I am sitting on a plane going to the West Coast to attend the graduation at the University of Southern California of my younger son Jordan, and I am dozing off. For unknown reasons, I start dreaming about strain during the plane ride. Why strain? It so happens that Jordan’s high school summer project involved measuring LV strain in normal subjects. The project was referred to as “Even a high schooler can measure strain.” Since that time, there has been a lot of excitement in the echo world about strain. Publications on strain have skyrocketed in the last five years. There have been two guidelines from ASE concerning strain as well as creation of a very productive strain standardization taskforce. Let’s now review: What is strain? How is it measured? How is it used? What are its limitations? How important is it to the ASE membership?
What is it?
Strain or muscle mechanics measured by 2D echo in its simplest form is a measure of the deformation of muscle using most commonly, a technique called, speckle-tracking. It is defined as change in length divided by its initial length. The rate of change of strain is called strain rate. There are different forms of strain, Lagrangian vs. natural strain. There is 2D strain as well as 3D strain. Currently in clinical practice most often Langragian strain is used and can be divided into longitudinal, circumferential, or radial strain. Strain can be global or regional.
How is it Measured?
In most labs, it is reported as a global longitudinal strain (GLS) with a negative value indicating shortening vs a positive value indicating lengthening ( Figure 1 ). The more negative, the better (i.e., −21% is better than −15%). There are many vendors that have an automated version of strain that uses three echo views including apical long axis, four chamber, and two chamber. If the speckle-tracking is good in all three views, then a polar plot is generated, and a GLS is measured which can be put into a structured report similar to ejection fraction (EF). In general, from the ASE guidelines a peak GLS in a range of −20% is the usual finding in a normal patient while a lower absolute value below this value is more associated with being abnormal. In our lab, an absolute value below −14.5% (> 2 standard deviations) is definitely abnormal. The exact cutoffs are dependent on the machine vendor, software, ethnicity and gender of the patient. It is recommended to try to repeat the strain studies using the same machine vendor.
How is it Measured?
In most labs, it is reported as a global longitudinal strain (GLS) with a negative value indicating shortening vs a positive value indicating lengthening ( Figure 1 ). The more negative, the better (i.e., −21% is better than −15%). There are many vendors that have an automated version of strain that uses three echo views including apical long axis, four chamber, and two chamber. If the speckle-tracking is good in all three views, then a polar plot is generated, and a GLS is measured which can be put into a structured report similar to ejection fraction (EF). In general, from the ASE guidelines a peak GLS in a range of −20% is the usual finding in a normal patient while a lower absolute value below this value is more associated with being abnormal. In our lab, an absolute value below −14.5% (> 2 standard deviations) is definitely abnormal. The exact cutoffs are dependent on the machine vendor, software, ethnicity and gender of the patient. It is recommended to try to repeat the strain studies using the same machine vendor.
