Fung JW, et al., A novel tool to assess systolic asynchrony and identify responders of cardiac resynchronization therapy by tissue synchronization imaging, J Am Coll Cardiol, 2005;45:677–84.
    Crossref | PubMed
  27. Jansen AH, van Dantzig, Bracke F, et al., Quantitative observation of left ventricular multiphasic septal motion and septal-to-lateral apical shuffle predicts left ventricular reverse remodelling after cardiac resynchronisation therapy, Am J Cardiol, 2007;99:966–9.
    Crossref
  28. Gorcsan J 3rd, Kanzaki H, Bazaz R, et al., Usefulness of tissue synchronization imaging to predict acute response to cardiac resynchronization therapy, Am J Cardiol, 2004;93:1178–81.
    Crossref | PubMed
  29. Gorcsan J 3rd, Abraham T, Agler DA, et al., Echocardiography for cardiac resynchronization therapy: recommendations for performance and reporting – a report from the American Society of Echocardiography Dyssynchrony Writing Group endorsed by the Heart Rhythm Society, J Am Soc Echocardiogr, 2008;21:191–213.
    Crossref | PubMed
  30. Delgado V, Ypenburg C, van Bommel RJ, et al., Assessment of left ventricular dyssynchrony by speckle-tracking strain imaging comparison between longitudinal, circumferential, and radial strain in cardiac resynchronization therapy, J Am Coll Cardiol, 2008;51:1944–52.
    Crossref | PubMed
  31. Suffoletto MS, Dohi K, Cannesson M, et al., Novel speckle-tracking radial strain from routine black-and-white echocardiographic images to quantify dyssynchrony and predict response to cardiac resynchronization therapy, Circulation, 2006;113:960–8.
    Crossref | PubMed
  32. Tanaka H, Hara H, Saba S, Gorcsan J 3rd, Prediction of response to cardiac resynchronization therapy by speckle-tracking echocardiography using different software approaches, J Am Soc Echocardiogr, 2009;22:677–84.
    Crossref | PubMed
  33. Tops LF, Suffoletto MS, Bleeker GB, et al., Speckle-tracking radial strain reveals left ventricular dyssynchrony in patients with permanent right ventricular pacing, J Am Coll Cardiol, 2007;50:1180–8.
    Crossref | PubMed
  34. Becker M, Kramann R, Franke A, et al., Impact of left ventricular lead position in cardiac resynchronization therapyon left ventricular remodelling. A circumferential strain analysis based on 2D echocardiography, Eur Heart J, 2007;28:1211–20.
    Crossref | PubMed
  35. Knebel F, Schattke S, Bondke H, et al., Evaluation of longitudinal and radial two-dimensional strain imaging versus Doppler tissue echocardiography in predicting long-term response to cardiac resynchronization therapy, J Am Soc Echocardiogr, 2007;20:335–41.
    Crossref | PubMed
  36. Lim P, Buakhamsri A, Popovic ZB, et al., Longitudinal strain delay index by speckle tracking imaging: a new marker of response to cardiac resynchronization therapy, Circulation, 2008;118:1130–7.
    Crossref | PubMed
  37. Tanaka H, Nesser HJ, Buck T, et al., Dyssynchrony by speckle-tracking echocardiography and response to cardiac resynchronization therapy: results of the Speckle Tracking and Resynchronization (STAR) study, Eur Heart J, 2010;31:1690–1700. 38. Nesser HJ, Winter S, Speckle tracking in the evaluation of dyssynchrony, Echocardiography, 2009;26:324–36.
    Crossref
  38. Tanaka H, Hara H, Saba S, Gorcsan J 3rd, Usefulness of three-dimensional speckle tracking strain to quantify dyssynchrony and the site of latest mechanical activation, Am J Cardiol, 2010;105:235–42.
    Crossref | PubMed
  39. Kapetanakis S, Kearney MT, Siva A, et al., Real-time threedimensional echocardiography: a novel technique to quantify global left ventricular mechanical dyssynchrony, Circulation, 2005;112:992–1000.
    Crossref | PubMed
  40. Tanaka H, Hara H, Adelstein EC, Comparative mechanical activation mapping of RV-pacing to LBBB by 2D and 3D speckle tracking and association with response to resynchronization therapy, JACC Cardiovasc Imaging,2010;3:461–71.
    Crossref | PubMed
  41. Thebault C, Donal E, Bernard A, et al., Real-time three-dimensional speckle tracking echocardiography: a novel technique to quantify global left ventricular mechanical dyssynchrony, Eur J Echocardiogr, 2011;12:26–32.
    Crossref | PubMed
  42. Tatsumi K, Tanaka H, Matsumoto K, et al., Mechanical left ventricular dyssynchrony in heart failure patients with narrow QRS duration as assessed by three-dimensional speckle area tracking strain, Am J Cardiol, 2011;108:867–72.
    Crossref | PubMed
  43. Beshai JF, Grimm RA, Nagueh SF, et al., Cardiac-resynchronization therapy in heart failure with narrow QRS complexes, N Engl J Med, 2007;357:2461–71.
    Crossref | PubMed
  44. Chung ES, Leon AR, Tavazzi L, et al., Results of the predictors of response to CRT (PROSPECT trial), Circulation, 2008;117:2608–16.
    Crossref | PubMed
  45. Gayat E, Ahmad H, Weinert L, et al., Reproducibility and inter-vendor variability of left ventricular deformation measurements by three-dimensional speckle-tracking echocardiography, J Am Soc Echocardiogr, 2011;24(8):878–85.
    Crossref | PubMed
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