Archived Policies - Radiology
Myocardial Deformation Imaging (Strain Imaging)
Myocardial deformation imaging (strain imaging) is considered experimental, investigational and/or unproven.
Strain imaging, or more appropriately called ‘myocardial deformation imaging’, offers a means to directly quantify the extent of myocardial contraction and literature suggest it may overcome many of the limitations of left ventricular ejection fraction (LVEF). Strain is the percentage change in the length of a myocardial segment during a given period of time and has a unit of %. Strain rate is the rate at which shortening or lengthening is taking place and has a unit of 1/s. As the myocardium shortens during systole, the strain and strain rate have negative value but when there is stretch or lengthening of the myocardium, the strain and strain rate become positive. The myocardial strain imaging was initially developed as an extension of the Doppler velocity imaging. However, given the angle-dependence of Doppler imaging, only longitudinal strain could be measured with this approach and very little information could be derived about the other components of myocardial deformation.
The more recently developed speckle tracking echocardiography (STE) is a gray-scale based technique which is angle-independent and hence permits more comprehensive assessment of myocardial deformation. As we know, a gray-scale image on echocardiography is composed of several bright speckles that are produced as a result of the scatter of the ultrasound beam by the tissue. The STE software identifies these speckles and then tracks them frame-by-frame using a ‘sum-of-the absolute differences’ algorithm. From this data, the software automatically resolves the magnitude of myocardial deformation in different directions and generates strain and strain rate curves. The longitudinal strain is measured from the apical long-axis images whereas the short-axis images are used for measuring radial and circumferential strain and rotation. Since STE utilizes gray-scale images, the strain derived by STE is also known as two-dimensional strain, to differentiate it from the Doppler-based strain.
Shah et al. (1) reported a review of myocardial deformation imaging. The authors noted that few studies have investigated the translation of myocardial deformation imaging into routine clinical practice, and that routine clinical use at the time of this authors review appeared premature. In addition the review noted the major hurdle is the proprietary nature of deformation software and resulting intervendor variability in the values produced. An additional fundamental limitation was the number of deformation measures produced; with the inclusion of strain and strain rate in systole and diastole in the longitudinal, circumferential, and radial dimensions, values are generated to characterize global myocardial deformation without consideration of segmental function or the temporal dispersion in regional deformation. Although these measures reflected a different aspect of deformation and provide insight into subtle alterations in deformation patterns, the sheer number generated confusion, and many parameters were highly correlated with each other. The ability to simplify this plethora of measures into a more succinct set of parameters that describe deformation would aid clinical translation. One approach is to focus on those parameters more closely associated with clinical outcomes, and in this respect longitudinal deformation currently appears most promising. In addition, the authors noted that few data are available regarding the feasibility and reproducibility of these measures when applied broadly, particularly for the regional measures. Moreover, data are lacking from large community-based cohorts to define normal ranges for these measures and to describe the manner in which they may vary by age and gender and to establish the relationship between these measures and clinical outcomes.
Larger studies in more diverse populations are needed to establish the incremental value of these measures beyond routine clinical assessments in a broad range of cardiovascular conditions. Speckle tracking echocardiography (STE) has rapidly evolved as a promising technique for the measurement of myocardial deformation with numerous, potential clinical applications. However, the significant, inter- end or variability remains the most important limitation precluding its widespread use in clinical practice at present. Standardization of the image processing and analysis algorithms is therefore urgently required to minimize this variability. This, coupled with some other technical refinements, should see STE evolve into an integral component of the standard practice of echocardiography.
Buss et al. (3) investigated the prognostic impact of left-ventricular (LV) cardiac magnetic resonance (CMR) deformation imaging in patients with non-ischemic dilated cardiomyopathy (DCM) compared with late-gadolinium enhancement (LGE) quantification and LV ejection fraction (EF). A total of 210 subjects with DCM were examined prospectively with standard CMR including measurement of LGE for quantification of myocardial fibrosis and feature tracking strain imaging for assessment of LV deformation. The predefined primary endpoint, a combination of cardiac death, heart transplantation, and aborted sudden cardiac death, occurred in 26 subjects during the median follow-up period of 5.3 years. LV radial, circumferential, and longitudinal strains were significantly associated with outcome. Using separate multivariate analysis models, global longitudinal strain (average of peak negative strain values) and mean longitudinal strain (negative peak of the mean curve of all segments) were independent prognostic parameters surpassing the value of global and mean LV radial and circumferential strain, as well as NT-proBNP, EF, and LGE mass. A global longitudinal strain greater than 212.5% predicted outcome even in patients with EF, 35% (P, 0.01) and in those with presence of LGE (P, 0.001). Mean longitudinal strain was further investigated using a clinical model with predefined cut-offs (EF, 35%, presence of LGE, NYHA class, mean longitudinal strain greater than 210%). Mean longitudinal strain exhibited an independent prognostic value surpassing that provided by NYHA, EF, and LGE (HR ¼ 5.4, P, 0.01). The authors concluded that pathological myocardial deformation identified patients with DCM at high risk for future cardiac events, surpassing the prognostic value of standard CMR imaging techniques, such as EF and LGE and that of established cardiac serological biomarkers. In addition, the authors noted that thorough evaluation of LV contraction with two-dimensional deformation imaging might become an additional diagnostic method to detect functional impairment and may serve as a novel CMR imaging biomarker in patients with DCM and cardiomyopathies in the future. However, larger, multi-centre trials using a standardized global longitudinal strain approach are warranted to confirm the findings of this examination and to determine whether the assessment of myocardial strain may aid structured patient treatment.
