Global Longitudinal Strain (GLS) is a sensitive measurement used to evaluate heart performance. It offers a detailed perspective on heart muscle function and is an important tool for understanding overall heart health, providing a comprehensive assessment.
Understanding Global Longitudinal Strain
Global Longitudinal Strain quantifies the percentage change in the length of the heart muscle as it deforms or contracts. This measurement reflects the deformation of the left ventricle from its relaxed state (diastole) to its contracted state (systole).
GLS is derived from speckle tracking echocardiography, an imaging technique that analyzes the movement of natural acoustic markers within the heart muscle during contraction. Unlike Left Ventricular Ejection Fraction (LVEF), which is an indirect measurement based on volume changes, GLS directly assesses myocardial changes. This allows GLS to detect subtle, early changes in heart function that LVEF might not identify, making it a more sensitive indicator of subclinical myocardial dysfunction.
What Abnormal GLS Means
An “abnormal” GLS value can vary based on age, sex, and the loading conditions of the left ventricle. A GLS value of less than -16% (a less negative number, closer to zero) is considered abnormal in adults.
Conversely, a GLS value greater than -18% (a more negative number) is considered within the normal range. Values falling between -16% and -18% are often categorized as borderline. Other sources suggest that a GLS around -20% is normal, with values between -15% and -17% being a grey zone, and anything less negative than -15% considered abnormal. A healthcare professional interprets these ranges in the context of an individual’s overall health.
Why Abnormal GLS Matters
An abnormal Global Longitudinal Strain value carries clinical importance, as it can indicate subclinical cardiac dysfunction, meaning early heart problems that may not yet cause symptoms. It serves as a more sensitive indicator of heart muscle changes compared to traditional measures like Left Ventricular Ejection Fraction (LVEF). Abnormal GLS has been shown to predict future deterioration of left ventricular function, even in patients whose LVEF has seemingly recovered. This predictive capability allows for earlier intervention, potentially improving patient outcomes.
Abnormal GLS is also associated with myocardial fibrosis, a condition where scar tissue forms in the heart muscle, which can impair its function. For instance, a GLS value less negative than -15% has been linked to replacement myocardial fibrosis. GLS also plays a role in cardiac prevention trials, particularly in monitoring cardiotoxicity, which is heart damage caused by certain treatments like chemotherapy. A reduction in GLS of more than 15% from baseline during cancer therapy can indicate cardiotoxicity, prompting the initiation of cardioprotective medications.
How GLS is Measured
Global Longitudinal Strain is assessed using speckle tracking echocardiography, a non-invasive imaging technique that provides detailed views of the heart’s movement. The process involves acquiring specific images of the left ventricle from apical views, including the four-chamber, two-chamber, and long-axis views. Specialized software then tracks natural acoustic markers, or “speckles,” within the heart muscle as it contracts and relaxes.
Measurement involves selecting the correct views, accurately defining the end-systolic phase of the cardiac cycle, and precisely tracing the boundaries of the myocardium, which is the heart muscle. Assessing tracking quality is important for accurate results. Challenges include cardiac rhythm synchronization (triggering) and correctly defining the region of interest for analysis.