State of the Art Review ArticleAssessment of Myocardial Mechanics Using Speckle Tracking Echocardiography: Fundamentals and Clinical Applications
Section snippets
Myocardial Strain Imaging
Regional strain is a dimensionless measurement of deformation, expressed as a fractional or percentage change from an object's original dimension.7 Strain rate, on the other hand, refers to the speed at which deformation (ie, strain) occurs. As a spatial derivative of velocity, strain rate provides increased spatial resolution for precise localization of diseased segments. However, strain rate needs high temporal resolution (>100 Hz) to avoid underestimation due to undersampling. Therefore,
Validation of Speckle-Tracking Echocardiography
Speckle tracking requires a thorough understanding of echocardiographic imaging technique for both image acquisition and myocardial border tracing. In addition, images must be of high-resolution quality to track regions of interest accurately. Myocardial strain derived from STE has been validated using sonomicrometry12, 13, 14 and tagged MRI.1, 12, 15, 16, 17 Speckle-tracking strain results correlate significantly with tissue Doppler–derived measurements. Tissue Doppler technology is dependent
Clinical Applications of Speckle-Tracking Echocardiography for Assessment of Left Ventricular Deformation
Table 1 presents a general classification scheme that may be helpful for the application of STE-derived multidirectional strains in clinical practice.34 In general, longitudinal LV mechanics, which are predominantly governed by the subendocardial region, are the most vulnerable component of LV mechanics and therefore most sensitive to the presence of myocardial disease. The midmyocardial and epicardial function may remain relatively unaffected initially, and therefore circumferential strain and
Coronary Artery Disease
The subendocardium is the area of the left ventricle most vulnerable to the effects of hypoperfusion and ischemia.35 LV longitudinal mechanics at rest may therefore be attenuated in patients with coronary artery disease (Table 2). For example, Liang et al36 found that a peak longitudinal strain rate of −0.83 s−1 and an early diastolic strain rate of 0.96 s−1 obtained from resting echocardiography could predict >70% coronary stenosis with sensitivity of 85% and specificity of 64%. Speckle
Myocardial Infarction
Consistent with DTI, longitudinal strains are significantly reduced in patients with myocardial infarctions, proportionately within the area of infarction,38, 39, 40, 41 and correlate closely with peak infarct mass and ejection fraction42, 43, 44 (Table 2). Patients with smaller infarcts and preserved global LV ejection fractions show reduced radial and longitudinal strain, although LV circumferential strains and twist mechanics remain relatively preserved.45 In contrast, a larger transmural
Stress Echocardiography
Tissue Doppler technology has shown that patients with newly developed myocardial ischemia have reduced peak longitudinal, circumferential, and radial systolic strains during dobutamine infusion, with the greatest deterioration of myocardial shortening occurring in the circumferential direction.49 In comparison with tissue velocity–derived strains, speckle tracking longitudinal strains during dobutamine stress echocardiography have similar accuracies for detecting ischemia in the left anterior
Revascularization
The effects of balloon occlusion and time to reperfusion on regional myocardial function have been evaluated using STE. Balloon occlusion during catheterization of the coronary arteries results in a transient reduction in systolic and diastolic strain at the proximal and distal at-risk segments, which return to normal following reperfusion.53 Shorter symptom-to-balloon times in patients with acute coronary syndromes typically result in lower impairment of systolic longitudinal strain, which
Valvular Disease
Because of adaptive remodeling of the left ventricle, patients can remain asymptomatic or minimally symptomatic for prolonged periods, even in the presence of severe valvular disease. STE improves the yield of routine 2D echocardiography in valvular heart diseases by providing insights into the pattern of adaptive remodeling and detecting the presence of subclinical cardiac dysfunction.
Left Ventricular Hypertrophy
STE has been used in detecting subclinical myocardial changes in LV hypertrophy, as well as in distinguishing the different causes of LV hypertrophy.
Dilated Cardiomyopathy
Dilated cardiomyopathy is associated with reduction of strains in all 3 directions95, 96, 97 (Table 6). LV rotation is reduced at the base and the apex, leading to attenuation of LV twist95, 96, 97 and untwisting velocity.98 Patients with fewer symptoms usually exhibit higher longitudinal strain and strain rate.99 Paradoxical reversal of direction of LV rotation may be seen, with the LV base showing counterclockwise rotation and the apex showing clockwise end-systolic rotation.95, 98
Stress Cardiomyopathy
Stress cardiomyopathy (also termed “takotsubo cardiomyopathy”) is a more recently described form of reversible LV systolic dysfunction. The most common form of stress cardiomyopathy is transient apical ballooning syndrome. STE has provided unique insights into the pattern of dysfunction characterized by systolic dysfunction and reduction of LV strains in a segmental territory that extends beyond any single vascular distribution pattern.100 A variety of abnormal strain patterns have been
Pericardial Diseases and Restrictive Cardiomyopathy
The pericardium has been suggested to have permissive action for facilitating LV twist deformation. Loss of normal compliance of pericardial tissue therefore alters the pattern of LV torsional recoil. For example, in congenital absence of the pericardium, LV torsion is significantly reduced, despite preservation of the longitudinal, radial, and circumferential systolic strains.104 Similarly, constrictive pericarditis is characterized by significantly reduced circumferential strain and twist,
Emerging Insights in Characterizing Heart Failure Syndromes
Traditional concepts of heart failure have largely focused on the hemodynamic consequences of LV systolic dysfunction. Using a time-dependent model of heart failure, it has been proposed that diastolic and systolic heart failure are phenotypic expressions of the same disease process that evolves gradually as a continuum of clinical events.106 Assessment of cardiac mechanics by STE has helped uncover this continuum of heart failure syndromes. Patients with diastolic heart failure have attenuated
Congenital Heart Diseases
Because echocardiography represents the noninvasive tool most commonly used in pediatric cardiology, application of STE for bedside assessment of LV strain and twist deformation may provide important insights into mechanical adaptive responses of the right ventricle and left ventricle in congenital heart diseases. For example, in the normal heart, both the right and left ventricles are coupled for twisting in the same direction.126 However, in patients with transposition of the great arteries,
Subclinical Cardiac Involvement in Systemic Diseases
STE is useful in preclinical detection of cardiac involvement in systemic diseases. For example, recent studies in type 1 diabetes mellitus have identified increased torsion, suggesting the presence of subclinical microvascular disease.132 This increase in LV torsional deformation seen in diabetes helps in compensating for reduction in the global longitudinal strain.133, 134, 135, 136 Circumferential and radial function may vary, depending on the severity of cardiac muscle involvement.134, 136
Limitations and Future Directions
Speckle-derived strain is superior to tissue Doppler strain, particularly with regard to noise and angle dependency. However, the accuracy of speckle tracking is dependent on 2D image quality and frame rates. Low frame rates result in unstable speckle patterns, whereas high frame rates reduce scan-line density and reduce image resolution. Longitudinal strain data generally have been shown to have higher reproducibility than radial strain data.17 The longitudinal displacement of the LV base may
Conclusions
A growing body of evidence suggests that assessment of LV deformation by STE provides incremental information in clinical settings. Resolving the multidirectional components of LV deformation offers important insights into the transmural heterogeneity in myocardial contractile function that is useful for detecting subclinical states that are likely to progress into either systolic or diastolic heart failure. With the advent of 3D echocardiography, newer algorithms for tracking LV deformation
Acknowledgment
The authors thank Kay Wellik for her contribution in literature research.
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G.C. is enrolled in PhD program, University of Messina, Messina, Italy.