Emerging clinical role of strain imaging in echocardiography.

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.