A recent European Association of Cardiovascular Imaging (EACVI) survey puts strain echo used at about 60-80% of left ventricular assessments.
Thamman said the survey also found that certain technical issues are holding some specialists back from using strain imaging. But even in centers where it is used regularly and they have strain on their systems or in post-processing, she said there are important points users need to learn to help make their strain imaging results consistent and reliable. These include:
- Make sure your region of interest is correctly placed. She said the standard now is to go mid-wall, but if you go further out, the global longitudinal strain (GLS) will be less. If you go into the endocardium, it will be higher.
- You need high-quality images to see the apex and to make sure you are not foreshortened.
- Frame rates need to be between 40-80 frames per second. Outside of this rate, you can get drop out of the image, especially on the right ventricle because its wall is so thin. In general, she added, higher frame rates give you better strain curves
Getting these three technical areas right in is important as patients are followed through serial exams. Thamman said this will help highlight if patient conditions are improving or getting worse.
For example, in HCM patients, serial strain exams can show when the disease is becoming more dangerous in non-obstructive patients. Another example she gave was monitoring patients with valve disease to determine when it is appropriate to send them for valve surgery. Research is now showing there may be predictive value in many other cardiac diseases.
"That is really the best part of GLS, where we might be able to find these patients before they are symptomatic so we can make an intervention and eventually improve outcomes," Thamman said.
In patients with arrhythmic mitral valve prolapse, it has not been known which patients are more prone to sudden cardiac arrest. However, she explained, strain curves can show patterns in the posterior lateral wall where it is being tugged by the prolapsing mitral valve leaflet. During systole, rather than a negative value, it can show a positive rise in some of these patients, corresponding to the tugging. Thamman said these are the patients who appear to be at a higher risk.
Advanced artificial intelligence (AI) algorithms are now being implemented by several vendors to automate strain imaging to help speed workflow and to make measurements more reproducible between sonographers. According to Thamman, AI might be able to provide additional value by helping with the analysis of strain curve patterns.
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