Original Article
Emerging Clinical Role of Strain Imaging in Echocardiography

https://doi.org/10.1016/j.hlc.2009.11.006Get rights and content

Myocardial strain is a measure of tissue deformation and strain rate is the rate at which deformation occurs. When applied to the heart, strain and strain rate give fundamental information on myocardial properties and mechanics that would otherwise be unavailable. Site specificity and angle independency are two unique characteristics of strain and strain rate data. Strain and strain rate can be obtained with tissue Doppler imaging or with 2D speck tracking. These two techniques derive information on strain and strain rate in two fundamentally different ways and each has its own advantages and limitations. Tissue Doppler imaging yields velocity information from which strain and strain rate are mathematically derived whereas 2D speckle tracking yields strain information from which strain rate and velocity data are derived. Data obtained from these two different techniques may not be equivalent due to limitations inherent with each technique. Strain and strain rate imaging have been used to assess myocardial function in a wide range of cardiac conditions. They are useful in detecting early left ventricular (LV) dysfunction in the setting of systemic diseases with cardiac involvement, in differentiating transmural from non-transmural infarction, and in identifying LV contractile reserve in regurgitant valve lesions. When used with dobutamine echocardiography, strain and strain rate imaging can identify viable myocardium and aid the detection of myocardial ischaemia. Strain and strain rate imaging can also be used to assess right ventricular and left atrial function. Despite significant promises, strain and strain rate imaging is technically challenging and signal to noise ratio may be potentially affected by a wide range of factors. As a result, strain and strain rate imaging have been slow to get incorporated into everyday clinical practice. Ongoing research and further technical development are likely to improve the quality of the data and the more general acceptance of these new modalities of imaging in echocardiography.

Section snippets

Background

Strain, represented by the symbol ɛ, is a dimensionless index that refers to the amount of tissue deformation normalised to its original shape. It represents the fractional change in one dimension, typically length, in response to a stress, and can be mathematically written asε=LL0L0,where L is the length of the myocardium after deformation and L0 is its original length. By convention, strain is defined as positive when the distance between the points of measurement is increasing (i.e.

Echocardiographic Imaging Modalities

To quantify myocardial strain and strain rate, there are two different types of echocardiographic imaging modalities: tissue doppler imaging (TDI) and two-dimensional (2D) speckle tracking. These imaging modalities derive information on myocardial strain and strain rate from two fundamentally different ways.

Normal Values

Application of strain and strain rate imaging in clinical practice depends on, amongst other things, establishment of a range of normal values through a wide age range and an acceptably low inter-observer and intra-observer and test–retest variability.

Similar to the age-dependency of tradition pulsed-wave Doppler velocities at the LV inflow, colour tissue Doppler velocities have been shown to be age-dependent with an age-related decrease in the S′ and E′ velocities and an increase in the A

LV Systolic and Diastolic Function

Strain and strain rate imaging have been used most extensively in the evaluation of LV systolic function. Both the peak and mean strain rate have been shown to show high correlations (r about 0.9) to the maximum elastance in animal models with tissue Doppler S′ velocities showing inferior correlations [9].

Strain and strain rate imaging have been used to assess ventricular function in a wide range of congenital and acquired heart disease as well as in the post-operative setting [8]. They have

Technical Considerations

Although strain and strain rate imaging are exciting developments in echocardiography and show promise in improving our understanding of myocardial mechanics and in enhancing our ability to evaluate function and risk stratify, attention to technical details is essential in order to obtain reliable and reproducible information. This is particularly important as strain and strain rate data are very susceptible to noise while technical factors play a pivotal role in affecting the signal to noise

Conclusions

Strain and strain rate imaging are emerging techniques in echocardiography. They have provided valuable tools in the understanding and assessment of the basics of myocardial properties and mechanics. Despite intense research interest, strain and strain rate imaging have not been successfully incorporated into everyday clinical practice and still remain primarily a research tool. There is considerable evidence to suggest strain and strain rate imaging further add to the information we can obtain

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