In a systematic review of the current literature, Thavendiranathan et al. (4) describes echocardiographic myocardial deformation parameters in 1,504 patients during or after cancer chemotherapy for 3 clinically-relevant scenarios. The systematic review was performed following the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines using the EMBASE (1974 to November 2013) and MEDLINE (1946 to November 2013) databases. All studies of early myocardial changes with chemotherapy demonstrated that alterations of myocardial deformation precede significant change in left ventricular ejection fraction (LVEF). Using tissue Doppler-based strain imaging, peak systolic longitudinal strain rate most consistently detected early myocardial changes during therapy, whereas with speckle tracking echocardiography (STE), peak systolic global longitudinal strain (GLS) appeared to be the best measure. A 10% to 15% early reduction in GLS by STE during therapy appears to be the most useful parameter for the prediction of cardiotoxicity, defined as a drop in LVEF or heart failure. In late survivors of cancer, measures of global radial and circumferential strain are consistently abnormal, even in the context of normal LVEF, but their clinical value in predicting subsequent ventricular dysfunction or heart failure has not been explored. The authors note that this systematic review confirms the value of echocardiographic myocardial deformation parameters for the early detection of myocardial changes and prediction of cardiotoxicity in patients receiving cancer therapy. In addition, the authors note that it remains to be understood about the role of cardiovascular imaging in the identification and management of cardiotoxicity from cancer chemotherapy. Whether strain-based approaches could be reliably implemented in multiple centers, including nonacademic settings, needs to be studied. The ability of strain changes to predict subsequent cardiotoxicity needs to be examined in larger multicenter studies and in cancers other than breast cancer, where treatment with potentially cardiotoxic regimens is provided. Whether strain measurements are required at multiple time-points or a single selected time-point has to be determined. An approach that uses strain as the primary marker of cardiotoxicity to initiate cardioprotective therapy needs to be compared with a traditional LVEF-based approach. The long-term effect of strain changes that occur during therapy needs to be understood. The use of vendor-neutral methods to measure strain and their ability to predict cardiotoxicity also need to be explored for this technique to be more widely applied. Finally, the prognostic significance of strain abnormalities in survivors of cancer and those receiving radiation therapy has to be understood along with whether intervention would change the natural course of the cardiac disease.
In a 2015 update from the American Society of Echocardiography (ASE) and the European Association of Cardiovascular Imaging (EACVI) (2) the document noted that two-dimensional STE-derived strain, particularly of the RV free wall, appears to be reproducible and feasible for clinical use. Because of the need for additional normative data from large studies involving multivendor equipment, no definite reference ranges are currently recommended for either global or regional RV strain or strain rate.”
This guideline noted that the most commonly used deformation parameter is longitudinal strain during LV systole. Similar to global strain, with current technology, regional deformation measurements may vary in amplitude, depending on the myocardial region being investigated, the measurement methodology, the vendor, and sample volume definition. Therefore, no specific normal ranges are provided in the guideline document. These values await the upcoming consensus document of the joint task force of the ASE, EACVI, and the industry for the standardization of quantitative function imaging.
Despite promising data, myocardial deformation imaging (strain imaging) is considered experimental, investigational and/or unproven at this time because of lack of reference values, suboptimal reproducibility, and considerable intervendor measurement variability.
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1. Shah, A., Solomon, S., et al. Circulation Topic Review: Myocardial Deformation Imaging - Current Status and Future Directions. Circulation 2012; 125:e244-e248.
2. Lang, R., Badano, L., et al. Recommendations for Cardiac Chamber Quantification by Echocardiography in Adults: An Update from the American Society of Echocardiography and the European Association of Cardiovascular Imaging. J Am Soc Echocardiography 2015; 28:1-39.
3. Buss, S., Breuninger, K., et al. Assessment of myocardial deformation with cardiac magnetic resonance strain imaging improves risk stratification in patients with dilated cardiomyopathy. European Heart Journal - Cardiovascular Imaging. September 21, 2014.
4. Thavendiranathan, P., Poulin, F. et al. Use of myocardial strain imaging by echocardiography for the early detection of cardiotoxicity in patients during and after cancer chemotherapy: a systematic review. J Am Coll Cardiol. Volume 63, Issue 25, Part A, 1 July 2014, Pages 2751–2768.
|12/1/2016||Reviewed. No changes|
|1/1/2016||New medical document. Myocardial deformation imaging (strain imaging) is considered experimental, investigational and/or unproven.|