to strain or not to strain

2D Echocardiography sTRAIN IMAGING

To STRAIN or not to STRAIN!?! That is the question.....

2D Strain imaging has been around for quite some time now, but it seems as though many echo labs still don't use it in day to day echo protocols. This leaves us wondering why?! 

Strain is useful for so many reasons and has been proven to be more accurate than traditional method of disks ejection fraction measurements when evaluating patients at risk for heart failure. Strain can be highly effective for the detection of cardiotoxicity, with strain abnormalities often showing on echo before there are any measurable declines in ejection fraction or any onset of clinical symptoms. Strain can be a valuable resource to evaluate decreased cardiac function and cardiotoxicity in patients with compromised left ventricular function, such as chemo patients. 

Many sonographers simply don't understand the benefits of strain and how to best utilize it within the day to day echo routine. The negative values with strain can be a little confusing, but in reality strain is simple and once you have a good understanding of how it works, you will see that it is easy to incorporate this into your lab protocols and is extremely beneficial to your patients.

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Left ventricular ejection fraction is the most commonly used parameter of systolic function. It is essential for the management of heart failure patients. The assessment of ejection fraction by Simpson’s biplane, measures changes in volume. It is often limited in sensitivity and reproducibility. Due to geometric modeling and inadequate visualization of the left ventricular apex, as well as measurement variability, this often limits the ability to detect small changes in left ventricular contractility and can often lead to decreased sensitivity and inaccurate EF measurements. Utilization of strain imaging can reduce many of these errors and provide a more reliable assessment.

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​So what is strain? There are three fundamental types of strain or deformation: Longitudinal, Radial and Circumferential. During systole, the left ventricle shortens along the longitudinal and circumferential axis, and it thickens in the radial dimension. Of the three, longitudinal strain has been proven to be the most reproducible. It has also been documented to correlate well with clinical outcomes. ​

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Global Longitudinal Strain assesses the twist of the left ventricle as it shortens along the longitudinal axis. Imagine a rubber band... when the 2 end points move away from each other as in diastole, strain is increased or positive. When the two points move closer together as in systole, strain is decreased or negative. Because of it's negative normal values, many sonographers aren't quite sure of how to assess strain and it can be confusing when you think in positive terms regarding ejection fraction. 

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So what is normal and what do we do with it?

Normal global longitudinal strain has a value of -20%. Some literature suggests that values higher than -17% predict severe heart failure or cardiotoxicity. Imaging with strain is pretty simple, if you can get your apical views, you can do strain imaging! Here are a few tips and tricks:

• Maximize image resolution
• Image at minimum depth necessary
• Use the highest possible transducer frequency
• Adjust gains, dynamic range, transmit, and lateral gain controls for best image optimization and endocardial definition
• Utilize a frame rate >40Hz if possible
• Obtain Apical four-chamber view with optimal alignment and avoidance of foreshortening
• Place calipers at right and left base, marking endocardial, mid and epicardial borders
• Repeat in Apical two-chamber and three-chamber/long axis views
• Document Bulls Eye report to demonstrate regional wall motion and strain deformation
• Consider blood pressure and heart rate when comparing Strain to Ejection Fraction - these should be similar for comparison

In summary, strain imaging is a simple tool that can be put to everyday use within your echo lab. Protocols for establishing baseline global longitudinal strain are extremely valuable when evaluating chemo patients for left ventricular function. Strain imaging can be easily incorporated into your daily routine.